Bad news: You know that last stomach bug you picked up, the one that gave you stomach cramps, diarrhea and nausea? You might have gotten that one because you got someone's vomit in your mouth.
Norovirus, the leading cause of stomach and intestinal infections in the United States, can be transmitted via airborne vomit particles, according to researchers who built a vomit machine to prove this unpleasant fact.
"Even though it's a small percentage [of the virus particles] that makes it into the bio-aerosolized form, and the majority is in the liquid form, when you convert these small percentages to absolute numbers, the numbers are large enough that they're above the infectious dose of the norovirus," study researcher Francis de los Reyes III, an environmental engineer at North Carolina State University, told Live Science.
In other words, even just a few airborne, vomited viruses can make you sick.
Norovirus causes about 21 million cases of illness a year in the United States, sending as many as 71,000 people to the hospital, according to the Centers for Disease Control and Prevention (CDC). Between 570 and 800 people in the U.S. die yearly from norovirus infections. [7 Devastating Infectious Diseases]
Much of the time, norovirus gets transmitted by the fecal-oral route, which is exactly what it sounds like. Often, feces-contaminated food or water is the culprit.
But outbreaks on cruise ships and in hospitals and restaurants have suggested that vomit can spew the virus around, too. For instance, some research has found that the closer people are to a vomiting incident in a room, the more likely they are to catch the virus, de los Reyes said.
To find out if puke could really be a pathway for norovirus' spread, North Carolina State University researchers, led by food scientist Lee-Ann Jaykus, decided to do something pretty weird. They built a vomiting device.
The device is a series of tubes, built to represent the human upper digestive system at one-quarter scale. A PVC pipe with a piston in it represents the stomach; a ball valve acts as the lower esophageal sphincter, which is the band of muscle that normally prevents the stomach contents from coming up. During vomiting, this band relaxes and gives vomit a way to escape.
A 2.5-inch (6.35 centimeter) flexible tube represents the esophagus, and a shorter tube stands in for the mouth. An agonized clay face tops off the creation, which spews its fake vomit into a sealed Plexiglas box. This box is equipped with a sensor that collects aerosolized particles that researchers can analyze for signs of virus.
Building the device was not so hard, de los Reyes said. Nevertheless, developing and calibrating it correctly took about three years.
"It really is quite difficult to create a vomiting machine because of the lack of data about the physics of vomiting," he said. "There's just not a lot known out there in terms of parameters." [7 Germs in Food That Make You Sick]
The vomit machine can't handle chunky substances, but the researchers can simulate a variety of vomit viscosities. Artificial saliva mimics watery barf, while vanilla flavor instant Jell-O pudding stands in for the thick stuff.
Noroviruses don't grow well in the lab, so the researchers used an equivalent (and harmless to humans) stand-in, a virus called MS2. In experiments, the researchers pushed a few times on the hand pump to pressurize the "stomach," and then flipped open the ball valve to shoot vomit out of the tiny clay mouth.
Experiments with different pressures and consistencies of vomit revealed that viral particles do, in fact, aerosolize. This means that a puking episode can send a fine mist of norovirus into the air.
At maximum, only about 0.01 percent of the virus contained in the vomit became aerosolized, the researchers reported today (Aug. 19) in the journal PLOS ONE, but that's more than enough to cause problems. Even episodes with the lowest levels of aerosolization would send 13,000 viral particles rocketing into the air. It takes only 20 to 1,300 viral particles to make someone sick.
Another study, published in May in the journal Clinical Infectious Diseases, found viable norovirus in air samples taken from hospitals and long-term care facilities in Canada. That study found the virus traveled several meters from its source.
And other research, that used a vomiting robot called Larry, has shown how barf can splatter.
The new study suggests that workers who clean up vomit in hospitals or restaurants, should use protection such as face masks, de los Reyes said.
The findings also open up new avenues of research into norovirus transmission. For example, aerosolized virus particles might cling to dust motes in the air, allowing them to float farther afield from the site of the puking incident. Norovirus can live for several days on surfaces, de los Reyes said. Bleach and hand-washing are the best defenses, according to health officials.
As for what to do when someone nearby is throwing up? The best solution is the simplest, de los Reyes said.
"You stay away," he said.