How bad of a norovirus wave is the US in for? 

Things could get real shitty.

Tired of bad infectious disease news clogging up your timeline? Sorry, bestie: Norovirus has entered the chat.

The bug, which causes intense but blessedly short episodes of vomiting and diarrhea — with or without a brief period of fever, chills, and body aches — has been on the rise in the UK.

And an uptick of cases has recently begun to appear in the US, too: As of February 4, 17 percent of norovirus tests in the US were coming back positive — more than at any point last season.

Is a big US norovirus wave upon us?

Maybe — and it wouldn’t be that shocking. Winter is and has always been norovirus season, and it’s not at all uncommon to see cases rising at this time of year.

From the data currently available, it’s hard to tell if the US is in for a shitstorm (sorry). And while it’s not entirely clear yet what this year’s norovirus trends will be, it’s still a very, very good idea to practice meticulous hand hygiene.

Seriously, wash your damn hands: Norovirus is primarily spread when traces of a sick person’s poop or vomit sneak into our mouths via our hands or food they’ve prepared. However, the virus also spreads through aerosols that hang around after someone barfs, so masking in public bathrooms is not the worst idea, either.

Even though norovirus numbers aren’t yet out of control, experts say the pandemic probably left us a little more vulnerable to the infection than we were before the pandemic in a number of ways. So if cases continue to rise, don’t be too surprised.

The data suggest pretty normal US norovirus trends — so far

It’s hard to know exactly how much norovirus is circulating in the US at any given moment: Many people don’t seek medical care for symptoms, and even if they do, norovirus isn’t a disease that doctors and laboratories are required to report when they diagnose it.

For that reason, the Centers for Disease Control and Prevention (CDC) doesn’t gather norovirus data from randomly selected laboratories or clinics. Instead, it counts norovirus outbreaks, clusters of cases all related to the same source — for example, in the same school, or from eating at the same restaurant. (States have varying rules about when schools and restaurants need to report outbreaks to them — but whatever those rules, all states must report the outbreaks they hear about onward to the CDC.)

Making things a bit more complicated: For the purposes of evaluating and comparing norovirus trends year to year, the CDC counts outbreaks not from the entire US, but from a sampling of 14 states across the nation. And during the pandemic, many states redirected most of their public health resources to Covid-19 — which means more norovirus outbreaks than usual might’ve gone uninvestigated and uncounted.

All told, this means the CDC’s numbers are a pretty significant underestimate of community norovirus spread, perhaps especially so over the past few years, said Lee-Ann Jaykus, a North Carolina State University microbiologist who directs NoroCORE, a food virology collaboration among multiple federal agencies. So CDC metrics are best viewed as an indicator of patterns — not as an accurate reflection of the number of norovirus cases rolling through communities.

In the week between December 26 and January 2, the number of norovirus outbreaks nationwide increased from 15 to 25 (a CDC representative said an update to these numbers is expected in the next week).

Notably, the uptick in outbreaks as of early January (shown in the orange line in the chart below) is only higher than the number of outbreaks that occurred at the same time of year during the Covid-19 pandemic (shown in the blue lines). Compared with pre-pandemic levels (which fall within the gray shaded area), these numbers are actually on the low end of normal for late December and early January.

It’s hard to make pronouncements about the current state of norovirus transmission on the basis of six-week-old numbers.

But if trends across the Atlantic are any indication — as they’ve often been with other infectious diseases — Americans can expect to see norovirus rebound to pre-pandemic levels this spring. As of now, although the virus is clearly on the rise in the US, there are no signals of a stratospheric increase, or a jump in cases at an unusual time of year.

That said, some scientists are a bit worried about an intensified threat from norovirus this year.

Pandemic-era protective behaviors protected us — but also set us up for a potentially bad season

We might not yet be seeing evidence of a huge seasonal norovirus surge. But the window of barfportunity is not yet over — and in some ways, the pandemic did leave us more vulnerable to norovirus than we were a few years ago.

