I reported last weekend on an apparent outbreak of food poisoning in China's Guangdong Province that sickened more than 100 kindergarten children. According to an article in this morning's People's Daily Online, government health officials have confirmed the source of the outbreak to be boxed milk contaminated with staphylococcal enterotoxin.
Staphylococcus aureus was apparently introduced into the milk when the processor added the calcium supplement. The fortified milk was not pasteurized properly after the supplement was added. Nor was the milk kept cold enough to prevent the microbe from multiplying and producing its toxin.
Staphylococcus aureus is a bacterium that is carried on the skin and in the nasal passages of a significant portion of the population. Poor personal hygiene when handling food can transfer the microbe from the skin into the food. Staph. aureus requires 4-5 hours of room temperature (or higher) growth in order to produce enough enterotoxin to make someone ill.
Staphylococcal enterotoxin is heat-stable, and cannot be inactivated by cooking. It's clear that this milk processor has more problems than inadequate pasteurization. The dairy's temperature control and worker hygiene procedures leave much to be desired. It appears, though, that the local health authorities took swift action to contain the outbreak.