Bacterial Food Poisoning
Food borne illness is an ever-present threat that can be prevented with proper care and handling of food products. It is estimated that between 24 and 81 million cases of food borne diarrhea disease occur each year in the United States, costing between $5 billion and $17 billion in medical care and lost productivity.
Chemicals, heavy metals, parasites, fungi, viruses and bacteria can cause food borne illness. Bacteria related food poisoning is the most common, but fewer than 20 of the many thousands of different bacteria actually are the culprits. More than 90 percent of the cases of food poisoning each year are caused by Staphylococcus aureus, Salmonella, Clostridium perfringens, Campylobacter, Listeria monocytogenes, Vibrio parahaemolyticus, Bacillus cereus, and Entero-pathogenic Escherichia coli. These bacteria are commonly found on many raw foods. Normally a large number of food-poisoning bacteria must be present to cause illness. Therefore, illness can be prevented by (1) controlling the initial number of bacteria present, (2) preventing the small number from growing, (3) destroying the bacteria by proper cooking and (4) avoiding re-contamination.
Poor personal hygiene, improper cleaning of storage and preparation areas and unclean utensils cause contamination of raw and cooked foods. Mishandling of raw and cooked foods allows bacteria to grow. The temperature range in which most bacteria grow is between 40 degrees F (5 degrees C) and 140 degrees F (60 degrees C). Raw and cooked foods should not be kept in this danger zone any longer than absolutely necessary. Undercooking or improper processing of home-canned foods can cause very serious food poisoning.
Since food-poisoning bacteria are often present on many foods, knowing the characteristics of such bacteria is essential to an effective control program.
Man's respiratory passages, skin and superficial wounds are common sources of S. aureus. When S. aureus is allowed to grow in foods, it can produce a toxin that causes illness. Although cooking destroys the bacteria, the toxin produced is heat stable and may not be destroyed. Staphylococcal food poisoning occurs most often in foods that require hand preparation, such as potato salad, ham salad and sandwich spreads. Sometimes these types of foods are left at room temperature for long periods of time, allowing the bacteria to grow and produce toxin. Good personal hygiene while handling foods will help keep S. aureus out of foods, and refrigeration of raw and cooked foods will prevent the growth of these bacteria if any are present.
The gastrointestinal tracts of animals and man are common sources of Salmonella. High protein foods such as meat, poultry, fish and eggs are most commonly associated with Salmonella. However, any food that becomes contaminated and is then held at improper temperatures can cause salmonellosis. Salmonella are destroyed at cooking temperatures above 150 degrees F. The major causes of salmonellosis are contamination of cooked foods and insufficient cooking. contamination of cooked foods occurs from contact with surfaces or utensils that were not properly washed after use with raw products. If Salmonella is present on raw or cooked foods, its growth can be controlled by refrigeration below 40 degrees F.
C. perfringens is found in soil, dust and the gastrointestinal tracts of animals and man. When food containing a large number of C. perfringens is consumed, the bacteria produce a toxin in the intestinal tract that causes illness. C. perfringens can exist as a heat-resistant spore, so it may survive cooking and grow to large numbers if the cooked food is held between 40 degrees F and 140 degrees F for an extensive time period. Meat and poultry dishes, sauces and gravies are the foods most frequently involved. Hot foods should be served immediately or held above 140 degrees F. When refrigerating large volumes of gravies, meat dishes, etc., divide them into small portions so they will cool rapidly. The food should be reheated to 165o F. prior to serving.
Botulism accounts for fewer than one of every 400 cases of food poisoning in the U.S., but two factors make it very important. First, it has caused death in approximately 30 percent of the cases; and secondly, it occurs mostly in home-canned foods. In 1975, for example, 18 or 19 confirmed cases of botulism were caused by home-processed foods, and the other was caused by a commercial product that was mishandled in the home. Cl. botulinum can exist as a heat-resistant spore, and can grow and produce a neurotoxin in under processed, home-canned foods. An affected food may show signs of spoilage such as a bulging can or an off-odor. This is not true in all cases, so canned foods should not be tasted before heating. The botulinum toxin is destroyed by boiling the food for 10 minutes.
