Home > Encyclopedia of Nursing & Allied Health > Food Poisoning

Definition

Food poisoning is a general term for health problems 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. Symptoms of food poisoning usually involve the prompt onset of vomiting and diarrhea. Some toxins also affect the nervous system.

Description

Every year millions of people suffer from bouts of vomiting and diarrhea that they blame on "something I ate." These people are generally correct. 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 each year. Many cases are mild and pass so rapidly that they are never diagnosed. Occasionally a severe outbreak creates a newsworthy public health hazard.

Classical food poisoning, sometimes incorrectly called ptomaine poisoning, is caused by a variety of different bacteria. The most common are Salmonella, Staphylococcus aureus, Escherichia coli O157:H7, 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. Sometimes food poisoning is called bacterial gastroenteritis or infectious diarrhea. Food and water can also be contaminated by viruses (cholera, rotavirus), environmental toxins (heavy metals), and poisons produced within the food itself (mushroom poisoning or fish and shellfish poisoning).

Careless food handling creates conditions for the growth of bacteria that make people sick. Food can become contaminated at many different points during its trip from farm to table. Vegetables that are 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 the bacteria.

Raw meats carry many foodborne bacterial diseases. The United States Food and Drug Administration (FDA) estimates that 90% 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. Thorough cooking kills the bacteria and makes the food harmless. However, properly cooked food can become recontaminated if it comes in contact with plates, cutting boards, counter tops, or utensils that were used with raw meat and not cleaned and sanitized.

Cooked foods can also be contaminated after cooking by bacteria carried by food handlers or from bacteria in the environment. It is estimated that 50% of healthy people have the bacterium Staphylococcus aureus in their nasal passages and throat, as well as on their skin and hair. Rubbing a runny nose, then touching food can introduce the bacteria into cooked food. Bacteria flourish at room temperature and will rapidly grow into quantities capable of making people sick. To prevent this growth, food must be kept hot or cold, but never just warm.

Although the food supply in the United States is probably the safest in the world, anyone can get food poisoning. Serious outbreaks are rare. When they occur, the very young, the very old, and those with immune system weaknesses have the most severe and life-threatening cases. For example, this group is 20 times more likely to become infected with the Salmonella bacterium than the general population.

Travel outside the United States to countries where less attention is paid to sanitation, water purification, and good food handling practices increases the chances that a person will get food poisoning. People living in institutions such as nursing homes are also more likely to get food poisoning.

Rotavirus is the most common cause of severe diarrhea in children and accounts for the hospitalization of an estimated 55,000 children in the United States and over 600,000 deaths of children worldwide per year.

Other less common but serious food-borne illnesses may arise from consuming animals infected with Bovine spongiform encephalopathy. Bovine spongiform encephalopathy (BSE) is a degenerative disorder affecting the central nervous system in cattle. It is also commonly referred to as "mad cow disease." BSE results from an "unconventional transmissible agent" which is yet to be determined precisely but is thought to be a pathogenic protein. Cell death leads to holes in the brain, creating a "sponge-like" consistency, which results in the animal's death. As of November 2000, there have been more than 177,500 cases of BSE confirmed in the United Kingdom (UK). However, no cases have been reported in the United States, where the food supply has been monitored closely. Imports of ruminants (suborder of mammals that includes sheep) and ruminant products have been restricted to some degree from countries where BSE was reported and has extended to all European countries. BSE is believed to be linked to a new variation of Creutzfeldt-Jakob disease (CJD) in humans, which is a progressive neurological disorder that can lead to death.

Causes and symptoms

The symptoms of food poisoning occur because foodborne bacteria release toxins or poisons as a byproduct of their growth in the body. These toxins (except those from C. botulinum) cause inflammation and swelling of the stomach, small intestine and/or large intestine. The result is abdominal muscle cramping, vomiting, diarrhea, fever, and the chance of dehydration. The severity of symptoms depends on the type of bacteria, the amount consumed, and the individual's general health and sensitivity to the bacterial toxin.

