The presence of a specific genotype of Legionella pneumophila serogroup 1 in a hospital and municipal water distribution system over a 12-year period.

The genotypic distribution of Legionella pneumophila serogroup 1 was investigated in the water distribution system of a 450-bed Swedish hospital and the surrounding community. A single genotype identified by amplified fragment length polymorphism (AFLP) analysis, was found in all 34 hospital isolates and in 18 out of 20 community isolates over a 12-y surveillance period. All isolates were either monoclonal antibody subtypes Benidorm or Bellingham. In a geographical comparison, the hospital genotype was also identified in 2 out of 6 Swedish hospitals, both located within 100 km of the studied community. In all, 70 isolates originating from 7 Swedish communities clustered in 4 groups, each also containing 1 AFLP type as defined by the European Working Group on Legionella Infections (EWGLI). It was concluded that a single Legionella pneumophila serogroup 1 genotype may colonize a large water distribution system over a long period of time, and that certain clones seem to be widely spread in the environment. Results from molecular typing of isolates originating from a limited geographical area must, therefore, be interpreted cautiously in epidemiological investigations of Legionnaires' disease.