Causes of food poisoning

By Dr Ananya Mandal, MD

Food poisoning is basically food or water borne infections. It may be caused due to bacteria, virus, parasites or toxins or chemicals present in food.

The onset of the symptoms and severity depends on the time that the infection takes to multiply and take hold. This time is called the incubation period.

There are over 250 food borne illnesses.

The CDC estimates that 68% of the cases of food poisoning are caused due to undetected or unknown organisms. This is because most cases resolve by themselves and do not need hospitalization.

Causes are mainly two – infectious organisms and toxins.

Food poisoning may be classified according to its severity and onset. (1-6)

Short incubation or less than 16 to 24 hours

This includes chemical causes like Scombroid poisoning that occurs due to under cooked or poorly stored fish.

There is release of the chemical histamine that may lead to sometimes fatal allergic reaction.

There may be Ciguatera poisoning which is another fish poisoning caused by grouper, snapper, and barracuda fish consumption.

Intake of poisonous mushrooms also leads to severe food poisoning due to the chemicals present in them.

Amanita mushrooms for example may lead to failure of the kidneys and even death.

Bacterial infections may also have short incubation periods. These include infections with Staphylococcus aureus (begins within 1 to 6 hours), Bacillus cereus, Clstridium perfringens (begins within 8 to 12 hours) etc.

Intermediate incubation from about 1 to 3 days

These infections may affect the large intestine or colon leading to bloody diarrhea, dysentery with passage of mucus along with severe abdominal cramps.

Common bacterial causes of such infections are caused due to Campylobacter, Shigella (from contaminated food and water), Salmonella (from poorly cooked food like eggs and poultry) and Vibrio parahemolyticus (due to contaminated saltwater shellfish). They lead to watery diarrhea that may or may not be bloody.

E coli (enterotoxigenic variety) may lead to Traveller’s diarrhea where there may be fever with bloody diarrhea.

Vibrio cholera leads to cholera causing copious watery diarrhea that may lead to severe dehydration.

There are several viral infections that may lead to food poisoning. These include Norwalk, rotavirus, adenovirus infections. These are accompanied by diarrhea, vomiting, fever with chills etc.

Botulism is caused by toxin from Clostridium botulinum that may lead to typical food poisoning symptoms along with weakness and even paralysis.

Long incubation 3 to 5 days

These conditions include bacterial infections like those with Hemorrhagic E. coli.

This causes inflammation of the colon leading to severe bloody dysentery. This may lead to major life threatening conditions like kidney failure especially in elderly individuals.

Yersinia enterocolitica infection causes inflamed lymph nodes and may mimic appendicitis with severe abdominal pain.

Very long incubation up to a month

This is usually seen with parasitic infections like Giardiasis (from contaminated water), Amoebiasis, Trichinosis (from undercooked pork or wild game), Cysticercosis (caused due to pork tapeworm infection. It may affect the brain causing seizures).

Bacterial infections with long incubation period include Listeria and Brucella infection due to unpasteurized milk, soft cheeses, and poorly stored processed meats and poultry.

Viral infections like Hepatitis A may spread due to contaminated food and water.

Some Protozoal infections like Toxoplasmosis arise from contamination with infected cat feces. This is particularly dangerous for those with weak immunity and pregnant women.

Prion protein may also lead to illness called Bovine Spongiform encephalopathy or mad cow disease. It comes from contaminated beef.

Improper preparation of food

Food poisoning may occur due to improper preparation, storage or consumption. Some causes are (5):

  • Not washing hands before cooking or eating
  • Not washing raw fruits before consumption or vegetables before cooking
  • Not cooking completely (especially meat, eggs and fish)
  • Not storing food properly. Not refrigerating dairy products and those containing mayonnaise for example
  • Eating food beyond expiry date

Edited by , BA Hons (Cantab)

Further Reading

What is Food poisoning?
Food poisoning Symptoms
Food poisoning Diagnosis
Food poisoning Treatments

Last Updated: Jun 14, 2012

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