American Journal of Epidemiology Copyright C 1992 by The Johns Hopkins University School of Hygiene and Pubic Health M rights reserved

Vol. 136, No. 5 Printed in U.S.A.

A Foodborne Outbreak of Gastroenteritis Involving Two Different Pathogens

On the evening of October 10, 1990, many of the 474 inmates of a state prison in Florida began to experience symptoms of gastroenteritis. An investigation included interviews with inmates, evaluation of the kitchen and food-handling practices, cultures of leftover food, stool cultures, and cultures from the nares and skin lesions of food handlers. Of the 331 inmates interviewed, 215 (65%) had diarrhea, vomiting, or both. The median incubation period was 5 hours (range, 1-41 hours). Cases with onset of illness 8 or more hours after the evening meal were more likely than those with earlier onset to have had only diarrhea without vomiting (p < 0.001). Eating turkey at the evening meal on October 10 was associated with risk of illness (relative risk = 4.8,95% confidence interval 1.7-13.7). Cases who became ill within 8 hours of the evening meal and those who became ill later were both more likely to have eaten turkey than those who did not become ill (p < 0.001 and p < 0.007, respectively). Salmonella Infantis and enterotoxin-producing Staphylococcus aureus were both isolated from samples of leftover turkey, and S. Infantis was isolated from 18 of 20 stool specimens. Cultures of the anterior nares and skin lesions of food handlers grew S. aureus, but phage typing failed to link these strains to the outbreak. Improper food-handling practices contributed to the development of this outbreak. This report highlights the importance of recognizing multiple-organism outbreaks, since the authors' recommendations for prevention of more cases depended upon knowing the risks associated with the distinct organisms and the possible sources of contamination. Am J Epidemiol 1992;136:611-16. disease outbreaks; food contamination; food poisoning; gastroenteritis; Salmonella food poisoning; staphytococcal food poisoning

Foodborne disease outbreaks continue to constitute a significant public health probReceived for publication September 11, 1991, and in final form April 28, 1992. Abbreviation: Cl, confidence interval. 1 Division of Field Epidemiology, Epidemiology Program Office, Centers for Disease Control, Atlanta, GA. 2 Environmental Epidemiology Program, Office of Environmental Health, Florida Department of Health and Rehabilitative Services, Tallahassee, Fl_ 3 Office of Laboratory Services, Florida Department of Hearth and Rehabilitative Services, Tallahassee, FL. Reprint requests to Dr. Patrick Meehan, Division of Public Health Services, New Hampshire Department of Health and Human Services, 6 Hazen Drive, Concord, NH 03301. The authors gratefully acknowledge the valuable help of Dennis Trimble, Emily Wilson, Archie Ray, Ken McCall, Edward Rensberger, Richard Land, Dr. Frank Kilgo, Sgt. Steve Arnold, and Ron Wffliams. For assistance with laboratory analysis, the authors thank the Nosocomial Infections Laboratory Branch, Hospital Infections Program, Center for Infectious Diseases, Centers for Disease Control, and the Midwest Laboratory for Microbiological Investigations, Food and Drug Administration.


lerri in the United States. In 1987, there were 387 outbreaks involving 16,500 cases reported to the Centers for Disease Control (1), and this represents only a fraction of outbreaks that occur. Factors that are known to contribute to the risk of a foodborne outbreak include contamination from infected or colonized food handlers, inadequate cooking temperatures, improper holding temperatures, and contaminated equipment (1). Since the same factors can potentially promote outbreaks caused by a variety of organisms, outbreaks of gastroenteritis involving multiple organisms are not unexpected, although they have been reported only infrequently (2-5). Identification of such outbreaks is of particular importance, however, as the route of contamination by the different implicated organisms may involve distinct mecha-

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Patrick J. Meehan,1 Thomas Atkeson,* Douglas E. Kepner,3 and Margaret Melton3




On the evening of October 10,1990, a large number of inmates in a low- to mediumsecurity section of a state prison experienced the sudden onset of vomiting, nausea, and/ or cramps. Prison medical personnel were immediately mobilized to screen affected inmates for dehydration, and oral glucose/ electrolyte solution was provided to all ill inmates. More inmates reported diarrhea over the next 36 hours, and many reported fever. Prison staff suspected that the illness was associated with the evening meal served on October 10. On October 10, the inmate population was 474, and all were adult males. Meals were prepared by inmates under the supervision of correctional officers. The cafeteria served only those inmates housed in the lowto medium-security section of the prison. Epidemiologic investigation

