By Dana Varinsky —
NBC News
Noroviruses, a group of related viruses that are highly contagious and cause vomiting and diarrhea, appear to be at their peak for the season, according to data from the Centers for Disease Control and Prevention (CDC).
The positive test rate for norovirus for the past three weeks has exceeded 15% on average.
This is
the highest infection rate recorded since the end of March 2022.
What are noroviruses and how are they transmitted?
Noroviruses are often called stomach flu, but they are not related to the flu virus.
Rather, it is a family of highly contagious viruses that often cause gastrointestinal symptoms such as
diarrhea, vomiting, nausea, and stomach pain.
They can also cause fever and mild pain.
A few virus particles are enough to make you sick.
The infection is easily spread through hands, surfaces, food, and water.
According to the CDC, an infected person can transmit the virus for days, even up to two weeks, after starting to feel well.
Percentage of Positive Tests in the US
These numbers reflect the average over three weeks, through February 8. Source: National Center for Immunization and Respiratory Diseases. Graphic: Nigel Chiwaya / NBC News
Until this Saturday, the Midwest region of the United States had the highest average number of positive cases of norovirus, with more than 19% positivity.
That number is the highest on record for any other week in the past year.
CDC tracks norovirus outbreaks through a network of 14 state health departments.
Although the network's data is lagging, its most recent tally indicates that state health departments reported
25 outbreaks through the first week of January
, the most since May.
Between August and early January, a total of 225 norovirus outbreaks were reported to CDC, up from 172 during the same period last season.
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“Norovirus outbreaks and cases reported by both state health departments and clinical laboratories are increasing, but remain within expectations for this time of year,” said Kate Grusich, CDC spokesperson.
“Prevention measures implemented during the COVID-19 pandemic were likely effective in preventing norovirus outbreaks.
As pandemic restrictions have been eased, the number of norovirus outbreaks has returned to levels similar to those of pre-
pandemic years,” he added.
How to avoid getting infected
Noroviruses are the leading cause of foodborne illness in the country.
Food can become contaminated if fruits or vegetables
are grown or washed with contaminated water
.
Oysters also pose a norovirus risk if harvested from contaminated water.
In December, a multistate outbreak was linked to the consumption of raw oysters in Texas, and nearly 300 norovirus cases were reported.
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Most norovirus outbreaks in the US occur between November and April.
On average, the country registers about 20 million cases a year, with about 110,000 hospitalizations and 900 deaths, the majority among people aged 65 and over.
There is no treatment for norovirus, but the
CDC recommends drinking plenty of fluids to prevent dehydration.
The disease usually regresses in a few days.
In England, norovirus rates this year are exceptionally high, according to the UK's Health Security Agency.
As of late January, norovirus laboratory reports were 66% higher than the average for the five seasons prior to the COVID-19 pandemic.
The agency attributes the increase primarily to people 65 and older reporting more about their health status.