In an outbreak scenario, public health systems must gather and synthesize data to accomplish a number of parallel objectives. Resources must be mobilized and directed appropriately. Stakeholders including government, health care providers, the business community and the public at large needs to understand current and forecasted risks to population health. The identity and natural history of the pathogen need to be investigated. This natural history of disease can include researching the demographics, timing and geography of the infected and of the subset that has infections classified as severe.
For this infectious disease outbreak occurring in May through December 2023 throughout California, our research team chose to investigate infection dynamics over time in Los Angeles County, which is a very populous, diverse, urban county in southern California. Hispanics represent the largest racial/ethnic group both in California as a whole and in Los Angeles County. We investigated counts and rates of severe infection across strata of sex.
Three original data sets containing infection counts, dates, severity classification and patient demographics were used to create a single dataset with aggregated severity metrics and to calculate infection and severity rates. They are as follows:
sim_novelid_CA.csv : Contains weekly case counts and case severity from 5/29/23 to 12/25/23, stratified by demographic variables (age group, race, and sex) and by geographic unit (county) for all California counties, excluding Los Angeles County.
sim_novelid_LACounty.csv : Contains weekly case counts and case severity from 5/29/23 to 12/25/23, stratified by demographic variables (age group, race, and sex) and by geographic unit (county) for all Los Angeles County.
ca_pop_2023.csv : Provides 2023 population estimates stratified by demographic group and county.
To create a single dataset for analyzing infections affecting the Hispanic population of Los Angeles County in 2023, substantial data harmonization was required. Using a shared data dictionary outlining all column definitions, equivalent fields were renamed to enable seamless merging. Dates, ethnicity values, and epidemiological week fields were standardized across all datasets. A unified county-wide infection dataset was then created from these aligned sources, followed by a subset containing only infection records for Hispanic patients residing in Los Angeles County. Population counts were derived from the California State population dataset and merged with the target population to support infection-rate calculations. The rate of severe infections was then calculated for both male and female Hispanic individuals with known infections in Los Angeles County, reported per 100,000 population.
In 2023, among the Hispanic population in Los Angeles County that tested positive for new infections, there was a comparable age distribution across both sexes. Females had slightly more new infections (median 723) and new severe infections (median 6) compared to males (median 709 new infections and 4 new severe infections).
| Characteristic | FEMALE N = 311 |
MALE N = 311 |
|---|---|---|
| New Infections | 6,946 (6,661) | 6,898 (6,619) |
| New Severe Infections | 164 (154) | 142 (135) |
| New Severe Rate of Infections per 100k | 7.8 (7.3) | 7.1 (6.8) |
| 1 Mean (SD) | ||
In 2023, among the Hispanic population in Los Angeles County that tested positive for new infections, there was a comparable age distribution across both sexes (Table 1). Females had slightly more new infections (median 723) and new severe infections (median 6) compared to males (median 709 new infections and 4 new severe infections).
In 2023, among the Hispanic population in Los Angeles County, females consistently had slightly more new severe infections compared to males over time (Figure 1).
In 2023, among the Hispanic population in Los Angeles County, the rate of new severe infections was consistently slightly higher for females compared to males, accounting for the size of the relevant demographic strata (Figure 2).
Overall the counts and rates of infection were balanced across males and females in the study population. There was a slight trend toward increased propensity of severe infection among Hispanic females relative to males for the first 24 weeks of the outbreak (May 29 to Nov 6) that equalized in November and December, during the period when infections had peaked and were in decline. Examining counts (Figure 1) as opposed to rates (Figure 2) makes the excess impact in females more pronounced as the total Hispanic population of the county is 51% female and 49% male.
It could be informative to investigate changes in risk behavior, treatment and prevention that may have causally connected the waning of the outbreak to the drop off in excess risk for Hispanic females relative to males. Given the initially high impact in females it is plausible that over time either 1) females were particularly targeted for various elements of the public health response efforts or 2) that females were particularly responsive to or invested in adopting measures that were rolled out without regard to sex, such as seeking medical care at an earlier point in the course of disease before the most severe manifestations of illness occur. A sex difference in the portion of the population no longer at risk due to immunity acquired from earlier infection may have played a role as well.