Clostridium bacteria are widely distributed throughout the world. Botulinus occur as both bacterium and spores in soils, in marine sediments, on the surfaces of fruits and vegetables, in the intestinal tracts of mammals and fish, and in the gills and vixcera of shellfish, such as crabs. This is because the immune system destroys the spores before they can grow and produce toxin. Infant botulism is caused by ingestion of the bacteria itself, and not necessarily by ingestion of the toxin. On some occasions, outbreaks have occurred as a result of improperly prepared commercially canned foods.
Infant botulism is the most common form of botulism.
Regardless of the source, children under one year of age possess immature immune systems and do not possess the necessary proteins in their intestines which destroy the bacterium or spores. Wound botulism is the rarest form of botulism. The entry wound for the spores may be small and seemingly inconsequential. Botulinum spores are not, in themselves, dangerous. Only bacteria which are actively metabolizing can produce the botulinus toxin.