Legionella pneumophila urinary antigen: diagnostic efficiency of a new quantitative ELISA test

Background. To provide a rapid and suitable diagnosis of Legionella pneumophila serogroup1 (LPsg1) infection, a total of 160 urine samples were collected from 56 suspected or diagnosed patients, 8 from the VEQ-NEQAS Program, 96 from healthy blood donors, to detect LPsg1 urinary antigen by a new automated single device quantitative Elisa assay (Urinary Legionella Antigen Chorus, Diesse).
Materials and Methods. An immunochromatographic rapid test (V-test Legionella, Coris) was used as a reference. Prevalence of specific IgM and IgG LPsg1 antibodies was assessed on 20 sera collected among the 56 patients with disease.
Results. Urinary Ag LPsg1 results of two direct tests from a total of 64 samples (patients and VEQ) showed an overall concordance of 90.6% (58 out of 64); all healthy blood donors resulted as negatives, as well (specificity 100%). Serology positive results (LPsg1 IgM and IgG antibodies) were revealed on 14 out of 20 diagnosed patients sera; instead, both urinary LPsg1 antigen tests resulted as positives in 18 out of 20 urine samples. The combined use of both LPsg1 urinary antigen and specific IgM antibodies improved the diagnostic efficiency than a single test approach, showing 20 out 20 patients with at least one positive LPsg1 specific marker.
Conclusions. The new LPsg1 urine antigen quantitative Elisa assay seems to be a useful tool for an early diagnosis of suspected LPsg1 infection and along the follow up of treated patients.