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Abstract
Legionella was first recognized as a pathogen in 1977, when Legionella pneumophila was identified as the agent responsible for an outbreak of severe pneumonia among attendees at the American Legion Convention in Philadelphia in 1976 (Fraser et al., 1977).
Legionellae are ubiquitous in environmental water sources and may cause sporadic as well as epidemic cases of atypical pneumonia after inhalation or aspiration of contaminated water droplets (Reischl et al., 2002).
There are more than 46 species of Legionellae with 68 distinct serogroups (Marston et al., 1994). L. pneumophila is the most common pathogenic species, accounting for up to 90% of legionellosis cases, of which 70% of strains belong to serogroup type 1 (Yu, 2000). It has been increasingly recognized as a pathogen causing both community-acquired and nosocomial pneumonia (Ruf et al., 1989).
Immunosuppression, chronic lung disease, cigarette smoking, advanced age, and general anaesthesia are risk factors for the disease (Edelstein, 1993)b; although in a large proportion of cases, there are no obvious predisposing factors (Murdoch et al., 1996).