OJITO PENDIENTE DE REVISAR - Multivariate inferential analysis

Colineality analysis

Categorical variables

Variable	Sex	Migration Status	Surgery Year categories	suryear	Surgical procedure (vincat classification)	Surgical procedure (study classification)	ASA classification	Degree of urgency	Wound class	Antibiotic prophylaxis	Minimally invasive surgery	Country of birth (Dicotomic)	Country of citizenship (Dicotomic)	Country of birth - World Region	Country of citizenship - World Region	Country of birth - Human Development Index category	Country of citizenship - Human Development Index category	RCA document	Yearly income category	Health insurance at the time of surgery	Total hip arthroplasty (THA)	Total knee arthroplasty (TKA)	Colon resection	Rectal resection	CABG - donor site incision	CABG - single incision	Valve replacement	CABG + valve replacement	Colorectal surgery	Cardiac surgery	Orthopedic surgery
Sex	1.000	0.003	0.126	0.145	0.321	0.320	0.229	0.053	0.039	0.046	0.020	0.004	0.035	0.059	0.032	0.044	0.024	0.045	0.116	0.007	0.026	0.238	0.002	0.038	0.247	0.060	0.012	0.040	0.027	0.233	0.224
Migration Status	0.003	1.000	0.128	0.139	0.080	0.074	0.062	0.031	0.030	0.053	0.020	0.996	0.670	0.858	0.498	0.791	0.487	0.664	0.144	0.049	0.003	0.032	0.037	0.011	0.056	0.028	0.024	0.019	0.025	0.062	0.030
Surgery Year categories	0.126	0.128	1.000	1.000	0.278	0.271	0.216	0.093	0.258	0.236	0.144	0.126	0.126	0.071	0.073	0.072	0.067	0.091	0.050	0.020	0.144	0.165	0.066	0.151	0.286	0.120	0.258	0.157	0.147	0.459	0.260
suryear	0.145	0.139	1.000	1.000	0.234	0.266	0.214	0.117	0.290	0.247	0.165	0.138	0.136	0.063	0.064	0.081	0.077	0.100	0.066	0.046	0.192	0.217	0.119	0.192	0.356	0.141	0.353	0.175	0.172	0.533	0.344
Surgical procedure (vincat classification)	0.321	0.080	0.278	0.234	1.000	1.000	0.386	0.145	0.579	0.190	0.896	0.080	0.105	0.067	0.065	0.075	0.083	0.079	0.062	0.042	1.000	1.000	1.000	1.000	1.000	1.000	1.000	1.000	1.000	1.000	1.000
Surgical procedure (study classification)	0.320	0.074	0.271	0.266	1.000	1.000	0.385	0.139	0.575	0.187	0.894	0.075	0.099	0.068	0.066	0.070	0.075	0.075	0.059	0.034	1.000	1.000	0.751	0.522	0.949	0.273	1.000	1.000	1.000	1.000	1.000
ASA classification	0.229	0.062	0.216	0.214	0.386	0.385	1.000	0.096	0.160	0.148	0.250	0.064	0.069	0.059	0.055	0.059	0.058	0.059	0.052	0.017	0.286	0.246	0.191	0.171	0.552	0.135	0.346	0.197	0.276	0.744	0.429
Degree of urgency	0.053	0.031	0.093	0.117	0.145	0.139	0.096	1.000	0.029	0.082	0.038	0.031	0.011	0.036	0.013	0.039	0.011	0.012	0.012	0.024	0.080	0.084	0.060	0.040	0.173	0.036	0.010	0.013	0.035	0.151	0.139
Wound class	0.039	0.030	0.258	0.290	0.579	0.575	0.160	0.029	1.000	0.046	0.896	0.030	0.038	0.033	0.032	0.027	0.034	0.032	0.046	0.019	0.351	0.366	0.751	0.528	0.261	0.075	0.187	0.084	0.996	0.369	0.605
Antibiotic prophylaxis	0.046	0.053	0.236	0.247	0.190	0.187	0.148	0.082	0.046	1.000	0.013	0.052	0.051	0.052	0.058	0.048	0.053	0.050	0.004	0.009	0.084	0.092	0.001	0.001	0.099	0.062	0.103	0.045	0.001	0.173	0.148
Minimally invasive surgery	0.020	0.020	0.144	0.165	0.896	0.894	0.250	0.038	0.896	0.013	1.000	0.019	0.020	0.046	0.046	0.034	0.052	0.027	0.059	0.018	0.321	0.322	0.710	0.416	0.238	0.069	0.161	0.077	0.894	0.331	0.542
Country of birth (Dicotomic)	0.004	0.996	0.126	0.138	0.080	0.075	0.064	0.031	0.030	0.052	0.019	1.000	0.660	0.862	0.494	0.795	0.483	0.654	0.144	0.050	0.002	0.032	0.036	0.009	0.058	0.028	0.022	0.019	0.025	0.062	0.030
Country of citizenship (Dicotomic)	0.035	0.670	0.126	0.136	0.105	0.099	0.069	0.011	0.038	0.051	0.020	0.660	1.000	0.492	0.744	0.470	0.728	0.991	0.115	0.035	0.001	0.058	0.042	0.017	0.078	0.015	0.037	0.009	0.025	0.086	0.051
Country of birth - World Region	0.059	0.858	0.071	0.063	0.067	0.068	0.059	0.036	0.033	0.052	0.046	0.862	0.492	1.000	0.666	0.726	0.493	0.353	0.102	0.055	0.057	0.046	0.046	0.062	0.118	0.053	0.052	0.021	0.052	0.117	0.080
Country of citizenship - World Region	0.032	0.498	0.073	0.064	0.065	0.066	0.055	0.013	0.032	0.058	0.046	0.494	0.744	0.666	1.000	0.479	0.726	0.532	0.086	0.036	0.048	0.044	0.043	0.052	0.105	0.066	0.065	0.020	0.051	0.118	0.074
Country of birth - Human Development Index category	0.044	0.791	0.072	0.081	0.075	0.070	0.059	0.039	0.027	0.048	0.034	0.795	0.470	0.726	0.479	1.000	0.650	0.332	0.105	0.049	0.046	0.023	0.044	0.017	0.088	0.062	0.048	0.025	0.045	0.105	0.048
Country of citizenship - Human Development Index category	0.024	0.487	0.067	0.077	0.083	0.075	0.058	0.011	0.034	0.053	0.052	0.483	0.728	0.493	0.726	0.650	1.000	0.511	0.073	0.037	0.039	0.035	0.047	0.032	0.088	0.075	0.060	0.019	0.054	0.112	0.056
RCA document	0.045	0.664	0.091	0.100	0.079	0.075	0.059	0.012	0.032	0.050	0.027	0.654	0.991	0.353	0.532	0.332	0.511	1.000	0.083	0.038	0.006	0.060	0.044	0.025	0.081	0.014	0.041	0.016	0.036	0.091	0.051
Yearly income category	0.116	0.144	0.050	0.066	0.062	0.059	0.052	0.012	0.046	0.004	0.059	0.144	0.115	0.102	0.086	0.105	0.073	0.083	1.000	0.013	0.024	0.061	0.046	0.033	0.030	0.020	0.006	0.023	0.059	0.024	0.034
Health insurance at the time of surgery	0.007	0.049	0.020	0.046	0.042	0.034	0.017	0.024	0.019	0.009	0.018	0.050	0.035	0.055	0.036	0.049	0.037	0.038	0.013	1.000	0.018	0.019	0.026	0.012	0.024	0.004	0.006	0.004	0.014	0.021	0.031
Total hip arthroplasty (THA)	0.026	0.003	0.144	0.192	1.000	1.000	0.286	0.080	0.351	0.084	0.321	0.002	0.001	0.057	0.048	0.046	0.039	0.006	0.024	0.018	1.000	0.296	0.264	0.183	0.210	0.060	0.151	0.067	0.352	0.298	0.579
Total knee arthroplasty (TKA)	0.238	0.032	0.165	0.217	1.000	1.000	0.246	0.084	0.366	0.092	0.322	0.032	0.058	0.046	0.044	0.023	0.035	0.060	0.061	0.019	0.296	1.000	0.277	0.192	0.220	0.063	0.158	0.071	0.368	0.312	0.607
Colon resection	0.002	0.037	0.066	0.119	1.000	0.751	0.191	0.060	0.751	0.001	0.710	0.036	0.042	0.046	0.043	0.044	0.047	0.044	0.046	0.026	0.264	0.277	1.000	0.171	0.196	0.056	0.141	0.063	0.751	0.278	0.456
Rectal resection	0.038	0.011	0.151	0.192	1.000	0.522	0.171	0.040	0.528	0.001	0.416	0.009	0.017	0.062	0.052	0.017	0.032	0.025	0.033	0.012	0.183	0.192	0.171	1.000	0.136	0.039	0.098	0.044	0.522	0.193	0.317
CABG - donor site incision	0.247	0.056	0.286	0.356	1.000	0.949	0.552	0.173	0.261	0.099	0.238	0.058	0.078	0.118	0.105	0.088	0.088	0.081	0.030	0.024	0.210	0.220	0.196	0.136	1.000	0.045	0.112	0.050	0.262	0.707	0.363
CABG - single incision	0.060	0.028	0.120	0.141	1.000	0.273	0.135	0.036	0.075	0.062	0.069	0.028	0.015	0.053	0.066	0.062	0.075	0.014	0.020	0.004	0.060	0.063	0.056	0.039	0.045	1.000	0.032	0.014	0.075	0.203	0.104
Valve replacement	0.012	0.024	0.258	0.353	1.000	1.000	0.346	0.010	0.187	0.103	0.161	0.022	0.037	0.052	0.065	0.048	0.060	0.041	0.006	0.006	0.151	0.158	0.141	0.098	0.112	0.032	1.000	0.036	0.188	0.508	0.261
CABG + valve replacement	0.040	0.019	0.157	0.175	1.000	1.000	0.197	0.013	0.084	0.045	0.077	0.019	0.009	0.021	0.020	0.025	0.019	0.016	0.023	0.004	0.067	0.071	0.063	0.044	0.050	0.014	0.036	1.000	0.084	0.226	0.116
Colorectal surgery	0.027	0.025	0.147	0.172	1.000	1.000	0.276	0.035	0.996	0.001	0.894	0.025	0.025	0.052	0.051	0.045	0.054	0.036	0.059	0.014	0.352	0.368	0.751	0.522	0.262	0.075	0.188	0.084	1.000	0.370	0.607
Cardiac surgery	0.233	0.062	0.459	0.533	1.000	1.000	0.744	0.151	0.369	0.173	0.331	0.062	0.086	0.117	0.118	0.105	0.112	0.091	0.024	0.021	0.298	0.312	0.278	0.193	0.707	0.203	0.508	0.226	0.370	1.000	0.513
Orthopedic surgery	0.224	0.030	0.260	0.344	1.000	1.000	0.429	0.139	0.605	0.148	0.542	0.030	0.051	0.080	0.074	0.048	0.056	0.051	0.034	0.031	0.579	0.607	0.456	0.317	0.363	0.104	0.261	0.116	0.607	0.513	1.000

Continuous variables

For every combination of continuous variables, we compute a correlation measure to examine the degree of colinearity. Since all continuous variables are not distribubted normally, except for age, we will compute the Spearman’s Correlation Coefficient. We also examine the scatterplot for each pair of variables, to check for linearity. All analysis are stratified by sex.

