Overview
- Wastewater surveillance from late May classed national norovirus concentrations as "HIGH" with rising levels in the Northeast and notable signals in the Midwest and San Francisco Bay Area.
- A cluster on the Pacific Crest Trail in Southern California sickened at least two dozen hikers over about two weeks and required at least one air rescue, prompting trail warnings and hiking-specific prevention advice.
- The CDC’s NoroSTAT program recorded 1,194 outbreaks from Aug. 1, 2025, to May 7, 2026, a figure health officials say falls within historical ranges but likely misses many infections because most people do not seek care.
- The GII.17 strain, which overtook GII.4 in 2024–25 and now accounts for roughly 75% of reported outbreaks, partly evades prior immunity and helps explain increased spread despite no new, more transmissible mutation being identified.
- Public-health guidance stresses soap-and-water handwashing, using EPA-registered disinfectants on surfaces, avoiding raw shellfish, staying home when sick, and watching for dehydration in young children and older adults.