Influence of suspending liquid, impactor type, and substrate on size-selective sampling of MS2 and adenovirus aerosols

Size-selective sampling methods for detecting viral aerosols are needed to assess the risk of airborne transmission of disease. Andersen and MOUDI nonviable cascade impactors were used to separate test aerosols containing MS2 bacteriophage or adenovirus into size fractions spanning much of the human respirable range. Culture-based methods and a fluorescent tracer dye allowed quantification of the viral particles that remained infective after being aerosolized into a test apparatus and collected by the impactors. In addition, various suspension fluids and impaction surfaces were evaluated for their effect on virus viability. Both the Andersen and MOUDI impactors were able to sample live viruses from test aerosols, although the relative recovery rate of MS2 was higher than adenovirus (P < 0.001). The MS2 and adenovirus aerosols were sensitive to different test factors. MS2 recovery was dependent on the suspension fluid (P < 0.0001) and RH (P = 0.001), whereas adenovirus recovery was dependent on aerodynamic particle size (P < 0.001). Relative recovery of adenovirus was highest in the 0.56-1.9 m diameter range. The results confirm that nonviable cascade impactors are capable of size-separating and detecting aerosolized viruses in the human respirable range, and that MS2 and adenovirus can retain viability after nebulization under experimental conditions. The findings cast doubt, however, on the suitability of MS2 as a general surrogate for human and animal viruses.