Here's what experts want you to know when stomach flu symptoms strike.

By Arielle Tschinkel
December 20, 2019
Getty Images/Moyo Studio

The stomach flu is one of those ailments that comes on hard and fast. One minute you feel fine, and the next you're battling tell-tale stomach flu symptoms like nausea and belly pain that have you running to the bathroom in a panic every few minutes. If you've ever battled these digestive troubles, you know that they can make you feel straight-up miserable—just like when you have the regular flu.

But even though the flu and the stomach flu are typically caused by viral infections, the two conditions actually have nothing to do with each other, says board-certified gastroenterologist Samantha Nazareth, M.D. The stomach flu is usually caused by one of three viruses: norovirus, rotavirus, or adenovirus. (Occasionally the stomach flu is the result of a bacterial infection instead of a virus—more on all of those causes in a bit.) Influenza, on the other hand, is typically caused by a different set of viruses that affect the respiratory system, including the nose, throat, and lungs, explains Dr. Nazareth.

Here's everything you need to know about the stomach flu, including what causes it, how it's diagnosed, how long it lasts, and how it's treated, so you can get back to feeling better ASAP. (In the meantime, keep an eye out for these super germy spots in the gym that might make you sick.)

What Is the Stomach Flu, and What Causes It?

The stomach flu (technically known as gastroenteritis) is a condition caused by a bacteria or virus that leads to inflammation in the digestive tract, says Carolyn Newberry, M.D., a gastroenterologist at NewYork-Presbyterian and Weill Cornell Medicine. "Gastroenteritis refers to the generalized inflammation that occurs with this condition," she adds.

Gastroenteritis is usually the result of one of three different viruses, all of which are "highly contagious," says Dr. Nazareth (hence why the stomach flu travels like wildfire in places like schools or offices). First, there's norovirus, which typically spreads via contaminated food or water but can also be transmitted through contact with an infected person or surface, she explains. "This one is the most common across all ages in the U.S.," adds Dr. Nazareth, noting that it's "a common virus you hear about on cruise ships." (Related: How Quickly Can You Really Catch an Illness On an Airplane—and How Much Should You Worry?)

There's also rotavirus, which is most commonly found in children and young adults and causes severe, watery diarrhea and vomiting, says Dr. Nazareth. Fortunately, this particular virus is largely prevented through the rotavirus vaccine (typically given in either two or three doses, around ages 2-6 months, according to the Centers for Disease Control and Prevention, CDC).

The least common cause of the stomach flu is adenovirus, says Dr. Nazareth. More on that one in a bit. (Related: Should I Be Worried About Adenovirus?)

When the stomach flu isn't caused by a virus, that means a bacterial infection is likely to blame, explains Dr. Newberry. Much like viruses, bacterial infections can also cause inflammation in the gastrointestinal tract and leave you with digestive troubles. "Bacterial infections should be investigated in people who are not getting better after a few days with the [stomach flu]," says Dr. Newberry.

Stomach Flu Symptoms

Regardless of the cause, hallmark stomach flu symptoms include diarrhea, nausea, vomiting, and stomach ache. Both Dr. Nazareth and Dr. Newberry say these signs usually show up within a day or two of exposure to a bacteria or virus. In fact, Dr. Newberry notes that in some cases, stomach flu symptoms can begin as soon as a couple of hours after exposure to the virus or bacteria, particularly if you were in contact with an infected person (as opposed to an infected surface or food).

"Symptoms of norovirus and rotavirus are similar (diarrhea, vomiting, belly pain, nausea) and treatment is the same: avoid dehydration," adds Dr. Nazareth. As for adenovirus, even though you're less likely to catch it, the virus has a much wider range of symptoms. In addition to the usual stomach flu symptoms of diarrhea, vomiting, stomach pain, and nausea, adenovirus can also cause bronchitis, pneumonia, and sore throat, she explains.

The good news: Stomach flu symptoms, whether they're the result of a virus or bacterial infection, usually aren't a major cause for concern, says Dr. Nazareth. "The viruses are usually self-limiting, meaning a person can fight them with time if their immune system is healthy and not compromised (by other diseases or medications)," she explains.

However, there are some "red flag" stomach flu symptoms to note. "Blood is definitely a red flag, from either end," says Dr. Nazareth. If you're vomiting blood or have bloody diarrhea, she recommends seeking medical treatment ASAP before your stomach flu symptoms worsen. (Related: 7 Foods to Ease an Upset Stomach)

If you have a high fever (above 100.4 degrees Fahrenheit), that's also a sign to seek immediate treatment, notes Dr. Nazareth. "The biggest thing that sends people to urgent care or an ER is the inability to keep any liquids down, which leads to dehydration, as well as symptoms like dizziness, weakness, and lightheadedness," she explains.

