Monoclonal antibody reactivity as a virulence marker for Legionella pneumophila serogroup 1 strains.

Using a panel of nine monoclonal antibodies, we subgrouped 85 environmental and 129 clinical Legionella pneumophila serogroup 1 isolates from Paris, France. Patients were unlikely to be epidemiologically linked either with each other or with the 44 sampled environmental sites (14 air conditioning systems and 30 buildings) that were selected at random in the Paris area. According to their monoclonal antibody patterns, isolates belonged to 14 subgroups. Monoclonal antibody 2 recognized 121 (93.8%) of 129 clinical isolates and 30 (35.3%) of 85 environmental isolates (P less than 10(-9)). Of the eight patients infected with L. pneumophila not recognized with monoclonal antibody 2, seven were immunocompromised; only 46.3% of the 121 patients infected with L. pneumophila reactive with monoclonal antibody 2 were immunocompromised (P = .02). We conclude that monoclonal antibody 2 can be used as a marker for the more virulent strains of L. pneumophila serogroup 1.