Epidemiological evidence of legionellosis transmission through domestic hot water supply systems and possibilities of control.

The use of epidemiological markers for a survey is essential because of the ubiquity of legionellae, particularly L. pneumophila serogroup (SG) 1. The two settings under study were an administrative building associated with a fatal Legionnaires' Disease (LD) case due to L. pneumophila SG 1, and a hospital with 11 cases due to L. pneumophila SG 1 and 3 cases due to L. anisa. Monoclonal antibody serotyping allowed us to establish a link between the outbreaks of LD and the contamination of the hot water supply systems. Two subtypes of L. pneumophila SG 1 and L. anisa were detected in the hospital water system. However the finding of only one subtype of L. pneumophila SG 1 in the patients raised the problem of the difference in virulence of each Legionella strain. By means of aerosol tests on normal and cyclophosphamide-immunosuppressed guinea pigs, we demonstrated the potential pathogenicity of hospital water in the immunosuppressed animals. Two decontamination methods were applied: chlorination and a rise in hot water temperature. Time-limited control measures in the hospital were inadequate, resulting in only temporary eradication, followed by a rapid recolonization of legionellae and the appearance of new nosocomial cases. Decontamination of the administrative building was found to be effective when a constant concentration of 5 ppm free chlorine was obtained at tap outlets, and the water temperature was maintained at 55 C.

Isolation of Legionella anisa from a hospital hot water system.

Several cases of Legionnaires' disease occurred in a French hospital in 1982. Thirteen strains of a legionella-like organism with several unusual characteristics were subsequently isolated from the hospital hot water system. The various features of these strains show that they are identical to the new species 'Legionella anisa' described by the Centers for Disease Control. The possible pathogenicity of these strains to man and their relationship with the recently described Legionella bozemanii serogroup 2 are discussed.