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Norovirus is easy to contract, but it can be difficult to recover from. Getty Images
  • A norovirus outbreak shut down an entire Colorado school district right before Thanksgiving.
  • Experts say norovirus is highly contagious and difficult to shake.
  • Tips on how to avoid the illness include thoroughly washing hands and staying away from people who are sick.

Dozens of schools in western Colorado are finally reopening this week after a suspected norovirus outbreak.

On its Facebook page, the Mesa County Valley School District 51 assured the community that its school buildings and buses had been thoroughly disinfected.

Students at the initial school began getting sick around Nov. 14. Then other schools began falling like dominoes.

A week before Thanksgiving, officials quickly closed all 46 schools in the district to try to reduce the spread of the outbreak among its 22,000 students.

This is the time of year we hear more about norovirus. And the illness can be brutal.

“When you have norovirus, the very dramatic symptom people have is often violent vomiting that hits you pretty suddenly,” said Amesh Adalja, MD, a spokesperson for the Infectious Diseases Society of America and a senior scholar at the Johns Hopkins University Center for Health Security in Baltimore, Maryland.

“You have nausea, vomiting, and diarrhea, and it usually lasts 24 to 48 hours,” he told Healthline. “It can be a pretty grueling 24 to 48 hours.”

The Centers for Disease Control and Prevention (CDC) reports the virus sickens millions of people each year. The very young, older people, and those with other illnesses are most vulnerable to severe dehydration.

Each year, as many as 71,000 people are hospitalized. Between 500 and 800 die.

“What’s very striking about norovirus is that it’s very highly infectious. And if you’re exposed to it, there’s a very high likelihood you could be infected by it, even if you’re in good health,” Adalja said.

Experts say that when someone is sick with norovirus, they have large amounts of the virus in them, although it only takes a little to make you sick.

“We know that people who have the virus shed it in very large numbers in their fecal material. We’re talking millions to billions of virus particles in a gram,” said Lee-Ann Jaykus, PhD, a professor in the department of food, bioprocessing, and nutrition sciences at North Carolina State University.

“It probably doesn’t take more than 100 particles to make you sick,” she told Healthline.

Jaykus says scientists know the virus is passed from person to person. That happens when an infected person doesn’t wash their hands after using the bathroom.

The surfaces they touch can become contaminated. If the infected person is a food handler, they can pass the virus onto your food.

They also know that when an infected person vomits, that surface will be contaminated.

But more recently, researchers learned that norovirus may also be transmitted in the air from the repeated vomiting.

“A lot of times this is what we call projectile vomiting, very forceful and severe, literally across the room,” Jaykus explained. “Some of that vomitus gets aerosolized, and it has norovirus in it.”

To study how this happens, Jaykus and a team of researchers actually built a vomiting machine to test how norovirus spreads. The machine simulated human vomiting.

The team used a surrogate virus, which wouldn’t make anybody sick. Then they measured the airborne virus particles.

The scientists published the findings of their study in the PLOS One journal in 2015.

“You can detect it. The numbers are not as high as in fecal material, but it’s there,” Jaykus added. “What happens is some of the virus gets aerosolized, people breathe it in. It hits the mucous membranes, goes into the stomach, and the infection process starts.”

And once it starts spreading through a community, the virus is hard to get rid of.

“This particular virus is extraordinarily resistant to the sanitizers and disinfectants that we commonly use at regulated concentrations and contact times,” Jaykus said.

“It’s also incredibly persistent. If I were to put norovirus on a surface in front of me right now, it would probably remain capable of causing infection for a month, maybe more,” she added.

Jaykus notes there’s no norovirus vaccine yet, although some are being developed.

“The real way to protect yourself is to wash your hands a lot. If you see somebody vomiting, go the other way. And if you’re on a cruise ship, tell somebody,” she said.

The CDC has put together some tips to help you keep norovirus from spreading:

  • Practice good handwashing for at least 20 seconds. Alcohol-based hand sanitizer alone won’t do.
  • Wash your fruits and vegetables. Cook seafood thoroughly.
  • If you’re sick, don’t cook or care for others for at least 2 to 3 days after you recover.
  • Clean contaminated surfaces first, then disinfect them. Use a chlorine bleach solution with a concentration of 1,000 to 5,000 ppm (5 to 25 tablespoons of household bleach [5.25 percent] per gallon of water) or other disinfectant registered as effective against norovirus by the Environmental Protection Agency.
  • Wash your laundry thoroughly.