METHODS: A case was defined as a Minnesota resident who had S. Newport isolated from stool after dining at Chain A or who developed diarrhea (≥3 stools in a 24-hour period) that either lasted ≥3 days or was accompanied by fever after dining at an affected Chain A location. Online order data was obtained from the Chain A corporate office. An analytic study including patrons of 6 restaurant locations was conducted. Expected consumption frequencies estimated from online orders were compared to case-control data. Implicated food items were traced back.
RESULTS: A total of 115 cases were identified; 81 were culture-confirmed and had isolates with 1 of 2 closely-related PFGE patterns (JJPX01.0030, JPX01.0011). The median case age was 32 years (range, 13-91 years); 53% of cases were female. Seventeen (15%) cases were hospitalized; no deaths occurred.
Cases reported eating at 27 Chain A locations in Minnesota between August 1 and September 25. 72% of cases reported meal dates during August 16-28.
Consumption of mild salsa was significantly associated with illness (92% cases vs. 47% controls; odds ratio, 12.4; 95% confidence interval, 2.8-55.0; p<0.001). The observed frequency of mild salsa consumption among controls was similar to the online order data set (47% vs. 53%). Ingredients in the mild salsa (tomato, jalapeño, cilantro, red onion, citrus, salt) were all consumed by ≥92% of the cases; however, only tomato was significantly associated with illness (p<0.001) in ingredient-specific analyses. The mild salsa is the only menu item that contains raw tomatoes.
The Minnesota Department of Agriculture worked with Chain A corporate officials to analyze supply chain data. Tomatoes served during the outbreak were likely sourced from a Virginia farm. Traceback documentation was shared with FDA.
CONCLUSIONS: This was a S. Newport outbreak associated with consumption of tomatoes in salsa at a restaurant chain. Tomatoes were traced back to an area from which produce has been associated with numerous S. Newport outbreaks. Ingredient-specific analytic studies were crucial in quickly identifying the outbreak vehicle among menu items with several common ingredients. Customer data from Chain A can be used to quickly estimate population consumption frequencies to support traditional analytic studies.