A highly contagious form of norovirus known as “winter vomiting disease” is spreading quickly across the country — including in Florida — based on wastewater analysis from 13 surveillance sites statewide.
Norovirus infections usually rise after Christmas and New Year’s gatherings, but CDC data shows an unusual spike in November. The agency relies on voluntary reporting from clinics and state health departments, although officials note the data is often incomplete because most people recover at home without seeking medical care.
While the CDC does not monitor wastewater for norovirus, data from WastewaterSCAN, a Stanford- and Emory-led academic program, shows national viral activity has been climbing since mid-October.
Monitoring sites in Altamonte Springs, Orange County, Jupiter, Key Biscayne, Miami, St. Petersburg, and Tallahassee all reported rising norovirus levels by late November. Southwest St. Petersburg reported the highest levels, while northwest Orange County saw the lowest.
The CDC records about 2,500 norovirus outbreaks each year. Some health experts worry that the GII.17 variant — responsible for last year’s surge — may have mutated and become more contagious.
For more than 30 years, the GII.4 strain caused most norovirus outbreaks, but last year, the GII.17 mutation accounted for roughly 75% of cases, according to the CDC.
Dr. Robert Atmar of Baylor College of Medicine said there are two possible explanations: the virus may have changed to become more transmissible, or shifts in population immunity may have made more people vulnerable.
“And probably it’s a combination of both,” Atmar said. “But whether it’s going to persist this year, I think, is one of the big questions in our scientific community.”
Symptoms of the GII.17 strain include forceful vomiting, severe diarrhea, and stomach cramps — especially dangerous for children under 5, adults over 85, and people with underlying health conditions. Dehydration is a major concern.
Because GII.17 is new, people have less immunity and may develop more severe illness.
“When new strains emerge, people are exposed to a strain that they have not previously been exposed to, and hence are more likely to get infected,” said Lee-Ann Jaykus, a professor at North Carolina State University.
“Historically, new strains emerge every seven to 10 years, and we were due for one, so this is not surprising,” Jaykus added.
Health experts emphasize vigorous hand-washing with hot water and soap and maintaining strong hygiene practices to help stop the spread. Norovirus spreads easily through direct contact with an infected person, consuming contaminated food or drinks, touching contaminated surfaces, and inadequate hand-washing.