Salmonella

According to the CDC, approximately 1.4 million cases of Salmonella contamination occur annually in the US, with about 40,000 being culture-confirmed cases reported to the CDC. Salmonella is found in egg yolks from infected chickens, in raw and undercooked poultry and in other meats, dairy products, fish, shrimp, and many more foods. The CDC estimates that one out of every 50 consumers is exposed to a contaminated egg yolk each year. However, thorough cooking kills the bacteria and makes the food harmless. Salmonella is also found in the feces of such pet reptiles as turtles, lizards, and snakes.

About one out of every 1,000 people get food poisoning from Salmonella. Of these, two-thirds are under age 20, with the majority under age nine. Most cases occur in the warm months between July and October. Salmonella poisoning manifests itself as salmonellosis, mostly caused by Salmonella enteritidis and Salmonella typhimurium. The incidence of salmonellosis has increased dramatically during the last two decades, due in part to the growing popularity of pet iguanas.

Symptoms of food poisoning begin 12–72 hours after eating food, water, or contact with animals contaminated with Salmonella. These include the traditional food poisoning symptoms of abdominal pain, diarrhea, vomiting, and fever. The symptoms generally last two to five days. Dehydration can be a complication in severe cases. People generally recover without antibiotic treatment, although they may feel tired for a week after the active symptoms subside. The CDC estimates that there are over 500 fatalities per year in the US, with 2% of the cases complicated by chronic arthritis.

Staphylococcus aureus

Staphylococcus aureus is found 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 cases of food poisoning from Staphylococcus aureus that occur each year, because its symptoms are so similar to those caused by other foodborne bacteria. Many cases are mild and the victim never sees a doctor.

Symptoms appear rapidly, usually two to eight hours after the contaminated food is eaten. The acute symptoms of vomiting, diarrhea, and severe abdominal cramps usually last only three to six hours and rarely more than 24 hours. Most people recover without medical assistance. Deaths are rare.

Escherichia coli (E. coli)

There are many strains of E. coli, and not all of them are harmful. The strain that causes most severe food poisoning is E. coli O157:H7. Food poisoning by E. coli occurs in three out of every 10,000 people. Foodborne E. coli is found mainly in food derived from cows such as dairy products and beef, especially ground beef.

Symptoms of food poisoning from E. coli are slower to appear than those caused by some of the other food-borne bacteria. E. coli produces toxins in the large intestine rather than higher up in the digestive system. This factor accounts for the delay in symptoms and the fact that vomiting rarely occurs in E. coli food poisoning.

One to three days after eating contaminated food, the victim with E. coli O157:H7 begins to have severe abdominal cramps and watery diarrhea that usually becomes bloody within 24 hours. There is little or no fever, and rarely does the victim vomit. The bloody, watery diarrhea lasts from one to eight days in uncomplicated cases. E. coli is the most common cause of "travelers' diarrhea," affecting people travelling to many high-risk areas such as Latin America, Asia, Africa, and the Middle East. It is most often caused by water or foods contaminated with fecal matter.

Campylobacter jejuni (C. jejuni)

According to the FDA, C. jejuni is the leading cause of bacterial diarrhea in the United States. It is responsible for more cases of bacterial diarrhea than Shigella and Salmonella combined. Anyone can get food poisoning from C. jejuni, but children under five and young adults between the ages of 15 and 29 are more frequently infected.

C. jejuni is carried by healthy cattle, chickens, birds, and flies. It is not carried by healthy people in the United States or Europe. The bacterium is also found in ponds and stream water. The ingestion of only a few hundred C. jejuni bacteria can make a person sick.

Symptoms of food poisoning begin two to five days after eating food contaminated with C. jejuni. These symptoms 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 10 days, and relapses occur in about one quarter of people who are infected. Dehydration is a common complication. Other complications such as arthritis-like joint pain and hemolytic-uremic syndrome (HUS) are rare.