Pairs of variables wit non-negligible correlation are:

Surgery duration - Preoperative length of stay: low positive (overall and female) or moderate positive (male) correlation
CoC HDI - CoB HDI: moderate positive correlation

Categorical-continous combinations

Point biserial [*no hemos hecho point biserial porque asume normalidad, hemos hecho un speraman recodificando la binaria como numérica]* correlation coefficient for combinations where the categorical variable is dichotomous:

sex
MS
atbprof
misurg
CoB_dic (no mirar colinealidad con MS ni con CoB_WR ni con CoB_hdicat)
CoC_dic (no mirar colinealidad con MS ni con CoC_WR ni con CoC_hdicat)
insurance

##                                            Age
## Sex                                      0.142
## Migration Status                        -0.172
## Antibiotic prophylaxis                  -0.008
## Minimally invasive surgery              -0.033
## Country of birth (Dicotomic)             0.171
## Country of citizenship (Dicotomic)       0.121
## Health insurance at the time of surgery  0.023
##                                         Preoperative length of stay (days)
## Sex                                                                 -0.190
## Migration Status                                                     0.036
## Antibiotic prophylaxis                                               0.116
## Minimally invasive surgery                                           0.255
## Country of birth (Dicotomic)                                        -0.037
## Country of citizenship (Dicotomic)                                  -0.055
## Health insurance at the time of surgery                             -0.044
##                                         Surgery duration (minutes)
## Sex                                                         -0.259
## Migration Status                                             0.060
## Antibiotic prophylaxis                                       0.125
## Minimally invasive surgery                                   0.111
## Country of birth (Dicotomic)                                -0.062
## Country of citizenship (Dicotomic)                          -0.082
## Health insurance at the time of surgery                     -0.012
##                                         Country of birth - Human Development Index
## Sex                                                                         -0.001
## Migration Status                                                            -0.870
## Antibiotic prophylaxis                                                      -0.043
## Minimally invasive surgery                                                   0.017
## Country of birth (Dicotomic)                                                 0.874
## Country of citizenship (Dicotomic)                                           0.554
## Health insurance at the time of surgery                                      0.050
##                                         Country of citizenship - Human Development Index
## Sex                                                                                0.025
## Migration Status                                                                  -0.540
## Antibiotic prophylaxis                                                            -0.040
## Minimally invasive surgery                                                         0.019
## Country of birth (Dicotomic)                                                       0.540
## Country of citizenship (Dicotomic)                                                 0.806
## Health insurance at the time of surgery                                            0.036

Pairs of variables with non-negligible correlation:

MS - CoB_hdi
MS - CoC_hdi
CoB_dic - CoB_hdi
CoB_dic - CoC_hdi
CoC_dic - CoB_hdi
CoC_dic - CoC_hdi

Continuous variables: exponentiality assumption

We examine whether exponentiality exists between each continuous variable and the incidence rate of SSI

Age

Continuous format

Categorical format

First, we regroup age by cuartiles (=<59, 60-68, 69-75, >75)

Then, we obtain the IR of SSI for each cuartile

The, we plot the IR to examine lineality

The graph above shows the IR of SSI for each age cuartile. From the graph we can see that the relation Therefore, age will be included as a categorical variable following cuartiles.

The graph above shows the distribution of SSI IR among 10-year age groups.

Preoperative length of stay

Continuous format

We plot the IR of SSI for every number of preoperative days, including a LOESS curve, excluding outlier values of SSI (> 10.000 per 100 person-year). We see that the IR increases significantly in patients with one day compared to patients intervened in the same admission day. The IR then increases progressively as the number of days go higher.

Categorical format

We categorize the preoperative length of stay in the following way:

Same day intervention
One day after admission
Two days after admission
3-7 days after admission
8-14 days after admission
15 days or more after admission

We then obtain IR with their respective CI and plot the IR for every preoperative length of stay category.

We see an increasing trend for the first three categories (same day > one day after > 2 days after), a decreasing trend for the next two categories (2 days > 3-7 days > 8-14 days), and finally an increasing trend for the last category, although with a wide CI.
We conclude that SSI IR doesn’t follow a monotonous nor an exponential relationship to preoperative length of stay. Therefore, it will be included as a categorical variable in the model.

We regroup the preopretive length of stay using a reduced number of categories: same day, 2 days, 3-7 days, more than 7 days, then plot the incidence rate of SSI for every category

Surgery duration

Continuous format

Country of birth -HDI (cont.)

Country of citizenship - HDI (cont.)

Poisson regression models: both sexes, all procedures

Model 1: sex and age

Age: cuartiles ——

We adjust a Poisson regression model with robust variance for SSI, considering:

Age: categorized following cuartiles (suarge_quart)
Sex
MS

>> Increasing age is associated with a reduced of ssi (statistically significant for Q3 and Q4 of age). Female sex is associated with a reduced risk of ssi, not statistically significant. Migrants have a statistically significant lower risk of ssi compared to non-migrants.

##                        exp(coef)     SE     CL     CU P-value
## (Intercept)               0.0014 0.0926 0.0011 0.0016  0.0000
## surage_quartQ2 (60–68)    0.9164 0.1251 0.7171 1.1712  0.4856
## surage_quartQ3 (69–75)    0.5979 0.1380 0.4562 0.7837  0.0002
## surage_quartQ4 (>75)      0.7530 0.1384 0.5740 0.9877  0.0404
## sexFemale                 0.8241 0.0985 0.6794 0.9996  0.0496
## MSYes                     0.6365 0.1923 0.4366 0.9279  0.0188

Age: many categories

We adjust a Poisson regression model with robust variance for SSI, considering:

Age: categorized as surage_cat
Sex
MS

##                    exp(coef)     SE          CL           CU P-value
## (Intercept)           0.0000 0.0817      0.0000       0.0000  0.0000
## surage_cat26-35 1200857.1890 0.3413 615192.9295 2344074.3858  0.0000
## surage_cat36-45  985972.2943 0.1880 682120.1257 1425176.1949  0.0000
## surage_cat46-55  446069.9617 0.1639 323526.9379  615028.8815  0.0000
## surage_cat56-65  528214.7029 0.1127 423561.9406  658724.8419  0.0000
## surage_cat66-75  354278.0085 0.1115 284753.3681  440777.6040  0.0000
## surage_cat76-85  400013.0787 0.1302 309921.1157  516294.1633  0.0000
## surage_cat86-95  577263.0462 0.3329 300640.4465 1108409.1590  0.0000
## sexFemale             0.8248 0.0992      0.6791       1.0018  0.0522
## MSYes                 0.5949 0.1961      0.4051       0.8736  0.0081

Age: 4 categories

We adjust a Poisson regression model with robust variance for SSI, considering:

Age: categorized as 16-55, 56-65, 66-75, 76-95
Sex
MS

>> Increasing age is associated with a reduced of ssi (statistically significant for 66-75 and 76-95 groups). Female sex is associated with a reduced risk of ssi, not statistically significant. Migrants have a statistically significant lower risk of ssi compared to non-migrants.

##                  exp(coef)     SE     CL     CU P-value
## (Intercept)         0.0015 0.1129 0.0012 0.0018  0.0000
## surage_cat256-65    0.8811 0.1392 0.6707 1.1575  0.3632
## surage_cat266-75    0.5916 0.1420 0.4479 0.7815  0.0002
## surage_cat276-95    0.6890 0.1553 0.5082 0.9342  0.0165
## sexFemale           0.8285 0.0993 0.6820 1.0064  0.0580
## MSYes               0.6255 0.1933 0.4283 0.9137  0.0152

Age: continuous

We adjust a Poisson regression model with robust variance for SSI, considering:

Age: continuous
Sex
MS

>> >> Increasing age is associated with a reduced of ssi (statistically significant). Female sex is associated with a reduced risk of ssi, not statistically significant. Migrants have a statistically significant lower risk of ssi compared to non-migrants.

##             exp(coef)     SE     CL     CU P-value
## (Intercept)    0.0033 0.2688 0.0019 0.0055  0.0000
## surage         0.9836 0.0042 0.9756 0.9916  0.0001
## sexFemale      0.8315 0.0984 0.6857 1.0083  0.0607
## MSYes          0.6111 0.1939 0.4179 0.8936  0.0111

Including MS and sex interaction

We adjust a Poisson regression model with robust variance for SSI, considering:

Age: categorized following cuartiles (suarge_quart)
Sex
MS
MS * sex

>> Increasing age is associated with a reduced of ssi (statistically significant for Q3 and Q4 of age). Female sex is associated with a statistically signficant reduced risk of ssi. Migrants have a statistically significant lower risk of ssi compared to non-migrants. The interaction term MS * Sex is not statistically significant.

##                        exp(coef)     SE     CL     CU P-value
## (Intercept)               0.0014 0.0923 0.0011 0.0016  0.0000
## surage_quartQ2 (60–68)    0.9136 0.1248 0.7153 1.1668  0.4689
## surage_quartQ3 (69–75)    0.5973 0.1379 0.4558 0.7826  0.0002
## surage_quartQ4 (>75)      0.7545 0.1383 0.5753 0.9895  0.0417
## sexFemale                 0.8016 0.1021 0.6563 0.9791  0.0303
## MSYes                     0.5267 0.2714 0.3094 0.8965  0.0182
## sexFemale:MSYes           1.5027 0.3775 0.7171 3.1490  0.2806

Model 2: sex, age and ASA

ASA: 5 categories

We adjust a Poisson regression model with robust variance for SSI, considering:

Age: quartiles
Sex
ASA
MS

##                        exp(coef)     SE     CL     CU P-value
## (Intercept)               0.0005 0.2534 0.0003 0.0008  0.0000
## surage_quartQ2 (60–68)    0.8779 0.1250 0.6872 1.1216  0.2975
## surage_quartQ3 (69–75)    0.5539 0.1378 0.4228 0.7256  0.0000
## surage_quartQ4 (>75)      0.6886 0.1399 0.5235 0.9059  0.0077
## sexFemale                 0.8569 0.1037 0.6994 1.0500  0.1363
## asaII                     2.8731 0.2553 1.7420 4.7385  0.0000
## asaIII                    2.8001 0.2608 1.6796 4.6682  0.0001
## asaIV                     3.1733 0.2741 1.8544 5.4300  0.0000
## asaV                      0.0001 0.5955 0.0000 0.0002  0.0000
## MSYes                     0.6268 0.1921 0.4301 0.9133  0.0150

ASA: 4 categories ——-

We adjust a Poisson regression model with robust variance for SSI, considering:

Age: quartiles
Sex
ASA: 4 categories (I, II, III and IV/V)
MS

>> Increasing age is associated with a reduced of ssi (statistically significant for Q3 and Q4 of age). Female sex is associated with a reduced risk of ssi, not statistically signficant. Increased ASA classification categories are associated with an increased rik of SSI, statistically significant. Migrants have a statistically significant lower risk of ssi compared to non-migrants.

##                        exp(coef)     SE     CL     CU P-value
## (Intercept)               0.0005 0.2534 0.0003 0.0008  0.0000
## surage_quartQ2 (60–68)    0.8785 0.1250 0.6876 1.1224  0.3001
## surage_quartQ3 (69–75)    0.5534 0.1378 0.4225 0.7250  0.0000
## surage_quartQ4 (>75)      0.6891 0.1399 0.5238 0.9065  0.0078
## sexFemale                 0.8575 0.1037 0.6998 1.0508  0.1382
## asa_2II                   2.8730 0.2553 1.7420 4.7385  0.0000
## asa_2III                  2.8005 0.2608 1.6798 4.6688  0.0001
## asa_2IV/V                 3.1585 0.2741 1.8458 5.4047  0.0000
## MSYes                     0.6275 0.1921 0.4306 0.9143  0.0153

Including MS and sex interaction

We adjust a Poisson regression model with robust variance for SSI, considering:

Age: quartiles
Sex
ASA: 4 categories (I, II, III and IV/V)
MS
MS * sex

>> INTERPRETATION
Increasing age is associated with a reduced of ssi (statistically significant for Q3 and Q4 of age). Female sex is associated with a lower risk of ssi, not statistically signficant. Increased ASA classification categories are associated with an increased rik of SSI, statistically significant. Migrants have a statistically significant lower risk of ssi compared to non-migrants. The interacion term (MS * sex) is not statistically significant.

