Stomach flu, viral gastroenteritis, is a viral infection in your digestive system. It causes gastrointestinal symptoms like vomiting and diarrhea. It’s usually brief, but can be very contagious.
Stomach flu is a viral infection that affects your stomach and intestines. The medical term is viral gastroenteritis. “Gastro” means stomach and “enter” means small intestine. “Itis” means inflammation, which is usually due to an infection. And “viral” means that a virus has caused the infection.
Stomach flu causes gastrointestinal (GI) symptoms like diarrhea, abdominal cramps and nausea. You might also call it a “stomach bug.” A stomach bug isn’t always a virus — sometimes it’s bacteria or a parasite — but in any case, the symptoms are similar. You might not be able to tell if your bug is a virus or not.
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Stomach flu isn’t related to “the flu” (influenza), which is a viral infection in your respiratory system. Different viruses cause the two conditions, and they affect different body systems. It’s not clear how the nickname “stomach flu” developed or why it’s been associated with influenza, but we can speculate.
Both are common viral infections that circulate during the same “flu season,” so people might use “flu” to simply mean, “I’m sick”. “Stomach flu” might be a way of saying, “I’m sick, and it’s the stomach one”. Even though a stomach bug isn’t always a virus, it’s likely to be, so “stomach flu” is a good guess.
Viral gastroenteritis is extremely common worldwide, but it’s hard to estimate exactly how many people get it each year. Many different viruses cause it, and most people don’t get clinically tested for it. Experts estimate that norovirus, the most common cause, infects 685 million people every year.
The most common stomach flu symptoms are:
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:
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.
The stages of stomach flu infection are:
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.
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.
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.
Many different viruses can infect your gastrointestinal system, causing gastroenteritis.
The most common ones are:
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.
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.
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.
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:
Healthcare providers often diagnose gastroenteritis based on your symptoms. They won’t know if it’s viral or which virus it is without doing a lab test to find out. But most of the time, this isn’t necessary. Since there isn’t any specific medicine for stomach flu, there’s no need to identify it, or the virus.
Your immune system gets rid of stomach flu through its own natural processes. It just takes a few days to do its work. Your symptoms, while unpleasant, are a sign that your immune system is working. There’s no medicine for stomach flu. Antibiotics don’t work on viruses — they’re for bacterial infections.
The best thing you can do to help your immune system do its work is to stay home and rest, stay hydrated and eat a little if you can. Give your body the energy it needs to fight the infection. To stay hydrated, take small sips throughout the day, before you feel thirsty, or suck on ice chips.
Some research shows that taking probiotics may help stomach flu go away faster. Probiotics are helpful bacteria that live in your gastrointestinal system. Having enough helpful bacteria in your gut is part of having a healthy immune system. Ask a healthcare provider if probiotics might help you.
What you eat won’t improve stomach flu, but it can make it worse. Foods high in fat, sugar, caffeine or dairy milk might make you more likely to throw up or have diarrhea. You might have little appetite or feel nauseous at the thought of food. Focus on foods that are easy to digest and give you a quick dose of energy, like fruit juice popsicles, broths and saltine crackers. The salt can help replace your electrolytes.
Healthcare providers can treat dehydration with intravenous fluids. This is a way of delivering hydration directly to your bloodstream, bypassing your digestive system. In some cases, healthcare providers may prescribe medications to reduce vomiting or diarrhea. They don’t prescribe these for children, though.
Contact a healthcare provider if:
You can reduce your risk of getting stomach flu or spreading it to others by practicing good hygiene.
For most people, symptoms get better in a few days. Contact a healthcare provider if they aren’t improving. People with weaker immune systems may need treatment for dehydration or medications to reduce their symptoms. It’s also possible that you have a different condition if you aren’t improving.
It’s best to say isolated until two days after your symptoms have stopped. This is the time when you’re most contagious. Even though your body has overcome the infection, you’ll still shed the live virus in your poop. If any trace of that poop comes into contact with another person, they could get sick.
Stomach flu isn’t related to “the flu” (influenza), which is a viral infection in your respiratory system. The flu vaccine won’t protect you from stomach flu. Different viruses cause these two conditions, and they affect different body systems. Most of their symptoms are different, though a few may overlap.
Influenza causes respiratory symptoms like congestion, a sore throat or a runny nose. Stomach flu causes gastrointestinal symptoms, like diarrhea, nausea and vomiting. Both may cause “systemic symptoms” like fever and fatigue. Children may have some gastrointestinal symptoms with both.
People probably mean different things when they use this phrase. They might be referring to symptoms of influenza. Or they might be referring to systemic symptoms, which are more common with viral infections in general than with other types. Some people might mean gastrointestinal symptoms.
Stomach flu and food poisoning are both infections that cause gastroenteritis, with similar symptoms. The different names describe the different origins of the infection. Viral gastroenteritis comes from a virus, while food poisoning comes from eating food that’s contaminated, either by a virus or something else.
Food poisoning can cause stomach flu if you get the virus from food. This is common, and in this case, both names describe the same condition. But other types of contamination can also cause food poisoning, like bacteria. Bacterial food poisoning has a few small differences from stomach flu.
A note from Cleveland Clinic
Almost everyone gets stomach flu at some point. Since many different viruses can cause it, you may get it more than once. Children in daycare centers and schools and people in care facilities are more at risk of getting it from their communities, and they may experience more severe symptoms with it.
For most people, stomach flu is unpleasant but brief. But for some, it can be dangerous. If you care for a child or older person with stomach flu, watch for signs of dehydration and stay in touch with a healthcare provider. Take steps to protect yourself from the virus and to prevent it from spreading to others.
Last reviewed by a Cleveland Clinic medical professional on 07/10/2023.
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