Shigella

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 food poisoning by Shigella appear 36 to 72 hours after eating contaminated food. These symptoms are slightly different from those associated with most foodborne bacteria. In addition to the familiar watery diarrhea, nausea, vomiting, abdominal cramps, and fever, up to 40% of children with severe infections show neurological symptoms, including seizures caused by fever, confusion, headache, lethargy, and a stiff neck that resembles meningitis.

The disease runs its course in two to three days. 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 die.

Clostridium botulinum (C. botulinum)

C. botulinum, which causes both adult botulism and infant botulism, is unlike any of the other foodborne bacteria. First, C. botulinum is an anaerobic bacterium that can live only in the absence of oxygen. Second, the toxins from C. botulinum are neurotoxins. They poison the nervous system, causing paralysis without the vomiting and diarrhea associated with other foodborne illnesses. Third, toxins that cause adult botulism are released when the bacteria grow in an airless environment outside the body. They can be broken down and made harmless by heat. Finally, botulism is much more likely to be fatal, even in tiny quantities.

Adult botulism outbreaks are usually associated with home canned food, although occasionally commercially canned or vacuum-packed foods are responsible for the disease. C. botulinum grows well in non-acidic, oxygen-free environments. If food is canned at too low heat or for too brief a time, the bacterium is not killed. It reproduces inside the can or jar, releasing its deadly neurotoxin. The toxin can be made harmless by heating the contaminated food to boiling for ten minutes. However, even a very small amount of the C. botulinum toxin can cause serious illness or death.

Symptoms of adult botulism appear about 18 to 36 hours after the contaminated food is eaten, although there are documented times of onset ranging from four hours to eight days. Initially a person suffering from botulism feels weakness and dizziness followed by double vision. Symptoms progress to difficulty speaking and swallowing. Paralysis moves down the body, and when the respiratory muscles are paralyzed, death results from asphyxiation. People who show any signs of botulism poisoning must receive immediate emergency medical care to increase their chance of survival.

Infant botulism is a form of botulism first recognized in 1976. It differs from foodborne botulism in its causes and symptoms. Infant botulism occurs when a child under the age of one year ingests the spores of C. botulinum. These spores are found in soil, but a more common source of spores is honey.

The C. botulinum spores lodge in the baby's intestinal tract and begin to grow, producing their neurotoxin.

COMMON PATHOGENS CAUSING FOOD POISONING
Pathogen	Common Host(s)
Campylobacter	Poultry
E.coli 0157:H7	Undercooked, contaminated ground beef
Listeria	Found in a variety of raw foods, such as uncooked meats and vegetables, and in processed foods that become contaminated after processing
Salmonella	Poultry, eggs, meat, and milk
Shigella	This bacterium is transmitted through direct contact with an infected person or from food or water that become contaminated by an infected person
Vibrio	Contaminated seafood

Onset of symptoms is gradual. Initially the baby is constipated, which is 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.

Rotavirus

The clinical characteristics of rotavirus include vomiting and watery diarrhea for three to eight days with abdominal pain and fever also frequently occurring. The incubation period is about two days. Subsequent bouts of rotavirus tend to be less severe than the initial infection. Illness can occur when in contact with contaminated food, water, or surfaces. Rotavirus infections are higher in countries with temperate climates (November to April in the United States) with most infections occurring in children under two years old. Adult cases tend to be milder.

Bovine spongiform encephalopathy and Creutzfeldt-Jakob disease

It is extremely unlikely that bovine spongiform encephalopathy will become a foodborne illness in the United States, because the feeding of ruminant by-products to other animals was probably a factor that lead to the outbreak in the United Kingdom. Furthermore, the FDA implemented a ban on ruminant feed in 1997 due to evidence that BSE can be transmitted to humans.

Creutzfeldt-Jakob disease has atypical clinical symptoms, including psychiatric or sensory symptoms early in its course, and neurological abnormalities and dementia later on. Incidence of CJD in people under 30 years is extremely rare in the US (less than 5 cases per 1 billion per year). In the UK, it primarily affects younger people, with over half of the patients who have died of CJD under 30 years old.

