Infectivity of influenza virus aerosols

The PR 8 strain of influenza virus can remain viable in ageing aerosols for considerable periods (Harper, 1961). However, viability of micro-organisms determined by their growth in vitro may not indicate their ability to infect animals via the respiratory route (Schlamm, 1960; Hood, 1961). If influenza is normally transmitted via this route it is epidemiologically important to establish whether any correlation exists between viability as measured by in vitro or in ovo methods and respiratory infectivity for a susceptible animal host. Previous reports on respiratory infectivity of aged influenza virus aerosols by Edward, Elford & Laidlaw (1943), Loosli, Lemon, Robertson & Appel (1943a) and Loosli, Robertson & Puck (1943b) lack such a comparison. Recently developed in vitro techniques for influenza virus assay (Fazekas de St Groth & White, 1958a), for holding aerosols for long periods (Goldberg, Watkins, Boerke & Chatigny, 1958) and for assessing physical decay of aerosols (Harper, Hood & Morton, 1958) facilitate a study of this kind. This paper describes an attempt to determine whether two strains of influenza virus lose respiratory infectivity with ageing in aerosols.