We asked all inmates to participate in a structured interview that began approximately 36 hours after the onset of the outbreak. The questionnaires covered demographics, duration and types of symptoms, and a food history for October 10, including the number of servings of each food item eaten at each of the day's three meals. Food service personnel (inmates and staff) were also asked to complete a self-administered questionnaire about illness prior to October 10. We inspected the kitchen and reviewed food preparation procedures with inmates and correctional officers involved in the preparation of each of the meals served on October 10. Samples of all available foods

served on that date had been sent to the state public health laboratory for analysis. A case was defined as an inmate with onset of diarrhea (three or more loose stools in 24 hours) and/or vomiting between 5:00 p.m. on October 10 and the time of the interview. An early-onset case was defined as a case with onset of symptoms prior to midnight on October 10. All other cases were late-onset cases. Two physicians and an environmental health representative examined all 10 food handlers who were involved in food preparation on October 10, to identify potentially infected skin lesions. From four of the food handlers, we obtained specimens for culture from lesions on the upper extremities or on exposed parts of the head and neck using a sterile swab dampened with saline. Nasal swabs were also cultured from all 10 food handlers. Stool specimens for culture were obtained from all inmates with diarrhea who were seen in the infirmary and would so consent. Skin and nasal cultures were placed in transport medium; stool cultures were placed in sterile containers. All specimens were immediately taken to the state laboratory and plated. Laboratory procedures

Samples of turkey, dressing, cole slaw, and cranberry sauce from the evening meal were analyzed by standard bacteriologic methods, including a plate count, total and fecal coliform analyses, and Staphylococcus aureus and Bacillus cereus analyses. Additionally, samples of turkey and dressing were tested for the presence of Salmonella and Campylobacter. Stool specimens were inoculated onto standard culture media and examined for colonies suspicious for Salmonella, Shigella, Aeromonas, Plesiomonas, and Campylobacter. Isolates with reactions suggestive of Salmonella were tested with appropriate Salmonella grouping antisera using a standard slide agglutination technique. Swabs were plated onto standard culture media. S. aureus isolates were identified by

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nisms, and prevention of additional disease may therefore require multiple interventions. We report here a dual-organism outbreak of gastroenteritis that involved organisms with distinct pathogenic mechanisms and different sources and mechanisms of contamination.

A Dual-Organism Gastroenteritis Outbreak

Statistical methods

Relative risk of illness (and a 95 percent confidence interval) was calculated for each food item served on October 10, using Epiinfo 5.0 software (Centers for Disease Control). Significance testing was done using the two-tailed Mantel-Haenszel chi-square. RESULTS Epidemiologic results

Interviews were conducted with 331 (70 percent) of the 474 inmates. Nonparticipation was due to refusal, routine parole, or transfer from the facility. Of the inmates interviewed, 215 (65 percent) met the case definition. Diarrhea and vomiting together were reported by 111 (52 percent) of cases; 84 (39 percent) of the cases reported diarrhea alone, and 20 (9 percent) reported vomiting

alone. There were no hospitalizations or deaths. An epidemic curve of illness onset by the number of hours after the evening meal is presented in figure 1. The incubation period ranged from 1 to 41 hours. Although the median incubation period was 5 hours, 25 percent of the patients reported disease onset 8 or more hours after the evening meal. This group of patients was more likely than those with onset within 7 hours of the evening meal to report having diarrhea without vomiting (p < 0.001). Of the 215 ill inmates, 212 (99 percent) had eaten turkey at the evening meal. The relative risk of illness among those who ate turkey was 4.8 (95 percent confidence interval (CI) 1.7-13.7; table 1). Cases with onset of illness prior to midnight on October 10 (within 7-8 hours after the evening meal) and those with onset after midnight (8 or more hours after the evening meal) were both more likely to have eaten the turkey than inmates who did not become ill (p < 0.001 and/? < 0.05,respectively).The dressing and the peaches were both weakly, but significantly, associated with illness. No other food served at any meal on October 10 was significantly associated with illness. Risk of illness was not associated with the number of servings of turkey eaten.


1 Diarrhea & Vomiting

L'_J Diarrhea Only H i

Vomiting Only

2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40 42 44 Hniire Frnm Evening Mefti t

A foodborne outbreak of gastroenteritis involving two different pathogens.

On the evening of October 10, 1990, many of the 474 inmates of a state prison in Florida began to experience symptoms of gastroenteritis. An investiga...
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