What is gastroenteritis?
Gastroenteritis refers to the infection of the intestinal tract and is most commonly due to viruses, although bacteria and parasites also contribute to a lesser degree. The most common viruses involved are rotavirus and norovirus, which together cause more than 90 percent of viral gastroenteritis cases. Less common viral etiologies include adenovirus and astrovirus.
Rotavirus is most likely to cause gastroenteritis in infants and young children and can lead to significant dehydration. Infection in adults is less common and is usually without symptoms. Transmission is by the fecal-oral route, and viral shedding from stools can last up to ten days. The incubation period is about forty-eight hours.
Norovirus affects all age groups, usually in settings such as restaurants with catered meals, hospitals, nursing centers, schools, day cares, and cruise ships. Transmission is by the fecal-oral route, with an incubation period of twenty-four to forty-eight hours. Norovirus is one of the top contributors of food-borne illnesses and is highly resistant to heating and chlorine disinfectants.
Gastroenteritis due to viruses usually affects the small bowel, leading to symptoms such as large-volume watery diarrhea, abdominal cramping, bloating, and gas. Fever and bloody stools are typically absent, although a low-grade fever can occur.
Bacterial causes of gastroenteritis are commonly due to Campylobacter, Salmonella, Shigella, and E. coli. Bacterial gastroenteritis is commonly transmitted through either ingestion of improperly cooked or handled food products or person-to-person contact. Campylobacter jejuni is the most common cause of Campylobacter infections and is often found in the gastrointestinal tract of food animals. Infection is usually caused by the ingestion of contaminated poultry. Most cases of Salmonella infections are due to S. typhimurium or S. enteritidis and are typically acquired from contaminated food products such as eggs, poultry, undercooked meats, unpasteurized dairy products, seafood, and fresh produce. Shigella is most commonly transmitted via person-to-person contact and is commonly due to S. dysenteriae, S. flexneri, S. boydii, and S. sonnei. There are different strains of E. coli that cause gastroenteritis, such as hemorrhagic versus toxigenic strains, the former of which produces more severe symptoms and is usually due to ingestion of undercooked beef. Less common bacterial causes of gastroenteritis include Vibrio cholera , Yersinia enterocolitica, Clostridium difficile, Staphylococcus aureus, and Bacillus cereus.
Gastroenteritis resulting from bacteria usually affects the large intestine and produces symptoms of colitis, such as fever, small-volume bloody diarrhea, and rectal urgency. The small intestine can also be affected by certain bacteria, and the symptoms are similar to those caused by viruses.
Parasitic causes of gastroenteritis primarily include Giardia lamblia, Cyclospora, Cryptosporidium, and Entamoeba histolytica. They predominantly lead to persistent watery diarrhea (which can in turn lead to bloody diarrhea), sometimes for weeks; this is contrary to the duration of most cases of viral and bacterial gastroenteritis, which are self-limited and usually resolve in three to five days. The most common mode of transmission is ingestion of contaminated food or water.
Because most forms of gastroenteritis are self-limited, the mainstay of therapy is symptomatic treatment, focusing on rehydration and replacing important fluids and electrolytes lost through the diarrhea. Typical rehydration fluids consist of water, salt, sugar, and baking soda. During the acute illness, it is also advisable to temporarily avoid lactose products and caffeine.
Antidiarrheal agents are often used in gastroenteritis for symptomatic treatment of diarrhea. Commonly used agents include loperamide, bismuth subsalicylate, and diphenoxylate-atropine. These medications are usually used in viral gastroenteritis or in cases where bloody diarrhea or high fevers are absent, because in the latter cases the use of these agents may worsen the illness.
Antibiotics are typically not warranted unless the illness is severe, as indicated by the presence of persistent high fevers, bloody diarrhea, and frequent bowel movements. Antiparasitics are used if stool tests reveal the presence of these organisms.
Gastroenteritis is a very common illness that produces significant health issues in developing countries, where the medical care may not be adequate in cases of severe illnesses. This is especially true for malnourished infants and young children, who are more susceptible to the effects of severe dehydration. In developed countries, medical advancements have led to the production of antibiotics, antidiarrheals, and rehydration solutions. Intravenous hydration is also possible in severe cases.
Because infectious gastroenteritis is so common, it is imperative to take standard precautions to prevent transmission of the disease. This includes hand washing after handling suspected sources of infection, such as fecal content or raw meat, as well as ensuring that ingested food and water are properly cooked and processed.
The frequency of rotavirus infections in children has led to the development of a rotavirus vaccine, which was approved in 2006 by the Food and Drug Administration (FDA) and is now universally recommended for infants. A study published in 2013 in the New England Journal of Medicine showed that norovirus has become the most common cause of acute gastroenteritis in US children under five, perhaps due to the widespread use of the rotavirus vaccine. Efforts are under way to develop a norovirus vaccine as well.
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