Diagnosis

One important aspect of diagnosing food poisoning is for doctors to determine if a number of people have eaten the same food and show the same symptoms of illness. When a cluster of cases occurs, food poisoning is strongly suspected. The diagnosis is confirmed when the suspected bacterium is found in a stool culture or a fecal smear from the person. Other laboratory tests are used to isolate bacteria from a sample of the contaminated food. Botulism is usually diagnosed from its distinctive neurological symptoms, since rapid treatment is essential. 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, it is not necessarily the most recent food one has eaten that causes the symptoms.

Treatment

Treatment of most food poisoning, except that caused by C. botulinum, focuses on preventing dehydration

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KEY TERMS

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Diuretic—Medication that increases the urine output of the body.

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.

Lactobacillus acidophilus—This bacterium is found in yogurt and changes the balance of the bacteria in the intestine in a beneficial way.

Platelets—Blood cells that help the blood to clot.

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by replacing fluids and electrolytes lost through vomiting and diarrhea. Electrolytes are salts and minerals that form electrically charged particles (ions) in body fluids. Electrolytes are important because they control body fluid balance and are important for all major body reactions. Pharmacists can recommend effective, pleasant-tasting, electrolytically balanced replacement fluids that are available without a prescription. When more fluids are being lost than can be consumed, dehydration may occur. Dehydration is more likely to happen in the very young, the elderly, and people who are taking diuretics. To prevent dehydration, a doctor may give fluids intravenously.

In very serious cases of food poisoning, medications may be given to stop abdominal cramping and vomiting. Anti-diarrheal medications are not usually given. Stopping the diarrhea keeps the toxins in the body longer and may prolong the infection.

People with food poisoning should modify their diet. During the period of active vomiting and diarrhea, they should not try to eat and should drink only clear liquids frequently but in small quantities. Once active symptoms stop, they should eat bland, soft, easily digested foods for two to three days. Such foods include bananas, rice, applesauce, and toast, all of which are easy to digest. Milk products, spicy food, alcohol, and fresh fruit should be avoided for a few days, although babies should continue to breastfeed. These modifications are often all the treatment that is necessary.

Severe bacterial food poisonings are sometimes treated with antibiotics. Trimethoprim and sulfamethoxazole (Septra, Bactrim), ampicillin (Amcill, Polycill) or ciprofloxacin (Ciloxan, Cipro) are most frequently used.

Botulism is treated in a different way from other bacterial 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.

Alternative treatment

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.

Prognosis

Most cases of food poisoning (except botulism) clear up on their own within one week without medical assistance. The patient may continue feel tired for a few days after active symptoms stop. So long as the sick person does not become dehydrated, there are few complications. 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 include arthritis-like symptoms that occur three to four weeks after infection. Although deaths from Salmonella are rare, they do occur, mostly in elderly people in nursing homes.

Adults usually recover without medical intervention, but many children need to be hospitalized as the result of E. coli food poisoning. 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 develop hemolytic-uremic syndrome, which results in sudden kidney failure and makes dialysis necessary. (Dialysis is a medical procedure used to filter the body's waste product when the kidneys have failed.)

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

Health care team roles

Definitive identification of food poisoning is made by a physician, usually with the aid of stool or blood cultures. Nurses, medical technologists, and other health care professionals often aid in taking and analyzing cultures, and in educating patients about preventive measures they can take to avoid food poisoning.

Prevention

Food poisoning is almost entirely preventable by practicing good sanitation and good food handling techniques. These include:

• Keep hot foods hot and cold foods cold.
• Cook meat to the recommended internal temperature. Use a meat thermometer to check. Cook eggs until they are no longer runny.
• Refrigerate leftovers promptly. Do not let food stand at room temperature.
• Avoid contaminating surfaces and other foods with the juices of uncooked meats.
• Wash fruits and vegetables before using.
• Purchase pasteurized dairy products and fruit juices.
• Throw away 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.

Crystal Kaczkowski, MSc.