V. parahaemolyticus is found on seafoods, and requires the salt environment of sea water for growth. V. parahaemolyticus is very sensitive to cold and heat. Proper storage of perishable seafoods below 40 degrees F, and subsequent cooking and holding above 140 degrees F, will destroy all the V. parahaemolyticus on seafoods. food poisoning caused by this bacterium is a result of insufficient cooking and/or contamination of the cooked product by a raw product, followed by improper storage temperature. It is a major problem in Japan where many seafoods are consumed raw. Vibrio vulnificus is another member of the vibrio genus that is found in the marine environment. V. vulnificus is truly an emerging pathogen, but it can be controlled with proper cooking and refrigeration.
B. cereus is found in dust, soil and spices. It can survive normal cooking as a heat-resistant spore, and then produce a large number of cells if the storage temperature is incorrect. Starchy foods such as rice, macaroni and potato dishes are most often involved. The spores may be present on raw foods, and their ability to survive high cooking temperatures requires that cooked foods be served hot or cooled rapidly to prevent the growth of this bacteria.
Before the 1980's most problems associated with disease caused by Listeria were related to cattle or sheep. This changed with food related outbreaks in Nova Scotia, Massachusetts, California and Texas. As a result of its widespread distribution in the environment, its ability to survive long periods of time under adverse conditions, and its ability to grow at refrigeration temperatures, Listeria is now recognized as an important food-borne pathogen.
Immunocompromised humans such as pregnant women or the elderly are highly susceptible to virulent Listeria. Listeria monocytogenes is the most consistently pathogenic species causing listeriosis. In humans, ingestion of the bacteria may be marked by a flu-like illness or symptoms may be so mild that they go unnoticed. A carrier state can develop. Death is rare in healthy adults; however, the mortality rate may approximate 30 percent in the immunocompromised, new born or very young.
As mentioned earlier Listeria monocytogenes is a special problem since it can survive adverse conditions. It can grow in a pH range of 5.0-9.5 in good growth medium. The organism has survived the pH 5 environment of cottage cheese and ripening cheddar. It is salt tolerant surviving concentrations as high as 30.5 percent for 100 days at 39.2 degrees F, but only 5 days if held at 98.6 degrees F.
The key point is that refrigeration temperatures don not stop growth of Listeria. It is capable of doubling in numbers every 1.5 days at 39.5 degrees F. Since high heat, greater than 170 degrees F, will inactivate the Listeria organisms, post-process contamination from environmental sources then becomes a critical control point for many foods. Since Listeria will grow slowly at refrigeration temperatures, product rotation becomes even more important.
Even though Yersinia enterocolitica is not a frequent cause of human infection in the U.S., it is often involved in illness with very severe symptoms. Yersiniosis, infection caused by this microorganism, occurs most commonly in the form of gastroenteritis. Children are most severely affected. Symptoms of pseudoappendicitis has resulted in many unnecessary appendectomies. Death is rare and recovery is generally complete in 1-2 days. Arthritis has been identified as an infrequent but significant sequel of this infection.
Y. enterocolitica is commonly present in foods but with the exception of pork, most isolates do not cause disease. Like Listeria this organism is also one that can grow at refrigeration temperatures. It is sensitive to heat (5%) and acidity (pH 4.6), and will normally be inactivated by environmental conditions that will kill Salmonellae.
jejuni was first isolated from human diarrhea stools in 1971. Since then it has continually gained recognition as a disease causing organism in humans.
jejuni enteritis is primarily transferred from animal origin foods to humans in developed countries. However, fecal contamination of food and water and contact with sick people or animals, predominates in developing countries.
Although milk has been most frequently identified throughout the world to be a vehicle for Campylobacter, one anticipates that future investigations will identify poultry and its products and meats (beef, pork, and lamb) as major reservoirs and vehicles.
jejuni dies off rapidly at ambient temperature and atmosphere, and grows poorly in food.
The principles of animal science will play a significant role in the control of this ubiquitous organism. Hygienic slaughter and processing procedures will preclude cross-contamination while adequate cooling and aeration will cause a decrease in the microbial load. In addition, thorough cooking of meat and poultry products followed by proper storage should assist in maintaining food integrity and less contamination.
