It sounds so innocent when you call it the "stomach flu," but a norovirus infection is anything but.

The highly contagious virus spreads through schools, cruise ships, shopping malls and any other crowded space. It's responsible for most stomach bugs in the U.S., resulting in diarrhea, vomiting and cramps. Not related to the real flu at all, noroviruses are actually a group of viruses that cause 19 to 21 million cases of acute gastroenteritis in the U.S. each year, according to the Centers for Disease Control and Prevention (CDC).

Winter is prime season for the spread of noroviruses as we spend so much time indoors, passing germs back and forth. Here's what you need to know about the causes, symptoms, treatment and how to try to avoid it in the first place.

Causes of norovirus

You can get a norovirus infection from eating contaminated food or water. You can also get sick from touching contaminated surfaces and then putting your hands in your mouth. The virus is also spread by being in close contact with someone who has the virus. It can be spread by shaking hands, touching or sharing food or utensils.

When someone with the virus vomits, the virus can spread through the air and contaminate nearby surfaces. Researchers have found that noroviruses can survive on surfaces for as long as 42 days.

And it doesn't take much. About 5 billion norovirus particles can be contained in just 1 gram (about 1/4 teaspoon) of feces. Yet one study found it only takes a mere 18 norovirus particles to make a person sick.

Symptoms

Symptoms usually start 12 to 48 hours after first exposure to the virus, according to the Mayo Clinic and last one to three days.

The most common symptoms of norovirus infection are:

  • Diarrhea
  • Nausea
  • Vomiting
  • Stomach pain

Other symptoms may include fever, headache, fatigue or body aches.

Some people may have no symptoms, but they're still contagious and can spread the virus to others.

Treatment

Like all viruses, noroviruses don't respond to antibiotics, which work to fight against bacteria, points out WebMD. Instead, the best way to treat a norovirus infection is with plenty of fluids to help avoid dehydration. Your doctor may also recommend medication for diarrhea and nausea. Most people feel better within a few days.

Prevention

washing hands with soap and water Plain soap and water is one of the most effective ways to prevent norovirus infections. (Photo: hxdbzxy/Shutterstock)

There's no vaccine to prevent a norovirus infection. The best prevention is good hygiene.

Wash your hands. Lather up often with soap and water, especially after using the bathroom or changing a diaper. Wash your hands before you eat or prepare food. Hand sanitizers aren't as effective as soap and water at removing norovirus particles, says the CDC.

Wash fruits and vegetables. Carefully wash raw fruits and vegetables before eating them.

Cook seafood thoroughly. Cook oysters and other shellfish before eating them.

Clean contaminated areas carefully. Soak up any vomit and fecal material then discard in a bag. Clean the entire area with paper towels, then disinfect with a bleach-based cleaner for at least five minutes. The CDC recommends a solution of 5 to 25 tablespoons of household bleach per gallon of water. Then clean the entire area again with soap and hot water. Be sure to wear gloves.

Stay home. If you're sick or someone in your household is sick, stay home from work or school. Don't prepare or touch food for anyone in the household while you're sick or eat anything prepared by someone who was sick. Most people can return to work or school after they have been symptom-free for two to three days.

Mary Jo DiLonardo writes about everything from health to parenting — and anything that helps explain why her dog does what he does.

How to prevent and treat norovirus infections
What to do when norovirus — the stomach flu — invades your home.