##                        exp(coef)     SE     CL     CU P-value
## (Intercept)               0.0005 0.2535 0.0003 0.0009  0.0000
## surage_quartQ2 (60–68)    0.8751 0.1246 0.6854 1.1173  0.2845
## surage_quartQ3 (69–75)    0.5526 0.1376 0.4220 0.7237  0.0000
## surage_quartQ4 (>75)      0.6905 0.1398 0.5250 0.9081  0.0080
## asa_2II                   2.8807 0.2552 1.7468 4.7507  0.0000
## asa_2III                  2.8035 0.2608 1.6816 4.6739  0.0001
## asa_2IV/V                 3.1731 0.2740 1.8547 5.4288  0.0000
## MSYes                     0.5130 0.2712 0.3015 0.8730  0.0139
## sexFemale                 0.8326 0.1070 0.6751 1.0270  0.0871
## MSYes:sexFemale           1.5455 0.3778 0.7370 3.2410  0.2492

Model 3: sex, age, ASA and surgical procedure

Surgical procedure: study classification

We adjust a Poisson regression model with robust variance for SSI, considering:

Age: quartiles
Sex
Surgical procedure: study classification
ASA: 4 categories
MS

>> INTERPRETATION:
Increasing age is associated with a reduced of ssi (statistically significant for Q3 and Q4 of age).
Female sex is associated with a higher risk of ssi, not statistically signficant.
Increased ASA classification categories are associated with an increased rik of SSI, statistically significant.
Considering THA as the reference category, CABG, CABG + valve replacement and colorectal surgeries have a higher risk of ssi, statistically significant. TKA surgeries have a higher risk of ssi, not statistically significant. Valve replacement surgeries have a lower risk of infection, not statistically significant.
Migrants have a statistically significant lower risk of ssi compared to non-migrants.

##                                    exp(coef)     SE     CL      CU P-value
## (Intercept)                           0.0003 0.2737 0.0001  0.0004  0.0000
## surage_quartQ2 (60–68)                0.9711 0.1244 0.7610  1.2392  0.8138
## surage_quartQ3 (69–75)                0.7013 0.1390 0.5341  0.9209  0.0107
## surage_quartQ4 (>75)                  0.7136 0.1444 0.5377  0.9471  0.0195
## sexFemale                             1.0652 0.1039 0.8689  1.3058  0.5433
## asa_2II                               1.7278 0.2578 1.0425  2.8636  0.0339
## asa_2III                              2.2323 0.2800 1.2895  3.8646  0.0041
## asa_2IV/V                             3.1888 0.3188 1.7073  5.9561  0.0003
## surtype_2TKA                          1.0728 0.1989 0.7264  1.5843  0.7239
## surtype_2Valve replacement            0.5703 0.3231 0.3028  1.0744  0.0822
## surtype_2CABG + valve                 2.5768 0.3524 1.2915  5.1414  0.0072
## surtype_2Colon or rectal resection    9.8843 0.1612 7.2070 13.5561  0.0000
## surtype_2CABG                         2.0863 0.2260 1.3398  3.2488  0.0011
## MSYes                                 0.6487 0.1915 0.4457  0.9441  0.0238

Surgical procedure: vincat classification

We adjust a Poisson regression model with robust variance for SSI, considering:

Age: quartiles
Sex
Surgical procedure: vincat classification
ASA: 4 categories
MS

>> INTERPRETATION
Increasing age is associated with a reduced of ssi (statistically significant for Q3 and Q4 of age).
Female sex is associated with a higher risk of ssi, not statistically signficant.
Increased ASA classification categories are associated with an increased risk of SSI, statistically significant.
Considering THA as the reference category, CABG with donor site incision, CABG + valve replacement, rectal surgeries and colon surgeries have a higher risk of ssi, statistically significant. TKA surgeries have a higher risk of ssi, not statistically significant. Valve replacement surgeries and CABG without donor site incision have a lower risk of infection, not statistically significant.
Migrants have a statistically significant lower risk of ssi compared to non-migrants.

##                          exp(coef)     SE     CL      CU P-value
## (Intercept)                 0.0003 0.2742 0.0001  0.0004  0.0000
## surage_quartQ2 (60–68)      0.9719 0.1250 0.7608  1.2417  0.8199
## surage_quartQ3 (69–75)      0.6967 0.1394 0.5301  0.9155  0.0095
## surage_quartQ4 (>75)        0.7197 0.1446 0.5421  0.9555  0.0229
## sexFemale                   1.0949 0.1049 0.8914  1.3448  0.3874
## asa_2II                     1.6889 0.2585 1.0175  2.8033  0.0427
## asa_2III                    2.2696 0.2805 1.3098  3.9328  0.0035
## asa_2IV/V                   3.1727 0.3192 1.6972  5.9308  0.0003
## surtypeRectal resection    13.8527 0.1760 9.8113 19.5588  0.0000
## surtypeTKA                  1.0676 0.1989 0.7229  1.5766  0.7422
## surtypeColon resection      7.6215 0.1741 5.4179 10.7213  0.0000
## surtypeCABG - DI            2.2096 0.2273 1.4151  3.4501  0.0005
## surtypeCABG - SI            0.7065 0.6158 0.2113  2.3623  0.5727
## surtypeValve replacement    0.5623 0.3229 0.2986  1.0588  0.0746
## surtypeCABG + valve         2.5567 0.3520 1.2825  5.0969  0.0077
## MSYes                       0.6333 0.1912 0.4354  0.9211  0.0169

Interaction term: MS * sex

We adjust a Poisson regression model with robust variance for SSI, considering:

Age: quartiles
Sex
Surgical procedure: study classification
ASA: 4 categories
MS
Interaction term: MS * sex

>> INTERPRETATION
Increasing age is associated with a reduced of ssi (statistically significant for Q3 and Q4 of age).
Female sex is associated with a higher risk of ssi, not statistically signficant.
Increased ASA classification categories are associated with an increased rik of SSI, statistically significant.
Considering THA as the reference category, CABG, CABG + valve replacement and colorectal surgeries have a higher risk of ssi, statistically significant. TKA have a higher risk of ssi, not statistically significant. Valve replacement surgeries have a lowe risk of ssi, not statistically significant.
Migrants have a statistically significant lower risk of ssi compared to non-migrants.
Compared to non-migrant males, migrant females have a higher risk of infection, not statistically significant.

##                                    exp(coef)     SE     CL      CU P-value
## (Intercept)                           0.0003 0.2738 0.0001  0.0004  0.0000
## surage_quartQ2 (60–68)                0.9668 0.1241 0.7581  1.2329  0.7856
## surage_quartQ3 (69–75)                0.7000 0.1390 0.5331  0.9191  0.0103
## surage_quartQ4 (>75)                  0.7150 0.1445 0.5386  0.9490  0.0202
## asa_2II                               1.7318 0.2578 1.0448  2.8705  0.0332
## asa_2III                              2.2339 0.2802 1.2899  3.8687  0.0041
## asa_2IV/V                             3.1952 0.3186 1.7111  5.9666  0.0003
## surtype_2TKA                          1.0760 0.1989 0.7287  1.5888  0.7126
## surtype_2Valve replacement            0.5697 0.3232 0.3024  1.0734  0.0817
## surtype_2CABG + valve                 2.5837 0.3524 1.2950  5.1547  0.0071
## surtype_2Colon or rectal resection    9.8902 0.1612 7.2107 13.5653  0.0000
## surtype_2CABG                         2.0949 0.2258 1.3458  3.2608  0.0011
## MSYes                                 0.5346 0.2720 0.3137  0.9110  0.0213
## sexFemale                             1.0360 0.1067 0.8405  1.2769  0.7401
## MSYes:sexFemale                       1.5163 0.3769 0.7243  3.1740  0.2694

Interaction term: MS * surgical procedure (study classification)

We adjust a Poisson regression model with robust variance for SSI, considering:

Age: quartiles
Sex
Surgical procedure: study classification
ASA: 4 categories
MS
Interaction term: MS * surtype_2

>> INTERPRETATION
Increasing age is associated with a reduced of ssi (statistically significant for Q3 and Q4 of age).
Female sex is associated with a higher risk of ssi, not statistically signficant.
Increased ASA classification categories are associated with an increased rik of SSI, statistically significant.
Considering THA as the reference category, CABG, CABG + valve replacement, TKA and colorectal surgeries have a higher risk of ssi, not statistically significant. Valve replacement surgeries have a lower risk of infection compared to THA, not statistically significant.
Migrants have a lower risk of ssi compared to non-migrants, not statistically significant.
Compared to non-migrants undergoing THA, migrants undergoing TKA, CABG, CABG + valve replacement and colorectal resection, have a higher risk of ssi, not statistically significant.
Compared to non-migrants undergoing THA, migrants undergoing valve replacement have a lower risk of ssi, statistically significant.

##                                          exp(coef)     SE     CL      CU
## (Intercept)                                 0.0003 0.2776 0.0001  0.0004
## surage_quartQ2 (60–68)                      0.9666 0.1243 0.7576  1.2332
## surage_quartQ3 (69–75)                      0.6994 0.1391 0.5325  0.9187
## surage_quartQ4 (>75)                        0.7126 0.1444 0.5369  0.9457
## asa_2II                                     1.7241 0.2581 1.0397  2.8592
## asa_2III                                    2.2312 0.2801 1.2886  3.8633
## asa_2IV/V                                   3.1808 0.3182 1.7049  5.9344
## surtype_2TKA                                1.0500 0.2032 0.7051  1.5637
## surtype_2Valve replacement                  0.6109 0.3236 0.3240  1.1518
## surtype_2CABG + valve                       2.4119 0.3636 1.1826  4.9192
## surtype_2Colon or rectal resection          9.6450 0.1642 6.9904 13.3078
## surtype_2CABG                               2.0463 0.2311 1.3010  3.2186
## MSYes                                       0.4395 0.7226 0.1066  1.8115
## sexFemale                                   1.0675 0.1039 0.8707  1.3087
## surtype_2TKA:MSYes                          1.5447 0.9354 0.2469  9.6625
## surtype_2Valve replacement:MSYes            0.0000 0.7831 0.0000  0.0000
## surtype_2CABG + valve:MSYes                 3.8219 1.2279 0.3444 42.4132
## surtype_2Colon or rectal resection:MSYes    1.6162 0.7717 0.3562  7.3344
## surtype_2CABG:MSYes                         1.4951 0.7973 0.3133  7.1339
##                                          P-value
## (Intercept)                               0.0000
## surage_quartQ2 (60–68)                    0.7844
## surage_quartQ3 (69–75)                    0.0102
## surage_quartQ4 (>75)                      0.0189
## asa_2II                                   0.0348
## asa_2III                                  0.0042
## asa_2IV/V                                 0.0003
## surtype_2TKA                              0.8102
## surtype_2Valve replacement                0.1277
## surtype_2CABG + valve                     0.0155
## surtype_2Colon or rectal resection        0.0000
## surtype_2CABG                             0.0019
## MSYes                                     0.2552
## sexFemale                                 0.5300
## surtype_2TKA:MSYes                        0.6421
## surtype_2Valve replacement:MSYes          0.0000
## surtype_2CABG + valve:MSYes               0.2749
## surtype_2Colon or rectal resection:MSYes  0.5339
## surtype_2CABG:MSYes                       0.6139

Interaction term: MS * surgical procedure (vincat classification)

We adjust a Poisson regression model with robust variance for SSI, considering:

Age: quartiles
Sex
Surgical procedure: vincat classification
ASA: 4 categories
MS
Interaction term: MS * surtype_2
- >> INTERPRETATION
- Increasing age is associated with a reduced of ssi (statistically significant for Q3 and Q4 of age).
- Female sex is associated with a higher risk of ssi, not statistically signficant.
- Increased ASA classification categories are associated with an increased rik of SSI, statistically significant.
- CABG with donor site incision (not statistically significant), CABG + valve replacement, TKA (not statistically significant) and colon surgeries and rectal surgeries have a higher risk of ssi, statistically significant. Valve replacement surgeries (not statistically significant) and CABG with no donor site incision have a lower risk of infection compared to THA, statistically significant.
- Migrants have a lower risk of ssi compared to non-migrants, not statistically significant.
- Compared to non-migrants undergoing THA, migrants undergoing TKA, rectal resection, CABG with donor site incision and valve replacement, have a higher risk of ssi, not statistically significant.
- Compared to non-migrants undergoing THA, migrants undergoing colon resection have a lower risk of ssi, not statistically significant.
- Compared to non-migrants undergoing THA, migrants undergoing rectal resection (not statistically significant), CABG without donor site incision and valve replacement have a lower risk of ssi, statistically significant.

