Food poisoning
Practical Action
poisoning that has many varied symptoms and is often fatal. In the United States, around 140 cases
are reported each year. Of these, approximately 15% are foodborne, 65% are infant, and 20% are wound.
Symptoms are blurred or double vision, weakness, difficulty in swallowing and breathing and, if
untreated, paralysis, unconsciousness and death. The symptoms appear with 18-36 hours of
eating the poison and should be treated promptly with a botulin anti-toxin.
The poison is destroyed by heating food to 90°C for at least 15 minutes but the bacterial spores
survive this processing and higher temperatures are required to destroy them. The most common
sources are canned meat, fish and vegetables, preserved meats and fermented fish products. A
high degree of technical knowledge and skill is needed when canning low acid foods or preparing
fermented meat and fish products.
Bacillus cereus
This type of bacterium produces two types of poisoning. The first is relatively mild diarrhoea and
stomach pains which occur 8-12 hours after eating contaminated food and last for about 12
hours. The second is more serious and causes vomiting and diarrhoea 1-5 hours after eating
food. Both are caused by a poison produced by the bacteria and are not fatal. The first type may
occur in a wide variety of foods including re-hydrated dried vegetables, soya bean sprouts and
potato products. The second type is mostly associated with cooked rice. Poisoning can be
prevented by good hygiene and by not holding cooked foods for long periods at room temperature.
Hepatitis A
This virus is transmitted from infected people to food. It is easily destroyed by heating and the
main sources are therefore raw foods or foods which are contaminated after heat processing. It
can be prevented by not allowing infected people to handle food.
Parasites
Trichinella spiralis is a common food poisoning parasite found in meat (especially pork). It can
be destroyed by heating the food to at least 60°C. Hygiene and sanitation are not involved as
causes of this illness. Other parasites include protozoa on vegetables, intestinal worms in meat
and fish and numerous other parasites (e.g. giardia and amoeba) in contaminated water.
Mycotoxins
There are a large number of poisons produced by moulds, but relatively few are involved in food
poisoning. Aflatoxin poisoning is, however, a significant problem associated with cereals and
oilseeds, particularly groundnuts, cotton seed, wheat, sorghum, maize and rice. It is a poison
produced by two moulds (Aspergillus flavus and Aspergillus parasiticus) when the cereals and
nuts are not dried sufficiently quickly or to a low enough moisture level. This is a particular
problem with unshelled groundnuts where the mould can grow on the nut, under the shell and
contaminate the nut with poison. These nuts become discoloured and should be discarded.
Poisoning can be prevented by not allowing the mould to grow – this means drying the food
quickly to a sufficiently low moisture content.
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