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Gastroenteritis or the stomach flu

What is Gastroenteritis?

Viral gastroenteritis is an intestinal infection caused by several viruses. Viral gastroenteritis is highly contagious and causes millions of cases of diarrhea each year.

Anyone can get viral gastroenteritis. Most people recover from gastroenteritis without any complications. However, viral gastroenteritis can be serious for people who cannot drink enough fluids to replace what is lost through vomiting and diarrhea, especially infants, young children, the elderly, and people with weak immune systems. Complications from vomiting also can occur, even in healthy people.

Symptoms of Gastroenteritis

The main symptoms of viral gastroenteritis are watery diarrhea and vomiting. Other symptoms of gastroenteritis include headache, fever, chills, and abdominal pain. The symptoms may appear within hours or a few days of infection. They usually last for 1 to 2 days, but may last as long as 10 days.

Causes of Gastroenteritis

The viruses that cause viral gastroenteritis damage the cells in the lining of the small intestine. As a result, fluids leak from the cells into the intestine and produce watery diarrhea. Four types of viruses cause most viral gastroenteritis.

  • Rotavirus is the leading cause of gastroenteritis among children 3 to 15 months old. Most children have been exposed to the virus by age 2. Children with rotavirus have vomiting and watery diarrhea for 3 to 8 days, along with fever and abdominal pain. Rotavirus can also infect adults who are in close contact with infected children, but the symptoms in adults are milder. Symptoms of rotavirus infection appear 1 to 2 days after exposure. In the United States, rotavirus infections are most common from November to April.
  • Adenovirus serotypes 40 and 41 cause gastroenteritis mainly in children younger than 2 years old. Infections occur all year round; vomiting and diarrhea appear approximately 1 week after exposure.
  • Caliciviruses cause infection in persons of all ages. This family of viruses is further divided into the noroviruses (example, Norwalk virus) and the sapoviruses (example, Sapporo virus). Caliciviruses are transmitted from person to person and also through contaminated water or food--especially oysters from contaminated waters. The noroviruses are often responsible for epidemics of viral gastroenteritis. In addition to vomiting and diarrhea, people infected with caliciviruses may have muscle aches. The symptoms appear within 1 to 3 days of exposure.
  • Astrovirus also infects primarily infants, young children, and the elderly. This virus is most active during the winter months. Vomiting and diarrhea appear within 1 to 3 days of exposure.

Viral gastroenteritis is often mistakenly called "stomach flu," but it is not caused by the influenza virus and it does not infect the stomach.

Transmission of Gastroenteritis

Viral gastroenteritis is highly contagious. The viruses are often transmitted on unwashed hands. People can get the viruses through close contact with infected individuals, such as sharing their food, drink, or eating utensils, or by eating food or drinking beverages that are contaminated with the virus. People who no longer have symptoms may still be contagious, since the virus can be found in the stool for up to 2 weeks after they recover from their illness. Also, people can become infected without having symptoms, and they can still spread the infection.

Outbreaks of viral gastroenteritis can occur in child care settings, schools, nursing homes, cruise ships, camps, dormitories, restaurants, and other places where people gather in groups. If you suspect that you were exposed to a virus in one of these settings, you may want to contact your local health department, which tracks outbreaks.

Diagnosis of Gastroenteritis

If you think you have viral gastroenteritis, you may want to see your doctor, although many people don't bother. Doctors generally diagnose viral gastroenteritis based on the symptoms and a physical examination. Your doctor may ask for a stool sample to test for rotavirus or to rule out bacteria or parasites as the cause of your symptoms. No routine tests are currently available for the other types of viruses.

Treatment of Gastroenteritis

Most cases of viral gastroenteritis resolve over time without specific treatment. Antibiotics are not effective against viral infections. The primary goal of treated gastroenteritis is to reduce the symptoms. Prompt treatment may be needed to prevent dehydration.

Your body needs fluids to function. Dehydration is the loss of fluids from the body. Important salts or minerals, known as electrolytes, can also be lost with the fluids. Dehydration can be caused by diarrhea, vomiting, excessive urination, or excessive sweating, or by not drinking enough fluids because of nausea, difficulty swallowing, or loss of appetite.

In viral gastroenteritis, the combination of diarrhea and vomiting can cause dehydration. The symptoms of dehydration are

  • excessive thirst
  • dry mouth
  • little or no urine or dark yellow urine
  • decreased tears
  • severe weakness or lethargy
  • dizziness or lightheadedness

If you notice any of these symptoms, you should talk to your doctor. Mild dehydration can be treated by drinking liquids. Severe dehydration may require intravenous fluids and hospitalization. Untreated severe dehydration can be life threatening.

Children present special concerns. Because of their smaller body size, infants and children are at greater risk of dehydration from diarrhea and vomiting. Oral rehydration solutions such as Pedialyte can replace lost fluids, minerals, and salts.

You can take several steps to help relieve the symptoms of viral gastroenteritis.

  • Allow your gastrointestinal tract to settle by not eating for a few hours.
  • Sip small amounts of clear liquids or suck on ice chips if vomiting is still a problem.
  • Give infants and children oral rehydration solutions to replace fluids and lost electrolytes.
  • Gradually reintroduce food, starting with bland, easy-to-digest food, like toast, broth, apples, bananas, and rice.
  • Avoid dairy products, caffeine, and alcohol until recovery is complete.
  • Get plenty of rest.

Prevention of Gastroenteritis

Prevention is the only way to avoid viral gastroenteritis. There is no vaccine available. You can avoid viral gastroenteritis by:

  • washing your hands thoroughly after using the bathroom or changing diapers
  • washing your hands thoroughly before eating
  • disinfecting contaminated surfaces
  • not eating or drinking foods or liquids that might be contaminated

Points to Remember

  • Viral gastroenteritis is a highly contagious infection of the intestines caused by one of several viruses.
  • Although it is sometimes called "stomach flu," viral gastroenteritis is not caused by the influenza virus and does not affect the stomach.
  • The main symptoms of viral gastroenteritis are watery diarrhea and vomiting.
  • Anyone can get viral gastroenteritis through unwashed hands, close contact with an infected person, or food and beverages that contain the virus.
  • Diagnosis is based on the symptoms and a physical examination. Currently only rotavirus can be rapidly detected in a stool test.
  • Viral gastroenteritis has no specific treatment; antibiotics are not effective against viruses. Treatment focuses on reducing the symptoms and preventing dehydration.
  • The symptoms of dehydration are excessive thirst, dry mouth, dark yellow urine or little or no urine, decreased tears, severe weakness or lethargy, and dizzinessor lightheadedness.
  • Infants, young children, the elderly, and people with weak immune systems have a higher risk of developing dehydration due to vomiting and diarrhea.
  • People with viral gastroenteritis should rest, drink clear liquids, and eat easy-to-digest foods.
  • For infants and young children, oral rehydration solutions can replace lost fluids, minerals, and salts.
  • Avoid viral gastroenteritis by washing hands thoroughly after using the bathroom or changing diapers, disinfecting contaminated surfaces, and avoiding foods or liquids that might be contaminated.

Reprinted from NIH Publication No. 03-5103. This article was originally printed in the April 2003.

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