Comparison of strains of Legionella pneumophila serogroup 1 isolated in four Amsterdam hospitals from patients and hot-water supplies.

Legionella pneumophila serogroup 1 was isolated from patients (14 strains) and hot-water taps (49 strains) in four hospitals in Amsterdam. Precipitation patterns obtained by reaction of heated cell suspensions and rabbit antisera in the double diffusion test revealed antigenic properties of serogroup 1 strains from water unique to each of the four hospitals. By this method similarity could be demonstrated between strains from patients and hot water in three of the four hospitals. No such relationship was present in the fourth hospital, a fact that could be explained by the case histories of the patients. Comparison of strain antigens in the double diffusion test is simple and suitable for epidemiological studies of L. pneumophila.