Food Poisoning

Food poisoning—often called foodborne illness, disease, or infection—is illness caused by eating food or drinking water contaminated with disease-causing bacteria, viruses, parasites, or environmental toxins. Toxins may also be present within the food itself, such as the poisons in some mushrooms. Food poisoning is sometimes referred to as gastroenteritis or infectious diarrhea.

Foodborne illness is a serious public health concern in the United States and around the world. More than 250 different foodborne diseases have been identified, primarily infections caused by pathogenic microorganisms. In 2011, the U.S. Centers for Disease Control and Prevention (CDC) reported that about 48 million Americans—one in six—suffer from food poisoning every year. Although unpleasant, most cases are not severe enough to require medical treatment. Nevertheless, food poisoning results in 128,000 hospitalizations and 3,000 deaths annually in the United States and is estimated to cost $3–$6 billion annually in direct medical care and lost productivity. The very young, the elderly, pregnant women, and people with weakened immune systems—such as HIV/AIDS, leukemia, and transplant patients—are more likely to suffer severe food poisoning that results in hospitalization and life-threatening complications.

Disease-causing organisms and chemicals can contaminate food at any point in the food production chain. The majority of food poisonings result from contamination with animal or human feces during slaughter, processing, transport, storage, or preparation. The U.S. Food and Drug Administration (FDA) estimates that 90% of raw poultry sold at retail stores carries some disease-causing bacteria. Other raw meat products and eggs are contaminated to a lesser degree. Fruits and vegetables can also be contaminated in the field with feces or pesticides, as well as during harvesting, processing, distribution, and storage. Oysters and other filter-feeding shellfish can concentrate harmful bacteria that are normally present in seawater.

Although thorough cooking kills most bacteria, the CDC estimates that about 97% of food poisonings are due to improper food handling, such as under-cooking or poor refrigeration, with 80% of such cases occurring in restaurants, cafeterias, or institutions such as nursing homes, schools, and prisons. The remaining 20% of cases come from improper food handling in the home.

Nevertheless, the U.S. food supply is probably the safest in the world, and serious outbreaks of food poisoning are relatively rare. Travel outside the United States, to countries with poorer sanitation, water purification, and food-handling practices, increases the risk of food poisoning. Bioterrorism experts are also concerned that disease-causing organisms could intentionally be introduced into the food or water supply to cause mass outbreaks of food poisoning.

Microorganisms responsible for common foodborne illnesses

SOURCE: U.S. Food and Drug Administration. “Foodborne Illness: What Consumers Need to Know.” https://www.fsis.usda.gov/wps/portal/fsis/topics/food-safety-education/get-answers/food-safety-fact-sheets/foodborne-illness-and-disease/foodborne-illness-what-consumers-needto-know/ct_index#2 (accessed April 2, 2018).

Food poisoning is primarily caused by a variety of different bacteria. According to the 2010 estimates, Salmonella infections accounted for the greatest number of hospitalizations (35%) and deaths (28%). In addition to Salmonella, other bacteria that commonly cause food poisoning include Campylobacter, Toxoplasma, Escherichia coli O157, Listeria, Clostridium perfringens, Staphylococcus aureus, Shigella, and Clostridium botulinum. Each has a slightly different incubation period and duration, but all except C. botulinum cause inflammation of the intestines and diarrhea. Food and water also can be contaminated by viruses (e.g., norovirus, cholera, rotavirus), environmental toxins (e.g., heavy metals), and poisons produced within the food itself (e.g., mushroom poisoning, shellfish poisoning).

BACTERIA. Bacterial contamination is the leading cause of food poisoning. At room temperature, bacteria reproduce at astounding rates. A single bacterium that divides every half hour can produce 17 million offspring in 12 hours. Bacteria fall into two general categories. One group causes symptoms of food poisoning by directly infecting the intestines causing irritation and diarrhea. The other group releases toxins (poisons) as they grow and reproduce.

These toxins affect the digestive system and often cause vomiting first, followed by diarrhea. Common bacteria include:

Rotavirus infection is the leading cause of severe diarrhea in infants and children. Two vaccines that prevent most rotavirus infections are available for infants in the United States. One vaccine requires two doses, the other three. The first dose must be given after age 6 weeks and before age 15 weeks. In countries where a rotavirus vaccine is available, the number of cases of serious diarrhea and death from dehydration in infants has decreased substantially. This virus still remains a major killer of infants in underdeveloped countries.

