The virus, often colloquially referred to as “stomach flu,” saw the percentage of positive tests double during the first week of January compared to last year. Positive test percentages for cases of norovirus in the United States are double what they were at the same period a year ago,

Norovirus, commonly called the stomach flu, is a gastrointestinal virus causing vomiting, diarrhea, abdominal cramping and a fever.

There were 91 suspected or confirmed norovirus outbreaks during the week of Dec. 5, according to data from the Centers for Disease Control and Prevention, exceeding any other week in 2024 and the same week in previous years.