Humidity-Dependent Survival of an Airborne Influenza A Virus: Practical Implications for Controlling Airborne Viruses

Relative humidity (RH) can affect influenza A virus (IAV) survival. However, the mechanism driving this relationship is unknown. We hypothesized that the RH-dependent survival of airborne IAV could be predicted by the efflorescence/deliquescence divergent infectivity (EDDI) hypothesis. We determined three distinct RH response zones based on the hygroscopic growth factor of carrier aerosols. These zones were classified as the super-deliquescence zone (RH > 75%), the hysteresis zone (43% < RH < 75%), and the sub-efflorescence zone (RH < 43%). We added IAV (H3N2) to protein-enriched saline and aerosolized it into sub-efflorescence or super-deliquescence zone air, yielding aerosols in the effloresced or noneffloresced state, respectively. We then adjusted the RH to an ergonomically comfortable RH (60%). Fifteen minutes post-aerosolization, the surviving fractions (arithmetic means +/- standard errors) of virus were higher in effloresced aerosols (9.5 +/- 0.5%) than in non-effloresced aerosols (0.40 +/- 0.05%). A virus suspension was also aerosolized directly into air within the super-deliquescence, hysteresis, and sub-efflorescence zones to assess the impact of the sudden change in RH from an initial 100% saturated RH to these zonal ranges. Fifteen minutes post-aerosolization, the surviving fractions were 3 +/- 0.4%, 2 +/- 0.1%, and 12 +/- 2%, respectively. Survival following gradual adaptation to the hysteresis zone RH range was sustained in effloresced and reduced in the non-effloresced aerosols. The EDDI model predicted the survival of IAV under seasonal conditions, offering strategies for controlling indoor air infection.

Automated summary

Relative humidity (RH) can affect the survival of influenza A virus (IAV), and the survival can be predicted by the efflorescence/deliquescence divergent infectivity (EDDI) hypothesis. The study found different survival rates of IAV in effloresced and non-effloresced aerosols, with implications for controlling indoor air infection. The sudden change in RH from saturated to specific ranges also impacted the virus survival differently, supporting the EDDI model for predicting IAV survival under seasonal conditions.