FOOD POISONING OVERVIEW
— Microbial foodborne illness, or food poisoning, occurs commonly throughout the world. It is estimated that, in the United States alone, approximately 48 million episodes occur annually, resulting in approximately 3000 deaths per year. Close to one in five episodes of diarrhea is likely to be due to a foodborne disease. This means that the average person in the United States will have a foodborne illness once every three to four years. Fortunately, most people recover from an episode of foodborne illness without any need to consult with a healthcare provider or without any long-term complications.
This topic review discusses the causes, signs and symptoms, and treatment of foodborne illness, along with ways to avoid it.
FOOD POISONING CAUSES
— There are many ways that food can lead to illness, such as contamination with microbes or chemicals, allergies to foods, and the illnesses associated with overeating food. This article will focus on illness caused by eating food that is contaminated by a microorganism: a bacterium, virus, or parasite.
Microorganisms that cause food poisoning — Some of the most common microorganisms that cause food poisoning include the following:
Salmonella — Salmonella is the leading cause of foodborne illness in the United States with an estimated one million cases of salmonellosis each year. There are many types of Salmonella, including those that cause typhoid fever and those that cause gastroenteritis. In the United States, the type that causes gastroenteritis is much more common.
Salmonella is very common in the intestines of animals and reptiles and often exists in the environment. When food is contaminated from the environment or from contact with animals, it can make humans sick when they subsequently consume that food. Contamination of food can occur on a farm, during food processing, or as a result of cross-contamination (transfer from raw meat to salad) in the home, at a restaurant, or at some other point in the supply chain. Thus, most cases of Salmonella food poisoning are due to either cross-contamination or undercooking of raw meat or poultry products or contamination of fresh produce. However, there have also been large outbreaks of Salmonella from unusual foods, such as peanut butter.
Escherichia coli — Escherichia coli is a common cause of food poisoning and traveler’s diarrhea. Infection with E. coli can occur when food or water becomes contaminated with bacteria from infected feces. Some types of E. coli infection can be very serious, resulting in kidney failure or worse.
Hepatitis A virus — Hepatitis A virus is transmitted in foods contaminated by an infected human such as a food handler or from raw shellfish. Symptoms do not usually appear until 15 to 50 days after infection, which can make it difficult to determine the source of infection. In nonimmune individuals, post-exposure administration of passive immune globulin might prevent or mitigate clinical infection.
Detailed information about hepatitis A is available in a separate topic review.
Norovirus — Norovirus infection is the most common foodborne illness and is often acquired when infected food handlers contaminate the food they are preparing (eg, in restaurants). Norovirus is very infectious and easily passed from person to person. Symptoms usually start 24 to 48 hours after exposure with nausea, vomiting, diarrhea, and abdominal pain. Most cases resolve without medical treatment.
Listeria monocytogenes — Listeria is a bacteria that has traditionally been found in unpasteurized or contaminated milk, soft cheese, and other dairy products or in contaminated processed/delicatessen meats, hot dogs, and smoked seafood. More recently, Listeria monocytogenes has been found in a variety of other ready-to-eat foods such as hummus, sunflower seeds, and frozen vegetables. Listeria infection may cause gastrointestinal symptoms, which usually develop within 24 hours and include fever, watery diarrhea, nausea, vomiting, headache, and pains in joints and muscles. A much more serious infection, known as listeriosis, may occur one to three weeks later if the bacteria invade the bloodstream. Listeriosis can occur without any of the gastrointestinal symptoms. Listeriosis is usually seen in pregnant women or older adults and the immunocompromised.
Other microorganisms — More than 200 different microbes are known to cause food poisoning. Detailed information about some of these microbes is available separately.
FOOD POISONING RISK FACTORS
— There are several factors that can increase your risk of developing food poisoning. Ask a healthcare provider if you are in a group that needs to take extra precautions to avoid foodborne illness.
●A weakened immune system – The immune system plays a major role in protecting against a foodborne illness; when your immune system is weakened, you become more vulnerable. A healthcare provider should be able to provide guidance on whether you fall into this group. A few examples of people with a weakened immune system include the very young, older adults, people with chronic disease, pregnant women, and people who take certain types of medication that reduce the ability to fight off foodborne infections.
●Improper food storage or handling, leaving prepared food at room temperature for more than two hours, or improperly cooking or reheating food increase the risk of food poisoning. Use a food thermometer to check internal temperatures of meat, poultry, and seafood before eating them to make sure they are properly cooked. Food should not be left out for more than two hours at room temperature. The “best before” or “use by” dates printed on food are markers of quality, not safety, and should not be used to determine if a food is “safe” to eat. Just because a food looks and smells okay does not mean that it is safe to eat.
●Cross-contamination of food can occur when one contaminated food touches another or when a food comes in contact with a contaminated food preparation surface, such as a counter or cutting board. Keep foods like meat, poultry, and raw fish separate from foods that will not be cooked, such as salads.
●Anyone who handles food should wash their hands before handling food and after using the bathroom, changing diapers, or handling pets. It is easy to pass microbes from the hands into food. Food handlers who fail to wash their hands after using the bathroom can contaminate food with fecal microorganisms.
FOOD POISONING SYMPTOMS
— The symptoms of food poisoning depend upon which microbe you eat. Symptoms can appear hours after the food is ingested or may not appear until days or weeks later. The most common symptoms include:
●Diarrhea, which may be watery or bloody
Less commonly, neurologic symptoms develop, such as blurry vision, dizziness, or tingling in the arms. In some instances, the most life-threatening problems occur several days after the start of intestinal symptoms, and these can include kidney failure, meningitis, arthritis, and paralysis, depending on which foodborne microbe you have been exposed to.
