Norovirus

Key takeaways

• Symptoms start: 12 to 48 hours after exposure
• Usual length: 1 to 3 days
• Most useful single change: Sip water, oral rehydration solution or broth often to replace lost fluids.
• Commonest mistake: Cooking or serving food for others while sick and for 2 days afterward.
• See a doctor if any of the signs under "When to get help" below apply to you.

Why it matters

It is the leading cause of vomiting, diarrhea and foodborne illness in the US, and it spreads easily through food, surfaces and close contact.

The numbers, in one place

Published figures for Norovirus

Measure	Figure
Symptoms start	12 to 48 hours after exposure
Usual length	1 to 3 days
Hand cleaning	soap and water for at least 20 seconds; hand sanitizer alone does not work well
Cleaning surfaces	a bleach solution or an EPA-registered disinfectant labeled for norovirus
Preparing food for others	wait at least 2 days after symptoms stop

What helps

• Sip water, oral rehydration solution or broth often to replace lost fluids
• Wash hands with soap and water after using the toilet, changing diapers and before eating or cooking
• Wear disposable gloves to clean up vomit or diarrhea, then disinfect the area
• Wash soiled laundry on the longest hot cycle and machine dry it

What to avoid

• Cooking or serving food for others while sick and for 2 days afterward
• Relying on alcohol-based hand sanitizer instead of hand washing
• Sending children back to child care or school before your provider or program says it is safe

In depth

Norovirus infects the lining of the small intestine, damaging the tiny finger-like projections that absorb fluid and nutrients and disturbing how the gut moves. The result is a sudden burst of vomiting, watery diarrhea and cramps. In most healthy adults, the immune system clears the virus within a few days, but the rapid loss of fluid can cause dehydration, especially in young children, older adults and people with other health conditions.

Norovirus spreads so easily because very few virus particles are needed to make someone sick, while an infected person sheds huge numbers in vomit and stool. Vomiting can also send tiny droplets into the air and onto nearby surfaces. The virus can survive on countertops, doorknobs and fabrics for days, resists many common cleaners, and is not reliably killed by alcohol-based hand sanitizer.

There are many strains of norovirus, and immunity after infection does not last long, so you can catch it many times over your life. Outbreaks are common wherever people share close quarters, food or bathrooms: nursing homes, hospitals, cruise ships, schools, child care centers and restaurants. Most cases happen from November to April, which is why it is sometimes called winter vomiting disease.

Signs and symptoms

• Sudden nausea and vomiting, often forceful and without warning
• Watery diarrhea, usually without blood
• Stomach cramps and aching
• Low-grade fever, chills, headache and body aches
• Dry mouth and throat, dizziness on standing and passing little urine, which signal dehydration
• In young children, crying with few or no tears, fewer wet diapers or unusual sleepiness

Causes and risk factors

• Eating food handled by someone who is sick or did not wash their hands well
• Touching contaminated surfaces and then your mouth
• Caring for, or sharing food and utensils with, someone who is sick
• Eating raw or undercooked shellfish, especially oysters, from contaminated water
• Eating raw produce that was contaminated during growing, harvest or preparation
• Living in or visiting close-quarters settings during an outbreak

How it is checked

Norovirus is usually recognized from the pattern of symptoms, especially sudden vomiting and diarrhea that spreads through a household or group. Most people do not need a test, because the result would not change how they are cared for. When an outbreak is suspected in a restaurant, school or care facility, health departments may test stool samples to confirm the cause and trace the source.

Your doctor will focus on how dehydrated you are, checking things like heart rate, blood pressure, urine output and how alert you are. Blood tests, stool tests for other germs or imaging may be ordered if there is blood in the stool, a high fever, severe belly pain, symptoms lasting more than a few days, or a weakened immune system, to look for other causes.

Related topics

• The Evidence on Infection Prevention at Home, Without the Hype (Immunity)
• What the Guidance Really Says About Diarrhea (Digestive Health)
• Travelers' Diarrhea: What the Evidence Actually Says (Travel Health)
• Common Childhood Infections: What the Evidence Actually Says (Children's Health)

Where to go next

• Norovirus at a Glance
• What the Guidance Really Says About Norovirus
• Infectious Diseases: The Complete Guide
• Strep Throat: What Published Guidance Supports
• Hepatitis A: Sorting the Evidence From the Noise

When to get help

Call your doctor if vomiting or diarrhea lasts more than a few days, there is blood in the stool, or a baby, older adult or someone with a chronic condition cannot keep fluids down. Call 911 for signs of severe dehydration, such as very little or no urine, dizziness when standing, fainting, confusion, or a child who is unusually sleepy or fussy and cries without tears.

Where this comes from

• CDC — About Norovirus
• EPA — List G: EPA's Registered Antimicrobial Products Effective Against Norovirus

How this page was put together

Every figure, recommendation and warning above is taken from the guidance named in Where this comes from. Nothing on this page is inferred, summarized or generalized beyond what those bodies publish: where they give a number, it is their number, and where they are silent, so are we. Pages are rebuilt whenever the underlying record changes. Sign-off by a named clinician, where it has happened, is shown at the top of the page along with the date.

Medical disclaimer

This article is general information, not medical advice. It cannot account for your own history, medication or circumstances. Always speak to your doctor, pharmacist or another qualified health professional before making changes that affect your treatment, and never delay seeking medical advice because of something you have read here. In an emergency, call 911.