The United States is suffering its worst flu season in almost a decade. While most people understand that large droplets of fluid produced by coughing and sneezing can spread the virus, new research may explain why it seems so contagious. As Maggie Fox at NBC news reports, simply breathing may contribute to the spread of flu.
Researchers have long suspected that the flu virus could be airborne, but did not have enough data to say for sure. So researchers at the University of Maryland School of Public Health decided to investigate.
Researchers examined 142 people with confirmed cases of the flu. They swabbed the noses and throats of participants and then put them in a machine dubbed Gesundheit II, which measures the droplets produced by breathing, coughing and sneezing. They conducted 218 of these breathing sessions on patients, examining their saliva droplets for evidence of the flu virus.
In 76 percent of the fine aerosol particles collected from breathing, both when patients coughed or didn't cough, the samples contained detectable flu virus. But of the 23 samples in which patients did not cough, flu was still detected in around 48 percent, which suggests coughing may not be the only way to spread the flu. Just exhaling may release some amount of the virus into the environment. The research appears in the Proceedings of the National Academies of Sciences.
“People with flu generate infectious aerosols (tiny droplets that stay suspended in the air for a long time) even when they are not coughing, and especially during the first days of illness,” co-author Donald Milton says in a press release. “So when someone is coming down with influenza, they should go home and not remain in the workplace and infect others.”
Allison Aiello, a professor of epidemiology at the University of North Carolina who wasn't involved in the study, tells Fox that these latest findings sound reasonable. But, she adds, unlike other viruses like measles, studying how flu spreads is challenging. The virus constantly mutates and each different strain could have different transmissibility and different virulence from year to year.
This is not the first study to suggest that small droplets can carry flu virus. In 2013, researchers found that hospital patients being treated for flu had a six-foot radius in which small airborne infectious doses of the virus may travel. The study also suggests that some people can be super spreaders, producing 32 time more virus than other people. In another 2013 study, similar to but smaller than the latest study, Milton and his team found that fine airborne particles tend to carry almost nine times as much virus as coarse droplets.
The latest study, however, isn't the end all in the discussion of flu transmission. As Jamie Ducharme at Time reports, the study did not track transmissions of flu, so it’s not possible to say how infectious those tiny airborne particles are—or if they are infectious at all.
Do those tiny aerosol droplets matter? Milton is currently trying to figure this out in experiments with dormitory mates—one sick and one healthy. If the airborne drops do transmit flu, it could lead to new recommendations on how to prevent transmission in hospitals, classrooms, subway cars and other enclosed spaces.
But that future is still distant. Until then, it’s best to simply try to avoid becoming infected. “The take-home message is to stay away from other people when you’re sick with flu-like symptoms, even if you’re not coughing,” Milton tells Ducharme.
If the flu is spread by fine particles, even wearing a mask can’t stop you from spreading the virus or getting sick. “There’s not much evidence that any of that works very well. Surgical masks block mostly the large droplet spray, but the surgical masks don’t block the fine particle aerosols very well. The route of infection matters.”
What does work, or at least helps, is constant hand-washing, staying away from people who are coughing or obviously ill, avoiding closed rooms with poor air exchange and getting a flu shot.