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Bacterial food poisoning

Foodborne illness or food poisoning is caused by consuming food contaminated with pathogenic bacteria, toxins, viruses, prions or parasites. Such contamination usually arises from improper handling, preparation or storage of food. Foodborne illness can also be caused by adding pesticides or medicines to food, or by accidentally consuming naturally poisonous substances like poisonous mushrooms or reef fish. Contact between food and pests, especially flies, rodents and cockroaches, is a further cause of contamination of food. more...

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Some common diseases are occasionally foodborne mainly through the water vector, even though they are usually transmitted by other routes. These include infections caused by Shigella, Hepatitis A, and the parasites Giardia lamblia and Cryptosporidium parvum.

The World Health Organization defines it as diseases, usually either infectious or toxic in nature, caused by agents that enter the body through the ingestion of food. Every person is at risk of foodborne illness.

Good hygiene practices before, during, and after food preparation can reduce the chances of contracting an illness.

Symptoms and mortality

Symptoms typically begin several hours after ingestion and depending on the agent involved, can include one or more of the following: nausea, abdominal pain, vomiting, diarrhea, fever, headache or tiredness. In most cases the body is able to permanently recover after a short period of acute discomfort and illness. However, foodborne illness can result in permanent health problems or even death, especially in babies, pregnant women (and their fetuses), elderly people, sick people and others with weak immune systems. Similarly, people with liver disease are especially susceptible to infections from Vibrio vulnificus, which can be found in oysters.

Incubation period

The delay between consumption of a contaminated food and appearance of the first symptoms of illness is called the incubation period. This ranges from hours to days (and rarely months or even years), depending on the agent, and on how much was consumed. If symptoms occur within 1-6 hours after eating the food, it suggests that it is caused by a bacterial toxin rather than live bacteria.

During the incubation period, microbes pass through the stomach into the intestine, attach to the cells lining the intestinal walls, and begin to multiply there. Some types of microbes stay in the intestine, some produce a toxin that is absorbed into the bloodstream, and some can directly invade the deeper body tissues. The symptoms produced depend on the type of microbe.

Infectious dose

The infectious dose is the amount of agent that must be consumed to give rise to symptoms of foodborne illness. The infective dose varies according to the agent and consumer's age and health. In the case of Salmonella, as few as 15-20 cells may suffice .

Pathogenic agents

An early theory on the causes of food poisoning involved ptomaines, alkaloids found in decaying animal and vegetable matter. While some poisonous alkaloids are the cause of poisoning, the discovery of bacteria left the ptomaine theory obsolete.


Bacterial infection is the most common cause of food poisoning. In the United Kingdom during 2000 the individual bacteria involved were as follows: Campylobacter jejuni 77.3%, Salmonella 20.9%, Escherichia coli O157:H7 1.4%, and all others less than 0.1% .


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Food poisoning
From Gale Encyclopedia of Alternative Medicine, 4/6/01 by Patience Paradox


Food poisoning is a general term for health problems arising from eating food contaminated by viruses, chemicals, or bacterial toxins. Types of food poisoning include bacterial food poisoning, shellfish poisoning, and mushroom poisoning. The medical term for food poisoning is gastroenteritis.


The Centers for Disease Control and Prevention (CDC) estimates that there are from 6-33 million cases of food poisoning in the United States each year. Many cases are mild, and they pass so rapidly that they are never diagnosed. Occasionally, a severe outbreak creates a newsworthy public health hazard, but serious outbreaks are rare. Anyone can get food poisoning, but the very young, the very old, and those with compromised immune systems have the most severe and life-threatening cases.

Causes & symptoms

General indications of food poisoning include diarrhea, stomach pain or cramps, gurgling sounds in the stomach, fever, nausea, vomiting, and possibly a fever. Dehydration is a common complication, since fluids and electrolytes are lost through vomiting and diarrhea. Dehydration is more likely to happen in the very young, the elderly, and people who are taking diuretics.

Bacterial sources of food poisoning

Bacteria are major causes of food poisoning. Symptoms of bacterial food poisoning occur because foodborne bacteria release enterotoxins, or poisons, as a byproduct of their growth in the body. These toxins often diminish the absorptive ability of the intestines and cause the secretion of water and electrolytes that leads to dehydration. The severity of symptoms depends on the type of bacteria, the amount of bacteria and food consumed, and the individual's health and sensitivity to the bacteria's toxin.


Symptoms of poisoning begin 12-72 hours after eating food contaminated with Salmonella. Classic food poisoning symptoms, including fever, occur for about two to five days. Salmonella is usually transmitted through the consumption of food contaminated by human or other animal feces. This contamination is mostly due to lack of hand washing by food handlers.

