For staphylococcal food poisoning to occur following the ingestion of a given food, two conditions are necessary. First, S. aureus has to be present in the food; second, foods stored at incorrect temperatures and time allow growth of this pathogen and the production of enterotoxin.
Although S. aureus can be found in food-producing animals and raw foods, humans are considered the main reservoir for this pathogen. S. aureus can be present in healthy individuals, usually on the skin and mucous membranes, for example in the nasal cavity. Food can become contaminated during preparation if the food handler is a carrier of S.aureus and this is transferred to the food through direct contact with contaminated skin or by coughing and sneezing.
The growth of S. aureus in food to a sufficient level as to allow enterotoxin production is possible only under certain conditions. For example, it needs temperatures of between 7°C and 48°C to be able to grow, with an optimum temperature of 37°C. Enterotoxin production will only take place once the levels of this microorganism are large (greater than 10,000 S. aureus per gram of food).
The foods that have been most frequently implicated in cases of staphylococcal food poisoning are poultry and cooked meat products such as ham or corned beef. Other foods implicated were milk and milk products, canned food and bakery products.