Technically called viral gastroenteritis, the stomach flu can cause some pretty unpleasant symptoms.

By Amanda Gardner
December 07, 2018
Credit: Getty: MarsBars

It’s flu season again. And by that we mean not just the nasty flu that bothers your respiratory system, but also the “flu” that rumbles your tummy. Technically, the "stomach flu" is not actually influenza, which is caused by a virus that only affects your airways. So-called stomach flu symptoms show up in your gastrointestinal system.

“The 'stomach flu’ is a viral illness that affects the gastrointestinal tract, more accurately referred to as 'viral gastroenteritis,’” says Elena Ivanina, DO, MPH, a gastroenterologist at Lenox Hill Hospital in New York City. "It is not the same as the ‘flu' that we all get vaccinated for each year, which is the influenza virus and only affects the nose, throat, and lungs.”

Instead, the stomach flu is caused by other viruses, namely norovirus, as well as rotavirus, adenovirus, and astrovirus. You get the bug from someone who is sick—say by touching something they touched and then touching your mouth or nose or by sharing their germy utensil. Stomach flu viruses can also be spread through contaminated water or food, in which case you’d probably call the resulting symptoms food poisoning. 

Stomach flu symptoms

Symptoms of the stomach flu usually show up one to three days after you’re infected. Some cases are mild, lasting 24 or 48 hours, although some can linger for up to 10 days.

Watery diarrhea is one of the first signs of the stomach flu. This is because the infection prevents your large intestine from retaining fluid. Instead, all that liquid flushes out in the form of loose, watery poop. “It’s typically three or more times a day and sometimes a large volume,” says Sean Drake, MD, a general internist with Henry Ford Health System in Sterling Heights, Michigan.

The watery stool usually doesn't smell and isn't bloody, says Roopa Vemulapalli, MD, associate professor of internal medicine and a digestive diseases expert at UT Southwestern in Dallas. “If you see blood, that’s definitely much more of a problem,” she says–and a sign you should head to the emergency room. People with weakened immune systems or who were taking antibiotics before getting ill may have worse stomach flu symptoms, Dr. Vemulapalli adds.

If you have the stomach flu, watery diarrhea will be accompanied by nausea and vomiting about 70 to 80% of the time, although it’s possible “just one end or the other” will be affected, Dr. Drake says. And while you no doubt want these unpleasant symptoms to go away right now, they’re actually a good sign: Your body is trying to get rid of the bad stuff.

Not surprisingly, with your body furiously flushing fluids and more out of your system, chances are you’ll feel pretty weak. Abdominal cramps or abdominal pain are also common as “the gastrointestinal system trys to push the toxins out,” says Dr. Vemulapalli.

But the main danger from the stomach flu is dehydration. Signs of dehydration include feeling very thirsty, having a dry mouth, not urinating very often, and, when you do urinate, producing dark yellow pee. Dehydration may even make your skin bounce back more slowly when you press it. You can also feel dizzy, lightheaded, or confused if you’re dehydrated.

“It’s very important to maintain fluid status and replace fluids,” Dr. Vemulapalli says. “Patients do feel better [when hydrated].” Stick to water and clear liquids like chicken broth and juice.

You may also have a low-grade fever, which is usually nothing to worry about–but a higher one might be. A fever higher than 102 may be a sign dehydration is becoming severe, Dr. Drake says. (It’s also more common with actual influenza.)

Stomach flu treatment

If the symptoms above sound familiar, you might be wondering what to do about your case of the stomach flu. As far as treatment goes, you usually just need to let the stomach flu run its course (although antibiotics may help with bacterial stomach flu) and keep up with the extra fluids.

Usually, you don’t even need over-the-counter remedies. “Most patients shouldn’t take anti-motility drugs [like Imodium],” says Dr. Drake, since stomach flu typically gets better on its own. Viral infections usually come and go quickly: Norovirus generally lasts about two days while rotavirus symptom can linger for up to eight, says Dr. Vemulapalli. If your symptoms are severe or prolonged, then it’s time for meds, Dr. Drake says.

If you have a high fever, see blood in your stool, are losing a lot of weight, have severe abdominal pain, or can’t keep anything down for two days, go to the emergency room. That’s especially true if you’re in a high-risk group. “We’re a little more concerned with older patients because they’re more prone to getting dehydrated quickly,” Dr. Drake says.

While kids can get vaccinated against rotavirus, your best bet at preventing stomach flu is the tried-and-true: Wash your hands (with soap and water or alcohol-based sanitizers), disinfect any surfaces that might be contaminated, and avoid people who are sick as much as possible.