Current Outbreak Status in 2025

US norovirus outbreaks in the 2024-2025 season are significantly higher than previous years, with CDC NoroSTAT data indicating 495 reported outbreaks by December 11, 2024, surpassing the range from 2012-2024 seasons[1]. Test positivity rates have doubled from 7% in August to nearly 14% by November 15, signaling a rapid escalation[3].

The season began earlier, peaking in January 2025 driven by GII.17, unlike prior GII.4-dominated peaks in February or March[4]. Electronic health records highlight surges in emergency department visits since July in multiple states[3]. In contrast, England's reports up to week 49 of 2025 show activity rising but 16% below the 5-season average[2].

Minnesota alone tracked over 130 outbreaks in January 2025, affecting more than 4,000 people, underscoring regional intensities[6].

Rise of the GII.17 Variant

The GII.17 strain has overtaken GII.4, rising from under 10% of outbreaks in 2022-2023 to 75% in 2024-2025, per CaliciNet data[1][4]. From September to December 2024, it caused 46% of outbreaks, up from 13-17% previously[4].

This shift mirrors past patterns, like Asia's 2014 GII.17 replacement of GII.4, and shows no regional US differences[4]. CDC notes GII.17 at 69.7% of genotypes from September to December 2024[1]. UK genotyping confirms GII at 83%[2].

Experts call for ongoing surveillance to track if GII.17 persists and whether earlier seasonality continues[4].

Prevention and Symptoms

Symptoms include sudden vomiting, diarrhea, fever, and cramps, lasting 1-3 days. No vaccine exists, so prevention relies on handwashing with soap for 20 seconds, disinfecting surfaces with bleach solutions, and avoiding food preparation while ill.

Norovirus spreads via contaminated food, water, surfaces, or close contact, thriving in crowds like schools and cruise ships. Isolate for 48 hours post-symptoms and stay hydrated to manage dehydration risks, especially in children and elderly[7].

With surges ongoing, health departments emphasize these measures amid overlapping flu and COVID activity[5].