Food Poisoning

What is food poisoning?

Food poisoning is a term given to infections with bacteria, parasites, viruses, or toxins from germs that affects humans via contaminated food or water.

The commonest causative organisms are Staphylococcus or E. coli.

The Center for Disease Control and Prevention estimates that 76 million people become ill from food related diseases each year resulting in 325,000 hospitalizations and 5,000 deaths.

Diarrhea due to food poisoning kills millions worldwide, especially in developing and under developed nations.

Travellers to developing countries often encounter food poisoning in the form of Traveller’s diarrhea. (1, 2, 3)

Who does food poisoning affect?

Food poisoning may affect a single individual or a group of people who have taken the same tainted food.

It is common in a community, especially at large social functions, restaurants, school cafeterias etc.

Food poisoning is suspected if a minimum of two people are affected and contaminated food or water is identified as the source of the infection. (1, 4)

What foods frequently cause food poisoning?

Common foods that may carry the germs include spoilt meat or poultry, contaminated water, foods that contain mayonnaise, raw or undercooked meat, eggs, fish and oysters and so forth.

Faulty food handling during preparation may also be responsible for food poisoning. For example, inadequate hand washing, not washing cooking utensils, inadequate refrigeration of dairy and other products. (1)

Which germs cause food poisoning?

Germs that cause food poisoning may include Campylobacter enteritis, Cholera, E. coli enteritis, Staphylococcus aureus, Shigella, Listeria etc.

Who is most vulnerable to food poisoning?

Infants and the elderly are particularly vulnerable to food poisoning.

Those with suppressed immunity, those with kidney disease or diabetes or those travelling abroad where they are exposed to the germs are also susceptible.

Pregnant and lactating women need to be especially careful about avoiding food poisoning. (1, 2, 3)

Chemical toxins in food

Sometimes food poisoning involves chemical toxins which are produced in certain foods that are improperly stored or under cooked.

Scombroid poisoning occurs due to a large release of histamine chemical from the fish when it is eaten.

This may lead to severe allergic reaction with swelling of the face, itching, shortness of breath and difficulty swallowing. This may lead to death due to choking. (2)

Common symptoms of food poisoning

Food poisoning commonly manifests as pain in the abdomen with cramps, diarrhea, nausea, vomiting, weakness, fever with chills and tremors, headache etc.

Problems begin within 2 - 6 hours of eating the tainted food or water. This may be longer or shorter depending on the cause of the food poisoning. (1, 2, 5)

Treatment of food poisoning

Treatment involves keeping the patient hydrated with plenty of fluids and water. In most cases the condition resolves by itself.

Some patients may however need antibiotics for therapy.

Prevention of food poisoning is the key and can be achieved by maintaining clean hands, cooking surfaces, washing and cooking foods thoroughly. Drinking only filtered water also helps. (1-7)

Edited by April Cashin-Garbutt, BA Hons (Cantab)

Causes of food poisoning

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 April Cashin-Garbutt, BA Hons (Cantab)

Symptoms of food poisoning

Most food poisonings manifest within the first 2 to 6 hours after consumption of contaminated food or water. This is called the incubation period and may be longer or shorter depending upon the cause of infection.

General symptoms of food poisoning

The common general symptoms include (1-5) –

  • Abdominal cramps and pain
  • Nausea and vomiting
  • Headache
  • Weakness that may be severe or even lead to paralysis
  • Diarrhea – May be watery and copious or may be bloody at times.
  • Fever with chills and tremors or rigors
  • Muscle pains and aches

Characteristic symptoms of specific infections

Specific infections may have certain characteristic symptoms. Some of these maybe (2, 5) –

  • Infection with Escherichia coli (E. coli) – May lead to diarrhea with very little stool and large amounts of blood also called hemorrhagic colitis. This may occur up to 3 days after eating the tainted food.
  • Norovirus and viral infections – Mild infection with typical symptoms may be seen. Hepatitis A infection may lead to liver damage and jaundice in addition. Rotavirus infection often affects infants and may lead to severe watery diarrhea.
  • Clostridium botulinum – Typically may lead to weakness, blurred vision, double vision, paralysis, respiratory failure and even death.
  • Shigella, Salmonella and Campylobacter - May lead to fever, bloody diarrhoea, chills etc.
  • Mushroom poisoning – May lead to rapid onset liver damage, affection of the brain with delirium (confusion), vision problems, kidney failure and death.
  • Fish poisoning may lead to typical symptoms of food poisoning along with allergic symptoms like itching, swelling of the face, difficulty in swallowing and breathing that may lead to death. This is called anaphylaxis.

