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BACKGROUND: During early stages of investigations of multi-state outbreaks believed to have resulted from foodborne transmission, additional methods are needed to speed the identification of the vehicle.
METHODS: To determine whether the geographic distribution of early cases of human illness in the U.S. was associated with U.S. port of entry of implicated product, we examined five multi-state outbreaks due to produce items imported from Mexico or other Central American nations. Using retrospective U.S. Food and Drug Administration (FDA) import data, we analyzed the port of entry through which implicated products entered the U.S. and the amount of implicated produce items (e.g., kilograms) imported each day beginning approximately two months before the onset of illness date of the first reported case until a month following the final illness for each of the following five outbreaks: 1) 2008 Salmonella Saintpaul outbreak associated with jalapeno and serrano peppers from Mexico (n=1,495 illnesses in U.S.); 2) 2011 Salmonella Agona outbreak associated with papayas from Mexico (n=106 illnesses in U.S.); 3) 2011 Salmonella Panama outbreak associated with cantaloupes from Guatemala (n=20 illnesses in U.S.); 4) 2013 Cyclospora outbreak associated with pre-packed salad mix from Mexico (n=227 illnesses in Iowa and Nebraska); and 5) 2013 Salmonella Saintpaul outbreak associated with cucumbers from Mexico (n=84 illnesses in U.S.). Overall, these five outbreaks involved a total of 1,932 reported illnesses.
RESULTS: In each of the five outbreaks studied, we observed distinct patterns of geographic distribution of early cases of illness depending on the port through which the implicated products entered the U.S. For outbreaks in which the implicated produce items entered the U.S. through ports of entry in Texas or Arizona, initial cases of illness clustered either in the southwest region of the country or in the upper Midwest. In contrast, when products entered a port of entry in California, cases of illness appeared predominantly in the Pacific coastal states.
CONCLUSIONS: Our results suggest that geographic distribution of early cases of illness in outbreaks due to produce items imported from Mexico or Central America can be used to identify one or more ports of entry that FDA can focus on for sampling of produce items for microbiologic contamination in future outbreaks. This proactive investigative maneuver may be justified even before a specific product has been implicated using standard epidemiologic tools.