What is food poisoning?

Causes and Symptoms

Often a person feeling the symptoms of nausea, vomiting, diarrhea, and abdominal discomfort assumes that he or she has contracted influenza. The presence of a true influenza virus, however, is uncommon. More likely, these symptoms are caused by eating food that contains undesirable bacteria, viruses, or parasites. This is called food-borne illness, or food poisoning. Most food-borne pathogens are colorless, odorless, and tasteless. Fortunately, there are recommendations based on scientific principles to help prevent food-borne illness.

Food poisoning is a worldwide problem. In developing countries, diarrhea is a factor in child malnutrition and is estimated to cause millions of deaths per year. According to the Centers for Disease Control and Prevention (CDC) in 2014, based on data from 2011, approximately 48 million Americans are affected by food-borne illnesses every year, resulting in 3,000 deaths and 128,000 hospitalizations. Despite advances in modern technology, food-borne illness is a major problem in developed countries as well.

Certain foods, particularly foods with a high protein and moisture content, provide an ideal environment for the multiplication of pathogens. The foods with high risk in the United States are raw shellfish (especially mollusks), underdone poultry, raw eggs, rare meats, raw milk, and cooked food that another person handled before it was packaged and chilled. In addition to those foods listed, some developing countries could add raw vegetables, raw fruits that cannot be peeled, foods from sidewalk vendors, and tap water or water from unknown and contaminated sources.

Most of the documented cases of food-borne illness are caused by only a few bacteria, viruses, and parasites. As of late 2014, the CDC listed Norovirus as the leading cause of food-borne illness outbreaks in the United States. Extremely contagious, the tiny particles of the virus can easily be transferred to food, especially by those preparing the food; the virus causes inflammation of the stomach and intestines that leads to nausea, vomiting, and diarrhea.

Bacteria known as
Salmonella
are ingested by humans in contaminated foods such as beef, poultry, and eggs; they may also be transmitted by kitchen utensils and the hands of people who have handled infected food or utensils. Once the bacteria are inside the body, the incubation time is from eight to twenty-four hours. Since the bacteria multiply inside the body and attack the gastrointestinal tract, this disease is known as a true food infection. The main symptoms are diarrhea, abdominal cramps, and vomiting. The bacteria are killed by cooking foods to the well-done stage.

Another one of the major food-borne intoxications in the United States is caused by eating food contaminated with the toxin of Staphylococcus bacteria. Because the toxin or poison has already been produced in the food item that is ingested, the onset of symptoms is usually very rapid (between one-half hour and six hours). Improperly stored or cooked foods (particularly meats, tuna, and potato salad) are the main carriers of these bacteria. Since this toxin cannot be killed by reheating the food items to a high temperature, it is important that foods are properly stored.

Botulism is a rare food poisoning caused by the toxin of Clostridium botulinum. It is anaerobic, meaning that it multiplies in environments without oxygen, and is mainly found in improperly home-canned food items. Originally one of the sources of the disease was from eating sausages (the Latin word for which is botulus)—hence, the term “botulism.” A very small amount of toxin, the size of a grain of salt, could kill hundreds of people within an hour. Danger signs include double vision and difficulty swallowing and breathing.

Though everyone is at risk for food-borne illness, certain groups of people develop more severe symptoms and are at a greater risk for serious illness and death. Higher-risk groups include pregnant women, very young children, the elderly, and immunocompromised individuals, such as patients with acquired immunodeficiency syndrome (AIDS) and cancer.

Bacteria known as
Listeria
were first documented in 1981 as being transmitted by food. Most people are at low risk of becoming ill after ingesting these bacteria; however, pregnant women are at high risk. Listeria infection is rare in the United States, but it does cause serious illness. It is associated with consumption of raw (unpasteurized) milk, nonreheated hot dogs, undercooked chicken, various soft cheeses (Mexican style, feta, Brie, Camembert, and blue-veined cheese), and food purchased from delicatessen counters. Listeria cause a short-term illness in pregnant women; however, this bacteria can cause stillbirths and spontaneous abortions. A parasite called Toxoplasma gondii is also of particular risk for pregnant women. For this reason, raw or very rare meat should not be eaten. (In addition, since cats may shed these parasites in their feces, it is recommended that pregnant women avoid cleaning cat litter boxes.)

As the protective antibodies from the mother are lost, infants become more susceptible to food poisoning. Botulism generally occurs by ingesting the toxin or poison; however, in infant botulism it is the spores that germinate and produce the toxin within the intestinal tract of the infant. Since honey and corn syrup have been found to contain spores, it is recommended that they not be fed to infants under one year of age, especially those under six months.

Determining whether a disease is caused by a food-borne organism is highly skilled work. The CDC in Atlanta investigates diseases and their causes. It has been estimated that the true incidence of food-borne illness in the United States is ten to one hundred times greater than that reported to the CDC. The CDC report some of the more interesting cases and outbreaks in narrative form in the Morbidity and Mortality Weekly Report.

