Food Poisoning – Causes, Symptoms, Diagnosis, Treatment

What is food poisoning?

Food poisoning is a common acute condition where food or water contaminated with infectious agents causes inflammation of the gut. These infectious agents may be viruses, bacteria, protozoa or their toxins. Unlike with the ‘stomach flu’ (viral gastroenteritis) which is caused by viruses, food poisoning is more commonly caused by bacteria like E.coli, Salmonella and Shigella.

Once the bacteria enter the gut it causes inflammation and damage to the wall of the gut. This causes symptoms like nausea, vomiting, abdominal pain or cramps and diarrhea. Food poisoning is acute. It arises suddenly, within minutes to hours after consuming contaminated food or water and resolves within a few days. Medication like antibiotics may be necessary but sometimes supportive measures like bed rest and rehydration will suffice.

Causes of Food Poisoning

Bacteria that can cause diarrhea in human live in the intestines of healthy or infected people, or animals, like cattle, poultry or pets. Their stool may contaminate drinking or recreational water, soil, vegetables on fields, milk during milking, meat during slaughter, or food prepared with the hands contaminated with stool. Beside that, bacteria arising from the air or food storing surfaces may quickly multiply in a non-cooled food.

Sources of Infection:

  • Food borne infection (food poisoning): undercooked ground beef (hamburgers), chicken or other meat, shellfish (oyster, scallops), raw eggs (mayonnaise), raw unwashed fruits and vegetables, unpasteurized milk or fruit juices, or non-adequately stored or cooled food
  • Water borne infection: contaminated drinking or recreational water
  • Stool-to-mouth (fecal-oral) infection via stool-contaminated hands, toys, utensils, soil, etc.
  • Infections of ear, nose and throat, and urinary infections may also cause acute bacterial diarrhea.

Bacteria, Commonly Involved in Food Poisoning

  • E.coli 0157:H (2)
  • Campylobacter (3)
  • Salmonella (4)
  • Staphylococcus aureus (staph food poisoning)
  • Clostridium perfringens
  • Shigella (5,6)
  • Listeria – in pregnant women and persons with lowered immunity (7)
  • Yersinia
  • Vibrio cholerae (causing cholera)

Intestinal Changes in Bacterial Food Poisoning

Bacteria may cause inflammation of the stomach and small intestine (gastroenteritis), colon (colitis) or rectum (proctitis). Inflammation may lead to reduced absorption of nutrients and water from the intestine resulting in diarrhea. In heavy infection ulcers may develop, and in most severe cases bacteria may enter the blood (sepsis) and affect other organs.

Symptoms of Bacterial Food Poisoning

Symptoms of food poisoning caused by bacteria include:

  • Explosive diarrhea with frequent, loose or watery stools, urgency, bloating, abdominal cramps. If enough bacteria are ingested, diarrhea appears suddenly, usually within 48 hours (or within 5 days), and lasts for 1-3 days (or up to 10 days or more in heavy infection).
  • Nausea, vomiting (occasionally)
  • General malaise with fever (occasionally)
  • In severe diarrhea, symptoms of dehydration, like thirst, tiredness, sunken eyes, low amount of morning urine, may quickly appear

If you have persistent diarrhea or soft stools after a travel, read about traveler’s diarrhea and intestinal parasites, like Giardia and intestinal worms contracted by food.

The stool of the infected person is contagious during diarrhea and up to two weeks after the healing (in shigellosis possibly up to 1 year or more after symptoms cessation).

Diagnosis of Bacterial Food Poisoning

Doctor can suspect you have bacterial food poisoning from the history of

  • Sudden onset diarrhea
  • Diarrhea appearing several hours after eating fastfood, having a meal in a suspicious restaurant or drinking water from rivers or lakes
  • Other people who have eaten the same food as you and had diarrhea within the next two days
  • Close contact with people having diarrhea
  • Arriving from a country with good hygiene into country with poor hygiene habits.

If you have severe diarrhea, a doctor might order a stool culture test to determine causing bacteria to be able to prescribe you an appropriate antibiotic. Hemoccult, test for occult blood in the stool, is done when intestinal bleeding is suspected.

Treatment of Diarrhea Due to Bacterial Food Poisoning

Mild acute bacterial diarrhea usually resolves on its own within two to three days. Rehydration is essential to prevent complications. Water alone is not sufficient and oral rehydrating solutions need to be used to ensure the optimal concentration of electrolytes is administered and replaced. If dehydration is severe or a person cannot hold down fluid orally, then intravenous rehydration is necessary.

Antibiotics are prescribed only in prolonged (>5 days), profuse (>6 stools/day) or bloody diarrhea, with a high fever (> 38.5 °C or 101.3 °F), or severe abdominal pain. It is important that antibiotics are prescribed by a medical professional and that the entire course is completed as advised. Antibiotics may shorten the course of severe bacterial diarrhea if the bacteria are directly involved.

However, antibiotics may have limited benefit in cases where the toxins are responsible for the illness, as may be the case with E.coli 0157:H, Staphylococcus aureus, or Clostridium perfringens. Instead the toxins need to be flushed out of the system. This is one of the reasons that antidiarrheal agents like loperamide is not prescribed immediately for food poisoning. Sometimes activated charcoal may be prescribed to help neutralize these toxins.

Remedies in Food Poisoning

Antidiarrheal medication, like loperamide, diphenoxylate, bismuth sub-salycilate, are of limited value and can worsen the diarrheal illness if used very early (1). Therefore it is important to not stop the diarrhea as it is just a symptoms. Treatment must be directed at the underlying cause which is either the presence of the bacteria or toxins in the gut, as is the case with antibiotic use.

Conservative measures should focus on rest and recovery, restoring the normal intestinal flora (“good bowel bacteria”) and preventing dehydration. The following dietary and lifestyle remedies may therefore be helpful:

  • Ensure adequate electrolyte and fluid replenishment with oral rehydrating solutions (ORS). If a suitable commercial ORS is not available, then a home made solution can be prepared using 2 liters (68 ounces) of clean water, 8 teaspoons of sugar and one quarter teaspoon of table salt.
  • Use a suitable probiotic as advised by a doctor or pharmacist. Avoid live culture dairy like yogurt as the lactose (milk sugar) can worsen diarrhea. This is due to secondary lactose intolerance that arises temporarily in some cases of severe diarrheal illnesses.
  • Get plenty of rest and preferably strict bed rest. This helps limit dehydration that can occur with physical activity and avoid straining the body further.

Related Articles:


  1. Treatment of acute diarrhea  (
  2. E.coli 0157:H  (
  3. Campylobacter  (
  4. Salmonella  (
  5. Shigella carriers  (
  6. Shigella  (
  7. Listeria  (
About Jan Modric (249 Articles)
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