RELATED STORIES • Rotavirus • Dehydration

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Yesterday, you were enjoying a plate of raw oysters at your favorite restaurant, and now you're doubled over with cramps. These symptoms could be those of viral gastroenteritis — an intestinal infection marked by watery diarrhea, abdominal cramps, nausea or vomiting and sometimes fever. Often called the stomach flu, gastroenteritis is one of the most common acute illnesses worldwide, yet it has no effective treatment. Your best defense against this illness is prevention.

You usually develop gastroenteritis because you've been in contact with someone who's already infected or because you've ingested contaminated food or water. If you're otherwise healthy, you're likely to recover without any complications, although you may feel miserable for a week or more. But for infants, older adults and people with compromised immune systems, gastroenteritis can be deadly.

There's no effective treatment for gastroenteritis, so prevention is key. In addition to avoiding food and water that may be contaminated, thorough and frequent hand washing is your best defense.

Although it's commonly called stomach flu, gastroenteritis isn't the same as influenza. Real flu (influenza) affects 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.
• Abdominal cramps and pain.
• Nausea, vomiting or both.
• Occasional muscle aches or headache.
• Low-grade fever.

Depending on the cause, signs and symptoms may appear within one to three days after you're infected and can range from mild to severe. Symptoms usually last just a day or two, but occasionally they may persist as long as 10 days.

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

You're most likely to contract viral gastroenteritis when you eat or drink contaminated food or water, or share utensils, towels or food with someone who's infected.

Some shellfish, especially raw or undercooked oysters, can make you sick. Contaminated drinking water also can cause viral diarrhea. But in many cases, the virus is passed through the fecal-oral route — that is, someone with the virus handles food you eat without washing his or her hands after using the bathroom.

A number of viruses can cause gastroenteritis, including:

• Rotavirus. This is the most common cause of infectious diarrhea in infants and children worldwide — it's also a leading cause of death among children. Every year, thousands of children are hospitalized with complications of the infection. Your child is likely to have rotavirus at least once before age 3. Children are usually infected when they put their fingers or other objects contaminated with the virus into their mouths. Even tiny amounts of rotavirus may cause a serious illness.

  People with rotavirus infection are generally contagious for about 10 days after symptoms appear but may remain contagious after symptoms disappear. Adults who are infected with rotavirus usually don't develop symptoms, but can still spread the illness. Some individuals, particularly those in institutional settings, may spread the virus but not have any symptoms of illness.

  A vaccine against rotaviral gastroenteritis is available in some countries, including the United States, and appears to be effective in preventing severe symptoms. Talk to your doctor about whether to immunize your child.

• Noroviruses. There are many different strains of noroviruses, including Norwalk virus, that all cause similar symptoms. Children and adults are most likely to be affected. Noroviruses are responsible for more than 90 percent of viral gastroenteritis outbreaks in the United States each year. Norovirus infection can sweep through families and communities, leaving everyone it infects seriously ill. It's especially likely to spread among people in confined spaces. In addition to diarrhea, nausea and vomiting, you may experience muscle aches, headache, fatigue and low-grade fever. In most cases you pick up the virus from contaminated food or water, although person-to-person transmission also is possible. After exposure to the virus, you're likely to feel sick within 18 to 72 hours. Most people feel better in a day or two, but you're still contagious for at least three days — and up to three weeks — after you've recovered.

Another serious virus
If your immune system is compromised by HIV/AIDS, you're susceptible to other gastrointestinal infections, including cytomegalovirus (CMV). Although otherwise healthy people with CMV may never develop symptoms, the virus can be extremely serious if you have HIV or AIDS. In addition to severe diarrhea, CMV may cause blurred vision or blindness, and pain, weakness or numbness in your legs.

The virus spreads through body fluids, such as saliva, blood, semen, urine and vaginal secretions. Mothers with CMV can pass the virus to their infants in their breast milk. Although you can get CMV from sexual activity, you can also get it if you simply touch infected fluids and then touch your mouth or nose. You can also acquire CMV through blood transfusions or organ transplants.

The best way to avoid infection is by using condoms and washing your hands thoroughly and often. If you expect to have a blood transfusion, talk to your doctor. Most blood banks don't screen for CMV.

Gastroenteritis occurs all over the world, affecting people of every age, race and background. In developing nations, it's the leading cause of death in children.

Children in day care centers and older adults living in nursing homes are especially vulnerable. That's because children's immune systems aren't mature until about age 6, and adult immune systems tend to become less efficient later in life.

