BACKGROUND: In August 2016, the Maricopa County Department of Public Health (MCDPH) identified an outbreak of Salmonella Javiana Pulsed-Field Gel Electrophoresis (PFGE) pattern JGGX01.1855 via a combination of PulseNet surveillance and local case investigation. S. Javiana has been isolated from produce, meats and spices, but this PFGE pattern appeared only four times in the PulseNet database. A common seafood restaurant exposure (Restaurant A) between one typed and two un-typed Salmonella cases was identified. MCDPH and Maricopa County Environmental Services (MCES) investigated to determine the outbreak source and prevent further Salmonella transmission.
METHODS: MCES inspected restaurant A, collected food and environmental specimens for Salmonellaculture and obtained ingredient-specific menu item information. Standardized questionnaires were developed to gather information about grocery, restaurant and seafood exposures; cases reporting Restaurant A exposure were also interviewed with a menu-specific questionnaire. Non-ill dining partners of confirmed cases were identified and interviewed as controls. Gift card incentives were provided to cases and controls.
RESULTS: Forty confirmed and ten probable cases, including four closely related S. Javiana PFGE patterns were identified. Illness onset dates ranged from July 22nd to September 1st. Sixty-six percent of cases reported Restaurant A exposure in the week prior to illness; no other common exposures were identified among cases. On-site observations of restaurant A food preparation practices revealed no violations. Case-control study results revealed an odds ratio of 6.47 (CI= 1.6-33.01) for consumption of unfried shrimp among ill diners. No other food items were associated with illness. Salmonella Javiana PFGE pattern JGGX01.1855 was isolated from prepared, re-packaged shrimp and halibut and a freezer door handle swab. Subsequent collection of unopened frozen shrimp resulted in isolation of SalmonellaWeltevreden from one of five shrimp types. This frozen shrimp brand and lot was recalled by the Food and Drug Administration.
CONCLUSIONS: Highly related S. Javiana indicates a commonly supplied food item, possibly shrimp, was the outbreak source; the outbreak was likely amplified by ongoing cross-contamination of shrimp and other seafood during preparation prior to cooking. We hypothesize that higher Salmonella loads, following preparation, likely survived the 145°F recommended shrimp cooking temperature. Recommendations to reduce cross contamination included improved hand hygiene practices, ensuring employees did not work while ill and careful attention to food preparation practices prior to cooking. This outbreak highlights the importance of avoiding cross-contamination of seafood since recommended cooking temperatures may not be sufficient to eliminate high bacterial burden.