What is causing the current norovirus surge in the US?

A new, highly contagious strain called GII.17 is driving the current surge in norovirus cases across the US.

How infectious is the new GII.17 norovirus strain?

The GII.17 strain is about 50 percent more infectious than other norovirus strains and is now responsible for most infections.

Are norovirus cases rising in the US according to wastewater data?

Yes, levels of norovirus in wastewater are showing a continuing rise nationwide, indicating an increase in infections.

Home / Health / New Norovirus Strain Sparks Early Outbreak

New Norovirus Strain Sparks Early Outbreak

15 Dec, 2025

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Summary

A new, highly contagious norovirus strain GII.17 is causing an early surge in infections.
This strain is significantly more infectious, causing 50% more cases than others.
Wastewater levels indicate a continuing rise in norovirus cases nationwide.

New Norovirus Strain Sparks Early Outbreak

A novel and highly contagious strain of norovirus, identified as GII.17, has emerged as the primary driver behind an unusually early and severe stomach bug season in the United States. This new variant is considerably more infectious, leading to approximately 50% more cases compared to other strains and now accounts for at least 75% of all infections across the country.

While official test positivity rates have shown some variation, levels of norovirus detected in wastewater systems indicate a sustained and rising trend. This suggests that the actual number of infections may be significantly higher than currently reported, as many cases go untested. The Centers for Disease Control and Prevention (CDC) warns of escalating public health concerns, particularly with the ongoing widespread transmission.

Several elementary schools have already been forced to close temporarily for deep cleaning due to norovirus outbreaks, impacting hundreds of students. Health experts advise increased vigilance, noting that the situation is currently trending towards levels seen in previous severe years and may escalate further before subsiding. Nationwide wastewater monitoring shows 'medium' activity, with 'high' levels reported on the West Coast.