PARASITES. Parasites that cause food poisoning usually come from contaminated water. They often cause mild symptoms that are slow to develop but last for several weeks. Giardia causes watery diarrhea and is often acquired by drinking untreated water from lakes or streams. Cryptosporidium is a parasite that causes large amounts of watery diarrhea for 3–4 days. Healthy people usually recover quickly, but in people with weakened immune systems, symptoms can persist for a long time. Toxoplasma gondii is a parasite that is responsible for 24% of food poisoning deaths from identified agents.

NATURAL TOXINS. Natural poisons found in some wild mushrooms can cause anything from nausea and vomiting to hallucinations, coma, and death, depending on the amount and species of mushroom eaten. Mushroom poisoning is a medical emergency. People who believe they have eaten a poisonous mushroom should, if possible, take a sample of the mushroom or their vomit to the emergency room with them. Identifying the type of mushroom causing the illness can help determine the most effective treatment.

Oysters, clams, mollusks, and scallops can contain toxins that affect the nervous system. Symptoms usually begin with a tingling in the mouth, then the arms and legs. Individuals may become dizzy and may have difficulty breathing. Shellfish poisoning is a medical emergency because the muscles needed for breathing may become paralyzed. Similar symptoms result from eating the Japanese puffer fish which contains a natural poison in its skin and digestive system that affects the nervous system.

MAN-MADE TOXINS. Man-made toxins include all pesticides, fertilizers, disinfectants, and other chemicals remaining in food when it is eaten that can cause illness. Contamination is accidental, and often the result of ignorance or a misunderstanding of how to apply the chemical. Symptoms may develop rapidly or slowly depending on the type of chemical and the amount of exposure. Chemical poisoning requires prompt medical evaluation.

Other food-poisoning agents include toxins in poisonous mushrooms and reef fish, food contaminated with pesticides or herbicides, and certain communicable pathogens that are occasionally foodborne. The latter include the Shigella family of bacteria, hepatitis A virus, rotavirus, and the parasites Giardia lamblia and Cryptosporidium.

Ingested pathogens adhere to the intestinal lining and begin to multiply. Some types remain in the intestine and produce toxins that enter the bloodstream. Other pathogens invade deeper body tissues.

The agents responsible for food poisoning evolve over time and require constant surveillance. Whereas typhoid fever, tuberculosis, and cholera were once common foodborne illnesses, improved food safety—including milk pasteurization, safer canning methods, and water treatment—have overcome these diseases in the developed world. However other sources of food poisoning have emerged. For example, in 1991, the parasite Cyclospora contaminated Guatemalan raspberries. In 1998, a new strain of the bacterium Vibrio parahaemolyticus contaminated oyster beds in Galveston Bay.

Some foodborne bacterial infections appear to be on the increase. In 2011, at least 29 people died and at least 139 people across 28 states were sickened from eating cantaloupe contaminated with L. monocytogenes and traced to unsanitary conditions and poor handling at a single Colorado farm. Both listeriosis and salmonellosis can be transmitted to a fetus, causing miscarriage, fetal or newborn death, premature delivery, or severe illness in mother and infant. Since most listeriosis outbreaks are caused by contaminated animal products, pregnant women are often advised to avoid deli meats.

Complications of some foodborne infections are now being recognized as the cause of certain serious medical conditions. For example, Campylobacter can cause Guillain-Barré syndrome and E. coli O157:H7 and related bacteria can cause hemolytic uremic syndrome (HUS), the most common cause of acute kidney failure in children.

Contamination can occur at any point in the food-production chain:

Raw or undercooked meat, poultry, eggs, fish— especially filter-feeding shellfish such as oysters, clams, scallops, and mussels—and raw (unpasteurized) milk are common sources of food poisoning. Raw fruits and vegetables may have been exposed to fresh manure or contaminated water, and washing will reduce but not eliminate pathogens. Misidentified wild mushrooms, improperly canned foods, luncheon and deli meats, and soft cheeses, such as brie and feta, are also associated with food poisoning.

Processed foods that pool ingredients from multiple sources are particularly dangerous, since a pathogen from one animal can contaminate an entire batch. For example, a single hamburger can include meat from hundreds of animals, a glass of raw milk may be the pooled milk of hundreds of cows, unpasteurized fruit juice can be made from many individual fruits, and a restaurant omelet can contain eggs from hundreds of chickens. An estimated one in every 20,000 eggs is contaminated with Salmonella. Egg-containing products, such as mayonnaise or raw cookie dough, also carry a risk.

