On February 13, 2006 a physician in Benton County, Arkansas reported 4 cases of gastroenteritis among area residents to the Benton County Health Unit (BCHU). All four reported eating at the Sushi King Restaurant in Bentonville just prior to symptom onset. Laboratory test results of patients’ specimens were pending. An alert was sent to area health care providers and clinics advising them of a possible foodborne illness outbreak in the community. Laboratory results confirmed Salmonella Typhimurium (S. Typhimuirum) in patients, and by Friday, February 17 news of the outbreak was broadcast on local television. The BCHU was inundated with complaints from ill Sushi King patrons. The Arkansas Department of Health and Human Services (ADHHS) and the federal Centers for Disease Control and Prevention (CDC) joined the investigation.
BCHU staff collected information from persons reporting gastrointestinal symptoms using a standard interview form. Information collected included date of restaurant patronage, types of symptoms experienced, date of illness onset, and health care provider contact. In an effort to identify potential vehicles for illness and the mode of transmission, Sushi King patrons were asked about consumption of various menu items. Their answers were used to formulate a questionnaire which was administered to individuals selected for participation in a case-control study.
Sixty-three confirmed cases and 98 probable cases of S. Typhimurium were epidemiologically linked to Sushi King with onset of illnesses ranging from February 3 to February 19, 2006. The median incubation was 2 days. At least five persons were hospitalized. No deaths resulted from the outbreak.
For the purposes of the case-control study, a case was defined as a person age 5 years or older who had eaten at Sushi King from January 31 to February 17, 2006 with onset of diarrhea within one week of eating at the restaurant. A confirmed case was a person who was culture confirmed with S. Typhimurium. Controls were non-ill meal companions or acquaintances of cases who had eaten at Sushi King during the same time frame. The study questionnaire asked about food items consumed, clinical symptoms, treatment, the date of consumption, and whether or not food was shared.
Fifty-five cases and 18 controls were included in the case-control study. Onset of illness ranged from February 3 to February 19, 2006. Consumption of Sushi King California rolls was statistically associated with illness (Odds Ratio 6.0, 95% Confidence Interval 1.7-20.6, p-value=0.003). When specific ingredients of the crab roll were evaluated, only the imitation crab mix ingredient was statistically associated with illness (Odds Ratio 3.3, 95% Confidence Interval 1.0-10.7, p-value=0.05.)
On February 13 BCHU environmental health specialists conducted an on-site outbreak investigation at Sushi King with follow-up visits on February 15, 17 and March 10. The restaurant owner agreed to close the restaurant until the source was identified and the outbreak stopped. Before food service was halted, investigators observed unsafe food handling practices and temperature abuse at the facility.
During a site inspection, an employee working in the kitchen who handles both chicken and crabmeat was seen handling chicken and then other food items in the kitchen without washing his hands. During inspections, it was noted that food was left at inappropriate temperatures in the kitchen. Though the owner reports that food was never saved overnight to be served to patrons on the following day, some reports show that various food items were prepared in bulk in the kitchen without being served immediately.
Other errors noted during the February inspections included improper sanitation, improper storage, inadequate hand washing, and temperature abuse. On February 17 for example, inspectors found that rolls made with sushi rice were improperly cold held. The rolls were destroyed. Finally, on March 10 the restaurant received a clean inspection report and was allowed to reopen.
Eight of the 9 Sushi King employees submitted stool specimens for laboratory analysis. Of the 8 specimens, 5 specimens tested positive for S. Typhimurium. One worker reported having non-bloody diarrhea; the remaining employees claimed they were asymptomatic. All employees with laboratory confirmed S. Typhimurium were required to submit two stool specimens free of salmonella before they could return to work.
Dr. Nicholas Gaffga, Epidemic Intelligence Service officer at the CDC and lead outbreak investigator, concludes that a large outbreak of S. Typhimurium infections was associated with eating at Sushi King. He identifies consumption an ingredient of the California roll, imitation crab mix, as being associated with illness. Although Dr. Gaffga does not reach a conclusion as to how the Salmonella bacteria got into the restaurant, he cites improper food storage temperatures, ill food handlers, and food handling procedures as plausible means for the bacteria to multiply and sicken so many individuals.