Symptoms which signal the help of a physician is needed

Most cases of food poisoning resolve by themselves at home. However, help from the physician needs to be sought if (3, 5) –

  • There is severe vomiting and diarrhea for more than 48 or 72 hours respectively
  • Inability to keep anything down
  • Blood in vomit or stools
  • Seizures
  • Confusion or delirium
  • Blurring or difficulty in vision
  • Slurring speech
  • Paralysis or severe weakness
  • Signs of severe dehydration like dry mouth, sunken eyes and inability to pass urine for long durations.
  • If the patient is an elderly person, pregnant woman or child below three years.
  • Symptoms after recent foreign travel
  • Patient has other conditions like HIV/AIDS, cancer and undergoing chemotherapy, kidney disease etc.
  • If the eyes turn yellow (symptom of jaundice)
  • One or more joints swell or a rash breaks out on the ill person's skin.

Edited by April Cashin-Garbutt, BA Hons (Cantab)

Diagnosis of food poisoning

Food poisoning is usually a mild illness that may resolve on its own after a bout of stomach upset. However, in some cases it might be more serious needing therapy.

Symptoms of food poisoning like abdominal cramps, nausea and vomiting, diarrhea and weakness and association with a recent intake of contaminated food or water is often diagnostic of the condition.

However, sometimes blood tests, tests for the infected stools or even a sigmoidoscopy and other imaging tests may be prescribed to find out the causative organism. (1)

There are several steps for the diagnosis of food poisoning. (1-5)

History of intake of contaminated food

In most cases, the patient volunteers such information.

History of recent return from travel to a developing or underdeveloped country and drinking contaminated water or eating contaminated food should also be mentioned.

Physical examination

A complete physical examination may be needed especially to rule out signs of dehydration.

Dehydration is usually caused due to excessive fluid loss due to diarrhea or vomiting.

Dehydration is characterized by dry skin that remains tented after a pinch, sunken eyes, dry mouth, no sweating in the groins or armpits, no urination for long durations etc.

Weakness or paralysis may also be diagnosed on physical examination and may be indicative of Botulism which needs immediate therapy.

Blood pressure, pulse and temperature are also measured. Severe dehydration is manifested with weak pulse and low blood pressure.

If there is accompanying fever, temperature assessment may be helpful.

Routine blood tests

Routine blood tests may be ordered in some patients with severe food poisoning.

Sometimes these are ordered to check for levels of blood electrolytes and to check for adequate kidney functions.

In case of suspected hepatitis A liver function tests may also be ordered.

Stool examination

Stool samples are examined in case of Salmonella, Shigella and Campylobacter. These infections commonly lead to bloody diarrhea.

If there is a suspected parasitic infestation the stool samples are examined and the parasite is identified under the microscope.

Sometimes stool culture may be prescribed. The sample is allowed to stand in the laboratory in ideal environmental conditions and growth of the microorganism is checked.

Rectal examination

Rectal examination may be needed especially in case of bloody stools.

The doctor inserts a lubricated and gloved finger gently into the rectum for this tests and assess if there are breaks in the rectal wall.

Imaging studies

If the symptoms are suspected to be caused by any other illness, imaging studies are recommended.

These include CT scan of the abdomen.

Sometimes a sigmoidoscopy may be recommended. This involves insertion of a thin long tube within the rectum up to the colon. The tube has a camera on the tip. This helps diagnose any pathology within the intestinal walls.

Toxoplasmosis test

In pregnant women with symptoms there may be a risk of Toxoplasma infection. For this a toxoplasmosis test is advised.

Edited by April Cashin-Garbutt, BA Hons (Cantab)