Wondering how long the stomach flu lasts? Overall, the symptoms usually stick around for just a couple of days, though it's not uncommon for them to linger for up to a week, says Dr. Nazareth. Again, if stomach flu symptoms aren't resolving on their own after about a week, both experts suggest speaking to your doctor immediately to find out if you have a bacterial infection, which might require antibiotic treatment.

How Is the Stomach Flu Diagnosed and Treated?

If you want to confirm that what you're battling is, in fact, gastroenteritis, your primary care doctor can usually diagnose you based on stomach flu symptoms alone (including an abrupt onset of nausea, vomiting, diarrhea, and sometimes fever), says Dr. Newberry. "There are [also] tests that can be performed on the stool that can identify specific types of infections that cause this condition (including bacteria and viruses)," she adds. (Related: The No. 1 Reason to Check Your No. 2)

While your body can typically fight off a virus on its own with time, rest, and plenty of fluids, bacterial infections tend to play out a little differently, says Dr. Newberry. The main difference is that bacterial infections simply can't go away on their own, meaning your doctor will likely prescribe antibiotics, says Dr. Newberry. To be clear, antibiotics won't work in the case of a viral infection; they'll only help with a bacterial one, she notes.

Generally, otherwise healthy adults will be able to fight the stomach flu through ample rest and "fluids, fluids, and more fluids," says Dr. Nazareth. "Some people do need to go to the ER to get intravenous (IV) fluids because they simply are unable to keep any liquids down. Those who already have an affected immune system (such as if you're taking medications to suppress the immune system for other conditions) need to see a doctor as they may become severely ill." (Related: 4 Tips to Dodge Dehydration This Winter)

In addition to loading up on liquids, both Dr. Nazareth and Dr. Newberry recommend replacing lost electrolytes by drinking Gatorade. Pedialyte can also be used to combat dehydration, adds Dr. Newberry. "Ginger is another natural remedy for nausea. Imodium can also be used to manage diarrhea," she suggests. (Related: Your Complete Guide to Sports Drinks)

Once you feel well enough to eat, Dr. Nazareth recommends starting with bland foods—things like bananas, rice, bread, skinless/baked chicken. (Here are some other foods to eat when you're battling the stomach flu.)

If your stomach flu symptoms last beyond a week, or if your condition worsens, both experts say it's important to see your doctor ASAP to ensure that you're properly hydrated and that there aren't other underlying health issues at play.

How Long Is the Stomach Flu Contagious?

Unfortunately, the stomach flu is extremely contagious and remains that way until symptoms are resolved. "Usually it's passed by coming in contact with contaminated bodily fluids, including vomit and poop," says Dr. Nazareth. "Contaminated vomit can aerosolize [disperse through the air] and enter someone's mouth."

You can also get the stomach flu from contaminated water or even shellfish, adds Dr. Nazareth. These sea critters are "filter feeders", meaning they feed themselves by filtering seawater through their bodies, according to the Washington State Department of Health. So, if stomach flu-causing particles happen to be floating in that seawater, shellfish can collect and carry those particles all the way from the ocean to your plate.

"[Stomach flu] can also be passed by sharing food and utensils with someone who is infected," explains Dr. Nazareth. "Even if you touch a surface with the virus or your food hits a surface with infected poop or vomit particles, you can become infected."

If you come down with the stomach flu, you'll definitely want to stay home until your symptoms are fully resolved (i.e. a couple of days or, at most, a week) to avoid passing it to others, explains Dr. Nazareth. "Do not prepare food for others, and keep sick children away from where food is being handled," she adds. "Carefully wash veggies and fruits, and take care with leafy greens and raw oysters, which are commonly associated with these outbreaks."

You'll also want to be on top of your general hygiene habits when you have the stomach flu: Wash your hands frequently, keep your distance from others when possible, and try not to share personal items with others until your stomach flu symptoms are gone, says Dr. Newberry. (Related: 6 Ways to Clean Your Place Like a Germ Expert)

Stomach Flu Prevention

Considering the stomach flu is highly contagious, it might seem impossible to avoid catching it at some point. But rest assured, there are preventative measures you can take to help reduce your risk of catching the stomach flu.

"Eating a proper diet, getting plenty of rest, and staying hydrated are general ways to protect yourself from developing infections," suggests Dr. Newberry. "Additionally, washing your hands before meals or after exposure to public places (including restrooms, public transportation, etc.) can help you avoid the spread of pathogens that can cause illness."

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