Food poisoning refers to illness arising from eating contaminated food. Food may be contaminated by bacteria, viruses, environmental toxins, or toxins present within the food itself, such as the poisons in some mushrooms or seafood. Symptoms of food poisoning are usually gastrointestinal, such as nausea , abdominal pain , vomiting , and/or diarrhea . Some food-borne toxins can affect the nervous system. Food poisoning is sometimes called bacterial gastroenteritis or infectious diarrhea and is sometimes incorrectly called ptomaine poisoning.
Every year millions of people of all ages suffer from bouts of vomiting and diarrhea blamed correctly on something they ate. According to the Centers for Disease Control and Prevention (CDC), up to 33 million cases of food poisoning are reported in the United States each year. Many cases are mild and pass so rapidly that they are never diagnosed. Occasionally a severe outbreak affects many people at once, creating a newsworthy public health hazard. Although the food supply in the United States is probably one of the safest in the world, anyone can get food poisoning. Outbreaks have occurred in schools and colleges (up to 25 incidents reported annually in the United States), among restaurant clientele, in institutions such as long-term care facilities, and in other settings serving the public. Serious outbreaks are rare. When they occur, the very young, the very old, and those with weakened immune systems are subject to the most severe and life-threatening cases.
A variety of bacteria cause food poisoning, including Salmonella , Staphylococcus aureus , Campylobacter jejuni , Escherichia coli , Shigella , and Clostridium botulinum . Each type of bacteria has a different incubation period and duration, and all except the botulinum toxin cause inflammation of the intestines and diarrhea. Food and water can also be contaminated by viruses such as the Norwalk and hepatitis viruses. Environmental toxins (heavy metals) in foods or water, and poisonous substances in certain foods such mushrooms and shellfish are other causes of food poisoning.
Careless food handling between farm and table may create conditions for the growth of bacteria. Vegetables eaten raw, such as lettuce, may be contaminated by bacteria in soil, water, and dust during washing and packing. Home canned and commercially canned food may be improperly processed at too low a temperature or for too short a time to kill bacteria.
Raw meats carry many bacterial contaminants. The United States Food and Drug Administration (FDA) estimates that 60 percent or more of raw poultry sold at retail carries some disease-causing bacteria. Other raw meat products and eggs are contaminated to a lesser degree. Although thorough cooking kills bacteria and makes the food harmless, recontamination can occur in properly cooked food if it comes into contact with cutting boards, countertops, or utensils that were used with raw meat and not cleaned and sanitized after use. Food can also become contaminated by environmental contaminants and by food handlers carrying bacteria on their hands while preparing foods for the public.
It is estimated that 50 percent of healthy people have staphylococcus organisms in their nasal passages and throats and on their skin and hair. Rubbing a runny nose and then touching food can introduce the bacteria into cooked food. Bacteria flourish at room temperature and grow rapidly in quantities capable of causing illness. To prevent this growth, food must be kept hot or cold but never just warm or at room temperature.
Travel to countries where less attention is paid to sanitation, water purification, and good food-handling practices may expose individuals to bacterial contaminants. Institutional food preparation also increases the risk of food poisoning, especially if food is allowed to stand on warming trays, under warming lights, or at room temperature before being served.
Food poisoning is not spread from one individual to another but through direct contact with the causative bacteria, viruses, or other toxins in consumed food.
The Centers for Disease Control and Prevention (CDC) estimates that there are from six to 33 million cases of food poisoning in the United States annually, affecting men, women, and children. Food poisoning by E. coli occurs in three out of every 10,000 people. One out of every 1,000 people are reported to have food poisoning caused by Salmonella ; two-thirds are young people under age 20, and the majority are children under age nine. Although camplyobacter infections can occur in anyone, children under age five and young adults between ages 15 and 29 are more frequently infected.
Causes and symptoms
Classic food poisoning cases are caused by a variety of bacteria. The most common are the following:
- Staphylococcus aureus
- Campylobacter jejuni
- Escherichia coli
- Clostridium botulinum
Food poisoning symptoms occur when food-borne bacteria release toxins or poisons as a byproduct of their growth in the body. These toxins (except those from C. botulinum ) cause inflammation of the stomach lining and the small and/or large intestines, resulting in abdominal muscle cramps , vomiting, diarrhea, and fever . The severity of symptoms depends on the type of bacteria, the amount consumed, and the individual's general health and sensitivity to the toxin. Dehydration can result from loss of fluids through persistent vomiting and diarrhea; it is one of the most frequent and serious complications of food poisoning. When more fluids are being lost than are replaced, dehydration may occur in the very young and in the elderly, as well as in individuals who take diuretics.