FOOD POISONING DIAGNOSIS
— Food poisoning is usually diagnosed based on a person’s symptoms and history of what they have eaten in the prior week. However, it is not always possible or necessary to determine the particular food or microorganism that caused the illness, especially if the illness is mild and begins to improve within a few days.
When to seek help
— If your symptoms are persistent or severe, if you have an underlying medical condition, or if there are worrisome signs or symptoms (temperature greater than 100.4ºF/38ºC, severe abdominal pain, inability to eat or drink, bloody stool, or vomit), you should see a healthcare provider for evaluation and treatment.
Young children and older adults with these symptoms should also be evaluated quickly. Children and older people can lose fluid rapidly from vomiting or having diarrhea, which can quickly lead to dehydration.
The healthcare provider will ask questions about the type, duration, and severity of symptoms. The person’s blood pressure, pulse, weight, and temperature will be measured, and a physical examination will be performed. In some cases, blood or urine tests will be done to determine if the person is dehydrated or has signs of a body-wide infection.
If needed, a sample of stool or blood can be sent to a laboratory to determine which microorganism is responsible for the symptoms. The need for this type of testing depends upon the person’s symptoms and history.
If a microbe is found, the local health department may be contacted to help determine if the illness is linked to an outbreak in the community. If that happens, the health department may contact you too to ask about what foods you ate before you became sick and where you ate them.
FOOD POISONING TREATMENT
— In most cases of food poisoning, treatment is primarily supportive. Supportive treatment includes drinking adequate fluids, eating small, low-fat meals, and resting as needed.
Antibiotics are not usually needed or recommended but may be used for some types of food poisoning. In most cases, symptoms resolve quickly and no special treatment is necessary. In people with persistent diarrhea and/or vomiting, intravenous fluids may be needed to prevent dehydration. Antidiarrheal medications (eg, Imodium, Pepto-Bismol) are not generally recommended.
The treatment of nausea, vomiting, and diarrhea is discussed in detail in separate topic reviews.
FOOD POISONING PREVENTION
— Although it is not always possible to avoid exposure to a microbe that can cause food poisoning, certain precautions can decrease the chances that it will occur.
Food safety recommendations
— The following general precautionary measures are recommended by the federal government (www.foodsafety.gov):
●Do not drink raw (unpasteurized) milk or foods that contain unpasteurized milk.
●Wash raw fruits and vegetables thoroughly before eating using clean, cold running water.
●Keep the refrigerator temperature at 40ºF (4.4ºC) or lower; the freezer at 0ºF (-17.8ºC) or lower.
●Use precooked, perishable, or ready-to-eat food as soon as possible.
●Avoid cross-contamination; keep raw meat, fish, and poultry separate from other foods.
●Wash hands, knives, and cutting boards after handling uncooked food, including produce and raw meat, fish, or poultry.
●Thoroughly cook raw food from animal sources to a safe internal temperature and check the temperature by using a food thermometer: ground beef 160ºF (71ºC); chicken 165ºF (77ºC); turkey 165ºF (82ºC); pork 145ºF (71ºC).
●Seafood and shellfish should be cooked thoroughly to minimize the risk of food poisoning. Eating raw fish (eg, sushi) poses a risk for a variety of parasitic worms (in addition to the risks associated with organisms carried by food handlers). Freezing kills some, although not all, harmful microorganisms. Raw fish that is labeled “sushi-grade” or “sashimi-grade” has been frozen.
●Cook eggs thoroughly, until the yolk is firm.
●Refrigerate foods promptly. Never leave cooked foods at room temperature for more than two hours (one hour if the room temperature is above 90ºF/32ºC).
The following additional recommendations apply to pregnant women and those who have a weakened immune system:
●Do not eat hot dogs, pâtés, luncheon meats, bologna, or other delicatessen meats unless they are reheated until steaming hot; avoid the use of microwave ovens since uneven cooking may occur.
●Avoid spilling fluids from raw meat and hot dog packages on other foods, utensils, and food preparation surfaces. In addition, wash hands after handling hot dogs, luncheon meats, delicatessen meats, and raw meat, chicken, turkey, or seafood or their juices.
●Do not eat pre-prepared salads, such as ham salad, chicken salad, egg salad, tuna salad, or seafood salad.
●Do not eat soft cheeses such as feta, Brie and Camembert, blue-veined cheeses, or Mexican-style cheeses such as queso blanco, queso fresco, or Panela, unless they have a label that clearly states that the cheese is made from pasteurized milk.
●Do not eat refrigerated pâtés or meat spreads. Canned or shelf-stable products may be eaten.
●Do not eat refrigerated smoked seafood unless it has been cooked. Refrigerated smoked seafood, such as salmon, trout, whitefish, cod, tuna, or mackerel, is most often labeled as “nova-style,” “lox,” “kippered,” “smoked,” or “jerky.” The fish is found in the refrigerator section or sold at deli counters of grocery stores and delicatessens. Canned or shelf-stable smoked seafood may be eaten.
●Bacteria like Listeria can grow in the refrigerator so, even if you consume foods that are considered safe, be sure to eat them from freshly opened packs and not from leftovers in the refrigerator.
Preventing the spread of infection
— People with diarrhea and/or vomiting should be cautious to avoid spreading infection to family, friends, and coworkers. A person is considered infectious for at least as long as vomiting or diarrhea continues and sometimes longer depending upon the microbe.
Microorganisms that cause food poisoning are usually spread from one person to another by hand to mouth or hand to food contact. As a result, hand washing, care with diapering, and staying out of work or school are a few ways to prevent infecting family and other contacts.
WHERE TO GET MORE INFORMATION — Your healthcare provider is the best source of information for questions and concerns related to your medical problem.