Small numbers of bacteria in foods can multiply quickly under warm, moist conditions. A few bacteria in alfalfa or bean seeds can multiply to contaminate an entire batch of sprouts. Refrigeration or freezing generally prevents bacteria from multiplying. However L. monocytogenes and the foodborne bacterium Yersinia enterocolitica can grow and multiply at refrigerator temperatures. High levels of salt, sugar, or acid prevent bacteria from growing in preserved foods.

Food poisoning symptoms usually develop suddenly, within 1 to 48 hours after eating contaminated food, and resolve within one to a few days. Symptoms and their severity depend on the causative agent, the amount ingested, and the health of the individual; however food-poisoning symptoms tend to be similar, regardless of their cause:

Children commonly vomit everything in their stomachs for three or four hours, followed by mild or moderate vomiting. Severe vomiting, especially in combination with diarrhea, can cause dehydration—the excessive loss of body fluids. Young children can become dehydrated very quickly.

Chemical food poisoning is a medical emergency. Natural poisons found in some wild mushrooms can cause, in addition to nausea and vomiting, hallucinations, coma, and death. Shellfish toxins and Japanese puffer fish poison affect the nervous system, beginning with tingling in the mouth, arms, and legs, followed by dizziness and possibly difficulty breathing. Poisoning with man-made toxic chemicals varies with the type of chemical and degree of exposure.

In healthy people, food poisoning by a pathogen is usually a mild, short-lived illness that does not require specific diagnosis or medical treatment. Most mild food poisoning is diagnosed by the symptoms of vomiting, diarrhea, and stomach cramps coupled with information about what the individual has recently eaten. The length of time between eating the suspect food and the start of symptoms gives physicians a clue about what particular organism may be causing the food poisoning. Blood and urine tests may be ordered to determine the individual's degree of dehydration and electrolyte (chemical) imbalances. In most cases, determining the exact pathogen that is causing the food poisoning is relatively unimportant, as treatment tends to be the similar for most causes. However, if diarrhea is persistent, a stool culture may be done to provide more specific information.

Treatment for poisoning from a natural or man-made toxin may require precise identification of the chemical. With suspected mushroom poisoning, a sample of the mushroom or the patient's vomit should be brought to the emergency department, if possible. In other cases, extensive blood tests are required or the stomach may be pumped and its contents tested. Sometimes activated charcoal is used to help absorb the poison in the stomach.

Treatment for food poisoning usually involves preventing dehydration by replacing fluids and electrolytes lost through vomiting and diarrhea. Food poisoning can cause huge amounts of water and electrolytes to be lost very quickly, especially in infants and young children. The loss of 10%–15% of body fluid is very serious and the loss of 20% is fatal. Severe dehydration may require hospitalization and intravenous fluids. Drugs are sometimes prescribed to stop persistent vomiting. Vomiting and diarrhea in infants and young children require especially prompt professional treatment because small children can become dehydrated within hours.

Mild cases of food poisoning can usually be treated at home, especially if there is no fever. Dehydration can be prevented or treated with over-the-counter (OTC) oral-rehydration solutions such as Ceralyte, Pedialyte, or Oralyte. These are available in supermarkets and pharmacies without a prescription. An electrolyte-replacement fluid can be made at home with one teaspoon of salt and four teaspoons of sugar per quart of water. Small sips should be given to young children as soon as vomiting and diarrhea begin. Children may continue to vomit and have diarrhea, but some of the fluid will be absorbed. In the past, parents were told to withhold solid food from children who had diarrhea. New research indicates that it is better for children to be allowed to eat solid food should they want it, even though diarrhea continues.

Adults and older children with food poisoning should avoid drinking coffee, tea, and soft drinks, especially soft drinks that contain caffeine, as these liquids promote dehydration. Sports drinks, such as Gatorade, do not replace losses properly and should not be used to treat diarrheal illnesses. Over-the-counter medications to stop or slow diarrhea such as Kaopectate, Pepto-Bismol, or Imodium will not shorten the duration of the disease, but may give the individual some control over his or her bowels. Consult a physician before giving these over-the-counter medicines to children. They should not be used in the presence of high fever or blood in the stool.

