Patient education: Foodborne illness (food poisoning) (Beyond the Basics)

FOODBORNE ILLNESS OVERVIEW — Microbial foodborne illness, sometimes called 'food poisoning,' occurs commonly throughout the world, including in the United States. Fortunately, most people recover from an episode of foodborne illness without any need to consult with a health care provider and 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.

CAUSES OF FOODBORNE ILLNESS — There are many ways that food can lead to illness. This article will focus on illness caused by eating food that is contaminated by a microorganism: a bacterium, virus, or parasite.

Microorganisms that cause foodborne illness — Many different microorganisms can cause foodborne illness. Updated information on outbreaks may be found on websites maintained by the United States Centers for Disease Control and Prevention and the US Food and Drug Administration.

Some of the most common include the following:

Salmonella — Salmonella is the leading bacterial 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 may exist 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 foodborne illness 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 other foods, such as peanut butter.

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 or by touching contaminated surfaces. Symptoms usually start 24 to 48 hours after exposure with nausea, vomiting, diarrhea, and abdominal pain. Most cases resolve without medical treatment.

Escherichia coli — Certain Escherichia coli (E. coli) bacteria can cause foodborne illness, particularly an illness known as "traveler's diarrhea." Infection with E. coli can occur when food or water becomes contaminated with 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. Hepatitis A causes jaundice (yellowing of the skin or whites of the eyes) and occasionally liver failure. 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 vaccination or administration of immune globulin can help prevent infection. In the United States, a vaccine for hepatitis A is recommended for all children.

Detailed information about hepatitis A is available separately. (See "Patient education: Hepatitis A (Beyond the Basics)".)

Listeria monocytogenes — Listeria is a bacterium that has traditionally been found in unpasteurized or contaminated milk, soft cheese, and other dairy products or in contaminated processed/deli 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. 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. (See "Treatment and prevention of Listeria monocytogenes infection".)

FOODBORNE ILLNESS RISK FACTORS — There are several factors that can increase your risk of developing foodborne illness. Ask a health care 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 health care 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. Pregnant women, in particular, should avoid eating foods that may contain Listeria, including soft cheeses and delicatessen meats.

●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 foodborne illness. Use a food thermometer to check internal temperatures of meat, poultry, and seafood before eating them to make sure they are properly cooked. 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. (See 'Food safety recommendations' below.)

●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. (See 'Food safety recommendations' below.)

●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. (See 'Preventing the spread of infection' below.)

FOODBORNE ILLNESS SYMPTOMS — The symptoms of foodborne illness depend upon which microbe gets into your system. Symptoms can appear hours after you eat the contaminated food, or may not appear until days or weeks later. The most common symptoms include:

●Nausea

●Vomiting

●Abdominal pain

●Diarrhea, which may be watery or bloody

●Fever

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.

FOODBORNE ILLNESS DIAGNOSIS — Foodborne illness 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 100.4°F/38°C, severe abdominal pain, inability to eat or drink, bloody stool, or vomit), you should see a health care 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. (See "Patient education: Nausea and vomiting in infants and children (Beyond the Basics)" and "Patient education: Acute diarrhea in children (Beyond the Basics)".)

The health care 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.

FOODBORNE ILLNESS TREATMENT — In most cases of foodborne illness, treatment is primarily supportive. Supportive treatment includes drinking adequate fluids, eating small, low-fat meals, and resting as needed. Oral rehydration solutions (sample brand name: Pedialyte) are particularly useful for providing adequate hydration.

Antibiotics are not usually needed or recommended but may be used for some types of foodborne illness. 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, such as loperamide (brand name: Imodium), can be useful for the symptomatic treatment of watery diarrhea.

The treatment of nausea, vomiting, and diarrhea is discussed in detail in separate topic reviews. (See "Patient education: Acute diarrhea in adults (Beyond the Basics)" and "Patient education: Acute diarrhea in children (Beyond the Basics)" and "Patient education: Nausea and vomiting in infants and children (Beyond the Basics)".)

FOODBORNE ILLNESS PREVENTION — Although it is not always possible to avoid exposure to a microbe that can cause foodborne illness, certain precautions can decrease the chances that it will occur.

Washing your hands thoroughly with soap and clean, running water is the best way to prevent foodborne illness. Alcohol-based hand rubs are also useful. Handwashing is especially important after using the bathroom, after changing a diaper, before preparing food, and after touching animals.