Escherichia coli (E. coli)

Symptoms of food poisoning from E. coli 0157:H7 and similar strains of E. coli are slower to appear than those caused by some of the other foodborne bacteria. One to three days after eating contaminated food, the victim begins to have severe abdominal cramps and watery diarrhea that usually becomes bloody. The diarrhea may consist mostly of blood and very little stool, so the condition is sometimes called hemorrhagic colitis. There is little or no fever, the bloody diarrhea lasts from one to eight days, and the condition usually resolves by itself. Food contamination from E. coli O157:H7 has mostly been found in raw or undercooked ground beef. Raw milk has also been a source of food poisoning by E. coli.

Campylobacter jejuni C. jejuni infections are most often caused by contaminated chicken. Unchlorinated water and raw milk may also be sources of infection. Classic symptoms of food poisoning, including fever and diarrhea, begin two to five days after consuming food or water contaminated with C. jejuni. The diarrhea may be watery and may contain blood. Symptoms last from 7-10 days, and relapses occur in about one quarter of the people who are infected. Staphylococcus aureus (Staph) Staph is spread primarily by food handlers with Staph infections on their skin. However, contaminated equipment and food preparation surfaces may also be at fault. Almost any food can be contaminated, but salad dressings, milk products, cream pastries, and food kept at room temperature, rather than hot or cold, are likely candidates. Classic symptoms of food poisoning appear rapidly, usually two to eight hours after the contaminated food is eaten. Such symptoms usually last only three to six hours and rarely more than two days. Most cases are mild and the victim recovers without any assistance. Shigella

Symptoms of food poisoning by Shigella appear 36-72 hours after eating contaminated food. These symptoms are slightly different from those associated with most foodborne bacteria. In addition to the familiar symptoms of food poisoning, up to 40% of children with severe infections show neurological symptoms. These include seizures, confusion, headache, lethargy, and a stiff, sore neck. The disease runs its course in two to three days.

Clostridium botulinum C. botulinum is the deadliest of the bacterial foodborne illnesses. Sources for adult botulism are often improperly canned or preserved food. Symptoms of adult botulism appear about eighteen to thirty-six hours after the contaminated food is eaten, although there are documented times of onset ranging from four hours to eight days. Unlike other foodborne illnesses, there is no vomiting and diarrhea associated with botulism. Initially, a person suffering from botulism feels weakness, dizziness, and double vision. Symptoms progress to difficulty with speaking and swallowing. The toxins from C. botulinum are neurotoxins--they poison the nervous system, causing paralysis. If the disease proceeds unchecked, paralysis will move throughout the body. Eventually, without medical intervention, the respiratory muscles will become paralyzed and the victim will suffocate.

With infant botulism, the spores of C. botulinum lodge in the infant's intestinal tract. Honey, especially when consumed by infants younger than twelve months, is sometimes the source of these spores. Onset of the symptoms is gradual. The infant initially has constipation, followed by poor feeding, lethargy, weakness, drooling, and a distinctive wailing cry. Eventually the baby loses the ability to control its head muscles. Paralysis then progresses to the rest of the body.

Fish-associated food poisoning

Ciguatera fish poisoning is caused by toxins accumulated in the tissues of certain tropical fish, including groupers, barracudas, snappers, and mackerel. Signs of poisoning occur about six hours after eating the fish. Around the mouth, there may be numbness and tingling, which may spread to other places including the hands and feet. There is often muscle pain and weakness, headache, dizziness, joint pain, sensitivity to temperature, heart arrhythmias, dramatic changes in heart rate, and reduced blood pressure.

Pufferfish, or fugu, is a traditional gourmet dish served mostly in Japan. The skin and other organs of the pufferfish contain a strong poison called tetradotoxin. The first stage of tetradotoxin poisoning is indicated by numbness of the lips and tongue, which may occur 20-180 minutes after eating the fish. This is followed by tingling and numbness of the face, hands, and feet. Classic symptoms of food poisoning are accompanied by other neurological symptoms such as light-headedness, headache, and unsteady gait. The second stage of tetradotoxin poisoning brings on a progressive paralysis. Breathing, talking, and other movement becomes difficult. Cyanosis (bluish or purplish skin discoloration), low blood pressure, and arrhythmias may occur. Convulsions and mental impairment may happen right before death, or the person may be completely lucid, though unmoving. Death usually occurs four to six hours after ingestion of the fish if there is no proper intervention; that time, however, has been known to be as little as 20 minutes.