##                                exp(coef)     SE     CL      CU P-value
## (Intercept)                       0.0003 0.2776 0.0001  0.0004  0.0000
## surage_quartQ2 (60–68)            0.9628 0.1248 0.7539  1.2297  0.7616
## surage_quartQ3 (69–75)            0.6950 0.1395 0.5288  0.9135  0.0091
## surage_quartQ4 (>75)              0.7163 0.1443 0.5398  0.9505  0.0208
## asa_2II                           1.6845 0.2587 1.0145  2.7967  0.0438
## asa_2III                          2.2527 0.2804 1.3004  3.9025  0.0038
## asa_2IV/V                         3.1148 0.3182 1.6694  5.8115  0.0004
## surtypeRectal resection          13.1124 0.1811 9.1942 18.7005  0.0000
## surtypeTKA                        1.0454 0.2032 0.7020  1.5569  0.8269
## surtypeColon resection            7.7256 0.1766 5.4653 10.9208  0.0000
## surtypeCABG - DI                  2.1713 0.2327 1.3762  3.4259  0.0009
## surtypeCABG - SI                  0.7987 0.6166 0.2385  2.6746  0.7155
## surtypeValve replacement          0.6072 0.3234 0.3221  1.1445  0.1229
## surtypeCABG + valve               2.4183 0.3630 1.1871  4.9263  0.0150
## MSYes                             0.4385 0.7226 0.1064  1.8072  0.2539
## sexFemale                         1.0959 0.1049 0.8922  1.3461  0.3827
## surtypeRectal resection:MSYes     2.2010 0.7869 0.4708 10.2902  0.3161
## surtypeTKA:MSYes                  1.5541 0.9355 0.2484  9.7220  0.6374
## surtypeColon resection:MSYes      0.5112 1.0202 0.0692  3.7756  0.5107
## surtypeCABG - DI:MSYes            1.5992 0.7978 0.3349  7.6377  0.5562
## surtypeCABG - SI:MSYes            0.0000 0.9706 0.0000  0.0000  0.0000
## surtypeValve replacement:MSYes    0.0000 0.7830 0.0000  0.0000  0.0000
## surtypeCABG + valve:MSYes         3.8577 1.2259 0.3490 42.6427  0.2708

Model 4: age, sex, ASA, procedure, urgency, MS

Procedure: study classification

We adjust a Poisson regression model with robust variance for SSI, considering:

Age: quartiles
Sex
ASA: 4 categories
Surgical procedure: study classification
Urgency

>> INTERPRETATION:

Increasing age is associated with a reduced of ssi (statistically significant for Q3 and Q4 of age).
Female sex is associated with a higher risk of ssi, not statistically signficant.
Increased ASA classification categories are associated with an increased rik of SSI, statistically significant.
CABG, CABG + valve replacement and colon or rectal resection procedures have a higher ssi risk compared to THA, statistically significant. TKA procedures have a higher risk of ssi compared to THA, not statistically significant. Valve replacement surgeries have a lower ssi risk compared to THA, not statistically significant
Urgent and semi-elective surgeries hace a higher risk of ssi compared to elective surgeries, not statistically significant.
Migrants have a lower risk of ssi compared to non-migrants, statistically significant.

##                                    exp(coef)     SE     CL      CU P-value
## (Intercept)                           0.0003 0.2742 0.0001  0.0004  0.0000
## surage_quartQ2 (60–68)                0.9693 0.1245 0.7595  1.2371  0.8022
## surage_quartQ3 (69–75)                0.7015 0.1390 0.5342  0.9212  0.0108
## surage_quartQ4 (>75)                  0.7139 0.1445 0.5379  0.9477  0.0197
## sexFemale                             1.0635 0.1040 0.8675  1.3039  0.5535
## asa_2II                               1.7362 0.2585 1.0462  2.8813  0.0328
## asa_2III                              2.2421 0.2805 1.2939  3.8852  0.0040
## asa_2IV/V                             3.2040 0.3194 1.7131  5.9921  0.0003
## surtype_2TKA                          1.0728 0.1989 0.7264  1.5842  0.7240
## surtype_2Valve replacement            0.5692 0.3231 0.3022  1.0723  0.0812
## surtype_2CABG + valve                 2.5801 0.3526 1.2928  5.1492  0.0072
## surtype_2Colon or rectal resection    9.8690 0.1614 7.1926 13.5414  0.0000
## surtype_2CABG                         2.0932 0.2259 1.3445  3.2589  0.0011
## urgUrgent                             2.2475 1.0992 0.2607 19.3786  0.4613
## urgSemi-elective                      0.9543 0.2810 0.5502  1.6551  0.8677
## MSYes                                 0.6443 0.1929 0.4414  0.9403  0.0227

Procedure: vincat classification

We adjust a Poisson regression model with robust variance for SSI, considering:

Age: quartiles
Sex
ASA: 4 categories
Surgical procedure: vincat classification
Urgency
MS

>> INTERPRETATION:

Increasing age is associated with a reduced of ssi (statistically significant for Q3 and Q4 of age).
Female sex is associated with a higher risk of ssi, not statistically signficant.
Increased ASA classification categories are associated with an increased rik of SSI, statistically significant.
CABG with donor site incision, CABG + valve replacement, colon resection and rectal resection surgeries have a higher ssi risk compared to THA, statistically significant. TKA procedures have a higher risk of ssi compared to THA, not statistically significant. CABG without donor site incision and valve replacement surgeries have a lower ssi risk compared to THA, not statistically significant
Urgent and semi-elective surgeries hace a higher risk of ssi compared to elective surgeries, not statistically significant.
Migrants have a lower risk of ssi compared to non-migrants, statistically significant.

##                          exp(coef)     SE     CL      CU P-value
## (Intercept)                 0.0002 0.2747 0.0001  0.0004  0.0000
## surage_quartQ2 (60–68)      0.9703 0.1251 0.7594  1.2399  0.8097
## surage_quartQ3 (69–75)      0.6965 0.1394 0.5299  0.9153  0.0095
## surage_quartQ4 (>75)        0.7206 0.1447 0.5427  0.9569  0.0235
## sexFemale                   1.0924 0.1050 0.8893  1.3419  0.3997
## asa_2II                     1.6985 0.2592 1.0219  2.8228  0.0410
## asa_2III                    2.2806 0.2810 1.3149  3.9558  0.0033
## asa_2IV/V                   3.1863 0.3200 1.7018  5.9656  0.0003
## surtypeRectal resection    13.8432 0.1760 9.8045 19.5455  0.0000
## surtypeTKA                  1.0677 0.1989 0.7230  1.5767  0.7420
## surtypeColon resection      7.5747 0.1746 5.3800 10.6646  0.0000
## surtypeCABG - DI            2.2071 0.2273 1.4136  3.4460  0.0005
## surtypeCABG - SI            0.7060 0.6165 0.2109  2.3633  0.5722
## surtypeValve replacement    0.5601 0.3230 0.2974  1.0548  0.0727
## surtypeCABG + valve         2.5547 0.3523 1.2809  5.0955  0.0078
## urgUrgent                   2.8676 1.0978 0.3335 24.6595  0.3373
## urgSemi-elective            1.0141 0.2831 0.5822  1.7664  0.9605
## MSYes                       0.6281 0.1925 0.4307  0.9160  0.0157

Model 5: age, sex, procedure, ASA, preoperative length of stay, MS

Procedure: vincat

We adjust a Poisson regression model with robust variance for SSI, considering:

Age: quartiles
Sex
ASA: 4 categories
Surgical procedure: vincat classification
Preoperative length of stay: same day, 1-2 days, 3-7 days, > 7 days
MS

>> INTERPRETATION:

Increasing age is associated with a reduced of ssi (statistically significant for Q3 and Q4 of age).
Female sex is associated with a higher risk of ssi, not statistically signficant.
Increased ASA classification categories are associated with an increased rik of SSI, statistically significant.
CABG with donor site incision, CABG + valve replacement, colon resection and rectal resection surgeries have a higher ssi risk compared to THA, statistically significant. TKA procedures have a higher risk of ssi compared to THA, not statistically significant. CABG without donor site incision and valve replacement surgeries have a lower ssi risk compared to THA, not statistically significant
Preoperative length of stay: compared to patients intervened in the same day, patients intervened 1-2 days later have a lower risk of ssi, those intervened 3-7 days later have a higher higher risk of ssi, and those intervened >7 days later have a lower risk of ssi, NOT statistically significant
Migrants have a lower risk of ssi compared to non-migrants, statistically significant.

##                          exp(coef)     SE     CL      CU P-value
## (Intercept)                 0.0003 0.2771 0.0001  0.0004  0.0000
## surage_quartQ2 (60–68)      0.9711 0.1252 0.7598  1.2410  0.8145
## surage_quartQ3 (69–75)      0.6975 0.1397 0.5304  0.9172  0.0099
## surage_quartQ4 (>75)        0.7235 0.1448 0.5448  0.9610  0.0254
## sexFemale                   1.0938 0.1048 0.8907  1.3433  0.3921
## asa_2II                     1.6869 0.2583 1.0167  2.7989  0.0430
## asa_2III                    2.2519 0.2808 1.2987  3.9048  0.0038
## asa_2IV/V                   3.0933 0.3211 1.6487  5.8036  0.0004
## surtypeRectal resection    14.3917 0.2059 9.6130 21.5459  0.0000
## surtypeTKA                  1.0676 0.1989 0.7229  1.5767  0.7422
## surtypeColon resection      7.8485 0.2053 5.2482 11.7372  0.0000
## surtypeCABG - DI            2.1733 0.2591 1.3080  3.6111  0.0027
## surtypeCABG - SI            0.7115 0.6293 0.2073  2.4426  0.5886
## surtypeValve replacement    0.5695 0.3428 0.2908  1.1151  0.1006
## surtypeCABG + valve         2.5890 0.3710 1.2512  5.3575  0.0104
## preoplos_cat21-2 days       0.9403 0.1605 0.6865  1.2879  0.7013
## preoplos_cat23-7 days       1.2554 0.2469 0.7738  2.0368  0.3569
## preoplos_cat2>7 days        1.0240 0.2716 0.6013  1.7436  0.9305
## MSYes                       0.6266 0.1915 0.4305  0.9119  0.0146

Procedure: study classification

We adjust a Poisson regression model with robust variance for SSI, considering:

Age: quartiles
Sex
ASA: 4 categories
Surgical procedure: study classification
Preoperative length of stay: same day, 1-2 days, 3-7 days, > 7 days
MS

>> INTERPRETATION:

Increasing age is associated with a reduced of ssi (statistically significant for Q3 and Q4 of age).
Female sex is associated with a higher risk of ssi, not statistically signficant.
Increased ASA classification categories are associated with an increased rik of SSI, statistically significant.
CABG CABG + valve replacement, colon/rectal resection surgeries have a higher ssi risk compared to THA, statistically significant. TKA procedures have a higher risk of ssi compared to THA, not statistically significant. Valve replacement surgeries have a lower ssi risk compared to THA, not statistically significant.
Preoperative length of stay: compared to patients intervened in the same day, patients intervened 1-2 days later have a lower risk of ssi, those intervened 3-7 days later have a higher higher risk of ssi, and those intervened >7 days later have a lower risk of ssi, NOT statistically significant
Migrants have a lower risk of ssi compared to non-migrants, statistically significant.

