Viral gastroenteritis (stomach flu)

Viral gastroenteritis is an intestinal infection that includes signs and symptoms such as watery diarrhea, stomach cramps, nausea or vomiting, and sometimes fever.

The most common way to develop viral gastroenteritis — often called stomach flu — is through contact with an infected person or by consuming contaminated food or water. If you're otherwise healthy, you'll likely recover without complications. But for infants, older adults and people with compromised immune systems, viral gastroenteritis can be deadly.

There's no effective treatment for viral gastroenteritis, so prevention is key. Avoid food and water that may be contaminated and wash your hands thoroughly and often.

If you're an adult, call your health care provider if:

• You're not able to keep liquids down for 24 hours
• You've been vomiting or having diarrhea for more than two days
• You're vomiting blood
• You're dehydrated — signs of dehydration include excessive thirst, dry mouth, deep yellow urine or little or no urine, and severe weakness, dizziness or lightheadedness
• You notice blood in your bowel movements
• You have severe stomach pain
• You have a fever above 104 F (40 C)

For infants and children

See your child's health care provider right away if your child:

• Has a fever of 102 F (38.9 C) or higher
• Seems tired or very irritable
• Is in a lot of discomfort or pain
• Has bloody diarrhea
• Seems dehydrated — watch for signs of dehydration in sick infants and children by comparing how much they drink and urinate with how much is normal for them, and watching for signs such as a dry mouth, thirst and crying without tears

If you have an infant, remember that while spitting up may be an everyday occurrence for your baby, vomiting is not. Babies vomit for a variety of reasons, many of which may require medical attention.

Call your baby's doctor right away if your baby:

• Has vomiting that is frequent
• Hasn't had a wet diaper in six hours
• Has bloody stools or severe diarrhea
• Has a sunken soft spot (fontanel) on the top of his or her head
• Has a dry mouth or cries without tears
• Is unusually sleepy, drowsy or unresponsive

You're most likely to get viral gastroenteritis when you eat or drink contaminated food or water. You may also be likely to get gastroenteritis if you share utensils, towels or food with someone who has one of the viruses that cause the condition.

Many viruses can cause gastroenteritis, including:

• Noroviruses. Both children and adults are affected by noroviruses, the most common cause of foodborne illness worldwide. Norovirus infection can sweep through families and communities. It's especially likely to spread among people in confined spaces.

  In most cases, you pick up the virus from contaminated food or water. But it can also spread between people who are in close contact or who share food. You can also get the virus by touching a surface that's been contaminated with norovirus and then touching your mouth.

• Rotavirus. Worldwide, this is the most common cause of viral gastroenteritis in children, who are usually infected when they put their fingers or other objects contaminated with the virus into their mouths. It can also spread through contaminated food. The infection is most severe in infants and young children.

  Adults infected with rotavirus may not have symptoms, but can still spread the illness. This is of particular concern in institutional settings such as nursing homes because adults with the virus unknowingly can pass the virus to others. A vaccine against viral gastroenteritis is available in some countries, including the United States, and appears to be effective in preventing the infection.

Some shellfish, especially raw or undercooked oysters, also can make you sick. Contaminated drinking water is a cause of viral diarrhea. But in many cases the virus is passed when someone with a virus handles food you eat without washing his or her hands after using the toilet.

Gastroenteritis occurs all over the world and can affect people of all ages.

People who may be more susceptible to gastroenteritis include:

• Young children. Children in child care centers or elementary schools may be especially vulnerable because it takes time for a child's immune system to mature.
• Older adults. Adult immune systems tend to become less efficient later in life. Older adults in nursing homes are vulnerable because their immune systems weaken. They also live in close contact with others who may pass along germs.
• Schoolchildren or dormitory residents. Anywhere that groups of people come together in close quarters can be an environment for an intestinal infection to get passed.
• Anyone with a weakened immune system. If your resistance to infection is low — for instance, if your immune system is compromised by HIV/AIDS, chemotherapy or another medical condition — you may be especially at risk.

Each gastrointestinal virus has a season when it's most active. If you live in the Northern Hemisphere, for instance, you're more likely to have rotavirus or norovirus infections in the winter and spring.

The main complication of viral gastroenteritis is dehydration — a severe loss of water and essential salts and minerals. If you're healthy and drink enough to replace fluids you lose from vomiting and diarrhea, dehydration shouldn't be a problem.

Infants, older adults and people with weakened immune systems may become severely dehydrated when they lose more fluids than they can replace. Hospitalization might be needed so that lost fluids can be replaced through an IV in their arms. Dehydration can rarely lead to death.

The best way to prevent the spread of intestinal infections is to follow these precautions:

• Get your child vaccinated. A vaccine against gastroenteritis caused by the rotavirus is available in some countries, including the United States. Given to children in the first year of life, the vaccine appears to be effective in preventing severe symptoms of this illness.

• Wash your hands thoroughly. And make sure your children do, too. If your children are older, teach them to wash their hands, especially after using the toilet.

  Wash your hands after changing diapers and before preparing or eating food, too. It's best to use warm water and soap and to rub hands well for at least 20 seconds. Wash around cuticles, beneath fingernails and in the creases of the hands. Then rinse thoroughly. Carry sanitizing wipes and hand sanitizer for times when soap and water aren't available.

• Use separate personal items around your home. Avoid sharing eating utensils, drinking glasses and plates. Use separate towels in the bathroom.
• Prepare food safely. Wash all your fruits and vegetables before eating them. Clean kitchen surfaces before preparing food on them. Avoid preparing food if you're sick.
• Keep your distance. Avoid close contact with anyone who has the virus, if possible.
• Disinfect hard surfaces. If someone in your home has viral gastroenteritis, disinfect hard surfaces, such as counters, faucets and doorknobs, with a mixture of 5-25 tablespoons (73 to 369 milliliters) of household bleach to 1 gallon (3.8 liters) of water.
• Avoid touching laundry that may have been exposed to a virus. If someone in your home has viral gastroenteritis, wear gloves while touching laundry. Wash clothing and bedding in hot water and dry them on the hottest setting. Wash your hands well after touching laundry.
• Check out your child care center. Make sure the center has separate rooms for changing diapers and preparing or serving food. The room with the diaper-changing table should have a sink as well as a sanitary way to dispose of diapers.

Take precautions when traveling

When you're traveling in other countries, you can become sick from contaminated food or water. You may be able to reduce your risk by following these tips:

• Drink only well-sealed bottled or carbonated water.
• Avoid ice cubes because they may be made from contaminated water.
• Use bottled water to brush your teeth.
• Avoid raw food — including peeled fruits, raw vegetables and salads — that has been touched by human hands.
• Avoid undercooked meat and fish.