But intestinal infections can flourish anywhere people congregate — from schools and dormitories to campgrounds and luxury cruise ships. Adults whose resistance is low — often because their immune systems are compromised by HIV, AIDS or other medical conditions — are especially at risk.

Each gastrointestinal virus has a season when it's most active. If you live in the Northern Hemisphere, you're more likely to get rotavirus or the Norwalk virus between October and April.

If you're an adult, call your doctor if:

• You're not able to keep liquids down for 24 hours.
• You've been vomiting 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 a fever above 101 F.

See your doctor right away if your child:

• Has a temperature of 102 F or higher
• Seems lethargic 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

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 vomiting lasts more than three hours or if your baby has any of the following signs and symptoms:

• Hasn't had a wet diaper in three hours
• Has bloody stools or severe diarrhea
• Has a sunken fontanel (the soft spot on the top of a baby's head)
• Has a dry mouth or cries without tears
• Is unusually sleepy, drowsy or unresponsive

Your doctor will likely diagnose gastroenteritis based on symptoms, a physical exam and sometimes on the presence of similar cases in your community. A rapid stool test can detect rotavirus, 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.

Dehydration — a severe loss of water and essential salts and minerals — is the most common serious complication of gastroenteritis. If you're a healthy adult and drink enough to replace fluids you lose from vomiting and diarrhea, dehydration shouldn't be a problem. But infants, older adults and people with suppressed immune systems may become severely dehydrated when they lose more fluids than they can replace. In that case, they may need to be hospitalized and receive intravenous fluids. In extreme cases dehydration can be fatal.

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

• Wash your hands and your children's hands thoroughly. If your children are older, teach them to wash their hands, especially after using the bathroom. It's best to use warm water and soap and to rub hands vigorously for at least 10 seconds, remembering to wash around cuticles, beneath fingernails and in the creases of the hands. Then rinse thoroughly. Carry towelettes for times when soap and water aren't available.
• Use separate personal items around your home. Avoid sharing eating utensils, glasses and plates. Use separate towels in the bathroom.
• Keep your distance. Avoid close contact with anyone who has the virus, if possible.
• Make sure child care centers have 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. To help reduce your risk:

• Drink only well-sealed bottled or carbonated water.
• Avoid ice cubes, because ice cubes 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.
• Get vaccinated. A vaccine against gastroenteritis caused by the rotavirus is available in some countries, including the United States, and appears to be effective in preventing severe symptoms of this illness.

Unfortunately, there's often no specific medical treatment for gastroenteritis. Antibiotics aren't effective against most viruses, and overusing them can contribute to the development of antibiotic-resistant strains of bacteria. To help keep yourself more comfortable and prevent dehydration while you recover, try the following:

• Let your stomach settle. Stop eating and drinking for a few hours.
• Try sucking on ice chips or taking small sips of water. You might also try drinking clear soda such as 7UP or Sprite, clear broths, or noncaffeinated sports drinks such as Gatorade. Affected adults should try to drink at least eight to 16 glasses of liquid every day, taking small, frequent sips.
• Ease back into eating. Gradually begin to eat bland, easy-to-digest foods such as soda crackers, toast, gelatin, bananas, rice and chicken. Stop eating if your nausea returns.
• Avoid certain foods and substances until you're feeling better. These include dairy products, caffeine, alcohol, nicotine, and fatty or highly seasoned foods.
• Get plenty of rest. The illness and dehydration may have made you weak and tired.
• Use medications such as ibuprofen (Advil, Motrin, others) sparingly, if at all. They can make your stomach more upset. Use acetaminophen (Tylenol, others) cautiously. It sometimes can cause liver toxicity, especially in children.

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

• Give your child an oral rehydration solution such as Pedialyte. Don't use water — in children with gastroenteritis, water isn't absorbed well and won't adequately replace lost electrolytes. You can find oral rehydration solutions in most grocery stores. Talk to your doctor if you have questions about how to use them. Avoid giving your child apple juice for rehydration — it can make diarrhea worse.
• Get back to a normal diet slowly. Gradually introduce bland, easy-to-digest foods, such as toast, rice, bananas and potatoes.
• Avoid certain foods. Don't give your child dairy products and 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.
• Don't give children or teenagers aspirin. It may cause Reye's syndrome, a rare, but potentially fatal, disease. Avoid giving your child over-the-counter anti-diarrheal medications such as Imodium unless advised by your doctor. They can make it harder for your child's body to eliminate the virus.

If you have a sick infant, let your baby's stomach rest for 30 to 60 minutes, 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. Although your baby may be dehydrated, never dilute formula.