The stomach flu, also known as a stomach bug, is clinically known as viral or infectious gastroenteritis. Despite its popular nickname, this type of gastroenteritis isn’t caused by the influenza or flu virus.

Norovirus is the most common cause of the stomach flu, but other viruses, including rotavirus, adenovirus, and astrovirus, may also lead to symptoms.

The common stages of a viral stomach flu include:

  1. Exposure: Most viruses that cause the stomach flu are transmitted by direct contact with contaminated water and food (particularly raw cold food, like salads or oysters). Airborne transmission is also possible if someone with acute symptoms, like vomiting, coughs or sneezes near you. In rare cases, recently contaminated surfaces may also be a source of exposure if you touch them and then put your hand to your mouth. Noroviruses may be resistant to common disinfecting substances like alcohol or chlorine.
  2. Incubation period: Stomach bugs usually take a few days to cause symptoms after exposure, which is known as the incubation period. The norovirus has an estimated incubation period of 12 to 48 hours. That means that you could be in contact with the virus and not have any symptoms for up to 2 days after that.
  3. Acute symptoms: Once the incubation period is over, common first symptoms include nausea, vomiting, and non-bloody loose or watery diarrhea. Other symptoms may include fever, abdominal pain, and cramping. The acute stage usually lasts 1 to 3 days.
  4. Recovery: Depending on your overall health status and risk factors, recovery from the stomach flu may take between 3 days and 2 weeks, with symptoms gradually decreasing in intensity and severity.

Viral gastroenteritis is highly contagious during the acute symptoms stage.

In total, a stomach bug may last between 8 and 15 days from exposure to recovery.

The stomach flu cannot be prevented once you’ve been exposed to the virus, so there’s no treatment for stages one and two of the stomach flu.

The first line of treatment for acute symptoms of viral gastroenteritis is ongoing hydration to compensate for fluid loss due to vomiting and diarrhea. This may involve drinking sugar-free electrolyte beverages, broth, and water.

Dehydrated children, older adults, and people with compromised immune systems may require continued intravenous (IV) fluids.

Vomiting and nausea in adults may be managed with antiemetic medications like ondansetron (Zofran) and metoclopramide (Reglan). But these and other medications for nausea and vomiting may not be indicated for children or older adults.

Some healthcare professionals may prefer to avoid medications to stop diarrhea, particularly if you’re not dehydrated. It’s important to consult with them before starting this type of treatment at home.

Antibiotics don’t work on viral infections, but may be required if co-occurring bacterial infections are present.

The stages of the stomach flu may vary in intensity and duration depending on factors like your overall health status, ongoing hydration efforts, and the virus that caused the symptoms.

In general, you should start feeling better within a few days of experiencing the first symptoms. If you don’t, consider contacting a medical professional for an assessment.

Signs of dehydration, like dry mouth, dark urine, and dizziness, also merit prompt medical care. In children, medical care is often required if severe diarrhea and vomiting last for more than 2 days or worsen over time.