By Robert Preidt
In the study, researchers analyzed air around the exhaled breath of 142 people with the flu.
"We found that flu cases contaminated the air around them with infectious virus just by breathing, without coughing or sneezing," said study author Dr. Donald Milton, a professor of environmental health at the University of Maryland.
"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," he explained in a university news release. "So when someone is coming down with influenza, they should go home and not remain in the workplace and infect others."
In fact, nearly half (48 percent) of the airborne samples captured in the air around flu patients who were just breathing -- not coughing or sneezing -- contained detectable influenza virus, the researchers noted.
What's more, when patients did sneeze, that didn't seem to add much to the viral count in the samples, Milton's group added.
Of course certain steps -- "keeping surfaces clean, washing our hands all the time, and avoiding people who are coughing," can still help lower your odds of catching influenza, said Sheryl Ehrman, dean of the College of Engineering at San Jose State University, in California.
But if an infected person's breathing spreads flu virus, even those precautions do "not provide complete protection from getting the flu," she added.
That means that if you are unlucky enough to get the flu, "staying home and out of public spaces could make a difference," Ehrman said.
The researchers believe their findings could help improve mathematical models of the risk of airborne flu transmission and could also be used to develop better public health flu prevention measures.
For example, improvements could be made to ventilation systems in places such as offices, school classrooms and subway cars, to reduce the risk of flu transmission, the team said.
The United States is in the middle of a particularly nasty flu season, with nearly all states reporting high levels of severe flu, and hospitals swamped with cases. Experts blame the severity of this year's flu season on a particularly virulent strain of flu and prolonged periods of very cold weather.
The study was published Jan. 18 in the Proceedings of the National Academy of Sciences.