Viral Gastroenteritis (Stomach Flu)

How it spreads

Viruses that cause gastroenteritis spread very easily:

• through contact with an infected person's vomit or stool, often on hands
• by touching contaminated surfaces and then the mouth
• through contaminated food or water, including food handled by an infected person
• through tiny droplets released into the air during vomiting (norovirus)

Norovirus outbreaks are common in schools, child care centers, nursing homes, hospitals and cruise ships. As few as a handful of virus particles can cause infection, and alcohol-based hand sanitizers work less well against norovirus than soap and water.

Symptoms

• sudden nausea and vomiting
• watery diarrhea, without blood
• stomach cramps
• low-grade fever, chills
• headache and muscle aches
• tiredness

Vomiting tends to settle first, often within a day, while diarrhea can continue for several days.

Viral gastroenteritis vs food poisoning

There is overlap: norovirus is the most common cause of foodborne illness. Bacterial food poisoning from Salmonella, Campylobacter or E. coli is more likely to cause high fever, bloody diarrhea and illness lasting more than a few days. Symptoms starting within 1 to 6 hours of a meal suggest toxin-related food poisoning.

Dehydration: what to watch for

Dehydration is the main risk. Watch for:

Babies may also be irritable, have fewer wet diapers and a sunken soft spot on the head. See dehydration.

Diagnosis

Viral gastroenteritis is usually diagnosed from symptoms. Stool tests are only needed if there is blood in the stool, high fever, severe illness, symptoms lasting more than a week, a weakened immune system, recent travel (traveler's diarrhea), recent antibiotics (antibiotic-associated diarrhea), or during an outbreak investigation. Blood tests check for dehydration and electrolyte problems in more severe cases.

Treatment and home care

Fluids

• Oral rehydration solution (ORS) is the best choice, especially for children, older adults and anyone with significant diarrhea. Available in pharmacies as drinks, powders or ice pops.
• Small, frequent sips: start with a spoonful or a few sips every few minutes, gradually increasing.
• Keep breastfeeding babies; continue formula once vomiting settles.
• Adults can also drink water and broth. Avoid sugary sodas, undiluted juice and energy drinks, which can worsen diarrhea.

Food

• Return to normal food as soon as you feel hungry, starting with bland foods such as toast, rice, bananas, crackers, soup and yogurt.
• There is no need to fast or follow a strict restricted diet for long.

Medicines

• Fever and aches: acetaminophen (paracetamol) at the label dose.
• Antidiarrheal medicines such as loperamide may help adults with watery diarrhea without fever or blood; follow the label. Do not give them to children.
• Anti-nausea medicine may be prescribed for children or adults who cannot keep fluids down.
• Antibiotics do not help viral infections.
• IV fluids in hospital for severe dehydration.

How long is stomach flu contagious?

People are most contagious while they have symptoms and for the first few days after recovering. Norovirus can be shed in stool for 2 weeks or more. Stay home from work, school or child care until at least 48 hours after the last episode of vomiting or diarrhea, and avoid preparing food for others during that time.

Prevention

• Wash hands with soap and water for at least 20 seconds, especially after using the toilet or changing diapers and before eating or preparing food.
• Clean contaminated surfaces with a bleach-based cleaner.
• Wash soiled laundry on a hot cycle.
• Rotavirus vaccine for infants protects against severe rotavirus illness.
• Food safety: wash fruits and vegetables, cook shellfish thoroughly.

Frequently asked questions

How long does stomach flu last?

Most viral gastroenteritis, including norovirus, lasts 1 to 3 days. Vomiting usually settles within a day, while diarrhea can continue for several more days. Rotavirus in children can last up to a week. Seek care if symptoms last longer or dehydration develops.

Is stomach flu contagious?

Yes, very. It spreads through contact with an infected person's vomit or stool, contaminated surfaces, food and water. People are most contagious while sick and for a few days after, so stay home for at least 48 hours after symptoms stop.

What should I eat and drink with stomach flu?

Sip oral rehydration solution or water frequently in small amounts. Once vomiting eases, start with bland foods such as toast, rice, bananas, crackers and soup, then return to a normal diet as you feel able. Avoid sugary drinks, alcohol and very fatty foods at first.

Is stomach flu the same as influenza?

No. "Stomach flu" is a common name for viral gastroenteritis, which affects the stomach and intestines. Influenza is a respiratory virus that causes fever, cough and body aches. The flu vaccine does not protect against stomach flu.

When should I see a doctor for a stomach bug?

See a doctor for signs of dehydration, inability to keep fluids down, bloody diarrhea, high fever, severe abdominal pain, symptoms lasting more than a few days, or illness in babies, older adults, pregnant women and people with chronic health problems.