The food-poisoning strains of S. aureus are usually harbored by human food handlers, either in septic skin lesions (boils and whitlows) or as a part of the normal resident microbial flora of the nose or skin. Transfer of such organisms to food may be restricted by the use of a no-touch technique in its preparation. This is especially relevant for large-scale processing of food. Food poisoning does not occur if the contaminated food is either eaten before the bacteria have a chance to multiply, heated before the bacteria multiply and produce toxins (S. aureus are readily killed by heat), or refrigerated promptly and served chilled, to prevent multiplication of surviving bacteria.
If contaminated food is first refrigerated and then left standing for a considerable length of time in a warm room, the bacteria are able to multiply again. S. aureus multiplies rapidly over a wide range of temperatures, liberating its heat-stable enterotoxin. The type of food involved here is usually that which requires little or no cooking and has a high fat content, like cream cakes, trifles, and ham sandwiches. When eaten, the toxin acts on the host, causing symptoms of nausea, vomiting, and abdominal pain (but rarely with diarrhea) within 1 to 6 hours of ingestion. The toxin appears to act on nerve endings in the gut, transmitting its message to the center in the brain that controls vomiting.
Most cases are self-limiting. Recovery occurs rapidly, usually within 12 hours, and no treatment is required. If the infected food is heated to 70° C before serving, the S. aureus will be killed, but the toxin is still active, and even boiling for 30 to 60 minutes may not inactivate it. Moreover, S. aureus is not inhibited by a high concentration of salt. Therefore, foods like ham and other semi-preserved meat with a high salt and high fat content make an ideal medium for staphylococcal growth and multiplication. Prevention involves stringent measures for personal and environmental hygiene in the food preparation area, the covering of skin lesions with waterproof dressings, rapid refrigeration of prepared food that is not to be eaten right away, and thorough cooking of soups and meats before eating. Control of food handlers and use of the no-touch technique are important in the food manufacturing industry.
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