A sample of raw yellowfin tuna and a sample of sushi made with yellowfin tuna were contaminated with the outbreak strain of Salmonella Bareilly that has sickened at least 160 people, according to the Wisconsin Department of Health Services.
In a news release, the department said the Wisconsin State Laboratory of Hygiene at the University of Wisconsin, Madison found that Salmonella bacteria isolated from two food samples were an identical DNA match to the bacteria isolated from the outbreak victims.
The lab test results corroborate the earlier epidemiologic conclusion, arrived at through case interviews and product trace back, which identified frozen yellowfin tuna as the likely source of the outbreak.
Based on that earlier evidence from the outbreak investigation, Moon Marine USA Corp of Cupertino, CA recalled suspect frozen tuna product on April 13. The tuna, imported from India, was labeled as Nakaochi Scrape.
“Scrape” is the term for tuna shaved off the backbone after a fish has been filleted. Considered too good to be wasted, scrape may be chopped into even smaller bits but is not further processed. Raw fish scrape is commonplace in Japanese cuisine, sometimes served over rice, in sushi or on its own.
Like any food served raw, however, it can pose a potential risk from foodborne pathogens.
Moon Marine’s tuna scrape was not available for sale to individual consumers, but went to restaurants and grocery stores where it may have been used to make sushi, sashimi, ceviche and similar raw-fish dishes, according to the Centers for Disease Control and Prevention. It often is used to make “spicy tuna” sushi.
In investigating the sushi outbreak, the CDC and Food and Drug Administration said some of the ill people had eaten in “four clustered-associated” restaurants that had served tuna from a single source.
The FDA has now issued import alerts, authorizing the detention without physical examination of fresh and frozen tuna from the tuna scrape producer, Moon Fishery India Pvt Ltd. in Kerala state, India.
The import alert concludes that contamination with Salmonella Bareilly “is likely due to inadequate sanitary controls after harvest on the fishing vessels, during processing or packaging. Sources of contamination may include water contamination, and/or poor hygienic practices of workers that process the product, pests in packing facilities, and lack of adequate cleaning and sanitizing of equipment that comes in contact with the product.”
In its last update on the outbreak, the CDC said 160 confirmed cases had been reported by 20 states and the District of Columbia. At least 26 people had severe symptoms and were hospitalized.
The FDA has said it is continuing to trace forward the recalled tuna through its subsequent distribution from Moon Marine in California, but has not revealed any of the restaurants or grocery stores that sold sushi or other foods containing the tainted tuna.