In June 2014 Arkansas Department of Health (ADH) and Benton County Local Health Unit (BCLHU) epidemiologists and environmental health specialists investigated an outbreak of Shigella among persons who consumed food from Salsarita Mexican food bar, a food service vendor at the Walmart Home Office employee cafeteria. Salsarita’s is one of five food services in the Home Office cafeteria operated under contract with Eurest Dining Services. The Home Office cafeteria is not accessible to the general public; only Walmart employees and their guests have access to the café.

Initial reports of three patients who were laboratory confirmed with Shigella were received by ADH on June 17. One patient consumed salsa at a birthday party held on June 13. Both the birthday honoree and the host of the party work at the Walmart home office.  Thus, the host had access to the employee cafeteria where she purchased salsa from Salsarita’s. Other patients reported to ADH consumed food from Salsarita’s while dining in the Home Office cafeteria.

To identify other ill Salsarita customers, ADH initiated active surveillance in area hospitals and doctors’ offices.  Walmart assisted with case-patient finding by notifying all Home Office employees that a foodborne illness outbreak was underway.  Ill employees were asked to report illnesses to ADH or BCLHU.  All ill persons were interviewed by public health nurses or ADH epidemiologists. As of July 30, 2014, a total of 275 case patients were reported from nine states. This included 48 confirmed cases of Shigella and 227 probable cases which were defined as persons with diarrhea or fever and exposure to food from Salsarita’s.  Dates of onset of symptoms ranged from June 10 to June 29. There were 122 case-patients who sought medical care. Eleven persons were hospitalized. There were no deaths.  Public health investigators also identified secondary case patients who had close contact to a confirmed or probable outbreak associated case but no exposure to food prepared by Salsarita’s.

BCLHU environmental health staff inspected Salsarita’s on June 18. Nine violations were documented including 5 critical violations. Violations included improper hand washing practices, bare hand contact with ready-to-eat foods, raw chicken stored above ready to serve drinks, and improper cold holding temperatures for several salad bar items. Salsarita’s was closed after lunch meal service on June 18. In the days that followed BCLHU environmental health staff conducted several on-site inspections at the Walmart Home Office employee cafeteria kitchen. Repeated violations of poor employee hygiene were noted over the course of several visits. Finally on July 10 the Walmart Home Office cafeteria kitchen inspection concluded with no violations. Salsarita’s was allowed to reopen on July 16.

Menu items containing fresh produce prepared at Salsarita’s and served during the outbreak were discarded on June 17 prior to the first visit by BCLHU inspectors on June 18. During the June 18th inspection, BCLHU environmental health staff collected a sample of diced tomatoes from the self-serve salad bar and submitted the sample to the ADH Public Health Laboratory for testing.  A sample of salsa collected from the refrigerator of a Salsarita’s employee was collected on June 19 and sent to ADH for testing. Both samples were negative for Shigella but high counts of fecal coliforms and E. coli were evident.

Stool samples were collected from all food handlers working at the Walmart Home Office employee cafeteria. None of the food handlers tested positive for Shigella although specimens were collected at least one to two weeks after the outbreak occurred.

Public health investigators concluded that an outbreak of Shigella occurred among persons who consumed food from Salsarita’s Mexican food bar. They suspected that despite negative stool tests in food workers, the outbreak was caused by an ill food handler. They based this conclusion on repeated food handling violations noted during multiple inspections and reports of employees with diarrhea working prior to and during the outbreak. Epidemiologic evidence suggests a point source of exposure to Shigella beginning the week of June 8, a time when an ill food handler reportedly worked at Salsarita’s.  This peak could be explained by person to person transmission, or by continued exposure to contaminated products from the Walmart Home Office cafeteria kitchen.

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