Treatment and Therapy

In cases of severe food poisoning marked by vomiting, diarrhea, or collapse—especially in cases of botulism and ingestion of poisonous plant material such as suspicious mushrooms—emergency medical attention should be sought immediately, and, if possible, specimens of the suspected food should be submitted for analysis. Identifying the source of the food is especially important if that source is a public venue such as a restaurant, because stemming a widespread outbreak of food poisoning may thereby be possible. In less severe cases of food poisoning, the victim should rest, eat nothing, but drink fluids that contain some salt and sugar; the person should begin to recover after several hours or one or two days and should see a doctor if not well after two or three days.

Some types of food poisoning can be treated with antibiotics, and there is an antitoxin available for cases of botulism. However, the best “treatment” for food poisoning is prevention. While there is ample information regarding the prevention of food poisoning, many outbreaks still occur as a result of carelessness in the kitchen. Good food safety is basically good common sense, yet it can make sense only when one has acquired some knowledge of how food-borne pathogens spread and how to apply food safety steps to prevent food-borne illness. Based on the research literature, as well as on the suggestions made by the
World Health Organization (WHO) and other groups, the recommendations are to cook foods well, to prevent cross-contamination, and to keep hot foods hot and cold foods cold.

Cooking foods well means cooking them to a high enough temperature in the slowest-to-heat part and for a long enough time to destroy pathogens that have already gained access to foods. Cooking foods well is only a concern when they have become previously contaminated from other sources or are naturally contaminated. There are a number of possible sources of contamination of food products.

Coastal water may contaminate seafood. Filter-feeding marine animals (such as clams, scallops, oysters, cockles, and mussels) and some fish (such as anchovies, sardines, and herring) live by pumping in seawater and sifting out organisms that they need for food. Therefore, they have the ability to concentrate suspended material by many orders of magnitude. Shellfish grown in contaminated coastal waters are the most frequent carriers of a virus called hepatitis A.

Contaminated eggs can be another vehicle of food-borne illness. Contamination of eggs can occur from external as well as internal sources. If moist conditions are present and there is a crack in the shell, the fecal material of hens carrying the microorganism can penetrate the shell and membrane of the egg and can multiply. In the early 1990s, Salmonella enteritidis began to appear in the intact egg, particularly in the northeastern part of the United States. It is hypothesized that contamination occurs in the oviduct of the hen before the egg is laid. Food vehicles in which Salmonella enteritidis has been reported include sandwiches dipped in eggs and cooked, hollandaise sauce, eggs Benedict, commercial frozen pasta with raw egg and cheese stuffing, Caesar salad dressing, and blended food in which cross-contamination had occurred. Foods such as cookie or cake dough or homemade ice cream made with raw eggs are other possible vehicles of food-borne illness.

Milk, especially raw milk, can be contaminated. Sources of milk contaminants could be an unhealthy cow (such as from mastitis, a major infection of the mammary gland of the dairy cow) or unclean methods of milking, such as not cleaning the teats well before attaching them to the milker or unclean utensils (milking tanks). If milk is not cooled fast enough, contaminants can multiply.

Modern mechanized milking procedures have reduced but not eliminated food-borne pathogens. Postpasteurization contamination may occur, especially if bulk tanks or equipment have not been properly cleaned and sanitized. In 1985 in Chicago, one of the largest salmonellosis outbreaks occurred, with the causal food being pasteurized milk. More than sixteen thousand people were infected, and ten died. A small connecting piece in the milk tank which allowed milk and microorganisms to collect was determined to be the source of the contamination. Bulk tanks should be properly maintained and piping should be inspected regularly for opportunities for raw milk to contaminate the pasteurized product.

Recommendations for cooking temperatures are based not only on the temperature required to kill food-borne pathogens but also on aesthetics and palatability. Generally, a margin of safety is built into the cooking temperature because of the possibility of nonuniform heating. Based on generally accepted temperature requirements, cooking red meat until 71 degrees Celsius (160 degrees Fahrenheit) will reach the thermal death point. Hamburger should be well cooked so that it is medium-brown inside. If pressed, it should feel firm and the juices that run out should be clear. Cooking poultry to the well-done stage is done for palatability. Tenderness is indicated when there is a flexible hip joint, and juices should run clear and not pink when the meat is pierced with a fork. Fish should be cooked until it loses its translucent appearance and flakes when pierced with a fork. Eggs should be thoroughly cooked until the yolk is thickened and the white is firm, not runny. Cooked or chilled foods that are served hot (that is, leftovers) should be reheated so that they come to a rolling boil.

Cross-contamination occurs when microorganisms are transmitted from humans, cutting boards, and utensils to food. Contamination between foods, especially from raw meat and poultry to fresh vegetables or other ready-to-eat foods, is a major problem.

One of the best ways to prevent cross-contamination is simply washing one’s hands with soap and water. Twenty seconds is the minimum time span that should be spent washing one’s hands. To prevent the spread of disease, it is also recommended that the hands be dried with a paper towel, which is then thrown away. Thoroughly washed hands can still be a source of bacteria, however, so one should use tongs and spoons when cooking to prevent contamination.

