Legionella spp.: community acquired and nosocomial infections

The key points of this review are the increasingly recognized risk of home-acquired Legionnaires' disease; the significance and potential pathogenic role of other species of Legionella spp., different from L. pneumophila, and of other microorganisms that are phylogenetically close to Legionella and that have been named as Legionella-like amoebal pathogens; the breakthrough in the diagnosis of the disease caused by new commercially available urine antigen detection tests; the controversy over sensitivity and specificity of serological diagnostic methods; the recognition of a variety of possible mixed infections, particularly in the immunocompromised population; and new and controversial aspects of the therapeutic approach to legionellosis.

During the last year a number of articles have provided clinically relevant insights into our knowledge of Legionnaires' disease. In view of the fact that Legionella spp. have progressively become recognized as relatively common causative agents of both community-acquired and nosocomial legionellosis, this is an opportune moment for this review.

If domestic aquatic reservoirs were eventually confirmed as significant agents of transmission of legionellosis, the adoption of preventive measures would then be crucial. The progressive identification of other species, different from L. pneumophila, as causative agents of pneumonia should both encourage microbiologists and clinicians to improve their diagnostic methodology and increase the awareness of these infections. Finally, the awareness of mixed infections, probably far more severe and perhaps not so uncommon as previously thought, has important clinical connotations for both the diagnostic and the therapeutic approach to legionellosis in the immunosuppressed host, particularly in those cases of delayed clinical resolution.