Norovirus wave now more than double last year's peak, in CDC's data

This winter's question of norovirus infections has reached levels that are present much than treble past season's peak, successful figures published Monday by the Centers for Disease Control and Prevention tracking the notorious tummy bug.

Nearly 28% of norovirus tests tally implicit the week of the New Year's vacation came backmost affirmative for the highly contagious virus, which is the starring origin of foodborne unwellness similar vomiting and diarrhea successful the U.S.

That is much than treble the 13.52% of tests coming backmost affirmative reached during the highest of past season's question successful March, according to data from nationalist wellness laboratories astir the state tallied by the CDC. 

Labs usually trial samples of sick people's stool for the virus, which tin beryllium diagnosed up to 10 days aft symptoms begin. The microorganism tin besides beryllium recovered successful different samples, including contaminated nutrient oregon drinks that tin dispersed the virus. 

Rates of norovirus successful that CDC strategy person reached levels astatine oregon supra past season's highest successful each regions of the country. Norovirus trial positivity rates look to beryllium the worst successful the Midwest, successful a grouping of states spanning Kansas done Michigan. 

Since astir radical sick with norovirus get amended without needing to spell to the doctor, a bulk of cases spell unreported successful the U.S. Instead, wellness authorities and experts usage different measurements, specified arsenic the complaint of affirmative tests, to way trends of the virus. 

Data from WastewaterSCAN's sewer sampling besides suggests norovirus rates successful caller weeks person been highest successful the Midwest arsenic good arsenic the Northeast. Figures published by backstage investigating institution BioFire Diagnostics are besides supra erstwhile seasonal peaks for norovirus.

Why are norovirus cases truthful precocious successful 2025?

While norovirus rates ever worsen during the colder months, successful caller years astir trends tracking norovirus did not scope their highest until March oregon April.

That's antithetic from seasons starring up to the COVID-19 pandemic, which scrambled galore accustomed seasonal patterns of germs. During that time, norovirus outbreaks often reached highest levels arsenic aboriginal arsenic December and January.

Experts accidental this year's aboriginal and steep surge of cases is being driven by a new strain of norovirus called GII.17[P17], which has displaced a erstwhile strain that had dominated erstwhile waves of the microorganism successful the U.S. for a decade. 

That caller strain has been spotted everyplace astir the country, including successful galore cruise vessel outbreaks, a CDC authoritative told CBS News. Lower colonisation immunity to GII.17[P17] could explicate this year's antithetic question of the virus. 

More than 7 successful 10 outbreaks person been linked to this caller norovirus strain this season, according to the latest CDC figures.