Causes of Food Poisoning

A list and explanation of the common bacteria and viruses that causes Food Poisoning and Foodborne Illness, including Salmonella, E. coli, Campylobacter, and Botulism.

E Coli · Salmonella · Botulism · Campylobacter · Listeria · Hepatitis A · Giardia · Norovirus · Rotavirus · Shigellosis · Staphylococcus

E Coli

One of the common causes of foodborne illness is Escherichia coli (E. coli) O157:H7. While most strains of E. coli are harmless, this particular strain can cause severe illness. It is transmitted by eating raw or undercooked hamburger, unpasteurized milk or juices, or contaminated well water. Outbreaks of food poisoning due to E. coli have also occurred following ingestion of contaminated produce. The vast majority of E. coli cases are not fatal but the CDC (Center for Disease Control and Prevention) estimates that the illness affects 73,000 persons a year. It is often present in and on animals, and therefore farms and petting zoos can become sites of contamination. Once infected, poor hygiene can lead to its spread from person to person. Symptoms include diarrhea, bloody diarrhea, and stomach cramps, and typically occur within two and eight days of exposure and it rarely takes longer than 10 days for the ill individual to recover. In rare cases, long-term side effects include blindness and paralsysis. In the most severe cases, it can can cause kidney failure and death (about 3%-5% of all cases).    

There are many steps which can be taken to prevent the spread of E.Coli, including thoroughly cooking al meat, particularly ground beef. In the kitchen, raw meat should always be handled with care, separated from ready to eat food, and hands should be washed after contact. To further avoid the risk of infection, one should only drink milk, juice, or cider that has been pasteurized. This means that it has been heated to destroy the presence of any harmful pathogens, such as E. coli. Fruits and vegetables should be thoroughly washed before eating. Finally, those in contact with diarrhea (whether because they themselves are ill or because they are changing diapers, etc.) should thoroughly wash their hands with hot water and soap. Those with diarrheal illnesses should avoid actions that might spread the disease, such as swimming in public pools or lakes, sharing bathes, or involvement in the preparation of food.

Salmonella

Salmonella is the name of the bacterium that causes salmonellosis, a very common type of foodborne illness. The CDC (Center for Disease Control and Prevention) estimates that each year 1.4 million Americans suffer from the disease; approximately 500 of these cases are fatal.  The illness is most often transmitted by undercooked foods such as eggs, poultry, dairy products, and seafood. Severe cases usually affect those with compromised immune systems, elderly persons, and children. Symptoms, which appear between 12-72 hours following exposure, typically last for 4-7 days and include nausea, vomiting, crampy diarrhea, joint pain, and headache. Serious cases of diarrhea often require hospitalization and infections can, in some severe cases, spread from the intestines to the bloodstream and affect other areas of the body (septicemia). Unless prompt and proper antibiotic treatment ensues, this can result in death. Another possible complication of a Salmonella infection is Reiter’s Syndrome, also called reactive arthritis. Symptoms, which occur between 1-3 weeks following the infection, include pain in the joints (particularly fingers, toes, ankles, knees and hips), irritation of the eyes (conjunctivitis), and painful urination. Most recover in less than 1 year, but in some this can lead to chronic arthritis. It should be noted that other foodborne illness which cause gastroenteritis, such as Camplobacter and Shigella, may also cause Reiter’s Syndrome.   

Salmonella, which lives in the intestinal tract of humans and animals, is usually contracted by the ingestion of food or drink that has been contaminated, either by animal feces or contact with infected animals. It should be noted that contaminated foods in no way appear, taste, or smell different than non-contaminated foods. Salmonella contamination can also be the result of infected persons handling the food without properly washing their hands. Cross contamination is another concern. That is, food carrying the disease is prepared on a surface (a cutting board for example) and thus contaminates that surface. If the surface is not washed, other foods prepared on it will become contaminated.   Pets are also a potential source of infection. The feces (particularly diarrhea) of pets may carry the disease. Therefore, it is important to wash one’s hands after any contact with animal feces (cleaning a rodent’s cage, picking up after the dog, emptying the litter box, etc). Also, reptiles, even healthy ones, frequently carry salmonella on their skin. It is therefore important that hands be washed thoroughly after handling any reptile.    