The preventive measures people took to prevent the spread of Covid-19 — measures that intensified during last winter’s omicron peak — also prevented the spread of norovirus, said Jaykus. “Anything having to do with hand hygiene or surface disinfection” would greatly reduce transmission of the pathogen, she said, but “the biggest driver was the fact that people were not gathering in enclosed settings.”

So people were not exposed to norovirus as much during the pandemic — and that potentially makes them more vulnerable now. We’ve seen similar patterns with other viruses: Reduced RSV and flu transmission during the pandemic led to low population-wide levels of immunity to those infections — a concept that’s sometimes called “immunity debt” — and these viruses then tore through unprotected populations late last year.

In a similar way, reduced norovirus transmission during the pandemic might have left us less protected against that germ’s eventual resurgence.

As with RSV and flu, norovirus is spread largely by and among children. And much as they do with those other infections, people who catch norovirus do retain some protection from the specific strain that caused their illness for months or even years afterward.

Pandemic-era school closures and childcare precautions, especially avoiding gatherings, led to an interruption in norovirus spread — and therefore, an interruption in norovirus immunity.

Another change that affects the US’s norovirus risk is a little less intuitive, said Jaykus — and it has to do with changes in the nation’s labor market. One important source of norovirus outbreaks is restaurants — specifically, restaurant workers who show up to work sick. Restaurants have clear guidelines around hand and surface hygiene that theoretically should prevent transmission even from a worker who’s still shedding the virus. Nevertheless, a major preventive measure for reducing the spread of norovirus (and other foodborne diseases) is preventing workers from coming to work sick.

The problem is that right now, there’s not much slack in most restaurants’ systems to allow workers to stay home when they’re sick, said Jaykus. Not only is sick leave often unpaid, but because the labor market for restaurant workers has been so tight, workers may often feel pressured to come to work even if they’re feeling unwell, she said. And in an understaffed kitchen, people are incentivized to cut corners, cleaning hands and surfaces less often or less thoroughly than the guidelines suggest.

The good news: There’s no sign of a new norovirus variant — and old-school tools still work

In previous bad norovirus years, novel strains of the pathogen wreaked havoc because there was so little population immunity against them. That’s not what’s happening this time, said Jan Vinjé, who leads the CDC laboratory that monitors a range of viral infections nationwide. As of January 31, the norovirus strain responsible for the largest number of cases was the “Sydney” strain, which has been the dominant strain for the past few years.

Fortunately, hand washing, careful surface cleaning, keeping a distance from actively sick people, and masking if there’s a chance someone recently barfed in your vicinity still work to prevent the spread of this nasty infection. But to a certain degree, when kids are back in school, norovirus transmission is almost inevitably going to rise, said Jaykus. Children don’t wash their hands as regularly or as thoroughly as adults do, and they’re “in each other’s faces all the time,” she said.

And they don’t live alone. “Literally, if you have a little kid and he or she brings norovirus home, everybody’s gonna be sick,” said Jaykus.

If you do catch norovirus, take care of yourself and protect others

If you do get infected with this very gnarly bug, take some small comfort in the fact that it usually goes away almost as quickly as it comes on.

Staying hydrated is key: While nauseated, sip water or an electrolyte drink every 15 to 30 minutes, and if you feel like lying down afterward, prop yourself up to reduce reflux. There’s no need to slam a liter of fluid at a time — you just want to get enough in to produce some urine at least every six hours. Wait until you have an appetite to start eating solids, and start with bland foods like bananas and dry toast.

Alcohol-based sanitizer doesn’t kill norovirus all that well, so clean your hands with soap and water. And clean shared surfaces with a bleach-based product — only a few virus particles are needed to cause infection, and it can live for weeks on surfaces, so be as thorough as you can.

If you develop bloody diarrhea, you can’t keep enough fluids down to make some urine, or your symptoms last longer than three days, it’s time to seek medical care.

Otherwise, thank your lucky stars it’s over, and keep washing those hands: People often shed norovirus for weeks after that first spectacular bathroom moment.