Food safety recommendations — The following general precautionary measures are recommended by the United States 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 40°F (4.4°C) or lower; the freezer at 0°F (-17.8°C) 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 160°F (71°C); chicken 165°F (77°C); turkey 165°F (82°C); pork 145°F (71°C).

●Seafood and shellfish should be cooked thoroughly to minimize the risk of foodborne illness. 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 90°F/32°C).

The United States Centers for Disease Control and Prevention (CDC) has a similar set of guidelines, which they categorize into four themes: "clean, separate, cook, and chill" (www.cdc.gov/foodsafety/keep-food-safe.html).

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. This includes avoiding or limiting contact with others, until the person gets better, and washing hands frequently. A person is considered infectious (contagious) for at least as long as vomiting or diarrhea continues and sometimes even longer, depending upon the microbe.

WHERE TO GET MORE INFORMATION — Your health care provider is the best source of information for questions and concerns related to your medical problem.

This article will be updated as needed on our website (www.uptodate.com/patients). Related topics for patients, as well as selected articles written for health care professionals, are also available. Some of the most relevant are listed below.

Patient level information — UpToDate offers two types of patient education materials.

The Basics — The Basics patient education pieces answer the four or five key questions a patient might have about a given condition. These articles are best for patients who want a general overview and who prefer short, easy-to-read materials.

Patient education: Food poisoning (The Basics)
Patient education: Diarrhea in teens and adults (The Basics)
Patient education: Diarrhea in children (The Basics)
Patient education: Nausea and vomiting in adults (The Basics)
Patient education: Bloody stools in adults (The Basics)
Patient education: Bloody stools in children (The Basics)
Patient education: Avoiding infections in pregnancy (The Basics)
Patient education: Giardia (The Basics)
Patient education: Reactive arthritis (The Basics)
Patient education: Cryptosporidiosis (The Basics)
Patient education: Salmonella infection (The Basics)
Patient education: Travelers' diarrhea (The Basics)
Patient education: Enteric (typhoid and paratyphoid) fever (The Basics)
Patient education: Listeria infection (The Basics)
Patient education: Campylobacter infection (The Basics)
Patient education: When to worry about a fever in adults (The Basics)

Beyond the Basics — Beyond the Basics patient education pieces are longer, more sophisticated, and more detailed. These articles are best for patients who want in-depth information and are comfortable with some medical jargon.

Patient education: Hepatitis A (Beyond the Basics)
Patient education: Nausea and vomiting in infants and children (Beyond the Basics)
Patient education: Acute diarrhea in children (Beyond the Basics)
Patient education: Acute diarrhea in adults (Beyond the Basics)

Professional level information — Professional level articles are designed to keep doctors and other health professionals up-to-date on the latest medical findings. These articles are thorough, long, and complex, and they contain multiple references to the research on which they are based. Professional level articles are best for people who are comfortable with a lot of medical terminology and who want to read the same materials their doctors are reading.

Approach to the adult with acute diarrhea in resource-abundant settings
Botulism
Yersiniosis: Infection due to Yersinia enterocolitica and Yersinia pseudotuberculosis
Campylobacter infection: Clinical manifestations, diagnosis, and treatment
Clinical manifestations and diagnosis of Listeria monocytogenes infection
Shigella infection: Epidemiology, clinical manifestations, and diagnosis
Shiga toxin-producing Escherichia coli: Clinical manifestations, diagnosis, and treatment
Cryptosporidiosis: Epidemiology, clinical manifestations, and diagnosis
Pathogenic Escherichia coli associated with diarrhea
Shigella infection: Treatment and prevention in adults
Overview of shellfish, pufferfish, and other marine toxin poisoning
Treatment and prevention of Listeria monocytogenes infection
Nontyphoidal Salmonella: Gastrointestinal infection and asymptomatic carriage
Causes of acute infectious diarrhea and other foodborne illnesses in resource-abundant settings

The following organizations also provide reliable health information.

●Centers for Disease Control and Prevention (CDC)

(www.cdc.gov)

●Food and Drug Administration

(www.fda.gov)

●National Institute of Allergy and Infectious Diseases

(www.niaid.nih.gov)

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ACKNOWLEDGMENT — The UpToDate editorial staff acknowledges David WK Acheson, MD, FRCP, who contributed to earlier versions of this topic review.