By Norovirus cases are surging across the country this winter, according to Centers for Disease Control and Prevention (CDC) data.
There were 91 outbreaks reported by state health departments during the week of Dec. 5, up from 69 in the last week of November, according to the CDC.
The highest number for the same period over the last several years was 65 outbreaks.
But the data are not comprehensive. Currently, state, local and territorial health departments are not required to report individual cases of norovirus illness to the CDC, and only 15 states participate in the National Outbreak Reporting System.
Additionally, the CDC pointed out some people may not seek health care for their illness, and most hospitals and doctor’s offices do not generally test for norovirus.
Norovirus is extremely contagious and can cause diarrhea, vomiting, nausea and stomach pain within 12 hours to 47 hours after being exposed, the agency said.
Most people with norovirus get better within one to three days, but they can still spread the virus for a few days after.
Norovirus is the leading cause of foodborne illness in the United States. Each year, there are about 2,500 reported outbreaks. They can occur throughout the year but are most common between November and April, the CDC said.
Anyone can get infected and sick with norovirus, and people of all ages get infected during its outbreaks.
However, anyone who consumes raw shellfish is at higher risk of contracting norovirus. Children younger than 5 years old, older adults and people with weakened immune systems are more likely to develop severe infections.
A person gets infected by getting tiny particles of feces or vomit in their mouth from a person infected with norovirus. The virus spreads through contaminated water, food and surfaces; it only takes a few norovirus particles to make people sick, the CDC said.
The best prevention is for people to wash their hands well with soap and water; hand sanitizer alone does not work well against norovirus.
The virus often spreads in spaces including prisons, cruise ships, day care centers, and college dorms where people are living in close proximity.