An outbreak of food poisoning in a kindergarten caused by milk powder containing toxigenic Bacillus subtilis and Bacillus licheniformis

In February 2000 an outbreak of food borne intoxication was registered in a small kindergarten in the town of Split (Croatia). Out of 25 exposed children, 12 exhibited symptoms of nausea, headache and vomiting 5-8 hours after eating breakfast which consisted of sandwiches made of sliced bread and rolled ham together with milk and cocoa reconstituted from milk and cocoa powder. Food analysis regarding contamination with potentially toxigenic food borne bacteria which was performed according to ISO Standards revealed no pathogenic microflora, including rotaviruses and adenoviruses. The same applies to the swabs of hands, noses, throats of the kitchen staff and from working surfaces and utensils from the kindergarten. Analysis of stool samples taken from staff as well as infected children also revealed no pathogenic microorganisms. The samples of milk and cocoa powder were examined in parallel using nonselective media. Contamination of milk powder with toxin producing B. licheniformis and B. subtilis was proved by vacuolation assay and MTT cell culture test. The examination of reconstituted milk performed in our lab showed that both species of Bacillus were able to enter the log phase of growth within 2 hours storage of the reconstituted milk at room temperature. Therefore, it was concluded that the main error in milk powder handling was to prepare the milk and cocoa beverage 2 hours prior to consumption without boiling instead of preparing it immediately before consumption taking care to boil the beverage. The application of the main HACCP principles is therefore recommended in order to avoid such incidents in small kindergartens.