A 2001 CDC report states that culture-confirmed cases of salmonella poisoning affected almost 50,000 people in the United States. However, it is believed that between 2 and 4 million unconfirmed cases actually occur each year. Salmonella is found in egg yolks from infected chickens, raw and undercooked poultry and other meats, dairy products, fish, shrimp, and many other foods. The CDC estimates that one of every 50 consumers is exposed to a contaminated egg yolk each year, although thorough cooking kills the bacteria, making the food harmless. Salmonella is also found in feces of pet reptiles such as turtles, lizards, and snakes. Most cases of salmonella poisoning occur in the warm months between July and October.
Symptoms of food poisoning, such as abdominal pain, diarrhea, vomiting, and fever, begin eight to 72 hours after eating food contaminated with salmonella. Symptoms generally last one to five days. Dehydration can be a complication of severe cases with persistent vomiting and/or diarrhea. People generally recover without antibiotic treatment, although they may feel tired for a week or so after the active symptoms subside.
Staph organisms are found on humans and in the environment in dust, air, and sewage. The bacteria are spread primarily by food handlers using poor sanitary practices. Almost any food can be contaminated, but salad dressings, milk products, cream pastries, and any food kept at room temperature, rather than hot or cold, are likely candidates. It is difficult to estimate the number of annual cases of Staphylococcus food poisoning because its symptoms are so similar to those caused by other food-borne bacteria. Many cases are mild. Victims may miss a day of school or work but never see a doctor for confirmation of food poisoning. Symptoms appear rapidly, usually one to six hours after the contaminated food is eaten. Acute symptoms of vomiting and severe abdominal cramps without fever usually last three to six hours and rarely more than 24 hours. Most people recover without medical assistance. Deaths are rare.
Escherichia coli (E. coli)
The many strains of E. coli are not all harmful. Nonpathogenic E. coli are, in fact, a major part of normal gut flora. The strain that causes the most severe food poisoning, however, is E. coli O157:H7 , which affects three people in every 10,000. The food-borne organisms are found and transmitted mainly in food derived from cows, such as raw milk and raw or rare ground beef. Fruit or vegetables can also be contaminated.
Symptoms of E. coli poisoning are slower to appear than those caused by other food-borne bacteria. Because E. coli toxins are produced in the large intestine rather than higher up in the digestive system, symptoms typically occur from one to three days after eating contaminated food. Those affected have severe abdominal cramps and watery diarrhea that usually becomes bloody within 24 hours, a condition that can last from one to eight days. There is little or no fever and vomiting occurs only rarely.
Campylobacter is the leading cause of bacterial diarrhea worldwide, responsible for more cases (2 million or more) of bacterial diarrhea in the United States than Shigella and Salmonella combined. Campylobacter is carried by healthy cattle, chickens, birds, and flies. It is also found in ponds and stream water and has been found in bottled water and on salad vegetables washed with water. Although eating chicken is a known risk factor, drinking water and eating salads have not been considered significant risks until studies of causes released in 2003 showed possible association with Campylobacter diarrheal infections. It is not known whether contamination occurs at the site of production or in the home or institution after contact with other contaminated foods, surfaces, or utensils. The ingestion of only a few hundred Campylobacter bacteria can cause food poisoning symptoms, which may begin two to five days after eating contaminated food. Symptoms will typically include fever, abdominal pain, nausea, headache , muscle pain, and diarrhea. The diarrhea can be watery or sticky and may contain blood. Symptoms last from seven to ten days and relapses occur in about one-fourth of infected individuals. Dehydration is a common complication. Other complications, such as arthritis-like joint pain and hemolytic-uremic syndrome (HUS), occur in rare cases.
Shigella is a common cause of diarrhea in travelers to developing countries. It is associated with contaminated food and water, crowded living conditions, and poor sanitation. The bacterial toxins affect the small intestine. Symptoms of Shigella infection appear about 36–72 hours after eating contaminated food. In addition to the familiar watery diarrhea, nausea, vomiting, and abdominal cramps, the individual may also have chills, fever, and neurological symptoms. The diarrhea may be quite severe with cramping and progresses to classic dysentery. Up to 40 percent of children with severe infections show neurological symptoms. These include confusion, headache, lethargy, a stiff neck, and possible seizures. The symptoms of food poisoning by Shigella organisms may resemble meningitis and a differential diagnosis must be made by isolating the causative bacteria.
