Food poisoning

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A foodborne illness or food poisoning is any illness resulting from the consumption of food contaminated with pathogenic bacteria, toxins, viruses, prions or parasites. Such contamination usually arises from improper handling, preparation, or food storage. Good hygiene practices before, during, and after food preparation can reduce the chances of contracting an illness. The action of monitoring food to ensure that it will not cause foodborne illness is known as food safety.


Some common diseases are occasionally transmitted to food through the water vector. These include infections caused by Shigella, Hepatitis A and the parasites Giardia lamblia and Cryptosporidium parvum. Contact between food and pests, especially flies, rodents and cockroaches, are other food contamination vectors.

Foodborne illness can also be caused by the presence of pesticides or medicines in food, or by unintentionally consuming naturally toxic substances like poisonous mushrooms or reef fish.

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, such as in the case of Salmonella Typhi (typhoid fever)), 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. [1]

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 overall health. In the case of Salmonella, as few as 15-20 cells may suffice [2].

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% [3].

Symptoms for bacterial infections are delayed because the bacteria need time to multiply. They are usually not seen until 12-36 hours after eating contaminated food.

Common bacterial foodborne pathogens are:



In addition to disease caused by direct bacterial infection, some foodborne illnesses are caused by exotoxins which are excreted by the cell as the bacterium grows. Exotoxins can produce illness even when the microbes that produced them have been killed. Symptoms typically appear after 1-6 hours depending on the amount of toxin ingested.

For example Staphylococcus aureus produces a toxin that causes intense vomiting. The rare but potentially deadly disease botulism occurs when the anaerobic bacterium Clostridium botulinum grows in improperly canned low-acid foods and produces a powerful paralytic toxin.

Preventing bacterial food poisoning

The prevention is mainly the role of the state, through the definition of strict rules of hygiene and a public service of veterinary survey of the food chain, from farming to the transformation industry and the delivery (shops and restaurants). This regulation includes:

  • traceability: in a final product, it must be possible to know the origin of the ingredients (originating farm, identification of the harvesting or of the animal) and where and when it was processed; the origin of the illness can thus be tracked and solved (and possibly penalized), and the final products can be removed from the sale if a problem is detected;
  • respect of hygiene procedures like HACCP and the "cold chain";
  • power of control and of law enforcement of the veterinarians.

At home, the prevention mainly consists of:

  • separating foods while preparing and storing to prevent cross contamination. (i.e. clean cutting boards, utensils, and hands after handling meat and before cutting vegetables, etc.)
  • washing hands and/or gloves before handling ready-to-eat foods.
  • respecting food storage methods (hot foods hot and cold foods cold) and food preservation methods (especially refrigeration), and checking the expiration date;
  • avoiding over-long storage of left-overs;
  • washing the hands before preparing the meal and before eating;
  • washing the fresh fruits and vegetables with clear water, especially when not cooked (e.g. fruits, salads), scrubbing firm fruits and vegetables with a brush to clean;
  • washing the dishes after use, rinsing them well in hot water and storing them clean and dry;
  • keeping work surfaces and chopping boards clean and dry;
  • keeping the kitchen and cooking utensils clean and dry;
  • not relying on disinfectants or disinfectant-impregnated cloths and surfaces as a substitute for good hygiene methodology (as above);
  • preventing pets walking on food-preparation surfaces.

Bacteria need warmth, moisture, food and time to grow. The presence, or absence, of oxygen, salt, sugar and acidity are also important factors for growth. In the right conditions, one bacterium can multiply using binary fission to become four million in eight hours. Since bacteria can be neither smelled nor seen, the best way to ensure that food is safe is to follow principles of good food hygiene. This includes not allowing raw or partially cooked food to touch dishes, utensils, hands or work surfaces previously used to handle even properly cooked or ready to eat food.

High salt, high sugar or high acid levels keep bacteria from growing, which is why salted meats, jam, and pickled vegetables are traditional preserved foods.

The most frequent causes of bacterial foodborne illnesses are cross-contamination and inadequate temperature control. Therefore control of these two matters is especially important.

Thoroughly cooking food until it is piping hot, i.e. above 70 °C (158 °F) will quickly kill virtually all bacteria, parasites or viruses, except for Clostridium botulinum and Clostridium perfringens, which produces a heat-resistant spore that survives temperatures up to 100 °C (212 °F). Once cooked, hot foods should be kept at temperatures out of the danger zone. Temperatures above 63 °C (145 °F) stop microbial growth.

Cold foods should also be kept colder than the danger zone, below 5 °C (41 °F). However, Listeria monocytogenes and Yersinia enterocolitica can both grow at refrigerator temperatures.

