Case-control studies of sporadic enteric infections complement information from outbreak investigations.

For example, a case-control study of sporadic infections enabled an unprecedented response time during the large U.S. listeriosis outbreak in 2011. Data collected by the Listeria Initiative led to the identification of an association with cantaloupe within days rather than weeks or months (CDC, 2011a). We estimate that the commercial recall of the implicated cantaloupe just 12 days from outbreak detection prevented 20% of the cases and deaths that would otherwise have occurred (CDC, unpublished data, 2012). Cantaloupe is included in the Listeria initiative questionnaire as a direct result of a case-control study of sporadic listeriosis conducted in the Foodborne Diseases Active Surveillance Network (FoodNet) (Varma et al., 2007).