Why Norovirus spikes in the winter months

• Norovirus ("stomach flu") is the leading cause of stomach illness in the U.S., spreading quickly in schools, nursing homes, restaurants, and crowded settings.
• Outbreaks happen year-round but peak in winter (November–March), with cases often doubling or tripling.
• The virus survives longer on cool, dry surfaces and spreads easily in indoor gatherings, schools, and holiday events.
• Contaminated foods—especially shellfish, frozen berries, and ready-to-eat items—often trigger winter outbreaks.

Norovirus, often called the "stomach flu," is a very contagious virus that causes sudden illness by infecting your stomach and intestines. It is the leading cause of vomiting and diarrhea in the United States, and the most common cause of foodborne illness.

Symptoms

• Sudden nausea
• Vomiting, sometimes many times in a row
• Watery diarrhea
• Stomach cramps
• Mild fever or body aches (less common)

Symptoms usually appear 1 to 2 days after exposure and last from 12 hours to 3 days for most people. The good news is that norovirus typically goes away on its own, but you can still spread it to others for a few days after you feel better, so taking precautions is important.

Why Norovirus Peaks in Winter

Norovirus can spread any time of year, but cases surge during the colder months, especially from November to March, with the highest numbers in December, January, and February. The CDC’s Norovirus Surveillance System (NoroSTAT) shows that cases can double or triple in winter compared to summer.

Reasons for Winter Spikes

• More time indoors: In colder weather, people gather indoors in close contact, making it easier for the virus to spread.
• Longer survival on surfaces: Norovirus lasts longer on surfaces like doorknobs or countertops in cooler, drier air.
• Holiday gatherings: Family events, school activities, and busy restaurants during the holidays create more opportunities for the virus to spread.
• Food contamination: Contaminated foods, such as produce, shellfish, or ready-to-eat items, are a common source of outbreaks. The FDA has warned about norovirus in foods like oysters or frozen berries, especially in winter when demand for these items rises.

How Norovirus Spreads

Norovirus is extremely contagious because only a tiny amount of the virus—sometimes just a few particles—can make you sick. It spreads in several ways:

Person-to-Person Contact

• The virus is present in vomit and stool. When someone vomits, tiny particles can spread into the air and land on nearby surfaces.
• If you touch a contaminated surface (like a doorknob, phone, or toy) and then touch your mouth, you can get infected.
• Norovirus can linger on surfaces for days if not properly cleaned with a disinfectant like bleach-based cleaners.

Contaminated Food and Water

• Food handled by someone with norovirus, especially uncooked items like salads, fruits, or sandwiches, can carry the virus.
• Shellfish, like oysters, can become contaminated if harvested from polluted waters.
• Frozen or packaged foods, such as berries, can also spread norovirus since the virus survives cold temperatures.

Where Outbreaks Happen

Because norovirus is so easily transmitted, outbreaks frequently occur in places where people are in close proximity.

• Schools and daycare centers
• Nursing homes
• Cruise ships
• Restaurants

In restaurant settings, one sick person can infect many others, especially if hygiene practices, like handwashing, aren’t followed carefully. Even after symptoms stop, people can spread the virus for a few days, which makes outbreaks hard to control.

Ways to Reduce Your Risk

Although norovirus is hard to avoid completely, you can lower your risk by following strict hygiene and cleaning habits.

Cleaning Up After Vomiting or Diarrhea

These moments are when norovirus spreads most easily, as virus particles can spread through the air or onto surfaces. To clean safely:

• Wear disposable gloves (and a mask if possible) to avoid direct contact.
• Use paper towels to clean up the mess and seal them in a plastic bag for disposal.
• Apply a bleach-based cleaner to all nearby surfaces, not just the visible mess.
• Let the bleach sit for a few minutes before wiping with soap and hot water.
• Wash contaminated clothes or bedding in hot water with detergent and dry on high heat.
• Wash your hands thoroughly with soap and water afterward.

Everyday Habits to Reduce Risk

• Wash hands with soap and water for at least 20 seconds, especially before preparing or eating food and after changing diapers.
• Don’t cook for others until at least 48 hours after symptoms end.
• Use bleach or EPA-approved disinfectants on high-touch items like light switches, phones, and doorknobs.
• Rinse produce well before cutting, even if labeled “pre-washed.”
• Cook shellfish thoroughly and avoid raw oysters.
• At potlucks or parties, use separate serving spoons and avoid sharing utensils.
• Check FDA food safety warnings; if there’s a recall on frozen fruit or other foods linked to norovirus, don’t use them.
• If someone at home is sick, isolate them as much as possible and assign a separate bathroom if available.

Stay hydrated: If you get sick, sip water, electrolyte drinks, or oral rehydration solutions to prevent dehydration. This is especially important for children and older adults.

When to Seek Medical Help

Most people recover from norovirus without medical treatment, but it can cause dehydration, especially in young children, older adults, or those with weakened immune systems. Watch for these warning signs that you should contact a doctor or seek emergency care:

• Unable to keep fluids down for more than 24 hours
• Signs of severe dehydration, such as very dry mouth, no tears, sunken eyes, or little to no urination
• Blood in vomit or stool
• Severe stomach pain that worsens
• High fever that doesn’t improve
• In babies: fewer wet diapers, no tears when crying, extreme sleepiness, difficulty waking, or constant crying