The nature of the organism responsible for a food-poisoning outbreak is often suggested by the pattern of the outbreak. Whether it is confined to a household or involves large numbers of people, the time relationships, the nature and severity and duration of the symptoms, and so on.
Except in salmonellosis the investigation of an outbreak has little bearing upon treatment and is principally concerned with finding out what went wrong and preventing further outbreaks. The laboratory's contribution is to try to isolate the responsible organism, by culture of faeces and vomit (if available) from a manageable proportion of the patients and by microscopy and culture of the offending food if it can be identified and if some of it is still available.
Sometimes the history of the outbreak clearly incriminates a particular item or at least a meal, but in other cases detailed detective work is necessary. If the food is available and either salmonella, a heat-resistant Clostridium welchii, or a Bacillus cereus is involved, there is not usually much difficulty in growing the organisms from the food and from at least some of the patients, and in. showing that they are identical.
Clostridium botulinum is also likely to be recoverable from the food, and although it is unlikely to be recovered from the patients it produces a highly characteristic clinical picture. The case against a staphylococcus, however, may be difficult or impossible to prove. These organisms, being less heat-resistant than their enterotoxin, may have been killed during cooking, and there is no simple and satisfactory procedure for demonstrating the presence of the enterotoxin, though it can be detect tests used in specialized food-hygiene laboratories.
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