Combined use of two rapid test in Legionella pneumophila infections

Legionella pneumophila serogroup 1 (LPSg1) is the prevalent cause of legionellosis in many geographical areas of the world. LPSg1 infection may presents a severe pulmonary disease whose clinical picture is undistinguishable from that of other pneumotropic agents. In addition, a low clinical suspicion and some limitations in diagnostic tests (overall the lack of a “gold standard”) make a correct diagnosis of legionnaires’ disease easy to be missed. To provide a rapid and suitable diagnosis in patients with clinical signs and symptoms resembling legionnaires’ disease, specific antibodies (IgM and IgG) against LPSg1 were detected in 25 sera collected from 22 male and female subjects using a rapid ELISA test (Legionella Chorus). Results were compared with those obtaiened by a standard ELISA (Legionella Vircel), which was set as the reference. In addition, a total of 16 urine specimen from individual patients were furtherly assessed for LPSg1 antigen by a rapid immunochromatographic test (BinaxNOW Legionella). In a control group of 104 healthy subjects, IgM and IgG Legionella Chorus specificity values were 99%.Agreement of IgM and IgG values with those obtained by the Legionella Vircel test were 98% and 95.5%, respectively. In patients with confirmed legionnaires’ disease, IgM agreement between the above reported tests was 88%; IgM Legionella Chorus sensitivity was 88%. LPSg1 urine antigen was positive in 12 out of 16 examined specimen.Among these, 9 showed IgM positive sera. Conversely, 4 patients with IgM positive sera were negative upon urinary antigen. Although antigen detection remains the method of choice to diagnose LPSg1 infection, the combination antigen detection plus rapid serology methods provides an additional tool for rapid diagnosis.