Airborne Influenza Transmission

Understanding how influenza is transmitted is key to limiting the impact of both seasonal disease and future influenza pandemics. An ongoing concern is that influenza may be transmitted from infected individuals not simply by coarse (>5 μm) respiratory particles, but also by fine (≤5 μm) respiratory particles that can persist in the air for prolonged periods.

To address this issue, investigators conducted a community-based study involving 142 volunteers with confirmed influenza infection during the 2012–2013 flu season. The researchers used both molecular and culture techniques to assess the presence of influenza virus in 218 paired nasopharyngeal (NP) swabs and 30-minute exhaled breath (fine and course) aerosol samples that were collected as the participants breathed normally, spoke, coughed, and sneezed during the first 3 days of illness.

Infectious virus was present in 89% of the NP samples and 39% of fine aerosol samples. Geometric mean RNA copy numbers for fine and coarse aerosol samples were 3.8×10⁴ and 1.2×10⁴ per 30 minutes, respectively, compared with 8.2×10⁸ per NP swab. The amount of viral shedding in fine aerosol samples declined with the number of days after symptom onset and was increased for males and with coughing, although shedding occurred without coughing or sneezing. Self-reported flu vaccination in both the 2012–2013 and previous flu seasons was associated with fine aerosol shedding but not NP or coarse aerosol shedding.