##                                    exp(coef)     SE     CL      CU P-value
## (Intercept)                           0.0003 0.2776 0.0001  0.0004  0.0000
## surage_quartQ2 (60–68)                0.9706 0.1246 0.7604  1.2391  0.8109
## surage_quartQ3 (69–75)                0.7014 0.1394 0.5337  0.9218  0.0110
## surage_quartQ4 (>75)                  0.7178 0.1448 0.5405  0.9533  0.0220
## sexFemale                             1.0627 0.1037 0.8672  1.3022  0.5579
## asa_2II                               1.7230 0.2577 1.0397  2.8554  0.0348
## asa_2III                              2.2128 0.2804 1.2772  3.8335  0.0046
## asa_2IV/V                             3.1192 0.3204 1.6646  5.8446  0.0004
## surtype_2TKA                          1.0738 0.1989 0.7272  1.5858  0.7203
## surtype_2Valve replacement            0.5712 0.3424 0.2920  1.1176  0.1020
## surtype_2CABG + valve                 2.5798 0.3707 1.2475  5.3350  0.0106
## surtype_2Colon or rectal resection   10.0944 0.1926 6.9202 14.7247  0.0000
## surtype_2CABG                         2.0499 0.2565 1.2400  3.3890  0.0051
## preoplos_cat21-2 days                 0.9621 0.1589 0.7047  1.3135  0.8078
## preoplos_cat23-7 days                 1.2716 0.2436 0.7889  2.0497  0.3240
## preoplos_cat2>7 days                  0.9553 0.2674 0.5657  1.6134  0.8642
## MSYes                                 0.6437 0.1919 0.4419  0.9376  0.0217

Model 6: age, sex, procedure, ASA, duration, MS

Procedure: vincat

We adjust a Poisson regression model with robust variance for SSI, considering:

Age: quartiles
Sex
ASA: 4 categories
Surgical procedure: vincat classification
Duration (quartiles): <90, 90-120, 121-186, >186
MS

>> INTERPRETATION:

Increasing age is associated with a reduced of ssi (statistically significant for Q3 and Q4 of age).
Female sex is associated with a higher risk of ssi, not statistically signficant.
Increased ASA classification categories are associated with an increased rik of SSI, statistically significant.
Colon resection and rectal resection surgeries have a higher ssi risk compared to THA, statistically significant. Valve replacement surgery have a lower risk of ssi compared o THA, statistically significant. TKA, CABG + valve replacement, CABG with donor site incision procedures have a higher risk of ssi compared to THA, not statistically significant. CABG without donor site incision have a lower ssi risk compared to THA, not statistically significant.
Surgery duration: increased duration is associated to an increased risk of ssi, statistically significant for 121-1886 and >186

Migrants have a lower risk of ssi compared to non-migrants, statistically significant.

##                          exp(coef)     SE     CL      CU P-value
## (Intercept)                 0.0002 0.3048 0.0001  0.0004  0.0000
## surage_quartQ2 (60–68)      0.9715 0.1257 0.7594  1.2429  0.8181
## surage_quartQ3 (69–75)      0.6903 0.1396 0.5250  0.9076  0.0079
## surage_quartQ4 (>75)        0.7123 0.1450 0.5362  0.9464  0.0193
## sexFemale                   1.1261 0.1047 0.9172  1.3825  0.2567
## asa_2II                     1.7127 0.2595 1.0299  2.8482  0.0381
## asa_2III                    2.2164 0.2811 1.2775  3.8456  0.0046
## asa_2IV/V                   3.1425 0.3209 1.6753  5.8947  0.0004
## surtypeRectal resection    10.7224 0.1980 7.2743 15.8049  0.0000
## surtypeTKA                  1.1479 0.2017 0.7731  1.7043  0.4941
## surtypeColon resection      6.4765 0.1831 4.5235  9.2726  0.0000
## surtypeCABG - DI            1.3998 0.2713 0.8225  2.3824  0.2151
## surtypeCABG - SI            0.4819 0.6233 0.1421  1.6350  0.2415
## surtypeValve replacement    0.3790 0.3489 0.1913  0.7509  0.0054
## surtypeCABG + valve         1.5673 0.3807 0.7432  3.3050  0.2378
## duration_cat90–120          1.2274 0.1764 0.8686  1.7344  0.2454
## duration_cat121–186         1.4845 0.1874 1.0281  2.1435  0.0351
## duration_cat>186            2.0530 0.2138 1.3501  3.1218  0.0008
## MSYes                       0.6313 0.1911 0.4341  0.9181  0.0161

Procedure: study classification

We adjust a Poisson regression model with robust variance for SSI, considering:

Age: quartiles
Sex
ASA: 4 categories
Surgical procedure: study classification
Duration (quartiles): <90, 90-120, 121-186, >186
MS

>> INTERPRETATION:

Increasing age is associated with a reduced of ssi (statistically significant for Q3 and Q4 of age).
Female sex is associated with a higher risk of ssi, not statistically signficant.
Increased ASA classification categories are associated with an increased rik of SSI, statistically significant.
Colorectal resection surgeries have a higher ssi risk compared to THA, statistically significant. Valve replacement surgery have a lower risk of ssi compared o THA, statistically significant. TKA, CABG and CABG + valve replacement procedures have a higher risk of ssi compared to THA, not statistically significant.
Surgery duration: increased duration is associated to an increased risk of ssi, statistically significant for 121-1886 and >186

Migrants have a lower risk of ssi compared to non-migrants, statistically significant.

##                                    exp(coef)     SE     CL      CU P-value
## (Intercept)                           0.0002 0.3045 0.0001  0.0004  0.0000
## surage_quartQ2 (60–68)                0.9656 0.1251 0.7556  1.2340  0.7799
## surage_quartQ3 (69–75)                0.6922 0.1392 0.5269  0.9093  0.0082
## surage_quartQ4 (>75)                  0.7070 0.1447 0.5324  0.9389  0.0166
## sexFemale                             1.1055 0.1039 0.9019  1.3551  0.3343
## asa_2II                               1.7513 0.2589 1.0543  2.9093  0.0305
## asa_2III                              2.1830 0.2809 1.2587  3.7861  0.0055
## asa_2IV/V                             3.1639 0.3211 1.6863  5.9362  0.0003
## surtype_2TKA                          1.1559 0.2018 0.7783  1.7167  0.4729
## surtype_2Valve replacement            0.3508 0.3476 0.1775  0.6933  0.0026
## surtype_2CABG + valve                 1.4170 0.3783 0.6751  2.9741  0.3568
## surtype_2Colon or rectal resection    7.7573 0.1746 5.5096 10.9222  0.0000
## surtype_2CABG                         1.2022 0.2651 0.7151  2.0213  0.4872
## duration_cat90–120                    1.1950 0.1765 0.8455  1.6890  0.3129
## duration_cat121–186                   1.5395 0.1860 1.0692  2.2168  0.0204
## duration_cat>186                      2.2923 0.2094 1.5206  3.4556  0.0001
## MSYes                                 0.6422 0.1915 0.4412  0.9347  0.0207

Model 7: age, sex, procedure, ASA, duration, surgery year, MS

Surgery year: categorical

We adjust a Poisson regression model with robust variance for SSI, considering:

Age: quartiles
Sex
ASA: 4 categories
Surgical procedure: study classification
Duration (quartiles): <90, 90-120, 121-186, >186
Surgery year (suryear_cat)
MS

>> INTERPRETATION:

Increasing age is associated with a reduced of ssi (statistically significant for Q3 and Q4 of age).
Female sex is associated with a higher risk of ssi, not statistically signficant.
Increased ASA classification categories are associated with an increased rik of SSI, statistically significant.
Colorectal resection surgeries have a higher ssi risk compared to THA, statistically significant. Valve replacement surgery have a lower risk of ssi compared o THA, statistically significant. TKA, CABG and CABG + valve replacement procedures have a higher risk of ssi compared to THA, not statistically significant.
Surgery duration: increased duration is associated to an increased risk of ssi, statistically significant for 121-1886 and >186
Surgery year: compared to patients intervened in the 2008-2012 period, those intervened in later periods have a significantly higher risk of ssi.

Migrants have a lower risk of ssi compared to non-migrants, statistically significant.

##                                    exp(coef)     SE     CL      CU P-value
## (Intercept)                           0.0002 0.3183 0.0001  0.0003  0.0000
## surage_quartQ2 (60–68)                0.9675 0.1252 0.7570  1.2365  0.7916
## surage_quartQ3 (69–75)                0.6940 0.1404 0.5270  0.9138  0.0093
## surage_quartQ4 (>75)                  0.7093 0.1454 0.5335  0.9431  0.0181
## sexFemale                             1.1047 0.1040 0.9010  1.3544  0.3382
## asa_2II                               1.7574 0.2597 1.0563  2.9236  0.0299
## asa_2III                              2.2167 0.2814 1.2770  3.8479  0.0047
## asa_2IV/V                             3.2135 0.3214 1.7116  6.0333  0.0003
## surtype_2TKA                          1.1539 0.2032 0.7748  1.7184  0.4812
## surtype_2Valve replacement            0.3917 0.3479 0.1981  0.7747  0.0071
## surtype_2CABG + valve                 1.5473 0.3791 0.7360  3.2530  0.2496
## surtype_2Colon or rectal resection    7.7370 0.1749 5.4912 10.9013  0.0000
## surtype_2CABG                         1.3076 0.2643 0.7789  2.1951  0.3103
## duration_cat90–120                    1.1936 0.1786 0.8411  1.6939  0.3218
## duration_cat121–186                   1.5515 0.1917 1.0655  2.2592  0.0220
## duration_cat>186                      2.3216 0.2155 1.5217  3.5420  0.0001
## suryear_cat2013-2016                  1.4145 0.1622 1.0293  1.9439  0.0325
## suryear_cat2017-2020                  1.3774 0.1648 0.9971  1.9027  0.0521
## suryear_cat2021-2024                  1.1049 0.1449 0.8318  1.4676  0.4912
## MSYes                                 0.6480 0.1928 0.4441  0.9456  0.0244

Surgery year: original format

We adjust a Poisson regression model with robust variance for SSI, considering:

Age: quartiles
Sex
ASA: 4 categories
Surgical procedure: study classification
Duration (quartiles): <90, 90-120, 121-186, >186
Surgery year (suryear)
MS

>> INTERPRETATION:

Increasing age is associated with a reduced of ssi (statistically significant for Q3 and Q4 of age).
Female sex is associated with a higher risk of ssi, not statistically signficant.
Increased ASA classification categories are associated with an increased rik of SSI, statistically significant.
Colorectal resection surgeries have a higher ssi risk compared to THA, statistically significant. Valve replacement surgery have a lower risk of ssi compared o THA, not statistically significant. TKA, CABG and CABG + valve replacement procedures have a higher risk of ssi compared to THA, not statistically significant.
Surgery duration: increased duration is associated to an increased risk of ssi, statistically significant for 121-1886 and >186
Surgery year: compared to patients intervened in the year 2008, those intervened in later years have a higher riks of ssi (statistically significant for 2022), except for years 2009, 2012 and 2024 (lower risk of ssi, not statistically significant).

Migrants have a lower risk of ssi compared to non-migrants, statistically significant.

