Norovirus outbreaks are increasing across the US: Which regions have it the worst?

(NEXSTAR) – An uptick in outbreaks of norovirus may be contributing to rising cases across the country — but some regions are feeling it more than others.

Norovirus, sometimes called the “stomach flu,” is generally a seasonal virus that causes acute gastroenteritis, leading to symptoms including diarrhea, vomiting and nausea, according to the Centers for Disease Control and Prevention (CDC). Despite its nickname, this type of “stomach flu” isn’t caused by the influenza virus, but rather “by accidentally getting tiny particles of feces (poop) or vomit from an infected person in your mouth,” the CDC says.

Outbreaks of norovirus generally peak between November and April of any given year, though early reporting from labs across the country shows an earlier uptick when compared to the previous norovirus season.

Between Aug. 1, 2022, and Jan. 8, 2023, there were 225 norovirus outbreaks among the 14 states that participate in the CDC’s NoroSTAT reporting program, a significant increase over the same time period between Aug. and Jan. 2022, when there were only a reported 172 outbreaks.

These findings aren’t entirely unexpected, according to Marisa Lubeck, a health communication specialist with the CDC.

“Prevention measures implemented during the COVID-19 pandemic were likely effective in preventing norovirus outbreaks,” Lubeck explained in an emailed statement. “As pandemic restrictions have relaxed, the number of norovirus outbreaks has returned to levels similar to pre-pandemic years.”

That said, Lubeck confirmed that the current outbreak count is still “within the expected range” for any given norovirus season.

Despite this, some parts of the country have noted especially high positivity rates slightly earlier than in previous years, mirroring an overall national trend. Participating laboratories in the Midwest, for instance, had observed a 19.4% positivity rate among patients who took polymerase chain reaction (PCR) tests as of Feb. 4 — topping the previous year’s high of 16.1%, recorded in April 2, 2022.

The Western region also appears on track to exceed last year’s top positivity rate of 13.49% (observed at the end of April) with recent positivity rates at 13.42%, and likely rising, as of Feb. 4.

Positivity rates in the Northeast and Southern regions have yet to exceed 2022’s peaks, despite being slightly higher than where they were at the same time last year, according to the CDC’s data.

The CDC generally records roughly 2,500 outbreaks of norovirus each year, with around 19 to 21 million thought to be infected annually. Of those, approximately 110,000 will be hospitalized, and around 900 die, on average.

Tips for preventing the spread of norovirus include frequent handwashing (especially after using the bathroom, and before handing food or caring for sick individuals) as well as disinfecting shared surfaces. Sickened individuals can still spread the virus for weeks afterward, even if symptoms subside within days, according to the CDC.

There is no current treatment for norovirus, though experts recommend drinking lots of fluids to prevent dehydration.