This winter's wave of norovirus infections has reached a level that is now more than double last season's peak, according to data published Monday by the Centers for Disease Control and Prevention, which tracks the infamous stomach bug.
About 28% of norovirus tests conducted over the New Year holiday week came back positive highly contagious Viruses, which are the leading cause of foodborne illness vomiting and diarrhea in America
This is more than double the 13.52% of tests that came back positive during the peak of last season's wave in March. data The results were matched by CDC to public health laboratories across the country.
Labs usually test stool samples from sick people for the virus, which can be diagnosed as early as 10 days after symptoms begin. The virus can also be found in other samples, including contaminated food or drinks that can spread the virus.
Norovirus rates in that CDC system have reached levels at or above last season's peak in all regions of the country. Norovirus test positivity rates appear to be the worst in the Midwest, a group of states stretching from Kansas to Michigan.
Because most people sick with norovirus recover without needing to see a doctor, most cases in the U.S. go unreported. Instead, health officials and experts track trends in the virus and the rate of positive tests. Just like other measurements are used.
data from WastewaterScan Sewer sampling also shows that norovirus rates in recent weeks have been highest in the Midwest as well as the Northeast. The figures published by private testing company Biofire Diagnostics are also above the previous seasonal peak of norovirus.
Why are there so many norovirus cases in 2025?
While norovirus rates always worsen during the colder months, most trends tracking norovirus in recent years did not reach their peak until March or April.
It is different from the seasons that came before it Covid-19 pandemicWhich destroyed many of the normal seasonal patterns of germs. During that time, norovirus outbreaks often peaked in December and early January.
Experts say the early and rapid increase in cases this year is happening for a reason New strain of norovirus GII.17 is called[P17]That has displaced the previous strain that dominated previous waves of the virus in the US for a decade.
A CDC official told CBS News that this new strain has been seen everywhere across the country, including in several cruise ship outbreaks. Low population immunity to GII.17[P17] That could explain the unusual wave of the virus this year.
According to the latest CDC data, more than 7 in 10 outbreaks this season have been linked to this new norovirus strain.