Collection and measurement of aerosols of viable influenza virus in liquid media in an Andersen cascade impactor

The modes of person-to-person transmission of influenza viruses, particularly the contribution of airborne transmission via inhalation of fine (,5 microns) particles are highly debated. Furthermore, airborne influenza virus particles collected from patients in recent studies used methods that, unfortunately, cannot discriminate between viable (infectious) or nonviable virus. We aimed to assemble an aerosol-generating and -measuring system to safely generate size-characterized aerosols of viable influenza virus, and evaluated the method of use of a six-stage Andersen cascade impactor for the collection of influenza virus aerosols. The long-term goal was to develop a facile sampling method for use in future field studies of viable airborne influenza virus in clinical settings. Experimental results showed that the aerosol-generating system safely and consistently produced fine aerosols with a count median aerodynamic diameter (CMAD) of 0.87 μm. Sampling of aerosolized viable virus was first attempted by direct impaction of the aerosol onto monolayers of indicator cells. We found that cultures of MDCK and Mv1-Lu cells initially kept under a minimal layer of cell growth medium in plastic Petri dishes could survive short-term desiccation resulting from a flowing airstream, in an Andersen single-stage impactor (100% up to 4 minutes). Unfortunately, the cells’ sensitivity to the stresses of transport indicated that direct collection onto live cell monolayers was impractical outside of a laboratory setting. In contrast, recovery of viable virus was effective and facile if the aerosol was collected in liquid media in Petri dishes in an Andersen cascade impactor and then inoculated onto cell cultures. Collection efficiencies in all investigated air samplers ranged from 3%–6%, which highlights the need for more effective air samplers for airborne virus collection.