Epidemiologic Notes and Reports Salmonellosis in a School System -- Oklahoma

Between April 2 and April 6, 1986, an outbreak of salmonellosis occurred among 2,130 students and employees of a public school system in a small Oklahoma community. A sample of 420 persons were interviewed at the four schools. Forty (9.5%) of those interviewed developed diarrhea (defined as three or more loose stools in 24 hours) during the time of the outbreak. Based on extrapolation, the total number of cases was estimated at 202. Accompanying symptoms included nausea (87.5%), vomiting (72.5%), abdominal cramps (85%), and fever (77.5%). At least 22 students and employees were hospitalized with gastroenteritis.

Salmonella was isolated from 32 patients with outbreak-related illnesses--S. heidelberg, from 27; and S. stanley, from five. The attack rate was slightly greater for students (39/401, 9.7%) than for teachers (1/19, 5.2%), but did not differ by age, sex, grade, or school attended. Of the 33 cafeteria workers, 11 (33.3%) had diarrheal illness, all with onsets after April 2. Illness was strongly associated with eating chicken from the school cafeteria on April 2 (relative risk = 5.6, 95% confidence interval (CI) = 1.9-27.5). No other foods were implicated.

All of the food served at the four schools was prepared at one location. A review of food-handling procedures revealed that the frozen chicken was left to thaw at room temperature on March 31. On April 1, part of the chicken was placed in water-filled pans and cooked in an oven for 2 hours at a dial setting of 177 C (350 F). The oven heat was then turned off, and the chicken was left overnight in the warm oven. The remainder of the chicken was cooked for 2 hours in a steam cooker and then left in the device overnight at the lowest possible setting.

The oven was tested by cooking a pan of baked beans for the same length of time and at the same temperature used for the chicken. When the beans were removed from the oven, the temperature at the edge of the pan was 49-60 C (120-140 F); however, it was only 29 C (84 F) at the center. In a similar test of the steam cooker, the temperature rose to 93 C(200 F) in 1 hour but fell to 43 C (110 F) at the lowest setting. When interviewed, the cafeteria workers were unable to identify any probable errors in food-handling procedures.

Control measures included emphasizing strict attention to hand washing and excluding cafeteria workers with diarrhea from food handling until they were asymptomatic. Cafeteria workers, many of whom had little training, received formal instruction in food service. Emphasis was placed on thawing all frozen meat products in a refrigerator, using a meat thermometer to ensure thorough cooking (internal temperature 74 C (165 F)), storing foods at temperatures high enough ( 60 C (140 F)) or low enough (7 C (45 F)) to ensure that bacteria will not multiply, and serving food soon after cooking. Reported by R Carr, DO, Coweta, S Brown, A Goodall, D Head, B Stacy, Wagoner County Health Dept, R Bryce, Okmulgee County Health Dept, T Hill, G Istre, MD, State Epidemiologist, Oklahoma Dept of Health; Div of Field Svcs, Epidemiology Program Office, Enteric Diseases Br, Div of Bacterial Diseases, Center for Infectious Diseases, CDC.

Editorial Note

Editorial Note: Outbreaks of salmonellosis can be extremely costly. In this Oklahoma outbreak, medical expenses filed with the school's insurer totaled $40,000, and it is likely that these claims represent only a fraction of the economic costs of the outbreak. The cost of medical care and lost income per case in a 1976 outbreak of S. heidelberg infection was calculated at $645, or $1,290 in 1985 dollars (1,2). In 1984, the overall economic impact of salmonellosis, including the cost of the large number of unreported cases, was estimated at between $1.9 and $2.3 billion annually (3). Based on the 56,657 Salmonella isolates reported to CDC in 1985 (4), the minimum medical costs and lost income from Salmonella infections in the United States for that year were estimated at over $73 million.

Poultry in the United States is frequently contaminated with Salmonella, and improperly cooked or handled poultry is frequently implicated in foodborne outbreaks (5). In a survey of 15 poultry processing plants, from 2.5%-77.5% of the ready-to-market chicken carcasses contained Salmonella. S. heidelberg comprised 24% of all isolates and was the most frequently isolated serotype (6).

Between 1973 and 1984, CDC received 2,984 reports of foodborne outbreaks in which the vehicle was identified; poultry was implicated in 273 (9.0%) of these outbreaks. One hundred and ninety of these 2,984 outbreaks occurred in schools. Poultry was implicated in 25.2% of these school outbreaks, with turkey accounting for 20.0% of them, and chicken, for 5.2%. The contributing factors most frequently reported were inadequate storage and cooking of the poultry. Poultry was implicated in 8.5% of outbreaks not occurring in schools.

Lack of basic knowledge about food safety can result in large and costly outbreaks of foodborne illness. Nonetheless, the required training for school lunchroom supervisors and employees varies widely from state to state. Laws that require adequate training of food-service workers employed by schools may prevent many similar outbreaks.

References

1. Cohen ML, Fontaine RE, Pollard RA, VonAllmen SD, Vernon TM, Gangarosa EJ. An assessment of patient-related economic costs in an outbreak of salmonellosis. New Engl J Med 1978;299:459-60.

2. Tauxe RV. Antimicrobial resistance in human salmonellosis in the United States. J Anim Sci 1986;62(suppl 3):65-73.

3. Archer DL, Kvenberg JE. Incidence and cost of foodborne diarrheal disease in the United States. J Food Protect 1985;48:887-94.

4. CDC. Salmonella surveillance annual summary, 1985. Atlanta, Georgia: US Department of Health and Human Services, Public Health Service, 1985.

5. Horwitz MA, Gangarosa EJ. Foodborne outbreaks traced to poultry, United States, 1966-1974. J Milk Food Technol 1976;39:859-63.

6. Green SS, Moran AB, Johnston RW, Uhler P, Chiu J. The incidence of Salmonella species and serotypes in young whole chicken carcasses in 1979 as compared with 1967. Poultry Sci 1982;61:288-93.

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