Epidemiologic Notes and Reports Bacillus cereus Food Poisoning Associated with Fried Rice at Two Child Day Care Centers -- Virginia, 1993

Bacillus cereus, an infectious cause of foodborne illness, accounted for 2% of outbreaks with confirmed etiology that were reported to CDC during 1973-1987 (1). On July 21, 1993, the Lord Fairfax (Virginia) Health District received reports of acute gastrointestinal illness that occurred among children and staff at two jointly owned child day care centers following a catered lunch. This report summarizes the investigation of this outbreak.

The catered lunch was served on July 21 to 82 children aged less than or equal to 6 years and to nine staff; dietary histories were obtained for 80 persons. Staff and all children aged greater than or equal to 4 years were interviewed directly; staff and parents were questioned for children aged less than 4 years.

Of the 80 persons, 67 ate the catered lunch. A case was defined as vomiting by a person who was present at either day care center on July 21. Fourteen (21%) persons who ate the lunch became ill, compared with none of 13 who did not. Symptoms included nausea (71%), abdominal cramps or pain (36%), and diarrhea (14%). Twelve of the 14 cases occurred among children aged 2.5-5 years, and two occurred among staff. The median incubation period was 2 hours (range: 1.5-3.5 hours). Symptoms resolved a median of 4 hours after onset (range: 1.5-22 hours).

Chicken fried rice prepared at a local restaurant was the only food significantly associated with illness; illness occurred in 14 (29%) of 48 persons who ate chicken fried rice, compared with none of 16 who did not (relative risk=undefined; lower confidence limit=1.7); three persons who were not ill were uncertain if they had eaten the rice. B. cereus was isolated from leftover chicken fried rice (greater than 10 superscript 6 organisms per gram) and from vomitus from one ill child ( greater than 10 superscript 5 organisms per gram) but not from samples of leftover milk. Other food items (peas and apple rings) were not available for analysis.

The rice had been cooked the night of July 20 and cooled at room temperature before refrigeration. On the morning of the lunch, the rice was pan-fried in oil with pieces of cooked chicken, delivered to the day care centers at approximately 10:30 a.m., held without refrigeration, and served at noon without reheating.

Following the outbreak, health officials from the Lord Fairfax Health District recommended to day care staff and restaurant food handlers that the practice of cooling rice or any food at room temperature be discontinued, food be maintained at proper temperatures (i.e., below 41 F {5 C} or above 140 F {60 C}), and a thermometer be used to verify food temperatures.

Reported by: M Khodr, MD, S Hill, L Perkins, S Stiefel, C Comer-Morrison, S Lee, Lord Fairfax Health District, Winchester; DR Patel, D Peery, Virginia Div of Consolidated Laboratory Svcs, Dept of General Svcs; CW Armstrong, MD, GB Miller, Jr, MD, State Epidemiologist, Virginia Dept of Health. Div of Field Epidemiology, Epidemiology Program Office; Foodborne and Diarrheal Diseases Br, Div of Bacterial and Mycotic Diseases, National Center for Infectious Diseases, CDC.

Editorial Note

Editorial Note: B. cereus, a ubiquitous, spore-forming bacteria, causes two recognized forms of foodborne gastroenteritis: an emetic syndrome resembling that caused by Staphylococcus aureus and characterized by an incubation period of 1-6 hours and a diarrheal illness characterized by an incubation period of 6-24 hours (2). Fever is uncommon with either syndrome. The emetic syndrome -- which occurred in the outbreak described in this report -- is mediated by a highly stable toxin that survives high temperatures and exposure to trypsin, pepsin, and pH extremes; the diarrheal syndrome is mediated by a heat- and acid-labile enterotoxin that is sensitive to proteolytic enzymes (3).

The diagnosis of B. cereus food poisoning can be confirmed by the isolation of greater than or equal to 105 B. cereus organisms per gram from epidemiologically implicated food. Underreporting of such outbreaks is likely because illness associated with B. cereus is usually self-limiting and not severe. In addition, findings of a recent survey about culture practices for outbreaks of apparent foodborne illness indicate that 20% of state public health laboratories do not make B. cereus testing routinely available (South Carolina Department of Health and Environmental Control and CDC, unpublished data, 1991).

Fried rice is a leading cause of B. cereus emetic-type food poisoning in the United States (1,4). B. cereus is frequently present in uncooked rice, and heat-resistant spores may survive cooking. If cooked rice is subsequently held at room temperature, vegetative forms multiply, and heat-stable toxin is produced that can survive brief heating, such as stir frying (4). In the outbreak described in this report, vegetative forms of the organism probably multiplied at the restaurant and the day care centers while the rice was held at room temperature.

The day care staff and restaurant food handlers in this report were unaware that cooked rice was a potentially hazardous food. This report underscores the ongoing need to educate food handlers about basic practices for safe food handling.

References

1. Bean NH, Griffin PM. Foodborne disease outbreaks in the United States, 1973-1987: pathogens, vehicles, and trends. Journal of Food Protection 1990;53:804-17.

2. Benenson AS, ed. Control of communicable diseases in man. 15th ed. Washington, DC: American Public Health Association, 1990:177-8.

3. Kramer JM, Gilbert RJ. Bacillus cereus and other Bacillus species. In: Doyles MP, ed. Foodborne bacterial pathogens. New York: Marcel Dekker, Inc, 1989:21-70.

4. Terranova W, Blake PA. Bacillus cereus food poisoning. N Engl J Med 1978;298:143-4.

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