Overview
- CDC indicators show an early-season upswing since mid-October, with national test positivity reaching about 11.7% in late November and higher rates in the Western U.S.
- More than 150 outbreaks have been logged by CDC’s NoroSTAT since August, and WastewaterSCAN reports a 69% nationwide increase in norovirus concentrations since October.
- The GII.17 variant, responsible for roughly 75% of U.S. outbreaks last season, is frequently detected again this year and is a focal concern for wider spread.
- Local impacts include a two-day closure at Roberts Elementary in Medford, Massachusetts, and a CDC-reported outbreak on the AIDAdiva cruise ship affecting 4.8% of passengers.
- UKHSA reports recent increases in England for weeks 48–49, yet activity remains below the five-season average for the same period.