Single clonal origin of a high proportion of Legionella pneumophila serogroup 1 isolates from patients and the environment in the area of Paris, France, over a 10-year period.

Arbitrarily primed PCR with three primers and pulsed-field gel electrophoresis were used to characterize a set of 75 clinical Legionella pneumophila serogroup 1 isolates, with no apparent epidemiological link, obtained from 24 hospitals in Paris, France, from 1987 to 1997. Unexpectedly, 25 clinical isolates from 15 hospitals had an identical profile (termed type A) by both methods. The same profile was subsequently found in 16 of 64 randomly selected environmental L. pneumophila serogroup 1 isolates from 15 different sites in the Paris area. There was no evidence of geographic clustering or a peak incidence of type A isolation. Type A has not been found in France outside the Paris area, suggesting that a particular type of L. pneumophila serogroup 1 is specifically present in the Paris water distribution network.