There have been an unusually high number of norovirus outbreaks sickening people across the country in December, 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 CDC 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 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 million to 21 million people nationwide each year, can cause sudden and unpleasant gastrointestinal symptoms.

In December, 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.

— The New York Times