Food poisoning occurs when you swallow food or water that contains bacteria, parasites, viruses, or the toxins made by these germs. Most cases are caused by common bacteria such as Staphylococcus or E. coli.
Food poisoning can affect one person or a group of people who all ate the same food. It is more common after eating at picnics, school cafeterias, large social functions, or restaurants.
When germs get into the food, it is called contamination. This can happen in different ways:
Meat or poultry can come into contact with bacteria from the intestines of an animal that is being processed.
Water that is used during growing or shipping can contain animal or human waste.
Food may be handled in an unsafe way during preparation in grocery stores, restaurants, or homes.
Food poisoning can occur after eating or drinking:
Any food prepared by someone who does not wash their hands properly
Any food prepared using cooking utensils, cutting boards, and other tools that are not fully cleaned
Dairy products or food containing mayonnaise (such as coleslaw or potato salad) that have been out of the refrigerator too long
Frozen or refrigerated foods that are not stored at the proper temperature or are not reheated to the right temperature
Raw fish or oysters
Raw fruits or vegetables that have not been washed well
Raw vegetables or fruit juices and dairy products (look for the word "pasteurized," which means the food has been treated to prevent contamination)
Undercooked meats or eggs
Water from a well or stream, or city or town water that has not been treated
Many types of germs and toxins may cause food poisoning, including:
E. coli enteritis
Toxins in spoiled or tainted fish or shellfish
Infants and elderly people are at the greatest risk for food poisoning. You are also at higher risk if:
You have a serious medical condition, such as kidney disease, diabetes, cancer, or HIV and/or AIDS.
You have a weakened immune system.
You travel outside of the United States to areas where you are exposed to germs that cause food poisoning.
Pregnant and breastfeeding women should use extra care to avoid food poisoning.
Symptoms from the most common types of food poisoning will often start within 2 - 6 hours of eating the food. That time may be longer or shorter, depending on the cause of the food poisoning.
Your health care provider will look for signs of food poisoning. These may include pain in the stomach and signs your body has too little fluid (dehydration).
Tests may be done on your stools or the food you have eaten to find out what type of germ is causing your symptoms. However, tests may not always find the cause of the diarrhea.
In more serious cases, your health care provider may order a sigmoidoscopy. This test uses a thin, hollow tube with a light on the end that is laced in the anus to look for the source of bleeding or infection.
Most of the time, you will get better in a couple of days. The goal is to ease symptoms and make sure your body has the proper amount of fluids.
Getting enough fluids and learning what to eat will help keep you comfortable. You may need to:
Manage the diarrhea
Control nausea and vomiting
Get plenty of rest
You can drink oral rehydration mixtures to replace fluids and minerals lost through vomiting and diarrhea.
Oral rehydration powder can be purchased from a pharmacy. Be sure to mix the powder in safe water.
You can make your own mixture by dissolving ½ teaspoonful each salt and baking soda and 4 tablespoonsful of sugar in 4 ¼ cups (1 liter) water.
If you have diarrhea and are unable to drink or keep down fluids, you may need fluids given through a vein (by IV). This may be more common in young children.
If you take diuretics, ask your health care provider if you need to stop taking the diuretic while you have diarrhea. Never stop or change medicines before talking to your doctor.
For the most common causes of food poisoning, your doctor will NOT prescribe antibiotics.
You can buy medicines at the drugstore that help slow diarrhea.
Do not use these medicines without talking to your health care provider if you have bloody diarrhea, a fever, or the diarrhea is severe.
Do not give these medicines to children.
Most people fully recover from the most common types of food poisoning within 12 - 48 hours. Some types of food poisoning can cause serious complications.
Death from food poisoning in people who are otherwise healthy is rare in the United States.
Dehydration is the most common complication. This can occur from any causes of food poisoning.
Less common, but much more serious complications depend on the bacteria that are causing the food poisoning. These may include:
Sodha SV, Griffin PM, Hughes JM. Foodborne disease. In: Mandell GL, Bennett JE, Dolin R, eds. Principles and Practice of Infectious Diseases. 7th ed. Philadelphia, PA: Elsevier Churchill Livingstone; 2009:chap 99.
Craig SA. Gastroenteritis. In Marx JA, Hockberger RS, Walls RM, et al, eds. Rosen's Emergency Medicine: Concepts and Clinical Practice. 8th ed. Philadelphia, PA: Mosby Elsevier; 2013:chap 94.
Eric Perez, MD, St. Luke's / Roosevelt Hospital Center, NY, NY, and Pegasus Emergency Group (Meadowlands and Hunterdon Medical Centers), NJ. Review provided by VeriMed Healthcare Network. Also reviewed by David Zieve, MD, MHA, Isla Ogilvie, PhD, and the A.D.A.M. Editorial team.