Investigation of a staphylococcal food poisoning outbreak in a centralized school lunch program

The trend in many communities toward centralized school lunch preparation potentially increases the risk of foodborne illness. Foods often are prepared long before serving and may be distributed to satellite schools by persons with little formal training in safe techniques of food preparation or food service. In May 1990, an outbreak of staphylococcal food poisoning occurred in elementary schools in a Rhode Island community participating in such a program. In the investigation of the outbreak, students in schools that reported cases were interviewed. Food preparation, handling, and distribution were reviewed. At School E, 662 lunches were prepared and distributed to 4 additional schools (schools A-D). Schools A and B accounted for nearly all cases of the food poisoning, with rates of 47 percent and 18 percent. Eating ham increased the risk of illness (62 percent of those consuming ham and 3 percent of those who did not, relative risk = 18.0, 95 percent confidence interval = 4.0, 313.4). Large amounts of Staphylococcus aureus were cultured, and preformed enterotoxin A was identified in leftover ham. A food handler, who tested positive for the implicated enterotoxic strain S. aureus, reported having removed the casings from two of nine warm ham rolls 48 hours prior to service. Because of improper refrigeration, prolonged handling, and inadequate reheating, the ham was held at temperatures estimated at 10-49 degrees Celsius (50-120 degrees Fahrenheit) for a minimum of 15 hours. The potential for larger outbreaks prompted a statewide training program in safe food preparation for school lunch personnel, which may have applications for other communities.