In a 1:1 matched case-control study of 36 E. coli O157:H7 cases and 36 controls matched by age group, sex, and state of residence, consumption of raw cookie dough was strongly associated with illness. Results of this analysis are summarized in Table 2. Among cases, 91.7% reported eating raw cookie dough compared with 11.1% of controls, yielding a matched odds ratio of 41.2 (95% confidence interval 7.37 – >999.99; p <0.001). In contrast, the other hypothesized exposures from the hypothesis-generation phase (strawberries, ground beef, apples, and fruit rollups) had similar exposure frequencies among cases and controls and matched odds ratios with confidence intervals that included the null value, indicating no statistically significant association with illness in the matched analysis. These results support the conclusion that consumption of raw cookie dough was the most likely vehicle for this multistate outbreak of E. coli O157:H7 infection.
| Food Item | Case N (%) | Control N (%) | Matched Odds Ratio (95% C.I.\(^{a}\)) | p-value |
|---|---|---|---|---|
| Raw cookie dough | 33 (91.7%) | 4 (11.1%) | 41.2 (7.37 – >999.99) | <0.001 |
| Strawberries | 18 (50%) | 14 (38.9%) | 2.2 (0.76–6.33) | 0.14 |
| Ground beef | 27 (75%) | 26 (72.2%) | 3.5 (0.73–16.85) | 0.12 |
| Ice cream/frozen desserts not containing cookie dough | 11 (30.6%) | 26 (72.2%) | 0.25 (0.03–2.24) | 0.21 |
| Hot dogs | 7 (19.4%) | 15 (41.7%) | 0.5 (0.13–2) | 0.33 |
| Smoothies | 2 (5.6%) | 5 (13.9%) | 0.5 (0.09–2.73) | 0.42 |
| Bologna | 3 (8.3%) | 7 (19.4%) | 0.5 (0.09–2.73) | 0.42 |
| Mandarin oranges | 2 (5.6%) | 6 (16.7%) | 0.5 (0.09–2.73) | 0.42 |
| Bacon | 10 (27.8%) | 10 (27.8%) | 1.67 (0.4–6.97) | 0.48 |
| Raw carrots | 9 (25%) | 17 (47.2%) | 0.67 (0.19–2.36) | 0.53 |
| Fruit rollups | 9 (25%) | 6 (16.7%) | 1.5 (0.42–5.32) | 0.53 |
| Apples | 18 (50%) | 19 (52.8%) | 1.4 (0.44–4.41) | 0.57 |
| Chocolate chips\(^{b}\) | 10 (27.8%) | 12 (33.3%) | 2 (0.5–8) | 0.33 |
| Cucumbers | 7 (19.4%) | 13 (36.1%) | 0.75 (0.17–3.35) | 0.71 |
| Grapes | 12 (33.3%) | 17 (47.2%) | 1 (0.32–3.1) | 1 |
| Raspberries | 3 (8.3%) | 5 (13.9%) | 1 (0.14–7.1) | 1 |
| Smoothies from smoothie shop | 2 (5.6%) | 2 (5.6%) | 1 (0.14–7.1) | 1 |
| Cantaloupe | 5 (13.9%) | 6 (16.7%) | 1.33 (0.3–5.96) | 0.71 |
| Watermelon | 5 (13.9%) | 6 (16.7%) | 1.5 (0.25–8.98) | 0.66 |
| Milk | 20 (55.6%) | 29 (80.6%) | 2 (0.18–22.06) | 0.57 |
|
\(^{a}\) 95% CI = 95%
confidence interval \(^{b}\) Chocolate chips not consumed as part of raw commercial cookie dough. |