##                                    exp(coef)     SE     CL      CU P-value
## (Intercept)                           0.0001 0.5459 0.0000  0.0004  0.0000
## surage_quartQ2 (60–68)                0.9689 0.1253 0.7579  1.2387  0.8009
## surage_quartQ3 (69–75)                0.6934 0.1404 0.5266  0.9131  0.0091
## surage_quartQ4 (>75)                  0.7095 0.1450 0.5340  0.9427  0.0179
## sexFemale                             1.1106 0.1041 0.9057  1.3619  0.3132
## asa_2II                               1.7638 0.2610 1.0574  2.9420  0.0297
## asa_2III                              2.1998 0.2820 1.2657  3.8231  0.0052
## asa_2IV/V                             3.2373 0.3210 1.7256  6.0732  0.0003
## surtype_2TKA                          1.1492 0.2037 0.7708  1.7132  0.4950
## surtype_2Valve replacement            0.4507 0.3561 0.2242  0.9057  0.0252
## surtype_2CABG + valve                 1.8188 0.3832 0.8583  3.8541  0.1185
## surtype_2Colon or rectal resection    8.0030 0.1767 5.6606 11.3149  0.0000
## surtype_2CABG                         1.5547 0.2690 0.9176  2.6340  0.1009
## duration_cat90–120                    1.1964 0.1791 0.8422  1.6996  0.3168
## duration_cat121–186                   1.5583 0.1916 1.0704  2.2684  0.0206
## duration_cat>186                      2.2720 0.2159 1.4881  3.4689  0.0001
## suryear2009                           1.0535 0.5532 0.3562  3.1153  0.9250
## suryear2010                           1.1674 0.5360 0.4083  3.3381  0.7727
## suryear2011                           1.4518 0.5022 0.5426  3.8849  0.4578
## suryear2012                           0.9703 0.5162 0.3528  2.6687  0.9534
## suryear2013                           1.1811 0.5048 0.4392  3.1764  0.7416
## suryear2014                           2.0754 0.5101 0.7637  5.6398  0.1523
## suryear2015                           1.7136 0.5061 0.6354  4.6210  0.2873
## suryear2016                           2.0093 0.5043 0.7478  5.3991  0.1665
## suryear2017                           1.6224 0.5076 0.5999  4.3878  0.3404
## suryear2018                           1.7855 0.5019 0.6676  4.7753  0.2481
## suryear2019                           1.6677 0.5000 0.6259  4.4436  0.3064
## suryear2020                           1.5687 0.5070 0.5807  4.2377  0.3746
## suryear2021                           2.2005 0.5114 0.8076  5.9954  0.1230
## suryear2022                           1.1865 0.4765 0.4663  3.0189  0.7196
## suryear2023                           1.3070 0.4787 0.5114  3.3400  0.5760
## suryear2024                           1.0414 0.4821 0.4048  2.6789  0.9330
## MSYes                                 0.6568 0.1938 0.4493  0.9603  0.0301

Model 8: age, sex, procedure, ASA, duration, surgery year, income, MS

We adjust a Poisson regression model with robust variance for SSI, considering:

Age: quartiles
Sex
ASA: 4 categories
Surgical procedure: study classification
Duration (quartiles): <90, 90-120, 121-186, >186
Surgery year (suryear_cat)
Income
MS

>> INTERPRETATION:

Increasing age is associated with a reduced of ssi (statistically significant for Q3 and Q4 of age).
Female sex is associated with a higher risk of ssi, not statistically signficant.
Increased ASA classification categories are associated with an increased rik of SSI, statistically significant.
Colorectal resection surgeries have a higher ssi risk compared to THA, statistically significant. Valve replacement surgery have a lower risk of ssi compared o THA, statistically significant. TKA, CABG and CABG + valve replacement procedures have a higher risk of ssi compared to THA, not statistically significant.
Surgery duration: increased duration is associated to an increased risk of ssi, statistically significant for 121-1886 and >186
Surgery year: compared to patients intervened in the 2008-2012 period, those intervened in later periods have a significantly higher risk of ssi.
Income: differences not statistically significant

Migrants have a lower risk of ssi compared to non-migrants, statistically significant.

##                                    exp(coef)     SE     CL      CU P-value
## (Intercept)                           0.0002 0.3229 0.0001  0.0003  0.0000
## surage_quartQ2 (60–68)                0.9663 0.1250 0.7562  1.2346  0.7838
## surage_quartQ3 (69–75)                0.6920 0.1405 0.5254  0.9114  0.0088
## surage_quartQ4 (>75)                  0.7092 0.1458 0.5330  0.9438  0.0185
## sexFemale                             1.1081 0.1047 0.9026  1.3604  0.3266
## asa_2II                               1.7649 0.2599 1.0604  2.9373  0.0288
## asa_2III                              2.2293 0.2820 1.2826  3.8748  0.0045
## asa_2IV/V                             3.2451 0.3221 1.7262  6.1006  0.0003
## surtype_2TKA                          1.1534 0.2031 0.7746  1.7173  0.4823
## surtype_2Valve replacement            0.3889 0.3479 0.1967  0.7691  0.0066
## surtype_2CABG + valve                 1.5281 0.3791 0.7269  3.2126  0.2634
## surtype_2Colon or rectal resection    7.7382 0.1749 5.4923 10.9024  0.0000
## surtype_2CABG                         1.2971 0.2646 0.7722  2.1788  0.3256
## duration_cat90–120                    1.1940 0.1786 0.8414  1.6945  0.3207
## duration_cat121–186                   1.5568 0.1920 1.0686  2.2680  0.0211
## duration_cat>186                      2.3386 0.2161 1.5312  3.5718  0.0001
## suryear_cat2013-2016                  1.4102 0.1628 1.0249  1.9404  0.0348
## suryear_cat2017-2020                  1.3749 0.1643 0.9963  1.8974  0.0527
## suryear_cat2021-2024                  1.0995 0.1460 0.8259  1.4639  0.5157
## income18.000 - 100.000 euros          1.0404 0.0980 0.8585  1.2607  0.6864
## income> 100.000 euros                 0.7331 0.4219 0.3206  1.6761  0.4618
## MSYes                                 0.6530 0.1937 0.4467  0.9546  0.0278

Poisson regression models: females, all procedures

Model f7: age, sex, procedure, ASA, duration, surgery year, MS

We adjust a Poisson regression model with robust variance for SSI, considering only male patients.

Age: quartiles
ASA: 4 categories
Surgical procedure: study classification
Duration (quartiles): <90, 90-120, 121-186, >186
Surgery year (suryear_cat)
MS

>> INTERPRETATION:

Increasing age is associated with a reduced of ssi. NOT statistically significant.
Increased ASA classification categories are associated with an increased rik of SSI, NOT statistically significant.
Colorectal resection, CABG and CABG + valve surgeries have a higher ssi risk compared to THA, statistically significant. TKA procedures have a higher risk of ssi compared to THA, not statistically significant. Valve replacement surgerie have a lower risk of ssi compared to THA, not statistically significant.
Surgery duration: increased duration is associated to an increased risk of ssi, statistically significant for >186 minutes
Surgery year: compared to patients intervened in the 2008-2012 period, those intervened in later periods have a higher risk of ssi. Statistically significant for 2021-2014 period.

Migrants have a lower risk of ssi compared to non-migrants, NOT statistically significant.

##                                    exp(coef)     SE     CL      CU P-value
## (Intercept)                           0.0002 0.4354 0.0001  0.0004  0.0000
## surage_quartQ2 (60–68)                0.8453 0.2066 0.5638  1.2674  0.4161
## surage_quartQ3 (69–75)                0.7441 0.2117 0.4914  1.1268  0.1627
## surage_quartQ4 (>75)                  0.6891 0.2186 0.4489  1.0578  0.0885
## asa_2II                               1.6038 0.3459 0.8141  3.1593  0.1721
## asa_2III                              1.8337 0.3939 0.8473  3.9687  0.1238
## asa_2IV/V                             2.2994 0.5094 0.8472  6.2409  0.1022
## surtype_2TKA                          1.5396 0.2963 0.8613  2.7518  0.1453
## surtype_2Valve replacement            0.5607 0.5502 0.1907  1.6482  0.2929
## surtype_2CABG + valve                 3.4230 0.5757 1.1075 10.5793  0.0326
## surtype_2Colon or rectal resection   10.8564 0.2787 6.2876 18.7452  0.0000
## surtype_2CABG                         3.2451 0.4410 1.3672  7.7024  0.0076
## duration_cat90–120                    1.2622 0.2352 0.7961  2.0012  0.3221
## duration_cat121–186                   1.3079 0.2646 0.7787  2.1967  0.3103
## duration_cat>186                      2.3315 0.3100 1.2700  4.2805  0.0063
## suryear_cat2013-2016                  1.3350 0.2399 0.8342  2.1365  0.2284
## suryear_cat2017-2020                  1.2375 0.2418 0.7705  1.9875  0.3781
## suryear_cat2021-2024                  1.1189 0.2241 0.7213  1.7359  0.6160
## MSYes                                 0.7646 0.2740 0.4469  1.3082  0.3273

Model m7: age, sex, procedure, ASA, duration, surgery year, MS

We adjust a Poisson regression model with robust variance for SSI, considering only female patients.

Age: quartiles
ASA: 4 categories
Surgical procedure: study classification
Duration (quartiles): <90, 90-120, 121-186, >186
Surgery year (suryear_cat)
MS

>> INTERPRETATION:

Compared to patients aged <60 years, those aged 60-68 have a higher risk of ssi, NOT statistically significant, those aged 69-75 have a lower risk of ssi, statistically significant, and those aged >75 have a lower risk of ssi, NOT statistically significant
Increased ASA classification categories are associated with an increased rik of SSI, statistically significant for ASA III and ASA IV/V.
Colorectal resection surgeries have a higher ssi risk compared to THA, statistically significant. Valve replacement surgery have a lower risk of ssi compared o THA, statistically significant. TKA, CABG and CABG + valve replacement procedures have a lower risk of ssi compared to THA, not statistically significant.
Surgery duration: increased duration is associated to an increased risk of ssi, statistically significant for >186 minutes
Surgery year: compared to patients intervened in the 2008-2012 period, those intervened in later periods have a significantly higher risk of ssi.

Migrants have a lower risk of ssi compared to non-migrants, statistically significant.

##                                    exp(coef)     SE     CL     CU P-value
## (Intercept)                           0.0002 0.4571 0.0001 0.0004  0.0000
## surage_quartQ2 (60–68)                1.0386 0.1577 0.7624 1.4148  0.8104
## surage_quartQ3 (69–75)                0.6378 0.1920 0.4378 0.9292  0.0192
## surage_quartQ4 (>75)                  0.7356 0.1972 0.4999 1.0826  0.1194
## asa_2II                               1.9464 0.4017 0.8857 4.2772  0.0974
## asa_2III                              2.5568 0.4227 1.1166 5.8545  0.0264
## asa_2IV/V                             3.9721 0.4565 1.6235 9.7181  0.0025
## surtype_2TKA                          0.9512 0.3069 0.5213 1.7356  0.8704
## surtype_2Valve replacement            0.3148 0.4500 0.1303 0.7606  0.0102
## surtype_2CABG + valve                 0.9249 0.5027 0.3453 2.4775  0.8766
## surtype_2Colon or rectal resection    5.9596 0.2278 3.8133 9.3140  0.0000
## surtype_2CABG                         0.8619 0.3284 0.4528 1.6404  0.6508
## duration_cat90–120                    1.1267 0.2732 0.6595 1.9248  0.6624
## duration_cat121–186                   1.7427 0.2858 0.9953 3.0513  0.0520
## duration_cat>186                      2.3107 0.3127 1.2519 4.2650  0.0074
## suryear_cat2013-2016                  1.4715 0.2223 0.9518 2.2749  0.0822
## suryear_cat2017-2020                  1.4667 0.2281 0.9380 2.2935  0.0931
## suryear_cat2021-2024                  1.0841 0.1912 0.7453 1.5770  0.6727
## MSYes                                 0.5516 0.2744 0.3222 0.9445  0.0302

Poisson regression models: both sexes, selected procedures

Model 7colorect: age, sex, ASA, duration, surgery year, MS

We adjust a Poisson regression model with robust variance for SSI, considering only colorectal procedures

Age: quartiles
Sex
ASA: 4 categories
Duration (quartiles): <90, 90-120, 121-186, >186
Surgery year (suryear_cat)
MS

>> INTERPRETATION:

Compared to patients aged <60 years, older patients have a lower risk of ssi, not statistically significant
Female patients have a lower ssi risk compared to males, not statistically significant
Increased ASA classification categories are associated with an increased rik of SSI, not statistically significant.
Surgery duration: compared to patients with a surgery shorter han 9o minutes, those with a surgery 90-120 minutes have a lower ssi risk, not statistically significant, and those with a surgery 121-186 and >186 minutes have a higher ssi risk, statistically significant for >186 minutes.
Surgery year: compared to patients intervened in the 2008-2012 period, those intervened in later periods have a higher risk of ssi (except for those intervened in the 2017-2020 period), not statistically significant.

