Foodborne Nosocomial Outbreak of Salmonella reading -- Connecticut

This report describes an outbreak of nosocomial salmonellosis associated with consumption of improperly thawed and cooked turkey. Although the outbreak occurred 1 year ago, this report is a timely reminder of the importance of proper cooking and handling of turkey--especially during the holiday season.

On November 13, 1990, an acute-care hospital in Connecticut submitted three isolates of group B Salmonella to the Connecticut State Department of Health Services Laboratory for serotyping: two isolates were from patients and one was from a hospital food-service employee. Stool had been cultured from one patient on November 3 (12 days after admission) because of diarrhea, and from the other patient on November 4 (3 days after admission) because of an episode of loose stools. The hospital food-service employee had had onset of diarrhea on November 4 and stool had been cultured on November 6. All three isolates were serotyped as S. reading.

To identify other potential cases of S. reading infection, the hospital's infection-control department interviewed and obtained stool cultures from all 82 food-service employees, all 26 symptomatic nonfood-service employees, and a convenience sample of 24 asymptomatic nonfood-service employees. In addition, stool cultures were obtained from all 75 hospital inpatients who had had diarrhea or other symptoms suggestive of salmonellosis from November 1 through December 1.

S. reading was isolated from 20 (24%) food-service employees, four (8%) symptomatic nonfood-service employees, and three (4%) hospital inpatients. Onset of illness in symptomatic persons occurred from October 29 through November 12. Most persons had mild diarrhea, with a median duration of 2 days. The Connecticut State Department of Health Services had received no reports of other isolates of S. reading from the area or surrounding communities.

Analysis of stool-culture findings and a food-preference questionnaire administered to food-service employees implicated consumption of turkey as the likely source of salmonellosis. Of the 29 food-service employees who reported they regularly ate turkey in the hospital cafeteria, stool cultures from 19 (66%) yielded S. reading, compared with one from the 53 (2%) employees who ate turkey infrequently (relative risk=34.7; 95% confidence interval 4.9-246.3). The three hospital inpatients and the four nonfood-service employees who were culture-positive all reported eating turkey in the hospital during October 29-November 3.

Turkey salad, turkey sandwiches, and chef's salad with turkey were served in the hospital cafeteria and were on the inpatient menu every day. Frozen 18-20-pound turkey breasts were routinely cooked in a slow roaster oven for 5 hours at 250 F (121 C), then for 10 hours at 160 F (71 C); however, core temperatures were not measured. After cooking, turkey dishes were kept refrigerated for up to 72 hours.

On November 21, 1990, the hospital instituted proper cooking procedures for turkey (i.e., thawing frozen turkey before cooking in a standard oven to a core temperature of 165 F (74 C)). No additional cases of S. reading infection have been reported. Reported by: JR Sabetta, MD, S Hyman, MPA, J Smardin; ML Cartter, MD, JL Hadler, MD, State Epidemiologist, Connecticut State Dept of Health Svcs. Enteric Diseases Br, Div of Bacterial and Mycotic Diseases, National Center for Infectious Diseases; Div of Field Epidemiology, Epidemiology Program Office, CDC.

Editorial Note

Editorial Note: Because age and underlying medical conditions may predispose hospital patients to severe outcomes from Salmonella infection (1), the occurrence of even one case of suspected nosocomially acquired salmonellosis requires prompt investigation to determine the source. The investigation of this outbreak detected an improper cooking procedure for a frequently prepared food and resulted in the implementation of standard preventive measures.

Transmission of Salmonella is more likely to be associated with contaminated food that has been improperly prepared than with contamination of food by asymptomatically infected food handlers (2). For example, in this outbreak, 12 asymptomatically infected food-service employees prepared food (until culture results were obtained) and were potential sources for nosocomial infection; however, the investigation suggested that infection and illness were more likely to have been associated with consumption of improperly prepared turkey. Cooking procedures were not thoroughly reviewed until turkey was epidemiologically implicated by the infection-control department during the outbreak investigation.

A thorough review of food-preparation procedures--especially for foods at high risk for contamination with Salmonella (e.g., poultry, meat, and eggs)--during inspection or internal monitoring can reduce the potential for foodborne outbreaks in hospitals and other health-care facilities. In addition, employees with symptoms of gastrointestinal illness should be excluded from food-preparation activities or direct patient care. Employees asymptomatically infected with bacterial pathogens should be allowed to return to jobs involving food preparation only after negative stool cultures have been obtained.

From 1973 through 1987, eight foodborne outbreaks of S. reading infection were reported to CDC's Foodborne Disease Outbreak Surveillance System. Turkey was implicated as the source of infection in six of these outbreaks. In 1989, S. reading was the seventh most frequently isolated serotype from nonhuman sources; 627 (83%) of 757 S. reading isolates were from turkey (3). In addition, S. reading isolates from turkeys were reported to the National Salmonella Surveillance System each year from 1977 through 1986 but less frequently from other nonhuman sources, suggesting a turkey reservoir exists for this serotype (4).

During the holiday season, foodborne disease outbreaks caused by Salmonella and other pathogens associated with turkey may occur in a variety of settings. Food handlers, whether in institutions, restaurants, or homes, should thaw turkey under refrigeration, cook it thoroughly, and then hold it at an appropriate temperature until consumed. Cooked turkey should be held at temperatures too hot (greater than or equal to 140 F (greater than or equal to 60 C)) or too cold (less than or equal to 40 F (less than or equal to 4 C)) to permit multiplication of bacterial pathogens. Additional information on cooking and handling turkey is available from the U.S. Department of Agriculture Meat and Poultry Hotline ((800) 535-4555).

References

1. Pavia AT, Tauxe RV. Salmonellosis: nontyphoidal. In: Evans AS, Brachman PS, eds. Bacterial infections of humans: epidemiology and control. 2nd ed. New York: Plenum Medical Book Company, 1991:573-91.

2. Cruikshank JG, Humphrey TJ. The carrier food-handler and non-typhoid salmonellosis. Epidemiol Infect 1987;98:223-30.

3. CDC. Salmonella surveillance report 1989. Atlanta: US Department of Health and Human Services, Public Health Service, 1990.

4. Martin SM, Hargrett-Bean N, Tauxe RV. An atlas of Salmonella in the United States: serotype-specific surveillance 1968-1986. Atlanta: US Department of Health and Human Services, Public Health Service, 1989.

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