Many of the Clostridium welchii strains responsible for this condition differ from other members of type A in being able to survive prolonged boiling. They are also antigenically distinct. They are found in the intestines of man and animals, and meat is often contaminated with them either in the slaughter-house or at some other stage before it reaches the consumer.
A characteristic story of an outbreak of this type of food-poisoning begins with a large quantity of meat or stew being boiled for some hours and then left to cool. The clostridia find themselves in an excellent anaerobic culture medium, similar to Robertson's cooked meat medium which is used for growing just such organism in the laboratory. Cooling in the center of a large mass of food is slow, especially if it is not immediately refrigerated. Multiplication of the clostridia begins when the temperature falls below 5o' C, continues until it reaches 20 C or lower, and is resumed if the food is gently heated on the next or subsequent days before being served.
The bacilli are commonly found in very large numbers in food which has caused outbreaks of this form of poisoning. They are there in the vegetative form, but on ingestion they sporulate in the intestine. The final stage of sporulation involves lysis of the remainder of the vegetative cell, with liberation of an enterotoxin that was formed during the earlier stages and is the cause of the clinical manifestations.
Abdominal pain and diarrhoea, which is often violent, come on within 8 to 24 hours of eating the food.
Prostration is common, but there is no fever and seldom any vomiting.
In most cases recovery is complete by the next day, but occasional fatalities occur among the old and infirm.