If you’ve ever had the stomach flu, you may have had gastroenteritis.

Gastroenteritis — often referred to as stomach flu — is a very common condition in which the stomach lining becomes inflamed. It’s usually caused by a viral, bacterial, or parasitic infection.

Most often, it’s caused by a virus — usually norovirus — contracted from contaminated food or water. In fact, norovirus is the leading cause of foodborne illness and accounts for up to 58% of cases in the United States each year.

Symptoms usually include:

  • stomach pain
  • cramping
  • headache
  • nausea
  • vomiting
  • fever
  • diarrhea

Often, symptoms will go away on their own. In rare cases, a person may require hospitalization.

Since gastroenteritis is quite common, you may wonder how to know if you have it and whether you need to see a doctor for any lab tests.

This article tells you all you need to know about gastroenteritis, how healthcare professionals diagnose it, and when to seek medical care.

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In most cases, you probably won’t need a formal diagnosis of gastroenteritis since it’s considered a self-limiting condition. That means it often resolves on its own and symptoms should go away within a few days.

If you do seek medical care, a healthcare professional will likely ask for a brief health history, a summary of the foods you’ve recently eaten, and a list of places you’ve recently traveled to or visited.

They may also conduct a physical exam to rule out any other potential causes.

According to clinical guidelines from 2016, gastroenteritis is usually caused by:

  • Virus (most common): Viral causes include norovirus or rotavirus (e.g., poor hand hygiene, consuming contaminated food).
  • Bacteria (less common): Bacteria that cause gastroenteritis include E. Coli, Campylobacter, and Salmonella (often from contaminated food). Other bacteria can also cause gastroenteritis, such as Clostridium difficile, which is common in healthcare and long-term care settings, 2021 research suggests.
  • Parasite (least common): Parasite causes include cryptosporidium or Giardia (often from contaminated drinking or swimming water or contact with human or animal feces).

If you’re experiencing long-lasting or serious symptoms, a healthcare professional may order a stool sample to identify whether it’s a viral, bacterial, or parasitic infection. In some cases, they may also request blood tests.

Generally, most people will not require a lab test to diagnose gastroenteritis.

Lab tests are usually only recommended for people with severe symptoms of gastroenteritis, according to 2016 clinical guidelines. These symptoms include chronic diarrhea, extreme vomiting, and severe dehydration. This also applies if the symptoms last longer than 7 days.

If your healthcare professional orders a lab test to diagnose your gastroenteritis and its cause, they’ll likely order a stool test, according to 2015 research. A stool test examines whether any viruses, bacteria, or parasites are present in your stool.

If your healthcare professional has other concerns, they may also order a blood test.

Most gastroenteritis cases will resolve on their own within 1 or 2 days and are not severe. So you may be able to “wait it out” at home.

During this time, you’re more likely to be dehydrated, especially if you’re experiencing vomiting or diarrhea. Try to drink plenty of fluids and replace electrolytes with salty foods like soups, crackers, and electrolyte drinks.

If your symptoms have not improved after a few days or they have worsened, it’s important that you seek medical attention. These symptoms may increase your risk of severe dehydration and may be a sign of a more severe concern.

Symptoms of severe gastroenteritis include:

  • diarrhea or vomiting that lasts longer than 2 days
  • blood in stool or vomit
  • being unable to keep food or liquids down
  • showing signs of moderate to severe dehydration (e.g., lightheadedness, extreme thirst, severe weakness, dizziness, dark urine, decreased urination, dry mouth)
  • extreme pain
  • a fever greater than 101°F (38.3°C) for more than 3 days

Often, you can take steps to prevent gastroenteritis. Per the Centers for Disease Control and Prevention (CDC), these steps include:

  • Wash your hands before and after:
    • using the bathroom
    • changing diapers
    • touching soiled clothing
    • handing or preparing food
    • touching animals
    • throwing out garbage
    • touching other contaminated surfaces
  • Practice safe food handling, such as by:
  • Avoid eating perishable food that has been sitting out for longer than 2 hours.
  • Stay up-to-date with food recalls.
  • Avoid drinking untreated water.
  • Make sure to eat well-cooked or washed food, and drink bottled water if safe drinking water is not available, especially when traveling.
  • Limit or avoid contact with people who have symptoms like nausea or diarrhea.
  • Use alcohol-based hand sanitizers when you’re unable to wash your hands (though washing your hands is more effective in getting rid of norovirus).

Gastroenteritis, or the stomach flu, is something most of us will deal with at least once in our lives.

It’s usually caused by a viral infection but can also be caused by bacteria or a parasite. The most common causes of gastroenteritis include poor hand hygiene, consuming contaminated food, or coming into contact with someone with the infection.

It’s usually unnecessary to get a formal diagnosis from a stool or blood test unless you’re experiencing severe symptoms. Often, the condition will resolve on its own in a few days.

If you suspect you have gastroenteritis and your symptoms are mild, try to rest and replenish any lost electrolytes and fluids. If your symptoms worsen or do not go away after several days, check in with a healthcare professional.