BACKGROUND: In July 2016, through routine case interviews, the South Dakota Department of Health (SDDOH) identified five cases of Salmonella that shared a common exposure at a powwow held on a Native American reservation from June 24-26. The local tribe and Indian Health Service (IHS) unit were contacted and a collaborative investigation was initiated.
METHODS: The tribe appointed IHS as the lead agency for the outbreak investigation. SDDOH provided support by offering outbreak investigation guidance, laboratory testing, data management, data analysis, and traceback. A case-control study was conducted to evaluate specific food items from the powwow that may have been associated with illness. A probable case was defined as a person who subsequently became ill with diarrhea after eating food from the powwow or who was epi-linked to another probable or confirmed case; confirmed cases had Salmonella Javiana isolated from a clinical specimen with the outbreak PFGE pattern (JGGX01.0172). Controls were persons who ate food served at the powwow and reported no subsequent illness.
RESULTS: A total of 112 cases (46 confirmed, 66 probable) were identified in the outbreak. Illness onset dates ranged from June 25 to August 11. Numerous food items served at the powwow were statistically associated with illness by univariate analysis, with macaroni salad demonstrating the highest odds ratio (OR = 10.2; 95% CI, 4.8 to 21.8; p = 0.000). By multivariate analysis using logistic regression, macaroni salad (adjusted OR = 4.2; 95% CI, 1.6 to 11.1; p = 0.004) and kool-aid (adjusted OR = 2.7; 95% CI, 1.1 to 7.4; p = 0.05) remained independently associated with illness. An environmental investigation found that food served during large evening meals was left outside of temperature control, some for more than 6 hours. No food was available for laboratory testing.
CONCLUSIONS: This was an outbreak of Salmonella Javiana associated with food served at a powwow, and the second largest outbreak of salmonellosis in South Dakota history. The ultimate source of the Salmonella contamination was not determined. However, the most plausible source was either an unidentified infected food worker or an infected powwow attendee who contaminated the food(s) and/or serving utensils. This investigation highlights the importance of leveraging and maintaining partnerships with local tribes and IHS.