Individuals of all ages who are seriously dehydrated need to be treated promptly by a medical professional. In the case of severe dehydration, the individual may be hospitalized and fluids given intravenously (IV; directly into the vein). Drugs may also be prescribed to stop persistent vomiting. Although bacteria cause many cases of food poisoning, antibiotics are not routinely used in treatment. Some studies have shown that antibiotics are necessary only in about 10% of cases.

Botulism is treated in a different way from other food poisonings. Botulism antitoxin is given to adults, but not infants, if it can be administered within 72 hours after symptoms are first observed. If given later, it provides no benefit. Both infants and adults require hospitalization, often in the intensive care unit. If the ability to breathe is impaired, patients are put on a mechanical ventilator to assist their breathing and are fed intravenously until the paralysis passes.

Individuals who think their food poisoning symptoms may be caused by chemicals or natural toxins should always seek emergency medical care immediately. These types of food poisoning are too serious to try to treat at home.

Alternative practitioners offer the same advice as traditional practitioners concerning diet modification. In addition, they recommend taking charcoal tablets, Lactobacillus acidophilus, Lactobacillus bulgaricus, and citrus seed extract. 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 strongly recommended.

In a recent review by the Cochrane Collaboration of 63 studies involving a total of 8,000 people, probiotics seem able to shorten the duration of diarrhea by 25 hours when compared to no treatment at all.

Most people have unpleasant gastrointestinal symptoms—vomiting and diarrhea—for a few days and then recover fully from food poisoning. In young children, dehydration is always a cause for concern. Worldwide, dehydration from diarrhea is the biggest killer of children under age 5. If dehydration can be controlled in young children with food poisoning, most recover with few complications. However, E. coli 0157:H7 can cause fatal renal failure in 3%–5% of children. This bacteria is most often acquired by eating unpasteurized apple cider or apple juice, alfalfa, or bean sprouts.

Botulism is the deadliest of the bacterial foodborne illnesses. With prompt medical care, the death rate is less than 10%.

More serious long-term health problems often result from chemical poisonings. Toxins found in some wild mushrooms and some fish can cause permanent liver damage, requiring a liver transplant, or death. Pesticides and other chemical contamination can cause liver damage, kidney failure, and nervous system complications. In 2007, chemical contamination of pet food caused the death of hundreds of dogs and cats in the United States.

Healthcare professionals and individuals should report foodborne illnesses to their local health departments so that outbreaks can be detected, traced, and halted. However, most food poisonings are preventable by appropriate handling and processing at each level of the food-production chain. Breastfeeding is the best way to protect infants from food poisoning.

Growers should apply only approved pesticides and herbicides at no higher than recommended levels. Processors must use clean sources of water to wash produce, regularly disinfect processing machinery, and use only safe pesticides.

Proper refrigeration is required in stores, restaurants, and homes. Food should not be held under warming lights or at room temperature for long periods; they should be kept at above 140°F (60°C) or below 40°F (4°C). Fresh foods and leftovers should be promptly refrigerated or frozen. Frozen food should be defrosted in the refrigerator or microwave, rather than at room temperature, and cooked immediately. Food that has been at room temperature for 2–4 hours should be discarded. Large quantities of food should be divided into shallow containers to cool more rapidly.

Hands should be washed thoroughly with soap and water before, during, and after preparing food and after using the bathroom or changing diapers. Anyone with a diarrheal illness should not prepare food for others. Food preparation surfaces and utensils should be washed frequently during food handling. Produce should be washed thoroughly before and again after peeling to prevent salmonellosis. The outer leaves of lettuce and cabbage should be discarded. Cross-contamination of foods can be avoided by never placing cooked food on plates or surfaces that previously held raw food.

Heating food to an internal temperature of 160°F (78°C), for even a few seconds, kills most bacteria, viruses, and parasites. Clostridium produces heat-resistant spores that must be destroyed with temperatures above boiling. Food thermometers should be used to check the internal temperature of cooked meat. Egg yolks should be cooked until firm. Bacterial toxins vary in their heat sensitivity. Although botulism toxin is completely inactivated by boiling, staphylococcal toxin is not. Milk, juice, and cider should be pasteurized. Irradiation of meat and other foods also destroys contaminating microbes.

See also AIDS/HIV diet and nutrition ; Dehydration ; Digestive diseases ; Food contamination ; Food safety ; Free-range, grass-fed, and cage-free animals ; Irradiated food ; Senior nutrition .