It’s flu season. The National Institute for Occupational Safety and Health (NIOSH) conducts research on protecting health care providers and other workers from infectious diseases including influenza. A significant portion of our research deals with understanding how the influenza virus is transmitted. Influenza is known to be transmitted through respiratory secretions containing the virus. Airborne transmission of influenza by small aerosol droplets over longer distances is debated in the literature. Coughing, sneezing, speaking and breathing all generate potentially infectious aerosols (small airborne particles). Several studies suggest small aerosol particles can carry influenza virus, but how important is this route of transmission? If patients can readily infect others via aerosols produced during coughing, speaking, sneezing, and breathing, then interventions such as patient isolation and cohorting (grouping those exposed to a similar disease), increased air ventilation and filtration, air disinfection, and the use of respirators or other personal protective equipment may help to protect healthcare workers and other patients from the illness. Such precautions will not likely be implemented without data to support transmission as such interventions can be costly and time-consuming. A summary of one NIOSH study on influenza A virus detected in coughs and exhalations follows. Additional transmission research is available on the NIOSH website.
NIOSH researchers compared aerosol particles containing viable influenza virus generated during coughs and exhalations[i]. In this study, 61 adult volunteer outpatients with influenza-like symptoms were asked to cough and exhale three times into a spirometer. Fifty-three test subjects tested positive for influenza A virus. Of these, 28 (53%) produced aerosol particles containing viable influenza A virus during coughing, and 22 (42%) produced aerosols with viable virus during exhalation. Thirteen subjects had both cough aerosol and exhalation aerosol samples that contained viable virus, 15 had positive cough aerosol samples but negative exhalation samples, and 9 had positive exhalation samples but negative cough samples.