Here’s what to know about symptoms and treatment, as well as how to reduce your risk of infection.
There have been an unusually high number of norovirus outbreaks sickening people across the country this month, according to data from the Centers for Disease Control and Prevention.
There were 91 suspected or confirmed norovirus outbreaks in the first week of December, the most recent data available. This is a higher number than the C.D.C. has recorded during the same week in recent years. It also exceeds the number of outbreaks recorded in early December in the years leading up to the Covid-19 pandemic.
Outbreaks can occur throughout the year, but they are most common between November and April. The highly contagious virus, which sickens an estimated 19 to 21 million people nationwide each year, can cause sudden and unpleasant gastrointestinal symptoms.
This month, at least 80 people fell ill from norovirus linked to raw oysters served at a restaurant event in Los Angeles. The Food and Drug Administration has advised people not to eat the oysters implicated in that outbreak, which came from British Columbia, Canada, and had been sold in 14 states and the District of Columbia before being recalled. Other recent recalls linked to norovirus have involved fresh and frozen berries, according to an F.D.A. database.
How does norovirus spread?
Dr. William Schaffner, a professor of infectious diseases at the Vanderbilt University School of Medicine, said there are two characteristics that make norovirus “extraordinarily” contagious: It’s easily transmissible, and it’s hardy enough to survive on surfaces for days or even weeks. A person can contract norovirus from contact with an infected person or from contaminated food, water or surfaces.
Dr. Schaffner recalled a case in Tennessee in which a member of a bridge club became sick with norovirus and vomited in the parking lot. Everyone else at the table then became infected. He said that public health investigators later found norovirus on the playing cards.
A person sick with norovirus can shed significant amounts of the virus, and it doesn’t take much to infect someone else. Because of this, the virus thrives in crowded, indoor spaces like cruise ships, nursing homes, schools and day care centers, experts said.