Whilst the spread of influenza virus may commonly be thought to be due to coughing, sneezing, or contact with virus-laden surfaces, a new human volunteer study by researchers at the University of Maryland suggests that the act of breathing alone can spread the virus.
218 nasal swab samples were taken from 142 patients, aged 19-21, confirmed as suffering from either (or both) influenza A or B, while the patients also underwent 30-minute breath sampling capturing aerosols produced during normal breathing and speaking. Aerosols were collected via impaction, either directly (for particles > 5 µm, in this study termed ‘coarse’ particles) or following condensational growth (~ 50 nm to 5 µm, termed ‘fine’).
Of samples where no coughing was observed, viral RNA and active viruses were more likely to be found in the ‘fine’ fraction of aerosol than the ‘coarse’ fraction. This suggests that whilst coughing may produce larger virus-laden droplets from the upper airways, normal breathing alone can contribute significantly to virus aerosolisation. The findings could contribute to the modelling of influenza transmission and determining the effectiveness of measures intended to control spread of the disease such as increased ventilation and air filtration.