Enteropathogenic Escherichia Coli
Enteropathoginec E. coli is a significant cause of diarrhea in developing countries and localities of poor sanitation. In the U.S. it has been associated with "travelers' diarrhea." However the latest outbreak in North America occurred in a nursing home in Ontario. This was a severe outbreak of E. coli0157:H7 associated hemorrhagic colitis.
There are at least four subgroups of enteropathogenic E. coli: enterotoxigenic, enterinvasive, hemorrhagic, and enteropathogenic. Each strain has different characteristics.
The major source of the bacteria in the environment is probably the feces of infected humans, but there may also be animal reservoirs. Feces and untreated water are the most likely sources for contamination of food.
Control of enteropathogenic E. coli and other food-borne pathogens such as Salmonella and Staphylococcus aureus can be achieved. Precautions should include adequate cooking and avoidance of recontamination of cooked meat by contaminated equipment, water or infected food handlers. Food service establishments should monitor adequacy of cooking, holding times, and temperatures as well as the personal hygiene of food handlers.
- The first step in preventing food poisoning is to assume that all foods may cause food-borne illness. Follow these steps to prevent food poisoning:
- Wash hands, food preparation surfaces and utensils thoroughly before and after handling raw foods to prevent recontamination of cooked foods.
- Keep refrigerated foods below 40 degrees F.
- Serve hot foods immediately or keep them heated above 140 degrees F.
- Divide large volumes of food into small portions for rapid cooling in the refrigerator. Hot, bulky foods in the refrigerator can raise the temperature of foods already cooled.
- Remember the danger zone is between 40 degrees F and 140 degrees F.
- Follow approved home-canning procedures. These can be obtained from the Extension Service or from USDA bulletins.
- Heat canned foods thoroughly before tasting.
- When in doubt, throw it out
Infants, older persons, women who are pregnant and anyone with a compromised immune system are especially susceptible to food-borne illness. These people should never consume raw fish, raw seafood, or raw meat type products.
You are the key to preventing food-borne illness. By observing the simple rules of good handling, food poisoning can be eliminated.
Bacteria and Foodborne Illness
Provided by National Institute of Diabetes and Digestive and Kidney Diseases
- Risk Factors
- Food Irradiation
- Links to Other Disorders
- Common Sources of Foodborne Illness
- Points to Remember
- For More Information
Foodborne illness results from eating food contaminated with bacteria (or their toxins) or other pathogens such as parasites or viruses. The illnesses range from upset stomach to more serious symptoms, including diarrhea, fever, vomiting, abdominal cramps, and dehydration. Although most foodborne infections are undiagnosed and unreported, the Centers for Disease Control and Prevention estimates that every year about 76 million people in the United States become ill from pathogens in food. Of these, up to 5,000 die.
Harmful bacteria are the most common causes of foodborne illnesses. Some bacteria may be present on foods when you purchase them. Raw foods are not sterile. Raw meat and poultry may become contaminated during slaughter. Seafood may become contaminated during harvest or through processing. One in 20,000 eggs may be contaminated with Salmonella inside the egg shell. Produce such as lettuce, tomatoes, sprouts, and melons can become contaminated with Salmonella, Shigella, or Escherichia coli (E. coli) O157:H7. Contamination can occur during growing, harvesting, processing, storing, shipping, or final preparation. Sources of contamination are varied; however, these items are grown in the soil and therefore may become contaminated during growth or through processing and distribution. Contamination may also occur during food preparation in the restaurant or in the person's kitchen.
When food is cooked and left out for more than 2 hours at room temperature, bacteria can multiply quickly. Most bacteria grow undetected because they do not produce an "off" odor or change the color or texture of the food. Freezing food slows or stops bacteria's growth but does not destroy the bacteria. The microbes can become reactivated when the food is thawed. Refrigeration may slow the growth of some bacteria, but thorough cooking is needed to destroy the bacteria.
In most cases of foodborne illness, symptoms resemble intestinal flu and may last a few hours or even several days. Symptoms can range from mild to serious and include
- Abdominal cramps
- Risk Factors
Some people are at greater risk for bacterial infections because of their age or immune status. Young children, pregnant women and their fetuses, the elderly, and people with lowered immunity are at greatest risk.
