Norovirus is almost the perfect human pathogen because it mutates rapidly, it is highly contagious, and infected people shed it in high numbers.
Norovirus is almost the perfect human pathogen because it mutates rapidly, it is highly contagious, and infected people shed it in high numbers. Image courtesy NoroCORE Lab, NCSU

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<p>You may feel downright sick when you read how easy it is to get norovirus.

By Rose Hoban

Tens, even hundreds, of thousands of North Carolinians plunked down their hard-earned cash on a Powerball ticket this week, even though the odds of winning were about 23 million to one.

But according to NC State University food-safety researcher Ben Chapman, it’s far more likely that any one of those potential winners might be afflicted by norovirus – right now.

There are about 25 million cases of norovirus illness each year in the U.S.; about a quarter of them are associated with food. That means Americans have a one-in-16 chance of contracting norovirus in the course of a year.

“It’s safe to say that someone somewhere in North Carolina is barfing because of norovirus,” Chapman said Wednesday afternoon. “Your odds are pretty good, way better than winning the Powerball.”

And cases tick up significantly in winter months, he said.

“We freeze it to preserve it,” Chapman said. “Viruses are different from bacteria. They don’t need to be in a host; they can exist and persist. Winter just seems to be a good time for them, with the low humidity, and it’s cool.”

And people are cooped up together inside, spreading it around.

Sticky and sticking around

Persistence is one of the hallmarks of norovirus. Just ask Janet Clayton, the health director in Person County, where there was a big outbreak last fall.

“It’s a huge nightmare, especially when the outbreak is large and involves children,” she said.

Norovirus is more persistent on surfaces, different from other viruses, such as influenza, which lose their ability to infect people quickly. Image courtesy NoroCORE lab, NCSU.

Clayton’s nightmare outbreak started at Person High School on Sept. 2 and then spread to other schools, something that’s not unheard of, said Katie Overbey, a graduate student at NC State who is studying norovirus.

“You’ve got the kid in the elementary school who gets norovirus and now he goes home and his older sister is in the middle school,” Overbey said. “And now that kid’s teacher has to go give a talk in the high school, and now you have an entire school district that’s got it.”

And the virus is “sticky.” It can live for days, weeks, even months on a surface.

In Person County, they got lucky, Clayton said. The chain of transmission was broken by the Labor Day weekend, when kids were home for a few days and the district had time to really clean the schools.

Within about 10 days, it was over.

“We had a few more symptomatic individuals once the children returned, but not nearly the number that would have been affected if there hadn’t been a holiday weekend,” she said.

In the end, the Person outbreak had at least 99 affected people. Workers from the health department interviewed more than 600 people to investigate the outbreak, but they never found the initial source of infection.

In the meantime, the school district made a huge effort to wipe down everything with a dilute bleach solution to kill the virus.

Other cleaners just don’t cut it, Overbey said, not ammonia, not alcohol.


A lot of it.

This transmission electron micrograph reveals norovirus virions, or virus particles. Photo credit: Charles D. Humphrey, Centers for Disease Control and Prevention

“Norovirus is very, very, very resistant to most disinfectants used at manufacturer-recommended concentrations,” said Lee-Ann Jaykus, a food microbiology professor at NC State. “Actually, add another ‘very’ to that sentence.”

Jaykus said effectively cleaning up norovirus from a spot where someone vomited or pooped requires a concentration that’s at least five tablespoons of bleach per gallon of water. Better yet, about a half cup of bleach in a gallon of water if the surface came in contact with vomit or poop.

“But no one wants to use those high concentrations of chlorine because they cause bleaching of fabric,” Jaykus said. “And from a food-manufacturer standpoint, you don’t want to use those high levels of chlorine because they can have negative impacts on your food-preparation surfaces, and they exceed what’s allowed by FDA or EPA.”

Super pathogen

Why is norovirus so good at making humans sick? (By the way, Chapman said you can not get it from your dog.)

Norovirus is almost the perfect human pathogen because it mutates rapidly, it is highly contagious, and infected people shed it in high numbers. Image courtesy NoroCORE Lab, NCSU

“When it gets into the human body, it replicates quickly, and makes millions of particles,” Chapman said. “It takes over cells [and] releases more virus by making us have explosive diarrhea or projectile. So it spreads really well.”

And in case you haven’t figured it out by now, norovirus is really persistent in the environment.

“It can affect someone six weeks from now if they go into a restroom that wasn’t cleaned well,” Chapman said.

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Jaykus’ tips to avoid a norovirus infection

  • Frequent and thorough hand washing: “When momma said you have to wash your hands, she was right. You have to wash your hands throughout the day.”
  • “Don’t rely on hand sanitizers, they’re not a good replacement for handwashing. It doesn’t mean you shouldn’t use them, because they work against other pathogens. But for norovirus control, handwashing is best.”
  • “If you’re going to clean up after a vomiting or fecal contamination event, you’ve got to use high concentrations of chlorine. Clean first and then disinfect.”
  • Stay home; the virus takes about 48 hours to resolve. “Person County is a great example. A lot of people who called in sick to school were not sick, they just didn’t want to get the virus.”


That’s, in part, because of the structure of the virus. Norovirus has a lot of RNA packed into its tiny shell. Chapman explained that to the human immune system norovirus looks like a bunch of RNA with some surface receptors, something our immune systems are not great at creating antibodies against.

And unlike other viruses, it seems humans don’t create immunity against norovirus, which might explain why it’s estimated that in a 70-year lifespan a person will have six or seven incidents of norovirus.

North Carolina connection

One of the reasons we know so much about norovirus is because of Jaykus. In 2011, she was awarded a $25 million federal grant to create a consortium of norovirus researchers across the country. That group, called NoroCORE, has its hub at NC State.

The group has done a lot of seminal research on norovirus, she said. So now we know about what surfaces resist the growth of norovirus and how best to clean them. We now know more about the basic structure of the virus, how much of it is needed to make people sick and how it’s transmitted.

For her research, Jaykus built a vomiting machine.

“The vomiting machine was to prove that virus could be released into the air with a vomiting incident,” she explained. “The idea there was that if that’s true, it facilitates spread.”

Lee-Ann Jaykus in her lab. Image courtesy NC State University

She said epidemiologists suspected for a long time that when you vomit on the floor, it also got into the air, making people sick even if they never touched the place where the vomit landed.

“We made this model and enumerated how much virus was aerosolized,” Jaykus said.

One of the goals of the research is to create guidelines for prevention and cleanup for restaurants, schools and nursing homes, where norovirus outbreaks happen most frequently.

“We realized that norovirus is where it’s at when it comes to food-borne illness,” she said. “It’s amazing that we are not all barfing all the time.”

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