A salmonella infection can be diagnosed by means of specifically requested lab test on a stool sample. Upon diagnosis, further tests may be given to determine the details of the infection, in order to better select the antibiotic for treatment. Specific medical treatment is usually unnecessary because the body can defeat the infection in less than one week. In more severe cases a doctor may decide to prescribe antibiotics. Treatment of dehydration may also be necessary. Basic steps for reducing the likelihood of contracting a salmonella infection involve good hygiene and basic sanitary measures. Recommendations from the CDC include:

Botulism

Botulism is a rare but serious illness caused by the bacterium Clostridium botulinum. A quantity as small one microgram of this toxin is extremely dangerous and can cause paralysis and death in humans. This bacterium works by inhibiting nerve function, thereby preventing the use of muscles; recovery, if possible, is a long an arduous process.    

There are three primary types of botulism: foodborne, wound, and infant. While all forms are potentially fatal, foodborne botulism is particularly problematic for heath officials because many people can be affected by a single contaminated food source. Infants and young children are particularly at risk. It is most commonly transmitted in foods such as home-packed canned goods, honey, sausages, and seafood.    

Symptoms of botulism typically occur within a day of exposure and include blurred or double vision, drooping eyelids, slurred speech, difficulty swallowing, dry mouth, and muscle weakness. A physician may further find that the gag reflex and knee-jerk reaction are decreased or eliminated entirely. It is possible for symptoms to occur within six hours of exposure or to remain unseen for ten days. Diagnosis, particularly in isolated cases, is not a simple process. Because symptoms are similar to those of numerous other ailments, including strokes and other types of paralysis, special tests are often needed. These include brain scans, spinal fluid examinations, EMG tests, and tensilon tests. If, however, it is suspected that botulism is the source of the symptoms, a mouse inoculation test can confirm the diagnosis. Treatment options depend upon the stage in which the illness is diagnosed. Early diagnosis can be treated with an antitoxin that counteracts the effects of the toxin. Furthermore, doctors may induce vomiting or prescribe enemas in order to cleanse the stomach of any remaining contaminated food. Later stages of the illness, marked by respiratory failure and paralysis, require intensive medical care as well as the use of a ventilator. Recovery is slow, often lasting weeks, as the nerves are regenerated. The effects of botulism can last for years and include tiredness and shortness of breath. Long term therapy can help counteract these issues.   

Prevention of botulism mostly involves careful handling of home-canned goods. Proper hygienic procedures should be followed in the canning and preserving of food. Furthermore, it would be prudent to boil home-canned foods for ten minutes before eating them. Other causes of the illness can be avoided by refrigerating oils that are infused with garlic or herbs, immediately serving or refrigerating potatoes that have been baked in aluminum foil, and immediately discarding any preserved foods that appear or smell abnormal. A vaccine is currently being developed. Because botulism can be released in the air, it is considered a potential biological weapon for terrorists. Also of note, botulism is present in Botox and other cosmetic treatments. It was approved by the FDA in 2002 and potential side-effects are listed on the product. 

Campylobacter

Campylobacter is a bacterial pathogen and is the most commonly identified food-borne bacterial infection encountered in the world. The CDC (Center for Disease Control and Prevention) estimates that nearly 2.5 million Americans are affected by the illness each year. It causes mild illness with fever, watery diarrhea, headache, and muscle aches and is commonly transmitted by raw poultry, raw milk, and water contaminated by animal feces. While nearly always occurring in isolated incidents, larger outbreaks are possible and are primarily caused by unpasteurized milk.

