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Norovirus is making its seasonal rampage through countries that include the U.S., the U.K. and Canada. Impervious to hand sanitizers and able to remain infectious outside the body for weeks, the notoriously unpleasant gastrointestinal virus can strike any time of year, but cases tend to peak in the Northern Hemisphere between November and April.
“It’s one of the many viruses that affects our GI tract, but it’s the leading cause of vomiting and diarrhea from acute gastroenteritis in all ages in the United States,” says Christopher Cao, an assistant professor of gastroenterology at the Icahn School of Medicine at Mount Sinai in New York City. “So it causes a whole lot of infection.”
As of early March, U.K. Health Security Agency data show cases are more than double the five-season average prior to the pandemic. Agency officials have said levels “are currently the highest we have seen at this time of year in over a decade.” According to the U.S. Centers for Disease Control and Prevention, an average of 16.3 percent of norovirus PCR tests were positive as of March 4, 2023, compared with 14.6 percent on March 5, 2022. The CDC says the total number of outbreaks so far during the 2022–2023 season is still within the range of past norovirus seasons. But the national numbers may not reflect what’s happening in states that do not participate in the CDC’s norovirus reporting.
“While I think that there is a pretty good trend that overall, throughout the country, the number of norovirus outbreaks have not really increased, I don’t think it’s completely representative of all the different communities in the U.S.,” Cao says. “Anecdotally, I’ve seen a lot of norovirus in New York [City] recently in my patients, and that may not necessarily be reflected in the data that the CDC is providing because they don’t collect data from New York [State].” The available New York City Health Department data do not specify norovirus as a culprit but do show a recent increase in emergency room visits for vomiting or diarrhea.
Other health experts also have a hunch that norovirus is behind this trend. The virus is suspected to have sickened more than 100 students at a Phoenix elementary school and has prompted a school closure in Livonia, Mich., a suburb of Detroit. The states whose health departments participate in the CDC’s norovirus tracking program are Alabama, Massachusetts, Michigan, Minnesota, Nebraska, New Mexico, North Carolina, Ohio, Oregon, South Carolina, Tennessee, Virginia, Wisconsin and Wyoming.
What gives this persistent pathogen its superpowers? And is there any hope of dodging it amid a possible outbreak? Scientific American spoke to some experts about this year’s situation.
What are the symptoms of norovirus and who is most at risk for severe symptoms?
The virus commonly causes profuse diarrhea and vomiting, along with nausea and stomach cramps. Symptoms begin about 12 to 48 hours after exposure and usually last roughly one to three days.
“People who’ve had it a lot of time will just sleep on the floor of the bathroom because they’re going a lot,” says Melissa Jones, a virologist and an assistant professor of microbiology and cell science at the University of Florida. “It’s pretty miserable. Most people recover but are pretty dehydrated for a couple days.”
Norovirus targets the cells that line the small intestine, but not much is known about how it attacks the body so profoundly in such a short time. “They cause hundreds of millions of infections worldwide every year, but we actually know relatively little about how the virus actually does it,” says Jones, who is currently investigating if interactions with the gut microbiome might aid norovirus’s pathogenicity, which is the case for poliovirus.
Norovirus sickens 19 million to 21 million people in the U.S. each year, according to the CDC. Most people recover quickly, but severe cases—particularly among children under age five, adults age 85 or older and the immunocompromised—can lead to hospitalization and sometimes death. Globally it contributes to an estimated 50,000 infant fatalities per year, mostly in developing countries. Fevers are rare with norovirus, Jones says, but immunocompromised people can develop them and have other prolonged symptoms. In very rare cases, norovirus infection can persist in immunocompromised individuals for weeks or years.