We may pass the flu to others just by breathing, according to a study which contradicts the popular belief that people can catch the influenza virus by exposure to droplets from an infected person's coughs or sneezes.
The study provides new evidence for the potential importance of airborne transmission because of the large quantities of infectious virus researchers found in the exhaled breath from people suffering from flu.
"We found that flu cases contaminated the air around them with infectious virus just by breathing, without coughing or sneezing," said Donald Milton, from the University of Maryland in the US.
"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. So when someone is coming down with influenza, they should go home and not remain in the workplace and infect others," said Milton, lead researcher of the study.
The researchers characterised influenza virus in exhaled breath from 142 confirmed cases of people with influenza during natural breathing, prompted speech, spontaneous coughing, and sneezing, and assessed the infectivity of naturally occurring influenza aerosols.
For the study published in the journal Proceedings of the National Academy of Sciences, the participants provided 218 nasopharyngeal swabs and 218 half-an-hour samples of exhaled breath, spontaneous coughing, and sneezing on the first, second, and third days after the onset of symptoms.
The analysis of the infectious virus recovered from these samples showed that a significant number of flu patients routinely shed infectious virus, not merely detectable RNA, into aerosol particles small enough to present a risk for airborne transmission.
Surprisingly, 11 (48 per cent) of the 23 fine aerosol samples acquired in the absence of coughing had detectable viral RNA and eight of these 11 contained infectious virus, suggesting that coughing was not necessary for infectious aerosol generation in the fine aerosol droplets.
In addition, the few sneezes observed were not associated with greater viral RNA copy numbers in either coarse or fine aerosols, suggesting that sneezing does not make an important contribution to influenza virus shedding in aerosols.
"The study findings suggest that keeping surfaces clean washing our hands all the time, and avoiding people who are coughing does not provide complete protection from getting the flu," said Sheryl Ehrman, from San Jose State University in the US.
"Staying home and out of public spaces could make a difference in the spread of the influenza virus," Ehrman said.
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