Hot foods should be held at 57°C (135 °F) or hotter until ready to cool. Hot foods need to be cooled quickly to limit the amount of time the food is in the danger zone (temperature range at which bacteria can grow.) The food should be cooled from 57 °C (135 °F) to 20 °C (70 °F) within two hours. Then further chilled to less than 5 °C (41 °F) in 4 hours. Food should then be held chilled at 5 °C (41 °F) or less.


Viral infections make up perhaps one third of cases of food poisoning in developed countries. They are usually of intermediate (1-3 days) incubation period, cause illnesses which are self-limited in otherwise healthy individuals, and are similar to the bacterial forms described above.



Most foodborne parasites are zoonoses.


The scolex of Tenia solium

See also: Tapeworm and Flatworm



Giardia lamblia

Natural toxins

In contrast several foods can naturally contain toxins that are not produced by bacteria and occur naturally in foods, these include:

Red kidney beans

Other pathogenic agents


There are every year about 76 million foodborne illnesses in the United States (26,000 cases for 100,000 inhabitants), 2 million in the United Kingdom (3,400 cases for 100,000 inhabitants) and 750,000 in France (1,210 cases for 100,000 inhabitants).

In the United States

In the United States, there are approximately 76 million foodborne illnesses (26,000 cases for 100,000 inhab.):

  • 325,000 were hospitalized (111 per 100,000 inhab.);
  • 5,000 people died (1.7 per 100,000 inhab.).


In France

In France, for 750,000 cases (1,210 per 100,000 inhab.):

  • 70,000 people consulted in the emergency department of an hospital (113 per 100,000 inhab.);
  • 113,000 people were hospitalized (24 per 100,000 inhab.);
  • 400 people died (0.1 per 100,000 inhab.).

The causes of the illness (toxic factor) are:

Causes of foodborne illness in France
Cause cases per year
1 Salmonella ~8,000 cases (13 per 100,000 inhab.)
2 Campylobacter ~3,000 cases (4.8 per 100,000 inhab.)
3 Parasites
incl. Toxoplasma
~500 cases (0.8 per 100,000 inhab.)
~400 cases (0.65 per 100,000 inhab.)
4 Listeria ~300 cases (0.5 per 100,000 inhab.)
5 Hepatitis A ~60 cases (0.1 per 100,000 inhab.)

The causes of death by foodborne illness are:

Causes of death by foodborne illness in France
Cause cases per year
1 Salmonella ~300 cases (0.5 per 100,000 inhab.)
2 Listeria ~80 cases (0.13 per 100,000 inhab.)
3 Parasites ~37 cases (0.06 per 100,000 inhab.)
(toxoplasma in 95% of the cases)
4 Campylobacter ~15 cases (0.02 per 100,000 inhab.)
5 Hepatitis A ~2 cases (0.003 per 100,000 inhab.)



The vast majority of reported cases of foodborne illness occur as individual or sporadic cases. In most cases these originate, and occur, in the home. An outbreak occurs when two or more people suffer foodborne illness after consuming food from a contaminated batch.

Often, a combination of events contributes to an outbreak, for example, food might be left at room temperature for many hours, allowing bacteria to multiply which is compounded by inadequate cooking which results in a failure to kill the dangerously elevated bacterial levels.

Outbreaks are usually identified when those affected know each other. However, some are identified by public health staff from unexpected increases in laboratory results for certain strains of bacteria.


"Ptomaine" is a former name for a supposed group of chemical substances that were theorized to cause food poisoning. The word "ptomaine" is no longer used scientifically.

Political issues

United Kingdom

Since the 1970s, key changes in UK food safety law have taken place following serious outbreaks of food poisoning. These included the death of 19 patients in the Stanley Royd Hospital outbreak [4]; and the death of 17 people in the 1996 Wishaw outbreak of E.coli O157 [5], which was a precursor to the establishment of the Food Standards Agency which, according to Tony Blair in the 1998 white paper A Force for Change Cm 3830 "would be powerful, open and dedicated to the interests of consumers". There remain questions, however, over the nature of any agency funded by a government which has not an insignificant say in staffing.

United States

In 2001, the Center for Science in the Public Interest (CSPI) petitioned the United States Department of Agriculture to require meat packers to remove spinal cords before processing cattle carcasses for human consumption, a measure designed to lessen the risk of infection by variant Creutzfeldt-Jakob disease. The petition was supported by the American Public Health Association, the Consumer Federation of America, the Government Accountability Project, the National Consumers League, and Safe Tables Our Priority. This was opposed by the National Cattlemen's Beef Association, the National Renderers Association, the National Meat Association, the Pork Producers Council, sheep raisers, milk producers, the Turkey Federation, and eight other organizations from the animal-derived food industry. This was part of a larger controversy regarding the United States' violation of World Health Organization proscriptions to lessen the risk of infection by variant Creutzfeldt-Jakob disease [6].

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