A doctor can diagnose a Campylobacter infection with a stool sample. However, these cases are usually not treated because nearly all ill persons recover on their own. Drinking fluids until diarrhea ceases is helpful, and antibiotics may be used in some cases. While recovery is usually simply a matter of time, in rare cases more serious complications can arise. Arthritis is one long-term complication which can arise from a Campylobacter infection; another is Guillain-Barré Syndrome. The latter is characterized by weakness and temporary paralysis caused by attacks on the peripheral nervous system by the immune system. The infection triggers this action and it usually become evident within a few weeks following the illness. Immediate treatment, in most cases, leads to a full recovery.  

Basic sanitation and cleanliness are the best means of prevention of food contamination by Campylobacter, including:

Listeria

Listeriosis is a serious infection that is caused by eating food contaminated with the bacterium Listeria monocytogenes. It primarily affects pregnant women, newborns, elderly persons, and others with compromised immune systems. The CDC (Center for Disease Control and Prevention) estimates that while there are only 2,500 cases a year, approximately 500 of these cases result in death. A person with listeriosis often experiences fever, muscle aches, and sometimes gastrointestinal symptoms such as nausea or diarrhea. These symptoms usually appear within a month of the exposure. If the infection spreads to the nervous system, symptoms such as headache, stiff neck, confusion, loss of balance, or convulsions can occur. While pregnant women may only experience mild symptoms, the effects of a Listeriosis infection during pregnancy can be devastating, including the possibility of miscarriage, premature delivery, stillbirth, the blood infection septicemia, and meningitis in the newborn child. In addition, a child may be born with the illness if the mother ate contaminated food during pregnancy.

Listeria monocytogenes is found in soil and water. Vegetables can become contaminated from the soil or from manure used as fertilizer. Animals can carry the bacterium without appearing ill and can contaminate foods of animal origin, such as meats and dairy products. Food processing facilities and equipment can became contaminated as a result of infected animals. The bacterium has been found in a variety of raw foods, such as uncooked meats, fish, vegetables, as well as in processed foods that become contaminated after processing, such as soft cheeses and cold cuts at the deli counter. Unpasteurized milk or foods made from unpasteurized milk may also contain the bacterium.

Blood or spinal fluid tests can be used to diagnose listeriosis. Treatment involves the prescription of antibiotics. Means of preventing Listeriosis are similar to those of the prevention of other foodborne illnesses and include:

Some additional means of prevention include not consuming hotdogs or deli meats unless they are reheated to a high temperature, ensuring that the fluid from hotdog packages does not contaminate other surfaces, washing hands after handling hotdogs or deli meats, not eating soft cheeses unless they have been pasteurized, not eating refrigerated pâtés or meat spreads, and not eating refrigerated, smoked seafood, unless it is contained in a cooked dish.

Hepatitis A

Hepatitis A, caused by the hepatitis A virus (HAV), is a foodborne illness that affects the liver. According to the CDC (Center for Disease Control and Prevention), 100 of the 35,000 Hepatitis A cases each year result in death. Symptoms typically include fever, loss of appetite, fatigue, nausea, darkened urine, abdominal pain, and diarrhea. Jaundice, a yellowing of the skin and whites of the eyes, is an additional symptom. While in most cases symptoms go away within two months, in some instances they last as long as six.    

The Hepatitis A virus is transmitted from person to person or by fecal contamination of food. Person to person contact transmits the disease when persons place any contaminated object into their mouths or touch a contaminated surface and then place their fingers in their mouths. Contact with household members of sexual partners is a common means of transmission, while casual contact with people is highly unlikely to spread the illness. When food service professionals and others that handle food become infected and then fail to properly wash their hands, food may become contaminated. The disease is most communicable from two weeks prior to the onset of symptoms until approximately a week after the jaundice appears.

Diagnosis of Hepatitis A is made by means of a blood test. Recovery can be aided by rest and drinking fluids, but there is no medication or treatment method that effectively combats this disease. Most people make a full recovery after experiencing the illness and the body produces anti-bodies which prevent the individual from contracting the virus again. In a small number of cases, symptoms will last 6-9 months due to relapse or other complications.   

