The methods currently available to diagnose Legionnaires' disase are culture, urinary antigen detection, direct fluorescent antibody testing, detection of nucleic acid and detection of specific antibodies in serum samples. Presently, none of the diagnostic tests available offers the desired quality with respect to sensitivity and specificity. Culture should be obligatory, especially when hospitalized patients with underlying diseases are investigated. A positive culture is the prerequisite of molecular epidemiological investigations. Urinary antigen detection is a valuable tool in the majority of community-acquired cases when L. pneumophila serogroup 1 is the causative agent. In cases of nosocomial disease, when Legionella pneumophila serogroups other than sg 1 are frequent, this assay has limitations. The detection of nucleic acid is very useful method of diagnosis but requires further validation. The detection of antibodies in a patient's serum is of little use in the acute phase of the illness. Several molecular subtyping techniques are in use to subtype L. pneumophila strains in epidemiological investigations. Legionella pneumophila is genetically very heterogeneous thus allowing an individual fingerprint of each strain. However, the majority of clinical cases are caused by a limited number of clones that cause disease worldwide. The therapy for Legionnaires' disease requires drugs that can access and are active intracellularly. Currently, fluorochinolones and macrolides are the most active agents.

Further reading: Paul C. Lück in Legionella: Molecular Microbiology

Labels: bacteriology, bacterium, legionella