On average in the United States, norovirus annually causes 19 million to 21 million cases of acute gastroenteritis, meaning inflammation of the stomach or intestines or both, according to the CDC. This year, norovirus outbreaks reported to the CDC appear to be “pretty much on par with previous years,” Hall said. Thanksgiving is typically the unofficial start of the season, with another uptick near the holidays at the end of December.
“So far, we’re seeing essentially the same viruses in circulation as we saw during last season,” he said, with no indication of new or especially virulent strains. But it’s still early. Data from the last several years show that outbreaks probably will spike between February and March.
All states report norovirus outbreaks to the CDC, but agency officials also rely on a surveillance system that gets faster real-time assessments. Any outbreak reported to nine state health departments across the country is reported to the CDC within seven days.