Use of sequence-based typing for investigation of a case of nosocomial legionellosis.

A fatal case of nosocomial legionellosis in a low prevalence region (Calgary, Alberta, Canada) prompted investigation into the source of infection. Hospital water systems contaminated with Legionella pneumophila have been shown to pose a risk to compromised patients. Typing of an L. pneumophila serogroup 1 strain isolated from the patient using sequence-based typing (SBT) and amplified fragment length polymorphism (AFLP) analysis linked it to a persistent and widespread strain isolated from the hospital water system establishing a nosocomial mode of acquisition. Different SBT and AFLP patterns were determined for non-epidemiologically linked cases and isolates from different hospitals.