Differences in aerosol survival between pathogenic and non-pathogenic strains of Legionella pneumophila serogroup 1

A strain of Legionella pneumophila serogroup 1 known to be virulent for guinea-pigs was found to be least stable at a relative humidity (r.h.) of 60% when stored as a small particle aerosol. Three L. pneumophila serogroup 1 strains of different virulence for guinea-pigs were then tested at a r.h. of 60% at 20 degrees C. The most virulent strain was found to have the best survival and the avirulent strain was least stable. The strain of intermediate virulence did not survive as well as the virulent strain but was more stable than the avirulent strain. Strains of L. pneumophila serogroup epidemiologically associated with legionnaires' disease had better survival in small particle aerosols than strains which were not associated with disease. Subtyping with monoclonal antibodies also showed that the type more commonly associated with disease survived longer in aerosols than the other subtypes.