Experimental Air-Borne Influenza Infection. I. Influence of Humidity on Survival of Virus in Air. ∗

The ease with which infections with influenza A virus can be produced in susceptible animals by allowing them to breathe virus-containing air suggests that this may be an important mode of dissemination of the disease in man. 1 2 3 Its importance would depend on whether the virus survived in the air sufficiently long for an infective level to be built up. Previous studies have shown that the air in small chambers into which virus had been sprayed was infective for mice up to one hour. 3 Further studies have been made concerning the physical factors which influence the survival of virus in larger spaces simulating room environments. The data reported here include the effect of relative humidity on the persistence of virus in the air.

The experiments were performed in a room of 800 cubic feet capacity (10 × 10 × 8 feet). The air of the room was gently and continuously agitated by means of a centrally placed, slowly rotating vertical fan. The temperature varied from 27 to 29°C. The low humidity experiments were carried out during the winter months. The higher relative humidities were obtained by vaporizing steam into the room before each experiment. Influenza A virus (PR-8 strain) was employed and prepared from infected mouse lungs. The amount of virus used in each experiment varied from 2.4 to 3.6 cc of a 10 1 dilution by weight of ground lungs in 10% horse serum and broth. It was sprayed into the room with an atomizer which produced fine uniform-sized droplets. Following the atomization of the virus, groups of 10 mice were placed in the room for 20-minute periods at increasing intervals of time.