Gastroenteritis, often called the "stomach flu," is a common and normally short-lived illness characterized by diarrhea and low-grade fever, cramps, nausea, and vomiting. Most people don't require medical attention, although infants, young children, and the elderly are at higher risk for more severe disease. Gastroenteritis, or "stomach flu," is not actually caused by an influenza virus, but by other viruses, as well as many bacteria and parasites. Viral gastroenteritis is easily spread through the fecal-oral route; that is, by ingesting microscopic amounts of contaminated feces. This usually occurs because of inadequate washing after using the bathroom or diapering a baby. Bacterial gastroenteritis, also called food poisoning, is commonly caused by eating food that has spoiled or been contaminated, and often by uncooked meat (for example, steak tartar, which is a raw meat dish) or by eating meat that is cooked rare. Unclean water is another source of transmission of gastroenteritis-causing organisms.
Gastroenteritis is very common and often occurs in epidemics, either by spreading from person to person in an institution or from many people eating a common contaminated food source. Travelers to countries with poor sanitation are also at high risk for developing gastroenteritis, or "traveler's diarrhea."
Typically within one to two days of exposure, gastroenteritis causes diarrhea and often low-grade fever, cramps, nausea, and vomiting. Illness typically lasts a few days, with complete recovery in about a week.
While deaths are rare in developed countries, gastroenteritis is a leading cause of mortality of infants and young children in countries where sanitation is poor.
Gastroenteritis is most commonly caused by viruses, which are spread by the fecal-oral route.
A variety of viruses can cause gastroenteritis. They are usually spread by accidental ingestion of microscopic quantities of infected feces. This commonly occurs in several different ways, usually because of inadequate hand washing after using the bathroom or diapering a baby. Infection is easily spread from an infected person throughout a household, daycare center, or restaurant.
The viruses that can cause gastroenteritis include rotaviruses, adenoviruses, and astroviruses, Norwalk virus, and a group of Norwalk-like viruses.
The influenza virus does not cause gastrointestinal symptoms. Some viruses are more active at certain times of year; for example, rotavirus and astrovirus are most common in the winter in the U.S. Some virues are more common in certain age groups. For example, rotavirus is the most common cause of diarrhea in infants and young children, while Norwalk and related viruses affect older children and adults. Bacteria that commonly cause gastroenteritis include various types of E. coli, Salmonella, Shigella, and Campylobacter species, as well as organisms that cause cholera and dysentery. Illness may result from the bacteria themselves, or from toxins that are produced by some bacteria. Some toxins cause intestinal cells to secrete fluid, producing large amounts of watery diarrhea. Others damage the intestinal lining so that blood is visible in the stool. Some bacteria produce proteins that enable themselves to adhere to the intestinal wall and multiply, crowding out the normal beneficial intestinal bacteria.
Certain parasites found in food and water also cause gastroenteritis. Giardia and amebiasis are two examples of parasitic causes of gastroenteritis. Giardia is often contracted by campers who drink directly from streams. Infected individuals often develop a prolonged course of gastrointestinal symptoms. Amebiasis or amoebic dysentery is also caused by a parasite.
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