Dependence of Aerosol-borne Influenza A Virus Infectivity on Relative Humidity, Aerosol and Air Composition

GHISLAIN MOTOS, Aline Schaub, Laura Costa Henriques, Celine Terrettaz, Christos Kaltsonoudis, Irina Glas, Klein Liviana, Nir Bluvshtein, Beiping Luo, Kalliopi Violaki, Marie Pohl, Walter Hugentobler, Ulrich Krieger, Spyros Ν. Pandis, Silke Stertz, Thomas Peter, Tamar Kohn, Athanasios Nenes, Shannon David, EPFL, Switzerland

     Abstract Number: 60
     Working Group: Health-Related Aerosols

Abstract
Influenza causes 250’000 to 500’000 deaths and 3 to 5 million cases of serious illness each year and is arguably the most feared potential public health emergency globally. Aerosol experiments investigating the impact of relative humidity (RH) and aerosol matrix composition on the infectivity of influenza A virus (IAV) have suffered a lack of standardization and characterization of important parameters, leading to large discrepancies in the results reported in the literature. Surprisingly, the composition of the air surrounding the virus-containing particles only became a research focus area in very recent years. We developed a novel biosafety aerosol chamber equipped with state-of-the-art instrumentation for bubble-bursting aerosol generation, size distribution measurement, and condensation-growth collection to minimize sampling artifacts when measuring virus infectivity in aerosol particles. Using this facility, we investigated the effect of RH in very clean air without pH-modifying trace gases (except ~400 ppm CO2) on the preservation of IAV infectivity in saline aerosol particles. We characterized infectivity in terms of 99%-inactivation time, t99, a metric we consider most relevant to airborne virus transmission. The viruses remained infectious for a long time, namely t99 > 5 h, if RH < 30% and the particles are effloresced. Under intermediate conditions of humidity (40% < RH < 70%), the loss of infectivity was most rapid (t99 ≈ 15-20 min, and up to t99 ≈ 35 min at 95% RH). We added sucrose to our aerosolization medium and observed a modest protection of IAV at intermediate RH (55 %). Through a combination of chamber experiments and modeling, we tested the potential of acidic vapors to condense on aerosol particles, decrease their pH and inactivate the IAV they contain. We discuss the potential for humidification and acidification as possible intervention strategies for preconditioning air to minimize the risk of IAV transmission in indoor environments.