Proper hygiene can aid in the prevention of Hepatitis A. Individuals should wash their hands with hot water and soap after using the bathroom, changing a diaper (or any other contact with fecal matter), and before food preparation. Those who are already infected should not prepare food to prevent the spread of the disease. The best defense is a vaccine, which is licensed in the US and recommended for those at higher risk for contracting the disease or at a higher risk for becoming seriously ill if they do become infected. There are preparations of antibodies (immune globulin) that can be used to provide short term protection.

Giardia

Giardia (also known as beaver fever) is a foodborne illness caused by a parasite, not a bacterium or virus. Its symptoms typically manifest themselves within two weeks of contracting the parasite and include gastrointestinal distress, such as abdominal cramping, diarrhea and greasy stools, gas, bloating, and nausea. These symptoms typically last for 1-3 weeks and often cause weight loss and dehydration. However, in some cases, individuals do not exhibit systems of the infection. Giardia thrives in the intestines of people and animals. It is often transmitted by drinking contaminated water, usually from lakes or streams in cooler mountainous climates. The infection can also be spread from person to person by food or other items contaminated with feces from an infected person. Giardia is diagnosed by means of a stool sample and can be treated with anti-parasite drugs, though the body can destroy the infection without the aid of medication. 

Norovirus

Noroviruses, also called Norwalk-like viruses and caliciviruses, are the most common viral cause of adult food poisoning. The CDC (Center for Disease Control and Prevention) estimates that 23,000,000 people are affected by the virus each year. Noroviruses cause a mild illness (commonly known as the "stomach flu") with symptoms such as nausea, vomiting, diarrhea, abdominal pain, headache, and low-grade fever. These symptoms usually resolve in two to three days and affect children more severely than adults. Noroviruses are transmitted from water, shellfish, and vegetables contaminated by feces, as well as from person to person. They are extremely contagious, and outbreaks are common in densely populated areas such as nursing homes, schools, and cruise ships (the virus is also known as the "Cruise Ship Illness").

Some of the ways that a norovirus infection can be contracted include:

There is no direct method of treatment because no antiviral medication exists, and antibiotics do not work because norovirus is a viral infection and they can only aid in fighting bacterial infections. Steps can be taken to combat the effects of dehydration, which often occurs during norovirus infections due to vomiting and diarrhea. The best means of doing this is to drink a lot of water or juice. Dehydration is the most serious complication that arises from norovirus infections and can result in hospitalization, particularly for elderly persons and children.   

Prevention of norovirus infections involves practicing good hygiene and basic sanitary measures. Some common sense steps include the thorough washing of hands after any fecal contact (going to the bathroom, changing diapers), washing hands before preparing or eating food, washing fruits and vegetables before consuming, steaming shellfish before consuming, disinfecting areas that may have become contaminated, and promptly washing clothes and linens that may be contaminated. Infected persons should not prepare food for at least three days following recovery.   

Rotavirus

Rotavirus (also known as infantile diarrhea, winter diarrhea, or the stomach flu) is the most common cause of food poisoning in infants and children. According to the CDC, rotavirus causes approximately 55,000 children to be hospitalized in the United States each year and is the cause of death for more than 600,000 children worldwide. Symptoms, which typically appear within 48 hours of contracting the infection, last for 3-8 days and are primarily gastrointestinal, including vomiting followed by watery diarrhea and fever. Rotavirus is transmitted primarily from person to person by fecal contamination of food and shared play areas.  Rotavirus outbreaks typically occur between November and April (hence the name winter diarrhea) and predominantly affect children under the age of two (hence the name infantile diarrhea). Infected adults may experience mild symptoms.   

