Influenza in the Hospital: Droplet or Airborne?

Jesse T. Jacob, MD


April 23, 2013

Editorial Collaboration

Medscape &


These findings cast some doubt on the traditional view that most influenza is spread through droplets, but this small, single-center study does have important limitations. The infectivity of the particles detected by PCR was not confirmed with culture. The airborne human 50% infectious dose was extrapolated from the tissue culture infectious dose and a standard minute ventilation parameter, with a resulting wide dynamic range (> 1 log), making interpretation of this parameter challenging.

Moreover, air sampling was not controlled for duration or severity of illness and time from initiation of antiviral therapy (although these were measured), all of which could confound the results, as could the presence of an unknown source of influenza (healthcare worker or family/visitor). Air sampling at more than 6 feet would have been even more informative. Given the short duration of air sampling (20 minutes), the finding of small particles containing viral elements at theoretically infectious doses suggests that transmission by aerosol may occur even outside of typical aerosol-generating procedures.

These results must be taken in context with the observations that influenza is overwhelmingly a community-associated infection and nosocomial airborne transmission has not been widely described. Furthermore, studies evaluating the use of N95 masks for influenza prevention have not shown superiority over typical droplet precautions at preventing disease in healthcare workers.

In conclusion, hospitalized patients can generate influenza-containing aerosols up to 6 feet with concentrations higher than the infectious dose, but these findings require confirmation before widespread changes in infection control strategies are implemented. In the meantime, prevention by vaccination and early treatment of appropriate patients with antiviral agents present clear opportunities.