Flu may be spread by breathing

It is easier to spread the influenza virus (flu) than previously thought, according to a new University of Maryland-led study. People commonly believe that they can catch the flu by exposure to droplets from an infected person's coughs, sneezes or by touching contaminated surfaces. But, new information about flu transmission reveals that flu may be pass to others by breathing.

Infectious virus in exhaled breath of symptomatic seasonal influenza cases from a college community 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. Flu cases contaminated the air around them with infectious virus just by breathing, without coughing or sneezing.

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. Researchers from the University of Maryland, San Jose State University, Missouri Western State University and University of California, Berkeley contributed to this study.

Dr. Milton and his research team captured and characterized influenza virus in exhaled breath from people with influenza during natural breathing, prompted speech, spontaneous coughing, and sneezing, and assessed the infectivity of naturally occurring influenza aerosols. The participants provided nasopharyngeal swabs and 30-minute 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%) of the 23 fine aerosol samples acquired in the absence of coughing had detectable viral RNA and 8 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. Keeping surfaces clean, washing of hands all the time, and avoiding people who are coughing does not provide complete protection from getting the flu. Isolation of infected people from public places can reduce the spread of  the influenza virus.
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