New strains of norovirus now account for the majority of outbreaks nationwide, according to data from the Centers for Disease Control and Prevention. The emergence of a new strain, which has been confirmed to be circulating across the country and on cruise ships, explains the potential for infections over the past month. steep waves infection from stomach bug.
Scientists are calling this winter’s predominant norovirus strain GII.17 (P17). So far this season, samples taken from patients have tested positive for the new virus in nearly seven out of 10 norovirus outbreaks, according to data from a network of public health laboratories called CaliciNet.
“Although it is too early to tell whether this strain is associated with more severe norovirus disease, waning herd immunity may be the reason for the early spike in the likely seasonal increase in this virus. ,” said Jan Vinje, director of the CDC’s CaliciNet system. Get CBS News delivered to your email.
All previous waves of norovirus in the United States since 2012 have been dominated by a different strain that scientists call GII.4, Binje said. This season, only about 7% of norovirus outbreaks have been linked to the GII.4 strain.
Binier said the GII.17 strain is behind outbreaks “everywhere” across the country this season. highly contagious Contains a virus cruise ship occurrence.
The CDC has tracked at least six outbreaks of norovirus on ships last month, the most reported in the same month in more than a decade.
The most common cause is norovirus food poisoning Most people in the United States start climbing during the winter.
It’s impossible to know exactly how many Americans are sick because many cases resolve on their own without the need for medical testing or treatment. But virtually all data tracking the virus suggests norovirus is at peak levels across the country.
The rate of positive norovirus tests from different CDC laboratory networks is at its highest weekly level on record in years. Norovirus infection rates are also higher than past seasonal peaks, according to numbers from testing company BioFire Diagnostics.
In sewage, samples collected by WastewaterSCAN found “high” norovirus detection rates at nearly every facility the company monitors across the country.
Although versions of GII.17 have been in circulation for decades, it is only in recent years that this strain has caused a major wave of infections. A “sudden rise” in GII.17 was reported in some parts of Europe last year. The first waves of this tension were reported in Japan and China after 2014.
The CDC reported an increase in GII.17 cases last season, but it was a small number of all norovirus outbreaks in the United States at the time.
Is GII.17 causing an increase or worsening of norovirus cases?
Additional studies will also be needed to determine whether GII.17 is linked to differences in the severity of norovirus infections. Some previous changes to the virus appeared without causing new or significantly worsening symptoms.
“What we are seeing has happened before with noroviruses. Noroviruses are very diverse,” said Marion Koopmans, head of virus science at Erasmus MC.
Koopmans, who oversees a global consortium of norovirus researchers, warned that there are still gaps in data tracking norovirus cases around the world. Further research is also needed to prove whether this strain is actually causing an increase in disease.
“There are a lot of norovirus infections that occur every winter, and surveillance is pretty spotty, so I don’t think there’s enough surveillance to actually claim that this is causing an increase in the number of cases (my In my opinion),” Koopmans said.
When the latest GII.4 strain, called the Sydney variant, emerged in 2012, early data suggested it was causing an increase in outbreaks. The CDC then reported data from hospitals that suggested it was not actually leading to a significant increase or worsening of norovirus infections.
“Therefore, the observed increase in outbreak activity during the 2012-2013 season likely represents random seasonal and state variation rather than a direct result of the appearance of GII.4 Sydney.” concluded CDC scientists at the time.
Wisconsin health officials announced earlier this month that norovirus cases had hit an all-time high, but they told CBS News they don’t believe that makes a big difference in symptoms or duration of illness.
“It does not change recommendations regarding prevention or spread. This only means that we are in an outbreak period and therefore the importance of hand washing, staying home during illness and until at least 48 hours after recovery. “It’s an opportunity to really emphasize the importance of being present,” said Elizabeth Goodsitt. said a spokesperson for the Wisconsin Department of Health Services in an email.
