Gastroenteritis is an inflammation of the intestines that causes diarrhea, abdominal cramps, nausea, loss of appetite, and other symptoms of digestive upset. In adults, the two most common causes of gastroenteritis are viral and bacterial infections:
Viral gastroenteritis — In otherwise healthy adults, viral infections of the digestive tract are often responsible for mild episodes of gastroenteritis. These viral infections include the Norwalk virus, rotaviruses, adenoviruses and other agents. The viruses are very contagious, and usually spread from one person to another on unwashed hands, or by close contact with an infected person, such as sharing food or eating utensils. Viral gastroenteritis often spreads very easily in institutions and other situations where people live in close quarters, such as prisons, nursing homes, cruise ships, schools, college dorms and public campgrounds. The viruses also can be spread when someone either touches an infected person's stool or touches surfaces contaminated with infected stool. For this reason, health care professionals and child care workers have an especially high risk of viral gastroenteritis, particularly if they do not wash their hands thoroughly after dealing with soiled diapers, bedpans or bathroom fixtures. In some circumstances, the agents that cause viral gastroenteritis also can be carried in water or food, especially in drinking water or commercial shellfish that have been contaminated by sewage runoff. Infected food handlers who don't follow proper sanitary procedures also can spread viral gastroenteritis in meals served in restaurants and cafeterias.
Bacteria — Salmonella, shigella, Campylobacter jejuni, E. coli and many other types of bacteria can cause gastroenteritis. They can be spread by close contact with an infected person, or by drinking or eating infected food or water. In some cases, the disease is caused by a toxin that is produced by bacteria growing on food that has been prepared or stored improperly. If a person eats this germ-filled food, symptoms of gastroenteritis are triggered either by the bacteria themselves or by their irritating byproducts. Symptoms from a toxin usually begin within a few hours. Symptoms from the bacteria can occur within a few days.
Each year in the United States, millions of people develop gastroenteritis by eating contaminated food, while millions more suffer from mild bouts of viral gastroenteritis. In otherwise healthy adults, both forms of gastroenteritis tend to be mild and brief, and many episodes are never reported to a doctor. However, in the elderly and people with weakened immune defenses, gastroenteritis sometimes can produce dehydration and other dangerous complications. Even in robust adults, certain types of aggressive bacteria occasionally cause more serious forms of food poisoning that can cause high fever and severe gastrointestinal symptoms, such as bloody diarrhea.