Although it's commonly called stomach flu, gastroenteritis isn't the same as influenza. The flu (influenza) affects only your respiratory system — your nose, throat and lungs. Gastroenteritis, on the other hand, attacks your intestines, causing signs and symptoms such as:

• Watery, usually nonbloody diarrhea — bloody diarrhea usually means you have a different, more severe infection
• Nausea, vomiting or both
• Stomach cramps and pain
• Occasional muscle aches or headache
• Low-grade fever

Depending on the cause, viral gastroenteritis symptoms may appear within 1-3 days after you're infected and can range from mild to severe. Symptoms usually last just a day or two, but occasionally they may last up to 14 days.

Because the symptoms are similar, it's easy to confuse viral diarrhea with diarrhea caused by bacteria, such as Clostridioides difficile, salmonella and Escherichia coli, or parasites, such as giardia.

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.

Your doctor will likely diagnose viral gastroenteritis (stomach flu) based on symptoms, a physical exam and sometimes on the presence of similar cases in your community. A rapid stool test can detect rotavirus or norovirus, but there are no quick tests for other viruses that cause gastroenteritis. In some cases, your doctor may have you submit a stool sample to rule out a possible bacterial or parasitic infection.

There's often no specific medical treatment for viral gastroenteritis. Antibiotics aren't effective against viruses. Treatment first involves self-care measures, such as staying hydrated.

To help keep yourself more comfortable and prevent dehydration while you recover, try the following:

• Let your stomach settle. Stop eating solid foods for a few hours.
• Try sucking on ice chips or taking small sips of water often. You might also try drinking clear soda, clear broths or noncaffeinated sports drinks. In some cases you can try oral rehydration solutions. Drink plenty of liquid every day, taking small, frequent sips.
• Ease back into eating. As you're able, you can return to eating your normal diet. You might find that you can eat bland, easy-to-digest foods at first, such as soda crackers, soup, oats, noodles, bananas and rice. Stop eating if your nausea returns.
• Avoid certain foods and substances until you feel better. These include caffeine, alcohol, nicotine, and fatty or highly seasoned foods.
• Get plenty of rest. The illness and dehydration may have made you weak and tired.
• Try anti-diarrhea medications. Some adults may find it helpful to take loperamide (Imodium A-D) or bismuth subsalicylate (Pepto-Bismol, others) to manage their symptoms. However, avoid these if you have bloody diarrhea or fever, which could be signs of another condition.

For infants and children

When your child has an intestinal infection, the most important goal is to replace lost fluids and salts. These suggestions may help:

• Help your child rehydrate. Give your child an oral rehydration solution, available at pharmacies without a prescription. Talk to your doctor if you have questions about how to use it.

  Don't give your child plain water — in children with gastroenteritis, water isn't absorbed well and won't adequately replace lost electrolytes. Avoid giving your child apple juice for rehydration — it can make diarrhea worse.

• Get your child back to a normal diet once hydrated. Once your child is rehydrated, introduce him or her to his or her normal diet. This might include toast, yogurt, fruits and vegetables.
• Avoid certain foods. Don't give your child sugary foods, such as ice cream, sodas and candy. These can make diarrhea worse.
• Make sure your child gets plenty of rest. The illness and dehydration may have made your child weak and tired.
• Avoid giving your child store-bought anti-diarrheal medications, unless advised by your doctor. They can make it harder for your child's body to get rid of the virus.

If you have a sick infant, let your baby's stomach rest for 15-20 minutes after vomiting or a bout of diarrhea, then offer small amounts of liquid. If you're breast-feeding, let your baby nurse. If your baby is bottle-fed, offer a small amount of an oral rehydration solution or regular formula. Don't dilute your baby's already-prepared formula.

If you or your child needs to see a doctor, you'll likely see your doctor first. If there are questions about the diagnosis, your doctor may refer you to an infectious disease specialist.

What you can do

Preparing a list of questions will help you make the most of your time with your doctor. Some questions you might want to ask your or your child's doctor include:

• What's the likely cause of the symptoms? Are there other possible causes?
• Is there a need for tests?
• What's the best treatment approach? Are there any alternatives?
• Is there a need to take medicine?
• What can I do at home to ease the symptoms?

What to expect from your doctor

Some questions the doctor may ask include:

• When did symptoms begin?
• Have the symptoms been continuous, or do they come and go?
• How severe are the symptoms?
• What, if anything, seems to improve symptoms?
• What, if anything, appears to worsen symptoms?
• Have you been in contact with anyone with similar symptoms?

What you can do in the meantime

Drink plenty of fluids. As you're able, you can return to eating your normal diet. You might find you can eat bland, easy-to-digest foods at first. If your child is sick, follow the same approach — offer plenty of fluids. When possible, start having your child eat his or her normal diet. If you're breastfeeding or using formula, continue to feed your child as usual. Ask your child's doctor if giving your child an oral rehydration solution, available without a prescription at pharmacies, would help.