Norovirus Surge: What You Need to Know

Recent wastewater surveillance data from WastewaterSCAN indicates norovirus concentrations are at high levels nationally, particularly in the Northeast.

Current Outbreak Snapshot

From August 1 to May 7, the CDC's NoroSTAT program recorded 1,194 outbreaks, compared to 2,534 during the same period the previous year. This figure is consistent with past averages.

Strain Circulation

Several norovirus strains are currently circulating, including:

• GII.4 (common)
• GII.17 (a more mutated strain)

During the 2024–25 season, GII.17 became predominant in the U.S., causing about 75% of outbreaks. Both strains cause similar symptoms, though GII.17 spreads more easily due to lower population immunity.

Transmission: Highly Contagious

Norovirus is alarmingly contagious, with an average infected person spreading it to seven others.

It spreads through:

• Direct contact with an infected person
• Contaminated surfaces
• Contaminated food (especially raw shellfish, salads, and sandwiches)
• Untreated water

Symptoms and Treatment

Symptoms include vomiting, diarrhea, and stomach cramps, starting 12–48 hours after exposure. Most people recover within several days without treatment.

Dehydration is a primary risk, especially for young children and older adults.

Recommended Care

• Oral rehydration fluids are recommended for mild cases
• Severe cases may require intravenous fluids
• Hand sanitizers are ineffective against norovirus—soap and water are preferred