Shellfish poisoning is caused by toxins made by certain algae eaten by shellfish. The toxins are then accumulated in the bodies of the shellfish. Cockles, mussels, clams, oysters, and scallops are most often affected. Sometimes the toxin-producing algae multiply to such an extent that they cause the waters they live in to take on the reddish color of their bodies. This phenomenon is known as a red tide. Warnings are often given against eating shellfish from such areas. Symptoms of food poisoning show up within a half an hour to two hours of eating the shellfish, depending on the amount and type eaten. There may be burning and tingling in the face and mouth, numbness, drowsiness, muscular pain, dizziness, diarrhea, stomachache, confusion, nausea, vomiting, odd temperature sensations, difficulty breathing, and possibly coma. The symptoms may last from a few hours to a few days.

Histamine poisoning can occur from eating fish whose body tissues have begun to produce high levels of histamine. Mackerel, tuna, and mahi mahi are most often the sources. After consumption of the fish, immediate facial flushing and hives may occur, as well as classic symptoms of food poisoning becoming evident a few minutes later. Symptoms usually last less than twenty-four hours.

Mushroom poisoning

Mushroom poisoning is classified by the effects of the poisons. Protoplasmic poisons result in cell destruction, often in the liver, which progresses to complete organ failure. Neurotoxins cause neurological symptoms such as sweating, convulsions, hallucinations, excitement, depression, coma, and colon spasms. Gastrointestinal (G/I) irritants rapidly bring on the classic symptoms of food poisoning and then resolve just as quickly. Disulfiram-like poisons are generally nontoxic, except when alcohol is consumed within seventy-two hours of eating them. In these cases, the poisons cause headache, nausea, vomiting, flushing and cardiac disturbances for two to three hours.

Other possible sources

Other possible sources of food poisoning include ingestion of green or sprouting raw potatoes, ingestion of fava beans by susceptible persons, and ergot poisoning from ingestion of contaminated grain. Chemical contaminant food poisoning may result from the ingestion of unwashed produce sprayed with arsenic, lead, or insecticides. Food served or stored in lead-glazed pottery cadmium-lined containers may also lead to food poisoning.


An important aspect of diagnosing food poisoning is the clinical interview. A history of the illness should be thoroughly traced to include ingestion of food, recent travel, and contact with those showing similar symptoms of illness. Because it may take 30 minutes to three days for symptoms to develop, it is not necessarily the most recent food eaten that is the cause of the symptoms. Diagnosis is confirmed with a stool culture. Other laboratory tests may be used to examine vomitus, blood, or the contaminated food. A blood chemistry panel may be performed to determine the extent of any tissue damage or electrolyte imbalances. Many cases of food poisoning go undiagnosed, and treatment focuses on the short-lived G/I symptoms.

Botulism is usually diagnosed from its distinctive neurological symptoms, since rapid treatment is essential to save the patient's life. Electromyography, a test analyzing the electrical activity of muscles, may later be done to further confirm diagnosis. The test shows abnormal muscle activity in most cases of botulism.


Those suffering from food poisoning should reduce all sugar and normal food for eight to 24 hours, and increase fluids to avoid dehydration. Charcoal tablets, Lactobacillus acidophilus, Lactobacillus bulgaricus, and citrus seed extract are all recommended. For mild cases of food poisoning, the homeopathic remedies Arsenicum album, Veratrum album, Podophyllum, or Nux vomica are recommended. The remedy should be given in 12c potency every three to four hours until symptoms subside. If a ready-made electrolyte replacement is not available, a homemade one can be made by dissolving exactly one teaspoon (five ml) of salt and four teaspoons (about 20 ml) of sugar in one quart (one liter) of water.

Cinnamon (Cinnamonum zeylanicum), cloves (Syzigium aromaticum), oregano (Origanum vulgare), and sage (Salvia officinalis) are food herbs that are also strong inhibitors of bacteria. Liberal amounts can be added to foods, especially when traveling. Grapefruit seed extract has a natural antibiotic effect and may be of help. Large amounts of garlic, in food and in supplement form, are also recommended for the same reason.

Allopathic treatment

In very serious cases of food poisoning, medications may be given to stop abdominal cramping and vomiting. Medications are not usually given for the diarrhea, since stopping it might keep toxins in the body longer and prolong the illness. Severe bacterial food poisonings are sometimes treated with antibiotics, but their use is controversial. Washing out the stomach contents to remove the toxic substances may be required. This procedure is called gastric lavage, familiarly known as having the stomach pumped. Neurotoxins often interfere with the breathing process. If the ability to breathe is affected, patients may have to be put on a mechanical ventilator to assist their breathing and are fed intravenously until the paralysis passes.

