CDC collaborated with public health and regulatory officials in several states and the U.S. Food and Drug Administration (FDA) to investigate an outbreak of Salmonella Paratyphi B variant L(+) tartrate(+) and Salmonella Weltevreden infections linked to frozen raw tuna.
Public health investigators used the PulseNet system to identify illnesses that were part of this outbreak. PulseNet is the national subtyping network of public health and food regulatory agency laboratories coordinated by CDC. DNA “fingerprinting” is performed on Salmonella bacteria isolated from ill people by using a technique called pulsed-field gel electrophoresis, or PFGE. PulseNet manages a national database of these DNA fingerprints to identify possible outbreaks. A total of three rare DNA fingerprints were included in this investigation (“outbreak strains”).
A total of 65 people infected with one of the outbreak strains of Salmonella Paratyphi B variant L(+) tartrate(+) (64 people) or Salmonella Weltevreden (1 person) were reported from 11 states. The number of ill people reported from each state was as follows: Arizona (12), California (35), Illinois (1), Michigan (2), Minnesota (4), Mississippi (1), New Mexico (6), South Dakota (1), Virginia (1), Washington (1), and Wisconsin (1).
Illness onset dates ranged from March 5, 2015 to July 20, 2015. Ill people ranged in age from younger than 1 year to 83 with a median age of 31, and 54% were male. Among 62 people with available information, 11 (18%) were hospitalized, and no deaths were reported.
Investigation of the Outbreak
Epidemiologic, laboratory, and traceback findings indicated that frozen raw tuna was the likely source of this outbreak.
In interviews, ill people answered questions about foods eaten and other exposures in the week before they became ill. Of 49 ill people for whom information was known, 46 (94%) reported consuming sushi in the week before they became ill. This proportion was significantly higher when compared with results from a survey[PDF – 29 pages] of healthy people 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 45 people with information about their sushi exposure, 44 (98%) reported eating a sushi item containing raw tuna, and 28 (80%) of 35 with information reported eating a sushi item containing raw “spicy tuna.”
The Maricopa County Environmental Services Department working with the Arizona State Public Health Laboratory collected and tested unopened frozen ground tuna products from various retail locations. The Arizona laboratory isolated Salmonella Newport in one sample and Salmonella Weltevreden in another sample. The unopened frozen ground tuna products represented two different lots of product imported from Indonesia by Osamu Corporation. On May 27, Osamu Corporation recalled[PDF – 1 page] the two lots of ground frozen yellowfin tuna imported from Indonesia due to possible Salmonella contamination. A search of the PulseNet database did not identify any known human illnesses linked to the recall; however, state health departments continued to collect and test samples of frozen raw tuna products.
The Minnesota Department of Health and Department of Agriculture isolated the outbreak strain of Salmonella Paratyphi B variant L(+) tartrate(+) from samples of unopened frozen raw tuna products collected from a Minnesota grocery store where an ill person in this outbreak reported eating tuna sushi. The contaminated frozen raw tuna products collected from the store represented one lot of product from one processing plant in Indonesia imported by Osamu Corporation. On July 21, 2015, Osamu Corporation announced a voluntary recall of the lot of contaminated frozen raw tuna. Additionally, Osamu Corporation voluntarily recalled all frozen yellowfin tuna (loin, saku, chunk, slice, and ground market forms) sold to restaurants and grocery stores throughout the U.S. from May 9, 2014 to July 9, 2015 from the same processing plant in Indonesia.
Further laboratory testing of the product samples collected in Minnesota also isolated two different strains of Salmonella Weltevreden. A search of the PulseNet database identified one ill person from Arizona infected with one of the strains of Salmonella Weltevreden. This ill person reported consuming sushi containing raw tuna in the week before illness onset. As a result of these findings, this ill person was added to the total case count for the outbreak. The two Salmonella Weltevreden strains isolated from these samples were different from the Salmonella Weltevreden strain previously isolated from product tested in Arizona.
The National Antimicrobial Resistance Monitoring System (NARMS) is a U.S. public health surveillance system that tracks antibiotic resistance in foodborne and other enteric bacteria found in people, raw meat and poultry, and food-producing animals. NARMS is a partnership among the CDC, the U.S. Food and Drug Administration (FDA), the U.S. Department of Agriculture (USDA), and state and local health departments.
The NARMS human surveillance program at CDC monitors antibiotic resistance in Salmonella and other bacteria isolated from clinical specimens submitted to NARMS by public health laboratories. CDC’s NARMS laboratory conducted antibiotic resistance testing on clinical isolates collected from three ill people infected with the outbreak strain of Salmonella Paratyphi B variant L(+) tartrate(+) . Of the three isolates, one (33%) isolate was resistant to ampicillin and two (67%) were susceptible to all antibiotics tested on the NARMS panel.
This investigation is over; however, the recalled frozen tuna has a long shelf life and may still be in freezers. Restaurants and retailers unaware of the recalls could continue to serve and sell sushi made with recalled frozen tuna and people could get sick.
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