A Case–Case Study of Sporadic and Outbreak-Associated Listeriosis Exposures: <i>Listeria</i> Initiative Food History Data, 2016-2022

OBJECTIVES: Little is known about foods associated with sporadic listeriosis, a foodborne bacterial infection. We compared self-reported foods consumed by people with sporadic versus outbreak-associated listeriosis, overall and for certain populations. METHODS: Initiative. We used counterfactual random forests to identify foods associated with sporadic and outbreak-associated listeriosis in certain populations (eg, pregnant women). RESULTS: Of 3413 listeriosis cases reported during 2016-2022, 83.5% (n = 2849) were sporadic. Many foods showed no differential association between sporadic and outbreak-associated illness, indicating similar associations or lack thereof with both illness types. While a subset of foods were associated with sporadic versus outbreak-associated listeriosis, these associations varied by population. For example, strawberries (odds ratio [OR] = 2.48; 95% CI, 1.11-5.52) were the only foods associated with sporadic illness among nonpregnant females aged 15 to 49 years. Among adults aged ≥65 years, 10 foods, including deli-counter sliced cheese (OR = 1.78; 95% CI, 1.28-2.47), were associated with sporadic listeriosis. CONCLUSIONS: Foods associated with sporadic listeriosis differed from foods associated with outbreak-associated illness, with differences observed across population groups and by pregnancy status. These findings highlight variation in exposure patterns and underscore the need for further attribution studies focused on sporadic illness across demographic groups, to inform population-specific prevention messaging.