Migrants have a lower risk of ssi compared to non-migrants, not statistically significant.

##                        exp(coef)     SE     CL     CU P-value
## (Intercept)               0.0019 0.4745 0.0008 0.0048  0.0000
## surage_quartQ2 (60–68)    0.7656 0.1808 0.5371 1.0912  0.1396
## surage_quartQ3 (69–75)    0.7395 0.2009 0.4987 1.0964  0.1331
## surage_quartQ4 (>75)      0.6910 0.1996 0.4673 1.0217  0.0640
## sexFemale                 1.0174 0.1360 0.7794 1.3281  0.8989
## asa_2II                   1.7767 0.3755 0.8511 3.7087  0.1259
## asa_2III                  1.9256 0.4084 0.8649 4.2870  0.1086
## asa_2IV/V                 1.7369 0.8198 0.3483 8.6612  0.5007
## duration_cat90–120        0.9772 0.2847 0.5593 1.7075  0.9355
## duration_cat121–186       1.5017 0.2666 0.8905 2.5323  0.1272
## duration_cat>186          2.4788 0.2709 1.4577 4.2150  0.0008
## suryear_cat2013-2016      1.1405 0.2062 0.7613 1.7084  0.5238
## suryear_cat2017-2020      0.8996 0.2104 0.5955 1.3588  0.6151
## suryear_cat2021-2024      0.8327 0.2119 0.5497 1.2613  0.3874
## MSYes                     0.7148 0.2799 0.4130 1.2373  0.2304

Model7rect: age, sex, ASA, duration, surgery year, MS

We adjust a Poisson regression model with robust variance for SSI, considering only rectal resection procedures

Age: quartiles
Sex
ASA: 4 categories
Duration (quartiles): <90, 90-120, 121-186, >186
Surgery year (suryear_cat)
MS

>> INTERPRETATION:

Compared to patients aged <60 years, patients aged 60-68 years have a higher risk of ssi, not statistically significant, and patients aged 69-75 and >75 years have a lower risk of ssi, not statistically significant
Female patients have a higher ssi risk compared to males, not statistically significant
Increased ASA classification categories are associated with an increased rik of SSI, not statistically significant.
Surgery duration: compared to patients with a surgery shorter than 90 minutes, those with a longer surgery have a higher ssi risk, statistically significant for >186 minutes.
Surgery year: compared to patients intervened in the 2008-2012 period, those intervened in later periods have a higher risk of ssi, statistically significant for 2021-2024.

Migrants have a HIGHER risk of ssi compared to non-migrants, not statistically significant.

##                        exp(coef)     SE     CL      CU P-value
## (Intercept)               0.0024 0.6661 0.0006  0.0088  0.0000
## surage_quartQ2 (60–68)    0.8962 0.2571 0.5415  1.4832  0.6698
## surage_quartQ3 (69–75)    0.7915 0.2907 0.4477  1.3994  0.4213
## surage_quartQ4 (>75)      0.7677 0.2760 0.4470  1.3185  0.3381
## sexFemale                 1.1756 0.1994 0.7953  1.7378  0.4172
## asa_2II                   1.2580 0.4980 0.4739  3.3389  0.6450
## asa_2III                  1.5207 0.5533 0.5142  4.4978  0.4487
## asa_2IV/V                 1.0345 1.1652 0.1054 10.1516  0.9768
## duration_cat90–120        1.5716 0.4710 0.6244  3.9555  0.3371
## duration_cat121–186       1.7188 0.4416 0.7233  4.0843  0.2200
## duration_cat>186          2.4063 0.4404 1.0150  5.7046  0.0462
## suryear_cat2013-2016      1.1565 0.3219 0.6153  2.1735  0.6516
## suryear_cat2017-2020      1.0629 0.3285 0.5583  2.0234  0.8528
## suryear_cat2021-2024      0.7951 0.3377 0.4102  1.5413  0.4972
## MSYes                     1.0694 0.3201 0.5710  2.0028  0.8341

Model7col: age, sex, ASA, duration, surgery year, MS

We adjust a Poisson regression model with robust variance for SSI, considering only colon resection procedures

Age: quartiles
Sex
ASA: 4 categories
Duration (quartiles): <90, 90-120, 121-186, >186
Surgery year (suryear_cat)
MS

>> INTERPRETATION:

Compared to patients aged <60 years, older patients have a lower risk of ssi, statistically significant for 60-68.
Female patients have a lower ssi risk compared to males, not statistically significant
Increased ASA classification categories are associated with an increased rik of SSI, not statistically significant.
Surgery duration: compared to patients with a surgery shorter than 90 minutes, those with a surgery duration 90-120 minutes have a lower ssi risk not statistically significant, and those with a surgery duration 121-186 and >186 minutes have a higher ssi risk (statistically significant for >186 minutes).
Surgery year: compared to patients intervened in the 2008-2012 period, those intervened in later periods have a lower risk of ssi, not statistically significant.

Migrants have a lower risk of ssi compared to non-migrants, statistically significant.

##                        exp(coef)     SE     CL      CU P-value
## (Intercept)               0.0016 0.7428 0.0004  0.0069  0.0000
## surage_quartQ2 (60–68)    0.6636 0.2550 0.4026  1.0938  0.1077
## surage_quartQ3 (69–75)    0.7219 0.2803 0.4167  1.2505  0.2451
## surage_quartQ4 (>75)      0.6324 0.2884 0.3594  1.1129  0.1121
## sexFemale                 0.9150 0.1967 0.6222  1.3455  0.6516
## asa_2II                   2.5042 0.5951 0.7801  8.0390  0.1229
## asa_2III                  2.6485 0.6268 0.7752  9.0480  0.1202
## asa_2IV/V                 2.6041 1.1891 0.2532 26.7805  0.4209
## duration_cat90–120        0.8077 0.3648 0.3951  1.6510  0.5582
## duration_cat121–186       1.3202 0.3489 0.6662  2.6161  0.4260
## duration_cat>186          2.4234 0.3585 1.2002  4.8932  0.0135
## suryear_cat2013-2016      0.9731 0.2858 0.5558  1.7038  0.9240
## suryear_cat2017-2020      0.6861 0.2927 0.3865  1.2177  0.1980
## suryear_cat2021-2024      0.8287 0.2788 0.4799  1.4311  0.5002
## MSYes                     0.2190 0.7247 0.0529  0.9061  0.0361

Model 7orthopedic: age, sex, ASA, duration, surgery year, MS

We adjust a Poisson regression model with robust variance for SSI, considering only orthopedic procedures

Age: quartiles
Sex
ASA: 4 categories
Duration (quartiles): <90, 90-120, 121-186, >186
Surgery year (suryear_cat)
MS

>> INTERPRETATION:

Compared to patients aged <60 years, those aged 60-68 have a higher risk of ssi, and those aged 69-75 or >75 have a lower risk, not statistically significant
Female patients have a lower ssi risk compared to males, not statistically significant
Increased ASA classification categories are associated with an increased rik of SSI, statistically significant for ASA III.
Surgery duration: compared to patients with a surgery shorter than 9o minutes, those with a slonger surgery have a higher ssi risk, statistically significant for 121-186 minutes.
Surgery year: compared to patients intervened in the 2008-2012 period, those intervened in later periods have a higher risk of ssi (except for those intervened in the 2020-2024 period), statistically significant for 2013-2016 and 2017-2020.

Migrants have a lower risk of ssi compared to non-migrants, NOT statistically significant.

##                        exp(coef)     SE     CL      CU P-value
## (Intercept)               0.0001 0.4247 0.0001  0.0003  0.0000
## surage_quartQ2 (60–68)    1.3210 0.2684 0.7806  2.2354  0.2996
## surage_quartQ3 (69–75)    0.6797 0.2863 0.3878  1.1912  0.1774
## surage_quartQ4 (>75)      0.5926 0.3041 0.3265  1.0755  0.0853
## sexFemale                 0.9037 0.1923 0.6199  1.3172  0.5982
## asa_2II                   1.8374 0.3652 0.8981  3.7591  0.0958
## asa_2III                  3.3101 0.3885 1.5457  7.0889  0.0021
## asa_2IV/V                 3.4870 1.0625 0.4345 27.9817  0.2398
## duration_cat90–120        1.4586 0.2254 0.9377  2.2690  0.0940
## duration_cat121–186       2.0178 0.2904 1.1420  3.5652  0.0156
## duration_cat>186          3.5222 0.7603 0.7936 15.6315  0.0977
## suryear_cat2013-2016      1.5280 0.3047 0.8409  2.7765  0.1641
## suryear_cat2017-2020      1.6917 0.2869 0.9641  2.9684  0.0669
## suryear_cat2021-2024      0.5153 0.3701 0.2495  1.0645  0.0733
## MSYes                     0.6260 0.4625 0.2529  1.5497  0.3112

Model 7cardiac: age, sex, ASA, duration, surgery year, MS

We adjust a Poisson regression model with robust variance for SSI, considering only cardiac procedures

Age: quartiles
Sex
ASA: 4 categories
Duration (quartiles): <90, 90-120, 121-186, >186
Surgery year (suryear_cat). Since the 2014-2021 period doesn’t have any cardiac procedure, we exclude these years from the analysis
MS

>> INTERPRETATION:

Compared to patients aged <60 years, patients 69-75 have a lower risk of ssi, and those 60-68 and >75 years have a higher ssi risk, not statistically significant
Female patients have a higher ssi risk compared to males, statistically significant
Increased ASA classification categories are associated with an increased rik of SSI, statistically significant.
Surgery duration: compared to patients with a surgery shorter than 90 minutes, those with a longer surgery have a lower ssi risk, statistically significant for 121-186 and >186 minutes.
Surgery year: compared to patients intervened in the 2008-2013 period, those intervened in the 2022-2024 period have a higher risk of ssi, statistically significant.

Migrants have a lower risk of ssi compared to non-migrants, not statistically significant.

##                         exp(coef)     SE        CL          CU P-value
## (Intercept)                0.0000 1.2127    0.0000      0.0000  0.0000
## surage_quartQ2 (60–68)     1.2933 0.2431    0.8030      2.0829  0.2901
## surage_quartQ3 (69–75)     0.7474 0.2716    0.4389      1.2727  0.2837
## surage_quartQ4 (>75)       1.1437 0.2917    0.6457      2.0258  0.6452
## sexFemale                  1.3204 0.2032    0.8866      1.9666  0.1714
## asa_2II                 9828.2924 1.2490  849.7805 113670.9227  0.0000
## asa_2III                9392.2989 1.0961 1095.9037  80495.4692  0.0000
## asa_2IV/V              14851.0289 1.0942 1739.2615 126808.4542  0.0000
## duration_cat90–120         0.6894 0.7533    0.1575      3.0177  0.6215
## duration_cat121–186        0.2036 0.6151    0.0610      0.6796  0.0097
## duration_cat>186           0.3825 0.5351    0.1340      1.0918  0.0725
## suryear_card2022–2024      1.8347 0.2614    1.0991      3.0628  0.0203
## MSYes                      0.6162 0.3291    0.3233      1.1745  0.1412

Model 7cabg: age, sex, ASA, duration, surgery year, MS

We adjust a Poisson regression model with robust variance for SSI, considering only CABG procedures

Age: quartiles
Sex
ASA: 3 categories, droping asa I
Duration (quartiles): <90, 90-120, 121-186, >186
Surgery year (suryear_cat). Since the 2014-2021 period doesn’t have any cardiac procedure, we exclude these years from the analysis
MS

>> INTERPRETATION:

Compared to patients aged <60 years, patients 69-75 have a lower risk of ssi, and those 60-68 and >75 years have a higher ssi risk, not statistically significant
Female patients have a higher ssi risk compared to males, statistically significant
Compared to patients with ASA II, those with ASA III have a lower ssi risk and those with ASA IV/V have higher ssi risk, not statistically significant.
Surgery duration: compared to patients with a surgery shorter than 90 minutes, those with a longer surgery have a lower ssi risk, statistically significant for 121-186 and >186 minutes.
Surgery year: compared to patients intervened in the 2008-2013 period, those intervened in the 2022-2024 period have a higher risk of ssi, statistically significant.