The most common means of diagnosing a rotavirus infection is a stool sample. There is no direct method of treatment because no antiviral medication exists. The virus is self-limiting and infections rarely last longer than a week. Steps can be taken to combat the effects of dehydration, which often occurs during infections due to vomiting and diarrhea. The best means of doing this is to drink a lot of water or juice.  Dehydration is the most serious complication that arises from rotavirus infections and can result in hospitalization.   

The best method of prevention is vaccination. In 2006, the Food and Drug Administration approved a rotavirus vaccine for children. Other means of shielding oneself from infection include good hygiene and basic sanitary measures. Some common sense steps include the thorough washing of hands after any fecal contact (going to the bathroom, changing diapers), washing hands before preparing or eating food, washing fruits and vegetables before consuming, disinfecting areas that may have become contaminated, and promptly washing clothing and linens that may be contaminated.  

Shigellosis

Shigellosis is a foodborne illness caused by a group of bacteria called Shigella. The CDC (Center for Disease and Prevention) estimates that 18,000 Americans suffer from shigellosis infections each year, though the actual number is probably significantly higher because many mild cases going unreported. Most people who are infected with Shigella experience symptoms including diarrhea, fever, and stomach cramps, which begin a day or two after they are exposed to the bacteria. Severe cases are much more likely to affect those with compromised immune systems, elderly persons, and children. In these cases, infected persons may experience seizures due to high fevers and severe diarrhea that requires hospitalization. Another possible complication is the development of Reiter’s Syndrome, sometimes called reactive arthritis. It should be noted that other foodborne illnesses which cause gastroenteritis, such as Camplobacter and Salmonella, may also cause Reiter’s Syndrome. Additional complications arise if the infection spreads from the intestines to the bloodstream and other parts of the body.

Shigella infections may be acquired from eating contaminated food. Contaminated food usually looks and smells normal. Food may become contaminated by infected food handlers who fail to wash their hands after using the bathroom. Vegetables can become contaminated if they are harvested from a field with sewage in it. Flies can breed in infected feces and then contaminate food. Contact with contaminated water (swimming or drinking) can also cause Shigellosis. Water may become contaminated due to sewage runoff or contact with an infected person.   

Shigella is very contagious, and group settings (such as schools, nursing homes, and day care centers) are particularly susceptible to outbreaks. Children between the ages of two and four are most likely to contract the disease, primarily because of poor hygiene. It may also be spread by asymptomatic individuals, who are unaware of their own infection. A shigella infection can be diagnosed by a lab test on a stool sample. Upon diagnosis, further tests may be given in order to determine the details of the infection and select the antibiotic for treatment. Mild cases usually go without treatment.   

Basic steps for reducing the chances of contracting Shigellosis involve good hygiene and basic sanitary measures. Recommendations from the CDC include:

Staphylococcus

Staphylococcus aureus is a common bacterium that is often found on people and animals that are completely healthy. However, it is capable of secreting toxins that often cause food poisoning. It is not a contagious infection, and the toxins do not spread from person to person. Staphylococcal food poisoning causes moderate to severe illness with rapid onset of nausea, severe vomiting, dizziness, and abdominal cramping. Food usually becomes contaminated by food workers that carry the bacteria. In the food, the bacterium multiplies, producing the harmful toxins as it grows. It is resistant to both salt and heat and cannot be destroyed by cooking. Foods that are prepared by hand and not cooked, such as sliced meat, pudding, pastries, and sandwiches, are more likely to become contaminated. Contamination of salads at picnics is common if the food is not chilled properly.

Diagnosis of Staphylococcal food poisoning is typically done by an assessment of the patient’s signs and symptoms. However, tests can locate the toxin in vomit and stool samples and are used in outbreaks where multiple people are affected. Antibiotics are not useful for treatment. In the majority of cases, the victims will recover on their own. Rest and fluids can aid in this process. More severe cases, usually involving elderly persons or children, may require hospitalization and intravenous care and therapy.    

Steps which can be taken to protect food from contamination by the Staphylococcus bacterium include: 

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