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.
This study is ongoing. Thus far, information has been collected from 4 clusters at restaurants or grocery stores. The proportion of sushi orders that contained tuna as an ingredient averaged 61% (ranging from 43% to 71%). The proportion of sushi orders that contained "spicy tuna" as an ingredient averaged 37% (ranging from 29% to 53%). These data suggest there is an association between illness and consumption of sushi made with tuna, and specifically "spicy tuna."
Public health and regulatory officials also are visiting restaurants and grocery stores associated with ill persons and collecting information about the ingredients used in "spicy tuna" recipes. Based on available information from 5 of the 7 restaurant or grocery store clusters about ingredients used to make "spicy tuna", raw tuna was found to be a common ingredient among all 5 clusters.
State and local public health and regulatory officials are working with the U.S. Food and Drug Administration (FDA) to conduct a traceback of tuna. FDA has selected 4 of the clusters, which are located in Connecticut, Rhode Island, Texas, and Wisconsin, as the focus of the initial investigation. Information to date indicates that all 4 received the same imported frozen raw Nakaochi Scrape tuna product from a single tuna processing facility in India.
This investigation is ongoing. CDC and state and local public health partners are continuing surveillance to identify new cases. Further investigation is ongoing to identify possible sources of contamination and whether any other tuna products are linked with illness. CDC will update the public on the progress of this investigation as information becomes available.