People who show any signs of botulism poisoning must receive immediate emergency medical care. Both infants and adults suffering from food poisoning by C. botulinum require hospitalization, often in the intensive care unit. A botulism antitoxin is given to adults, if it can be administered within seventy-two hours after symptoms are first observed. If given later, it provides no benefit. Nasogastric intubation is recommended for the feeding of infants with active botulism. As well as supplying nutrition, it will stimulate peristalsis, helping in the elimination of C. botulinum.

Treatment of food poisoning that is not an emergency situation may include drugs such as ipecac syrup to induce vomiting or laxatives to empty the intestines. Intravenous fluids containing salts and dextrose may be given to correct dehydration and electrolyte imbalances. Pain medications are given for severe stomach pain. Atropine is given for muscarine-type mushroom poisoning. If illness comes on after eating unidentified mushrooms, vomiting should be induced immediately, and the vomitus saved for laboratory testing. Intravenous mannitol is sometimes used to treat severe ciguatera poisoning. Antihistamines may be effective in reducing the symptoms of histamine fish poisoning.

In mild cases of food poisoning, dietary modifications are often the only treatment necessary. During periods of active vomiting and diarrhea, people with food poisoning should avoid solid food for eight to twenty-four hours, and should increase fluids. Clear liquids should be consumed in small quantities. Once active symptoms stop, a diet of bland, easily digested foods such as broth, eggs, rice and other cooked grains, and toast is recommended for two to three days. Milk products, spicy food, alcohol, sweets, raw vegetables, and fresh fruit should be avoided.

Expected results

Many cases of food poisoning clear up on their own within a week without medical assistance. There are usually few complications once possible dehydration has been addressed. Fatigue may continue for a few days after active symptoms stop, however. In the more severe types of poisoning, especially those involving neurotoxins, the respiratory muscles may become paralyzed. In such cases, death will result from asphyxiation unless there is medical intervention. Deaths due to food poisoning are rare and tend to occur in the very young, the very old, and in people whose immune systems are already weakened.

C. botulinum, is likely to cause serious illness or fatalities, even when ingested in very small quantities. Children affected by food poisoning from E. coli often need to be hospitalized. In some cases, E. coli toxins may be absorbed into the blood stream where they destroy red blood cells and platelets, which are important in blood clotting. About 5% of victims, regardless of age, develop hemolytic uremia syndrome, which results in kidney failure.


Food poisoning prevention efforts include:

  • Hot foods should be kept hot, and cold foods should be kept cold.
  • Meat should be cooked to the recommended internal temperature. Eggs should be cooked until they are no longer runny.
  • Leftovers should be refrigerated promptly. Food should never be left to stand at room temperature.
  • Contact of utensils and surfaces with the juices of raw meats should be avoided.
  • Fruits and vegetables should be washed before using.
  • Unpasteurized dairy products and fruit juices should be avoided.
  • Bulging or leaking canned foods or any food that smells spoiled should be discarded.
  • Hands should be washed with soap before food preparation and after using the bathroom.
  • Food preparation surfaces should be sanitized regularly.
  • Infants under a year should not be fed honey, which may contain spores of C. botulinum.
  • Proper canning and adequate heating of home-canned food before serving are essential. (Boiling for three minutes is recommended.)

Taking Lactobacillus acidophilus or Lactobacillus bulgaricus may help prevent food poisoning, especially when traveling. Populating the intestines with these bacteria will make it less likely that harmful bacteria are able to gain a foothold.

Key Terms

A disrupted heartbeat pattern.
Disulfiram-like poison
Disulfiram is a chemical compound that causes a severe physiological reaction to alcohol. This poison behaves like disulfiram.
Salts and minerals in the body that are important because they control body fluid balance and support all major body reactions.
Nasogastric intubation
Insertion of a tube through the nose and mouth for delivery of food and oxygen.
A poison that acts on the central nervous system.
Waves of contractions, such as through the intestines, forcing the contents onward.

Types of Food Poisoning
Traveler's diarrhea Usually caused by E. coli bacteria found in contaminated food and water.
Salmonella Caused by bacteria in contaminated poultry, eggs, meat, and dairy products. Although it can be fatal, most cases are mild.
BotulismCaused by anaerobic bacteria that is found in home canned products and honey.
ViralCaused most often by contaminated raw seafood.
ChemicalCaused by pesticides.

Further Reading

For Your Information


  • Merck & Co., Inc. The Merck Manual Online.
  • Merck & Co., Inc. The Merck Manual Online.
  • FDA Center for Food Safety and Applied Nutrition.

Gale Encyclopedia of Alternative Medicine. Gale Group, 2001.

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