The disease runs its course usually in two to three days but may last longer. Dehydration is a common complication. Most people recover on their own, although they may feel exhausted. Children who are malnourished or have weakened immune systems may be severely affected and death can result.
C. botulinum causes both adult and infant botulism and differs significantly from other contaminants in its sources and symptoms. C. botulinum 's common food-borne form is an anaerobic bacterium that can only live and reproduce in the absence of oxygen. Exposure to the botulinum toxin usually occurs while eating contaminated food stored in an airless environment, as in home-canned or commercially canned or vacuum-packed food. Also, botulinum toxin is a neurotoxin that blocks the ability of motor nerves to release acetylcholine, the neurotransmitter that relays nerve signals to muscles. This neurological process can result in unresponsive muscles, a condition known as flaccid paralysis. Breathing may be severely compromised in progressive botulism because of failure of the muscles that control the airway and breathing. In infants, botulism may be caused by specific types of clostridia obtained from soil, inhaled spores, or honey containing the spores. Contamination from any of the sources results in growth of the bacteria in the infant's intestine and production of the neurotoxin.
Infant botulism is a form of botulism first recognized in 1976 that differs from food-borne botulism. Infant botulism occurs when a child younger than one year ingests the spores of C. botulinum . Although these spores are commonly found in soil, honey is a more frequent source of spores causing infant botulism by lodging in the baby's intestinal tract and producing the neurotoxin. Onset of symptoms is gradual. Initially, the baby is constipated, followed by poor feeding, lethargy, weakness, drooling, and a distinctive wailing cry. Eventually, the baby loses the ability to control its head muscles. From there the paralysis progresses to the rest of the body. Immediate treatment is required to avoid neurological complications and death. Infant botulism is much more likely to be fatal than other food poisoning infections. Infant botulism is a special form of food poisoning not related to the food-borne toxins that cause adult botulism.
Adult botulism outbreaks are usually associated with toxins found in home-canned food, although poisoning occasionally results from eating commercially canned or vacuum-packed foods. C. botulinum grows well in non-acidic, oxygen-free environments, meaning that if the cooking temperatures are too low or the cooking time too brief the bacteria in the food are not killed. Instead, bacteria may reproduce inside the can or jar, releasing the deadly neurotoxin. Heating canned food to boiling for ten minutes can render the toxin harmless. However, consuming even a very small amount of the toxin can result in serious illness or death because of lethal neurological complications.
Symptoms of adult botulism appear about 18–36 hours after the contaminated food is eaten, although times of onset have been documented ranging from four hours to eight days. Initially a person suffering from botulism feels weak and dizzy and later experiences double vision. Symptoms progress to difficulty speaking and swallowing. Paralysis moves down the body, and when the respiratory muscles are paralyzed, death can result from asphyxiation. Individuals with any signs of botulism poisoning must receive immediate emergency medical care to increase their chance of survival.
When to call the doctor
Any unexplained abdominal pain accompanied by persistent vomiting or diarrhea, whether or not a food source is suspected, should be reported to the doctor. A child having difficulty swallowing, speaking, holding the head up, or maintaining an upright posture should receive emergency medical attention. Signs of confusion, lethargy, headache, stiff neck, or seizures also require immediate medical attention.
One important part of diagnosing food poisoning is the need for doctors and community health professionals to determine if a number of people have eaten the same food and show the same symptoms. If this can be proven, food poisoning is strongly suspected. The diagnosis is confirmed when the suspected bacteria is identified in the culture of a stool sample or a fecal smear from the affected individual. In some cases, the suspected bacteria, virus, or toxin can be identified in the actual food source.
Laboratory tests are used to make a definitive diagnosis, but treatment of symptoms may be started immediately without waiting for test results, which may take up to two days. Diagnostic tests focus on identifying the organism causing the illness. This process may involve performing a culture on contaminated material from the suspect food, a stool sample, or swabs of the nose or throat of the affected individual if inhaled spores are a possibility. Culture results are available from the microbiology laboratory as soon as bacteria grow in a special plate incubated at temperatures at or above body temperature. The growth of specific bacteria confirms the diagnosis. The microbiology laboratory may use samples of the bacteria grown to perform other special techniques to help identify the causative organism.
