Norovirus is a huge public health problem, sickening as many as 21 million people a year in the U.S. But for all the gastric distress it causes, there are still some basic, unanswered questions about the virus.
One biggie: When an ill person vomits, does norovirus become aerosolized? That is, can an ill person's vomiting launch tiny viral particles into the air, where they might waft into your mouth or onto surfaces that you would later touch?
If you're now grossed out, you have good reason. Studies of the infection patterns that occur in outbreaks suggest that norovirus can indeed be aerosolized. And now there's some experimental evidence to add to that.
Researchers at North Carolina State and Wake Forest universities wanted to know what happens to norovirus when it's vomited out. "We first talked to a gastroenterologist and looked through the literature about what's known about vomiting," says Lee-Ann Jaykus, a food microbiologist at N.C. State and an author of the study. Not as much as you might think, it turns out. So the researchers worked with a civil engineer to construct a one-quarter scale vomiting device based on what is known about pressure, volume and other vomit metrics.
The device allowed the researchers to control the volume, viscosity and pressure of the simulated vomiting incidents. Jell-O instant pudding was added to make the lab vomit thicker.
Then they ran a series of experiments, changing the variables to simulate a range of vomiting behavior. They even ran one series of incidents with post-vomit retches.
Though they conducted the experiments in a sealed Plexiglas box under a biosafety hood, norovirus was still too dangerous to use. A person sick with norovirus can spread billions of infectious particles, and only 18 are enough to make another person ill, the Centers for Disease Control and Prevention says.
So the researchers enlisted a harmless stand-in, a bacteriophage that is often used in place of norovirus in experiments. Only a fraction of virus particles were aerosolized during a typical vomiting incident. But there were definitely enough to make you sick.
The results appear in the journal PLOS ONE.
Another recent study collected air samples from eight health care facilities during norovirus outbreaks and found viral particles outside patient rooms.
"Taken together, they start to paint a pretty good picture of why norovirus is so atrociously infectious," says Andrew Pavia, chief of the division of pediatric infectious diseases at the University of Utah and a spokesman for the Infectious Diseases Society of America.
Of course, though the researchers did their best to simulate human vomiting, they didn't do a complete mock-up of the human digestive system. (A robot named Vomiting Larry is more anatomically accurate, but is less precise with regard to pressure, says Pavia.) And while the bacteriophage was chosen because of its similarity to norovirus, it may not behave the same way when aerosolized, he says.
Katherine Hobson is a freelance health and science writer based in Brooklyn, N.Y. She's on Twitter: @katherinehobson