Migrants have a lower risk of ssi compared to non-migrants, not statistically significant.

##                        exp(coef)     SE     CL     CU P-value
## (Intercept)               0.0020 0.9736 0.0003 0.0136  0.0000
## surage_quartQ2 (60–68)    1.1510 0.2738 0.6730 1.9684  0.6075
## surage_quartQ3 (69–75)    0.7928 0.3060 0.4352 1.4442  0.4479
## surage_quartQ4 (>75)      1.2246 0.3237 0.6492 2.3097  0.5315
## sexFemale                 1.8883 0.2377 1.1849 3.0091  0.0075
## asacabgIII                0.9965 0.7526 0.2280 4.3559  0.9963
## asacabgIV/V               1.4207 0.7471 0.3285 6.1437  0.6383
## duration_cat90–120        0.4306 0.9124 0.0720 2.5746  0.3558
## duration_cat121–186       0.2490 0.6176 0.0742 0.8355  0.0244
## duration_cat>186          0.2827 0.5243 0.1012 0.7898  0.0159
## suryear_card2022–2024     1.7160 0.2681 1.0147 2.9023  0.0440
## MSYes                     0.6126 0.3484 0.3094 1.2126  0.1595

Model 7cabgdi: age, sex, ASA, duration, surgery year, MS

We adjust a Poisson regression model with robust variance for SSI, considering only CABG procedures with donor site incision:

Age: quartiles
Sex
ASA: 3 categories, droping asa I
Duration (quartiles): <90, 90-120, 121-186, >186
Surgery year (suryear_cat). Since the 2014-2021 period doesn’t have any cardiac procedure, we exclude these years from the analysis
MS

>> INTERPRETATION:

Compared to patients aged <60 years, patients 69-75 have a lower risk of ssi, and those 60-68 and >75 years have a higher ssi risk, not statistically significant
Female patients have a higher ssi risk compared to males, statistically significant
Compared to patients with ASA II, those with ASA III have a lower ssi risk and those with ASA IV/V have higher ssi risk, not statistically significant.
Surgery duration: compared to patients with a surgery shorter than 90 minutes, those with a longer surgery have a lower ssi risk, statistically significant for 121-186 and >186 minutes.
Surgery year: compared to patients intervened in the 2008-2013 period, those intervened in the 2022-2024 period have a higher risk of ssi, statistically significant.

Migrants have a lower risk of ssi compared to non-migrants, not statistically significant.

##                        exp(coef)     SE     CL     CU P-value
## (Intercept)               0.0031 0.9698 0.0005 0.0205  0.0000
## surage_quartQ2 (60–68)    1.1716 0.2823 0.6738 2.0373  0.5746
## surage_quartQ3 (69–75)    0.8113 0.3111 0.4409 1.4926  0.5014
## surage_quartQ4 (>75)      1.2881 0.3359 0.6668 2.4881  0.4511
## sexFemale                 1.9227 0.2494 1.1792 3.1350  0.0088
## asacabgIII                0.6494 0.7434 0.1512 2.7882  0.5614
## asacabgIV/V               0.9463 0.7377 0.2229 4.0175  0.9404
## duration_cat90–120        0.6460 0.9231 0.1058 3.9445  0.6359
## duration_cat121–186       0.3173 0.6331 0.0917 1.0974  0.0698
## duration_cat>186          0.2654 0.5254 0.0948 0.7433  0.0116
## suryear_card2022–2024     1.8513 0.2786 1.0724 3.1961  0.0271
## MSYes                     0.6422 0.3459 0.3260 1.2652  0.2005

Model 7cabgvalv: age, sex, ASA, duration, surgery year, MS

We adjust a Poisson regression model with robust variance for SSI, considering only CABG + valve replacement procedures:

Age: quartiles
Sex
ASA: 2 categories. ASA I droped (0 observations). ASA II/III created.
NOT INCLUDED - Duration (quartiles): <90, 90-120, 121-186, >186. Almost all patients undergoing CABG + valve had a surgery duration >186 minutes
Surgery year: 3 levels (2022, 2023 and 2024)
MS

>> INTERPRETATION:

Compared to patients aged <60 years, those aged 60-68 years old have a higher ssi risk, and those aged 69-75 have a lower ssi risk, not statistically significant
Female patients have a higher ssi risk compared to males, not statistically significant
Compared to patients with ASA II/III, those with ASA IV/V have a higher ssi risk, not statistically significant.
Surgery year: compared to patients intervened in 2022, those intervened in 2023 and 2024 have a lower risk of ssi, statistically significant for 2023.

Migrants have a higher risk of ssi compared to non-migrants, not statistically significant.

##                        exp(coef)     SE     CL      CU P-value
## (Intercept)               0.0017 1.0251 0.0002  0.0126  0.0000
## surage_quartQ2 (60–68)    0.6267 0.9349 0.1003  3.9158  0.6172
## surage_quartQ3 (69–75)    0.3961 0.9343 0.0635  2.4719  0.3215
## surage_quartQ4 (>75)      0.7981 0.9869 0.1153  5.5227  0.8193
## sexFemale                 2.0712 0.6468 0.5830  7.3580  0.2602
## asacabgvalvIV/V           1.5245 0.5847 0.4847  4.7952  0.4708
## suryearcabgvalv2023       0.6504 0.7234 0.1576  2.6848  0.5520
## suryearcabgvalv2024       0.6920 0.8078 0.1421  3.3710  0.6486
## MSYes                     2.2426 1.0078 0.3111 16.1666  0.4229

Resúmen resultado modelos, por variables (model 7)

MS
- Both sexes, all procedures: reduction, sign
- Females, all procedures: reduction, not sign
- Males, all procedures:
- Both sexes, colorectal surgeries:
- Both sexes, rectal resections:
- Both sexes, colon resections
- Both sexes, orthopedic surgeries
- Both sexes, cardiac surgeries
- Both sexes, cabg surgeries
- Both sexes, cabg + valve surgeries:
Age
- Both sexes, all procedures: reduction, sign
- Females, all procedures: reduction, not sign
- Males, all procedures:
- Both sexes, colorectal surgeries:
- Both sexes, rectal resections:
- Both sexes, colon resections
- Both sexes, orthopedic surgeries
- Both sexes, cardiac surgeries
- Both sexes, cabg surgeries
- Both sexes, cabg + valve surgeries:
Sex
- Both sexes, all procedures: females higher, not sign
- Females, all procedures:
- Males, all procedures:
- Both sexes, colorectal surgeries:
- Both sexes, rectal resections:
- Both sexes, colon resections
- Both sexes, orthopedic surgeries
- Both sexes, cardiac surgeries
- Both sexes, cabg surgeries
- Both sexes, cabg + valve surgeries:
ASA
- Both sexes, all procedures: higher, sig
- Females, all procedures: higher, not sig
- Males, all procedures:
- Both sexes, colorectal surgeries:
- Both sexes, rectal resections:
- Both sexes, colon resections
- Both sexes, orthopedic surgeries
- Both sexes, cardiac surgeries
- Both sexes, cabg surgeries
- Both sexes, cabg + valve surgeries:
Procedure
- Both sexes, all procedures: colorectal higher sig, valve repl lower sign
- Females, all procedures: CABG, CABG + valve and colorectal higher, sig
- Males, all procedures:
- Both sexes, colorectal surgeries:
- Both sexes, rectal resections:
- Both sexes, colon resections
- Both sexes, orthopedic surgeries
- Both sexes, cardiac surgeries
- Both sexes, cabg surgeries
- Both sexes, cabg + valve surgeries:
Duration
- Both sexes, all procedures: higher, sig
- Females, all procedures: higher, sig
- Males, all procedures:
- Both sexes, colorectal surgeries:
- Both sexes, rectal resections:
- Both sexes, colon resections
- Both sexes, orthopedic surgeries
- Both sexes, cardiac surgeries
- Both sexes, cabg surgeries
- Both sexes, cabg + valve surgeries:
Surgery year:
- Both sexes, all procedures: higher, sig
- Females, all procedures: higher, sig
- Males, all procedures:
- Both sexes, colorectal surgeries:
- Both sexes, rectal resections:
- Both sexes, colon resections
- Both sexes, orthopedic surgeries
- Both sexes, cardiac surgeries
- Both sexes, cabg surgeries
- Both sexes, cabg + valve surgeries:

OJITO PENDIENTE DE REVISAR - Multivariate inferential analysis - SSI No imputation

Abdelaziz Ibn abdelouahab

2025-07-15

Colineality analysis

Categorical variables

Continuous variables

Categorical-continous combinations

Continuous variables: exponentiality assumption

Age

Continuous format

Categorical format

Preoperative length of stay

Continuous format

Categorical format

Surgery duration

Continuous format

Country of birth -HDI (cont.)

Country of citizenship - HDI (cont.)

Poisson regression models: both sexes, all procedures

Model 1: sex and age

Age: cuartiles ——

Age: many categories

Age: 4 categories

Age: continuous

Including MS and sex interaction

Model 2: sex, age and ASA

ASA: 5 categories

ASA: 4 categories ——-

Including MS and sex interaction

Model 3: sex, age, ASA and surgical procedure

Surgical procedure: study classification

Surgical procedure: vincat classification

Interaction term: MS * sex

Interaction term: MS * surgical procedure (study classification)

Interaction term: MS * surgical procedure (vincat classification)

Model 4: age, sex, ASA, procedure, urgency, MS

Procedure: study classification

Procedure: vincat classification

Model 5: age, sex, procedure, ASA, preoperative length of stay, MS

Procedure: vincat

Procedure: study classification

Model 6: age, sex, procedure, ASA, duration, MS

Procedure: vincat

Procedure: study classification

Model 7: age, sex, procedure, ASA, duration, surgery year, MS

Surgery year: categorical

Surgery year: original format

Model 8: age, sex, procedure, ASA, duration, surgery year, income, MS

Poisson regression models: females, all procedures

Model f7: age, sex, procedure, ASA, duration, surgery year, MS

Model m7: age, sex, procedure, ASA, duration, surgery year, MS

Poisson regression models: both sexes, selected procedures

Model 7colorect: age, sex, ASA, duration, surgery year, MS

Model7rect: age, sex, ASA, duration, surgery year, MS

Model7col: age, sex, ASA, duration, surgery year, MS

Model 7orthopedic: age, sex, ASA, duration, surgery year, MS

Model 7cardiac: age, sex, ASA, duration, surgery year, MS

Model 7cabg: age, sex, ASA, duration, surgery year, MS

Model 7cabgdi: age, sex, ASA, duration, surgery year, MS

Model 7cabgvalv: age, sex, ASA, duration, surgery year, MS

Resúmen resultado modelos, por variables (model 7)

OJITO PENDIENTE DE REVISAR - Multivariate inferential analysis - SSI `No` imputation