Ah, norovirus: the bane of cruise ships and terror of grade-school parents and teachers alike.
Aptly known as the “winter vomiting disease,” norovirus has the startling ability to tear through schools, households, and digestive systems with reckless abandon, as seen recently in Medford, where an elementary school closed for two days this week amid a suspected outbreak.
And while it’s still early on in cold and flu season, Medford might not be alone in the coming weeks and months.
“I don’t think it’s ever a good idea to admire a pathogen, but this one is pretty unbelievable,” said Dr. Richard Malley, an infectious diseases clinician at Boston Children’s Hospital.
“In some ways, norovirus is the perfect pathogen,” agreed Dr. Neil Maniar, director of Northeastern University’s master of public health program. “It’s highly contagious, it can last on surfaces for up to two weeks, and it’s very difficult to kill.”
Just 10 to 100 viral particles is enough to make someone sick with norovirus — a miniscule amount, and only a small fraction of what you’d typically find in a sick person’s bodily fluids, Malley pointed out.
“It’s true that sometimes in a family, you have the index case — you know, somebody brings it in — and then before you know it, everybody in the home is having the same symptoms,” he said. “And hopefully, [they’re] not inviting anybody else to visit them.”
The winter months offer something of a perfect storm for transmission as people attend holiday parties and spend more time indoors, coming into contact with the same high-touch surfaces or possibly contaminated food, explained Maniar.
The Centers for Disease Control and Prevention notes there are typically about 2,500 reported norovirus outbreaks in the U.S. each year, most commonly between November and April.
“So far, it looks like the seasonality trend is holding this year as well,” Maniar said.
That can be particularly devastating for educational settings like Medford’s Roberts Elementary School, where Principal Michelle Crowell reported a “high volume of stomach illness cases” Wednesday and more than 130 student absences.
With present students and staff also reporting “symptoms of an upset stomach,” the school opted to close Thursday and Friday so that a professional company could deep clean the building. The Medford Board of Health was also due to examine cafeteria equipment to rule out “other potential causes.”
Norovirus in schools
In schools, norovirus “can wreak a lot of havoc, because this is such a highly transmittable virus,” Maniar said. “It’s an environment where it becomes very easy for norovirus to spread, and then once it starts spreading, it doesn’t take much for a large proportion of the population to be exposed to it.”
Malley likewise noted that schools are a common site for outbreaks.
“The school environment is, you know, a wonderful place for children to learn and to socialize,” he said. “It’s also, unfortunately, a very good place for norovirus to be transmitted.”
Malley acknowledged it’s tricky to determine when to close a school during an outbreak, as Medford did, and he stopped short of discussing specific criteria. However, when case numbers balloon and standard interventions fail — for example, using industrial-strength cleaners and asking parents to keep children home for some time after they’ve been sick — “it’s very reasonable to consider closing the school for a while,” he said.
“That is obviously not something that schools do lightly, because school closures pose all sorts of issues — psychological, financial, educational, there’s all sorts of issues involved,” Malley continued. “But obviously it’s better than letting an outbreak of norovirus go rampant in a school.”
When a significant percentage of the population seems to be exhibiting symptoms, Maniar said, a school closure is “certainly one way to try to break the cycle.”
“Any time you’re dealing with a very contagious virus like norovirus, it’s really hard to put the brakes on it completely, but you can … disrupt the spread enough to potentially limit an outbreak, which in itself is beneficial,” he added.
Reflecting on the Medford school closure, Dr. Shira Doron, chief infection control officer for Tufts Medicine and hospital epidemiologist at Tufts Medical Center, noted norovirus typically sees smaller numbers of people getting sick over a longer period of time. She suggested further investigation is needed in Medford to rule out other potential causes.
“So, did they all eat the same thing?” she explained. “Did they all eat food that was touched by the same equipment or person? You know, [is there] some contaminant in their environment, or food that could have gotten a lot of people sick at the same time?”
Because norovirus is notoriously difficult to kill, “there is definitely rationale for professional cleaning,” Doron added.
“You have to use specific chemicals at a specific concentration and for a specific period of time, meaning the surface has to stay wet with that chemical for a certain amount of time,” she said. “And we know from the real world that things can go wrong in that process.”
A newer norovirus strain takes over
Complicating matters, the GII.17 norovirus variant has become increasingly prevalent over the past few years, growing from less than 10% of cases during the 2022–23 season to 75% during the 2024–25 season, according to the CDC. The agency also noted a prolonged outbreak season in 2024, with cases continuing into the summer “likely [as] the result of sustained circulation of GII.17.”
This year, data from WastewaterSCAN shows norovirus generally trending upward in Massachusetts since October.
“We don’t yet know in terms of severity or other characteristics of the symptoms whether it’s worse or not, but there are a couple things that are a little bit puzzling” about the GII.17 variant, Malley said. “One of them is that the outbreak seems to be starting a little earlier this year than we would have expected.”
That’s a concern, he said, because an epidemic that starts earlier than usual allows more time for people to become infected before the outbreak passes.
While there remains some uncertainty around the GII.17 variant, Maniar said it’s generally a good idea to try to get ahead of norovirus with frequent and thorough handwashing, surface disinfectants, and self-isolation when feeling unwell. Alcohol-based hand sanitizers don’t work well against norovirus, so the CDC recommends washing hands with soap and water.
People should also avoid touching their faces or putting their fingers in their mouths, Doron advised. She reminded families to disinfect high-touch surfaces such as door knobs, countertops, and toilets.
“I have had norovirus go through my house several times. My kids are in their 20s, so I’ve been through it and never got it,” Doron said. “I do attribute that to just really being conscientious of where my hands are going and how often I’m cleaning them.”
Both she and Malley said dehydration from norovirus can warrant a trip to the doctor or emergency room, with small children and immunocompromised individuals particularly vulnerable. Still, Malley pointed out that while highly contagious, norovirus is generally a self-limited infection that resolves within a few days without long-term consequences.
And while Medford’s school closure is certainly notable, he emphasized it’s not necessarily unusual when dealing with such a tricky virus.
“Parents should not be surprised when they hear that schools are closed because of norovirus, because that happens all the time,” Malley said. “It shouldn’t trigger people into [thinking of] the school closures of COVID and other things which, of course, are still fresh on many people’s minds.”
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