It is especially important to wash one’s hands after certain activities, such as blowing the nose or sneezing, using the lavatory, diapering a baby, smoking, petting animals or pets, and before cooking or handling food.

Other sources of cross-contamination include utensils and cutting surfaces. If people use the same knife and cutting board to cut up raw chicken for a stir-fry and peaches for a fruit salad, they are putting themselves at great risk for food-borne illness. The bacteria on the cutting board and the knife could cross-contaminate the peaches. While the chicken will be cooked until it is well done, the peaches in the salad will not be. In this situation, one could cut the fruit first and then the chicken, and then wash and sanitize the knife and cutting board.

Cleaning and sanitizing is actually a two-step process. Cleaning involves using soap and water and a scrubber or dishcloth to remove the major debris from the surface. The second step, sanitizing, involves using a diluted chloride solution to kill bacteria and viruses.

Wooden cutting boards are one of the worst offenders in terms of causing cross-contamination. Since bacteria and viruses are microscopic, they can adhere to and grow in the grooves of a wooden cutting board and spread to other foods when the cutting board is used again. Use of a plastic or acrylic cutting board prevents this problem.

The danger zone in which bacteria can multiply is a range of 4.4 degrees Celsius (40 degrees Fahrenheit) to 60 degrees Celsius (140 degrees Fahrenheit). Room temperature is generally right in the middle of this danger zone. The danger zone is critical because, even though they cannot be seen, bacteria are increasing in number. They can double and even quadruple in fifteen to thirty minutes. Consequently, perishable foods such as meats, poultry, fish, milk, cooked rice, leftover pizza, hard-cooked eggs, leftover refried beans, and potato salad should not be left in the danger zone for more than two hours. Keeping hot foods hot means keeping them at a temperature higher than 60 degrees Celsius. Keeping cold foods cold means keeping them at a temperature lower than 4 degrees Celsius (40 degrees Fahrenheit).

Other rules are helpful for preventing contamination. When shopping, the grocery store should be the last stop so that foods are not stored in a hot car. When meal time is over, leftovers should be placed in the refrigerator or freezer as soon as possible. When packing for a picnic, food items should be kept in an ice chest to keep them cold or brought slightly frozen. Many instances of food-born illnesses and death could be prevented if such food safety rules were followed.

Perspective and Prospects

When the lifestyle of people changed from a hunting-and-gathering society to a more agrarian one, the need to preserve food from spoilage was necessary for survival. As early as 3000 BCE, salt was used as a meat preservative and the production of cheese had begun in the Near East. The production of wine and the preservation of fish by smoking were also introduced at that time. Even though throughout history people had tried many methods to preserve foods and keep them from spoiling, the relationship between illness and pathogens or toxins in food was not recognized and documented until 1857. It was then that the French chemist Louis Pasteur demonstrated that the microorganisms in raw milk caused spoilage.

Stories from the American Civil War (1860–1865) demonstrate the problems of institutional feeding of many people for long periods of time. Gastrointestinal diseases were rampant during that time period. During the first year of the war, of the people who had diarrhea and dysentery, the morbidity rate was 640 per 1,000 and increased to 995 per 1,000 in 1862. More men died of disease and illness than were killed in battle.

Food can be contaminated by disease-causing organisms at any step of the food-handling chain, from the farm to the table. An important role of government and industry is to ensure a safe food supply. In the United States, setting and monitoring of food safety standards are the responsibility of the Food and Drug Administration (FDA) under the auspices of the US Department of Health and Human Services and the Food Safety and Inspection Service (FSIS) under the auspices of the US Department of Agriculture (USDA). The FDA is responsible for the wholesomeness of all food sold in interstate commerce, except meat and poultry, while the USDA is responsible for the inspection of meat and poultry sold in interstate commerce and internationally. Some major food safety laws and policies that have guided the provision of safe food are the Federal Food and Drugs Act in 1906; the Federal Meat Inspection Act in 1906–7; the Food, Drug, and Cosmetic Act in 1938; and the Poultry Products Inspection Act in 1957.

Historically, the diseases of tuberculosis, scarlet fever, strep throat, typhoid fever, and diphtheria have been associated with raw or unpasteurized milk. The reporting of food-borne illness was initiated in the 1920s by the US Public Health Service (USPHS) when annual summaries of outbreaks of milk-borne disease were recorded and reported. Later, reports of waterborne and food-borne diseases were added.

The public attitude about what is hazardous in the food supply and that of the FDA have often differed. The public generally believes that the safety of additives and chemical contaminants in food is of a higher priority than that of the microbiological and nutritional hazards—the exact opposite of the FDA’s priorities. (For example, in the mid-1980s, the story about Alar, a chemical used to slow the ripening of apples, represented a very emotional topic. There was particular concern about the risks that this chemical might pose to children who ate large amounts of apple products.) As more reliable information is available about both areas of concern, the situation regarding priorities is likely to change.

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