Bacterial 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 6-33 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), 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 60% or more of raw poultry sold at retail carry 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 re-contaminated 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 bacteria Staphylococcus aureus in their nasal passages and throat, and 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 bacteria 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.

Causes & 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, Salmonella caused almost 50,000 documented cases of food poison in the United States in 1995. Between two and four million more are believed to have gone unreported. 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 pet reptiles such 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.

Symptoms of food poisoning begin 12-72 hours after eating food contaminated with Salmonella. These include 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.

Staphylococcus aureus

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 foodborne bacteria. E. coli produces toxins in the large intestine rather than higher up in the digestive system. This 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.

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 15-29 are more frequently infected.

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 7-10 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

Symptoms of food poisoning by Shigella appear 36-72 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. These include 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, but children who are malnourished or have weakened immune systems may die.

Clostridium botulinum (C. botulinum)

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 bacteria 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 18-36 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. Onset of symptoms is gradual. Initially the baby is constipated. This 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.

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 this happens, food poisoning is strongly suspected. The diagnosis is confirmed when the suspected bacteria 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 is the cause of the symptoms.

Treatment

Treatment of food poisoning, except that caused by C. botulinum, focuses on preventing dehydration by replacing fluids and electrolytes lost through vomiting and diarrhea. Electrolytes are salts and minerals that form electrically charges 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 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 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, easy to digest foods 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, 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 ill person may continue feel tired for a few days after active symptoms stop. So long as the ill 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. Most deaths caused by Salmonella food poisoning have occurred 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. Platelets 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%.

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.

Key Terms

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.

This bacteria 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.

Further Reading

For Your Information

Periodicals

• U. S. Food and Drug Administration. "The Unwelcome Dinner Guest: Preventing Food-Borne Illness." In FDA Consumer (December 1997).

  Organizations

• Centers for Disease Control and Prevention. http:// www.cdc.gov.

  Other

• U. S. Food and Drug Administration. Center for Food Safety and Applied Nutrition. Bad Bug Book. http://vm.cfsan.fda.gov.

Gale Encyclopedia of Medicine. Gale Research, 1999.