In infant botulism, the infant's stool may be cultured to isolate the organism; this test may be performed by the state health department or the Centers for Disease Control (CDC). Early diagnosis of botulism is critical so that treatment can begin in time to avoid neurological involvement. Although the definitive diagnosis comes from laboratory tests, it can usually be diagnosed by recognizing the distinctive neurological symptoms typical of contamination with C. botulinum .
While waiting for diagnostic test results, the doctor performs a physical examination and may ask about recently consumed food, possible open sores, recent activities and behavior, and other information that may help to rule out other disease possibilities. Imaging studies or additional diagnostic tests may be done to rule out other diseases or conditions with similar symptoms.
Many cases of food poisoning go undiagnosed, since a definite diagnosis is not necessary to effectively treat the symptoms. Because it takes time for symptoms to develop, the most recent food one has eaten may not be the cause of the symptoms.
Treatment of food poisoning, except for botulism, focuses on preventing or correcting dehydration by replacing critical fluids and electrolytes lost through vomiting and diarrhea. Electrolytes are mineral salts that form electrically charged particles (ions) in body fluids; they help control body fluid balance and participate in many essential body functions. Pharmacists can recommend effective, pleasant-tasting, electrolyte replacement fluids that are available without a prescription. To prevent dehydration, a doctor may decide to give fluids intravenously. In very serious cases of food poisoning, medications may be given to stop abdominal cramping and vomiting. Antidiarrheal medications are not usually given. Stopping the diarrhea actually maintains toxin levels in the body for longer periods and may prolong the infection. Severe bacterial food poisonings are sometimes treated with intravenous antibiotics .
Modifying the diet while recovering from food poisoning is usually recommended. During a period of active vomiting and diarrhea, solid food should be avoided and only small quantities of clear liquids should be consumed as frequently as possible. Once active symptoms stop, bland, soft, easy-to-digest foods should be consumed for two to three days. One example is the BRAT diet of bananas, rice, applesauce, and toast, all of which are easy to digest. Milk products, spicy food, and fresh fruit should be avoided for a few days, although babies should continue to breastfeed. These modifications are often the only treatment that is necessary.
Botulism is treated in an entirely different way. Older children and adults can be treated with injections of a specific antitoxin for botulism if it can be administered within 72 hours after symptoms are first observed. If given later, it provides little or no benefit. Infants, however, cannot receive this antitoxin and are usually treated instead with injections of human botulism immune globulin (BIG), an antiserum that neutralizes the botulinum toxin. This antiserum is available in the United States through the Infant Botulism Treatment and Prevention Program in Berkeley, California. Both infants and adults may require hospitalization , often in the intensive care unit. Mechanical ventilators may be used for those whose ability to breathe is impaired and intravenous nutrition may be provided until any paralysis is corrected.
Alternative practitioners offer the same advice as traditional practitioners concerning diet modification, treatment of diarrhea and vomiting, and prevention of dehydration. Charcoal tablets, Lactobacillus acidophilus , Lactobacillus bulgaricus , and citrus seed extract can be taken to help normalize the digestive system. An electrolyte replacement fluid can be made at home by adding one teaspoon of salt and four teaspoons of sugar to one quart of water. For food poisoning other than botulism, two homeopathic remedies, either Arsenicum album or Nux vomica , are recommended to help reduce symptoms.
Most cases of food poisoning (except botulism) clear up on their own within one week without medical assistance. As symptoms subside, the individual may continue to feel tired or weak for a few days. If dehydration has been effectively corrected or prevented, few complications can be expected. Deaths are rare and usually occur in the very young, the very old, and people whose immune systems are already weakened.
Complications of salmonella food poisoning may include arthritis-like symptoms that occur three to four weeks after infection. Although deaths from salmonella infection are rare, they do occur. Most deaths reported have occurred among elderly adults in long-term care.
Adults usually recover from E. coli poisoning without medical intervention, but many children require hospitalization for contamination with this organism. Toxins may be absorbed into the blood stream where they destroy red blood cells and platelets, tiny cells important in blood clotting. About 5 percent of victims develop hemolytic-uremic syndrome (HUS), which can result in sudden kidney failure that requires a medical procedure (dialysis) to perform the kidney's task of filtering the body's waste products.