Some micro-organisms, such as Listeria monocytogenes and Clostridium botulinum, cause far more serious illness than vomiting or diarrhea. They can cause spontaneous abortion or death.
In some people, especially children, hemolytic uremic syndrome (HUS) can result from infection by a particular strain of bacteria, E. coli O157:H7, and can lead to kidney failure and death. HUS is a rare disorder that affects primarily young children between the ages of 1 and 10 years and is the leading cause of acute renal failure in previously healthy children. The child may become infected after consuming a contaminated food, such as meat (especially undercooked ground beef), unpasteurized apple cider or apple juice, or raw sprouts.
The most common symptoms of infection are vomiting, abdominal pain, and diarrhea, which may be bloody. In 5 to 10 percent of cases, HUS develops about 2 to 6 days after the onset of illness. This disease may last from 1 to 15 days and is fatal in 3 to 5 percent of cases. Symptoms of HUS include fever, lethargy, irritability, and pallor. In about half the cases, the disease progresses until the kidneys are unable to remove waste products from the blood and excrete them into the urine (acute renal failure). A decrease in circulating red blood cells and blood platelets and reduced blood flow to organs may lead to multiple organ failure. Seizures, heart failure, inflammation of the pancreas, and diabetes can also result. However, most children recover completely.
You Need to See A Doctor Right Away If You Have Any of The Following Symptoms, With or Without Gastrointestinal Symptoms:
Signs of shock, such as weak or rapid pulse; shallow breathing; cold, clammy, pale skin; shaking or chills; or chest pain.
Signs of severe dehydration, such as dry mouth, sticky saliva, decreased urine output, dizziness, fatigue, sunken eyes, low blood pressure, or increased heart rate and breathing.
Confusion or Difficulty Reasoning.
Your doctor may be able to diagnose foodborne illness from a list of what you've recently eaten and results from the proper laboratory tests. Diagnostic tests for foodborne illness should include examination of the feces. A sample of the suspected food, if available, can also be tested for bacteria and their toxins as well as for viruses and parasites.
Most cases of foodborne illness are mild and can be treated by increasing fluid intake, either orally or intravenously, to replace lost fluids and electrolytes. In cases with gastrointestinal or neurologic symptoms, people should seek medical attention.
In the most severe situations, such as HUS, the patient may need hospitalization in order to receive supportive nutritional and medical therapy.
Maintaining adequate fluid and electrolyte balance and controlling blood pressure are important. Doctors will try to minimize the impact of reduced kidney function. Early dialysis is crucial until the kidneys can function normally again, and blood transfusions may be needed.
Most cases of foodborne illness can be prevented through proper cooking or processing of food, which kills bacteria. In addition, because bacteria multiply rapidly between 40°F and 140°F, food must be kept out of this "danger zone."
To prevent harmful bacteria from growing in food, always
Refrigerate foods promptly. If you let prepared food stand at room temperature for more than 2 hours, it may not be safe to eat. Set your refrigerator at 40°F or lower and your freezer at 0°F.
Cook food to the appropriate temperature (145°F for roasts, steaks, and chops of beef, veal, and lamb; 160°F for pork, ground veal, and ground beef; 165°F for ground poultry; and 180°F for whole poultry). Use a thermometer to be sure! Foods are properly cooked only when they are heated long enough and at a high enough temperature to kill the harmful bacteria that cause illness.
Prevent Cross - Contamination.
Bacteria can spread from one food product to another throughout the kitchen and can get onto cutting boards, knives, sponges, and countertops. So keep raw meat, poultry, seafood, and their juices away from other foods that are ready to eat.
Handle Food Properly.
Always wash your hands before touching food and after using the bathroom, changing diapers, or handling pets, as well as after handling raw meat, poultry, fish, shellfish, or eggs. Clean surfaces well before preparing food on them.
- Keep cold food cold and hot food hot.
- Maintain hot cooked food at 140°F or higher.
- Reheat cooked food to at least 165°F.
- Refrigerate or freeze perishables, prepared food, and leftovers within 2 hours.
- Never defrost food on the kitchen counter. Use the refrigerator, cold running water, or the microwave oven.
