This winter's wave of norovirus infections has reached more than double last season's peak, according to data released Monday by the U.S. Centers for Disease Control and Prevention tracking the notorious stomach bug.
Nearly 28% of norovirus tests came back positive within one week of the New Year holiday Highly contagious Viruses, which are the leading cause of foodborne illness, e.g. Vomiting and diarrhea in the united states
That number is more than double the 13.52% of tests that came back positive at the peak of last season in March, according to data from public health laboratories across the country compiled by the Centers for Disease Control and Prevention (CDC).
Laboratories typically test patients' stool samples for the virus and can diagnose the virus within 10 days of the onset of symptoms. The virus can also be found in other samples, including contaminated food or drinks that may spread the virus.
Norovirus infection rates in the CDC system have met or exceeded last season's peak levels in all regions of the country. Norovirus test positivity rates appear to be the worst in the Midwest, which includes a group of states from Kansas to Michigan.
Because most people infected with norovirus recover without needing to see a doctor, most cases in the United States go unreported.
WastewaterSCAN's sewer sampling data also shows that the incidence of norovirus in recent weeks has been highest in the Midwest and Northeast. Data released by private testing company BioFire Diagnostics are also higher than previous seasonal peaks for norovirus.
Why are there so many norovirus cases in 2025?
While norovirus incidence has always worsened in the colder months, most trends tracking norovirus in recent years have not peaked until March or April.
This is different from previous seasons Severe special infectious pneumonia pandemicwhich disrupts many common seasonal bacterial patterns. During this period, norovirus outbreaks tended to peak as early as December and January.
Experts say the surge in cases this year is due to New strain of norovirus Called GII.17[P17]which replaced the strain that dominated previous waves of the virus in the U.S. over the previous decade.
A CDC official told CBS News that the new strain has been found across the country, including in a number of cruise ship outbreaks. Ethnic groups have lower immunity to GII.17[P17] could explain this year's unusual wave of viruses.
According to the latest data from the Centers for Disease Control and Prevention, more than 7 in 10 outbreaks this season have been linked to this new strain of norovirus.
