Stomach Flu: All You Need To Know (2024)

What are stomach flu symptoms?

The most common stomach flu symptoms are:

  • Diarrhea.
  • Nausea and vomiting.
  • Loss of appetite.
  • Abdominal pain and cramping.

These symptoms come from inflammation in your stomach and intestines. (Although the name, gastroenteritis, refers to your stomach and small intestine, inflammation can spread to your large intestine, too). Inflammation is your immune system activating to fight the virus.

If your infection is more severe, or if your immune system reacts more strongly to it, you may have what are known as systemic symptoms. These symptoms come from inflammation in other body systems outside of your digestive system. This is the next level of immune response to the virus.

Systemic symptoms may include:

  • Fever.
  • Chills.
  • Fatigue.
  • Body aches.
  • Headaches.
  • Swollen lymph nodes.

What does the beginning of stomach flu feel like?

For many people, stomach flu symptoms seem to come on suddenly and out of nowhere. You might throw up or have diarrhea many times on that first day. Symptoms occur one to two days after you were exposed to the virus. Fortunately, they’re usually over just as quickly, resolving in one to two days.

What are the stages of stomach flu?

The stages of stomach flu infection are:

  1. Exposure. You’re most likely to get the stomach flu from someone in your community, especially in a closed environment like a school, nursing home or cruise ship. Since symptoms take some time to develop, you might hear about an outbreak later, after you were exposed.
  2. Incubation. Once you’ve contracted the virus, it’ll begin replicating inside your body. This is the incubation period. You won’t have symptoms until the virus replicates enough to alert your immune system. This usually takes a few days, depending on the virus.
  3. Acute infection. Viral gastroenteritis is an acute infection, which means it’s sudden and temporary. When your immune system registers the threat, it activates an inflammatory response to clear the virus. This is what causes symptoms of illness. When it succeeds, the symptoms will stop.
  4. Recovery. You’ll notice your symptoms lessening when your immune system has won the battle against the virus. Eventually, your symptoms will stop, and you’ll feel better. But you may continue to shed the virus in your poop (stool) for a few days, which means you’re still contagious.

How long does stomach flu last?

Stomach flu usually only lasts a few days, but it may last up to a week or two in severe cases. People with weaker immune systems may have a harder time defeating the virus, and it may take longer.

Is stomach flu contagious?

Yes, it’s very contagious. You should limit your contact with others when you have it. If you live with others, make sure to wash your hands often and disinfect shared surfaces, especially in the bathroom.

How long is the stomach flu contagious?

You’re most contagious during the acute phase of the infection (when you have symptoms) and for a few days after. However, you may still be a little contagious for up to two weeks after recovering.

What causes stomach flu?

Many different viruses can infect your gastrointestinal system, causing gastroenteritis.

The most common ones are:

  • Norovirus. This is the leading cause of stomach flu in adults, estimated to account for 50% of cases worldwide. It’s more resistant than others to temperature and disinfectants.
  • Rotavirus. Rotavirus is the leading cause of stomach flu in children worldwide. Most get it before age 3, which is why most adults are immune. There’s now a vaccine.
  • Astrovirus. Astroviruses mostly affect children younger than 3. They commonly spread through daycare centers. But they can also spread through elder care homes.
  • Adenovirus. Adenoviruses more often cause respiratory infections, but they can cause gastrointestinal infections if you accidentally ingest them. They infect all ages.


How does stomach flu spread?

Stomach flu usually spreads by the “fecal-to-oral route”. The virus lives in the poop — and vomit — of infected people. Microscopic traces of infected poop or vomit may linger on people’s hands or surfaces. These traces can transfer to food and water sources. You might ingest the virus through contaminated food or water, or by touching an infected person or surface and then touching your mouth.

Who gets stomach flu?

Anyone can get stomach flu, but certain people are more vulnerable. If you have a weaker-than-average immune system, you might be more likely to get an infection or get a more severe infection.

You might have a weaker immune system if you have a chronic disease that affects immunity or take immunosuppressant medications. Infants and elderly people are also more susceptible to infections.

What are the possible complications of stomach flu?

For most people, stomach flu is uncomplicated and self-limited. It goes away shortly by itself. But those with weaker immune systems may have a more severe infection and be more likely to experience complications.

The most likely complication is dehydration. This happens when you lose too many fluids and electrolytes from diarrhea or vomiting, and you can’t drink enough or drink fast enough to replace them.

People with weaker immune systems (especially children) are more likely to become dehydrated, and it can be especially dangerous for them. Stay alert for signs of dehydration, such as:

  • Thirst.
  • Lack of urine (pee) or dark-colored urine.
  • Lack of poop or hard, dry poop.
  • Weakness or malaise.
  • Sunken eyes.
  • Crying without tears.
  • Dehydration headache.
  • Dry lips and tongue.
Stomach Flu: All You Need To Know (2024)
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