- Never let food marinate at room temperature; refrigerate it.
- Divide large amounts of leftovers into small, shallow containers for quick cooling in the refrigerator.
- Remove the stuffing immediately from poultry and other meats and refrigerate it in a separate container.
- Do not pack the refrigerator. Cool air must circulate to keep food safe.
Food irradiation is the treatment of food with high energy such as gamma rays, electron beams, or x rays as a means of cold pasteurization, which destroys living bacteria, to control foodborne disease. The United States relies exclusively on the use of gamma rays, which are similar to ultraviolet light and microwaves and pass through the food leaving no residue or "radioactivity." Food irradiation is currently approved for wheat, potatoes, spices, seasonings, pork, poultry, red meats, whole fresh fruits, and dry or dehydrated products. Although irradiation destroys many bacteria, it does not sterilize food. Even if you're using food that has been irradiated by the manufacturer, you must continue to take precautions against foodborne illness, through proper refrigeration and handling, to safeguard against any surviving organisms.
Links to Other Disorders
Scientists suspect that foodborne pathogens are linked to chronic disorders and can even cause permanent tissue or organ destruction. Research suggests that when some people are infected by foodborne pathogens, the activation of their immune system can trigger an inappropriate autoimmune response, which means the immune system attacks the body's own cells. In some people, an autoimmune response leads to a chronic health condition. Chronic disorders that may be triggered by foodborne pathogens are
- Inflammatory bowel disease
- Kidney failure
- Guillain-Barré syndrome
- Autoimmune disorders
- Further research is needed to explain the link.
- Common Sources of Foodborne Illness
Source of Illness:
Raw and undercooked meat and poultry.
Abdominal pain, diarrhea, nausea, and vomiting.
Campylobacter jejuni, E. coli O157:H7, L. monocytogenes, Salmonella.
Source of Illness:
Raw (unpasteurized) milk and dairy products, such as soft cheeses.
Nausea and vomiting, fever, abdominal cramps, and diarrhea.
L. monocytogenes, Salmonella, Shigella, Staphylococcus aureus, C. jejuni.
Source of Illness:
Raw or undercooked eggs. Raw eggs may not be recognized in some foods such as homemade hollandaise sauce, caesar and other salad dressings, tiramisu, homemade ice cream, homemade mayonnaise, cookie dough, and frostings.
Nausea and vomiting, fever, abdominal cramps, and diarrhea. Bacteria: Salmonella enteriditis.
Source of Illness:
Raw or undercooked shellfish. Symptoms: Chills, fever, and collapse.
Vibrio vulnificus, Vibrio parahaemolyticus.
Source of Illness:
Improperly canned goods, and smoked or salted fish.
Double vision, inability to swallow, difficulty speaking, and inability to breathe. (Seek medical help right away!)
Source of Illness:
Fresh or minimally processed produce.
Diarrhea, nausea, and vomiting.
E. coli O157:H7, L. monocytogenes, Salmonella, Shigella, Yersinia enterocolitica, viruses, and parasites.
Points to Remember
Foodborne illness results from eating food that is contaminated with bacteria, viruses, or parasites.
People at greater risk for foodborne illness include young children, pregnant women and their fetuses, the elderly, and people with lowered immunity.
Symptoms usually resemble intestinal flu. See a doctor immediately if you have more serious problems, or if you do not seem to be improving as you'd expect.
Treatment may range from replacement of lost fluids and electrolytes for mild cases of foodborne illness, to hospitalization for severe conditions such as hemolytic uremic syndrome.
You Can Prevent Foodborne Illness By Taking The Following Precautions:
Wash your hands with hot, soapy water before preparing food and after using the bathroom or changing diapers.
Separate raw meat, poultry, or seafood from other foods to keep these foods and their juices away from ready-to-eat foods.
Cook foods properly and at a high enough temperature to kill harmful bacteria.
Refrigerate foods within 2 hours or less after cooking because cold temperatures will help keep harmful bacteria from growing and multiplying.
Clean surfaces well before using them to prepare foods.
Al b. Wagner, Jr.
The author is an Extension Food Technologist, Texas Agricultural Extension Service
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