Reinfection with Legionella pneumophila documented by pulsed-field gel electrophoresis.

A 50-year-old man with chronic lymphocytic leukemia experienced two episodes of community-acquired legionnaires' disease. For determining whether this was the result of relapse or reinfection, Legionella pneumophila strains, cultured from sputum specimens and his home water supply, were characterized by pulsed-field gel electrophoresis. Analysis of the restriction patterns and the clinical data indicated that the second disease period was most likely the result of reinfection. We conclude that after diagnosis of community-acquired legionnaires' disease in an immunocompromised patient, culturing of the domestic water supplies for L. pneumophila should be considered; if such cultures are positive, adequate measures to prevent reexposure have to be taken.