Botulism is the deadliest of the bacterial food-borne illnesses. With prompt medical care, the death rate is less than 10 percent in children and adults.
Food poisoning is almost entirely preventable by practicing good sanitation and good food handling techniques. These include the following measures:
Antitoxin —An antibody against an exotoxin, usually derived from horse serum.
Culture —A test in which a sample of body fluid is placed on materials specially formulated to grow microorganisms. A culture is used to learn what type of bacterium is causing infection.
Diuretics —A group of drugs that helps remove excess water from the body by increasing the amount lost by urination.
Electrolytes —Salts and minerals that produce electrically charged particles (ions) in body fluids. Common human electrolytes are sodium chloride, potassium, calcium, and sodium bicarbonate. Electrolytes control the fluid balance of the body and are important in muscle contraction, energy generation, and almost all major biochemical reactions in the body.
Hemolysis —The process of breaking down red blood cells. As the cells are destroyed, hemoglobin, the component of red blood cells which carries the oxygen, is liberated.
Lactobacillus acidophilus —Commonly known as acidophilus, a bacteria found in yogurt that changes the balance of the bacteria in the intestine in a beneficial way.
Neurological —Relating to the brain and central nervous system.
Neurotoxin —A poison that acts directly on the central nervous system.
Platelet —A cell-like particle in the blood that plays an important role in blood clotting. Platelets are activated when an injury causes a blood vessel to break. They change shape from round to spiny, "sticking" to the broken vessel wall and to each other to begin the clotting process. In addition to physically plugging breaks in blood vessel walls, platelets also release chemicals that promote clotting.
Spore —A dormant form assumed by some bacteria, such as anthrax, that enable the bacterium to survive high temperatures, dryness, and lack of nourishment for long periods of time. Under proper conditions, the spore may revert to the actively multiplying form of the bacteria. Also refers to the small, thick-walled reproductive structure of a fungus.
Toxin —A poisonous substance usually produced by a microorganism or plant.
- Keep hot foods hot and cold foods cold.
- Cook meat to the recommended internal temperature.
- Use a meat thermometer to check meat and cooking eggs until they are no longer runny.
- Refrigerate leftovers promptly, not letting food stand at room temperature.
- Before preparing other foods, carefully clean surfaces (cutting boards and counters, knives and other utensils) contaminated with the juices of uncooked meats.
- Do not refreeze meat once it has been thawed.
- Wash fruits and vegetables before using.
- Consume only pasteurized dairy products and fruit juices.
- Discard bulging or leaking cans or any food that smells spoiled.
- Wash hands well before and during food preparation and after using the bathroom.
- Sanitize food preparation surfaces regularly.
It is especially important to discard any food that seems spoiled and not to eat food that has been stored at room temperature or above for more than a few hours. Home canners must be diligent about using sterile equipment and following U.S. Department of Agriculture canning guidelines.
Infant botulism is perhaps the most difficult poisoning to prevent, because what goes into an infant's mouth is often beyond control. One important preventative measure, however, is to avoid feeding honey to infants younger than 12 months since it is a known source of botulism spores. As infants begin eating solid foods, the same food precautions should be followed as for older children and adults.
Symptoms of food poisoning can appear as early as an hour after consuming the contaminated food or up to several days later. Parents may be concerned about possible contamination from unknown sources and that symptoms may occur suddenly, without warning. Practicing good sanitation and good food handling techniques is the best way parents can prevent contamination. Normal watchfulness of the parents is sufficient to notice symptoms, paying attention to any change in eating, unusual crying, increases or decreases in bowel movements, the presence of vomiting or a lack of normal responses such as turning of the head and body movements. An early report of symptoms, even if no particular food is suspected of causing illness, helps get early treatment and avoid complications.
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Isle, Mick. Everything You Need to Know about Food Poisoning. New York: Rosen Publishing Group, 2001.
Rue, Nancy, and Anne Williams. Quick Reference to Food Safety and Sanitation. Boston, MA: Prentice Hall, 2002.
Trickett, Jill. The Prevention of Food Poisoning. Cheltenham, UK: Nelson Thornes, 2001.
Centers for Disease Control and Prevention. 1600 Clifton Rd., NE, Atlanta, GA 30333. Web site: http://www.cdc.gov.
"Food Safety." Available online at http://www.nlm.nih.gov/medlineplus/print/foodsafety.html (accessed November 20, 2004).
L. Lee Culvert Suzanne M. Lutwick, MPH