How Norovirus Spreads

What causes it

You can get norovirus by accidentally getting tiny particles of feces (poop) or vomit in your mouth from a person infected with norovirus.

If you get norovirus illness, you can shed billions of norovirus particles that you can’t see without a microscope. It only takes a few norovirus particles to make you and other people sick.

How it spreads

Norovirus is very contagious and spreads very easily and quickly in different ways.

Contaminated food

Norovirus can spread through contaminated food when:

• A person with norovirus touches food with their bare hands.
• Food is placed on a counter or surface that has poop or vomit particles on it.
• Tiny drops of vomit from a person with norovirus spray through the air and land on the food.
• Food is grown with contaminated water (like oysters), or fruit and vegetables are watered with contaminated water in the field.

Contaminated water

Recreational or drinking water can get contaminated with norovirus:

• At the source such as when a septic tank leaks into a well.
• When a person with norovirus vomits or poops in the water.
• When water isn't treated properly, such as with not enough chlorine.

Contaminated surfaces

Norovirus spreads through sick people and contaminated surfaces when:

• A person with norovirus touches surfaces with their bare hands.
• Food, water, or objects that are contaminated with norovirus are placed on surfaces.
• Tiny drops of vomit from a person with norovirus spray through the air, landing on surfaces or entering another person's mouth.
• A person with norovirus has diarrhea that splatters onto surfaces.

When you are contagious

You are most contagious:

• When you have symptoms of norovirus illness, especially vomiting.
• During the first few days after you feel better.

However, studies have shown that you can still spread norovirus for 2 weeks or more after you feel better.