Sushi has been fingered for a while in the 20 state Salmonella outbreak that has sickened 116 and hospitalized 12.  Today the CDC announced the results of its ongoing, collaborative (with various state and local health departments) investigation into the outbreak.  The product responsible for the outbreak is known as Nakaochi Scrape, from Moon Marine USA Corporation.  Nakaochi Scrape is a frozen raw yellowfin tuna product.

Here is the CDC’s summary:

Collaborative investigation efforts of state, local, and federal public health agencies indicate that a frozen raw yellowfin tuna product, known as Nakaochi Scrape, from Moon Marine USA Corporation is the likely source of this outbreak of Salmonella Bareilly infections. Nakaochi Scrape is tuna backmeat that is scraped from the bones of tuna and may be used in sushi, sashimi, ceviche, and similar dishes. The product looks like raw ground tuna. Hypothesis-generating interviews of ill persons conducted by local and state health departments in March and April, 2012 suggested consumption of sushi made with raw tuna as a source for these infections. To date, among 53 ill persons who have been asked questions about eating sushi and other seafood in the week before illness, 43 (81%) reported eating sushi. This proportion is significantly higher when compared with results from a survey [PDF – 29 pages] of healthy persons in which 5% reported eating “sushi, sashimi, or ceviche made with raw fish or shellfish” in the 7 days before they were interviewed. Of the 43 ill persons reporting eating sushi, 39 (91%) reported eating a sushi item containing tuna, and 36 (84%) reported eating a sushi item containing “spicy tuna.”

To date, a total of 7 clusters at restaurants or grocery stores have been identified where 2 or more unrelated ill persons reported eating in the week before illness. In each cluster, at least one ill person reported eating sushi purchased at the restaurant or grocery store. These clusters are located in 5 states: Connecticut, Maryland, Rhode Island, Texas, and Wisconsin.

Several methods were used to evaluate the association between tuna and illness in this outbreak. To estimate the frequency of consumption of tuna and “spicy tuna” among all sushi eaters, investigators assembled a comparison group from 1) diners who ate at one of the cluster restaurants or grocery stores or 2) a restaurant where a single ill person, who was judged to have a reliable memory, recalled consuming sushi only once in the week before illness. Records were collected on sushi orders that were placed at the same time of day (lunch or dinner) and as close to the date when the ill person ate at the restaurant.