Serologic diagnosis of leptospirosis: comparison of line blot and immunofluorescence techniques with the genus-specific microscopic agglutination test

Evaluation of four commercially available rapid serologic tests for diagnosis of leptospirosis

Four rapid tests for the serologic diagnosis of leptospirosis were evaluated, and the performance of each was compared with that of the current standard, the microscopic agglutination test (MAT). The four rapid tests were a microplate immunoglobulin M (IgM)-enzyme-linked immunosorbent assay (ELISA), an indirect hemagglutination assay (IHA), an IgM dipstick assay (LDS), and an IgM dot-ELISA dipstick test (DST). A panel of 276 sera from 133 cases of leptospirosis from four different geographic locations was tested as well as 642 sera from normal individuals or individuals with other infectious or autoimmune diseases. Acute-phase sera from cases (n = 148) were collected <or=14 days (median = 6.0) after the onset of symptoms, and convalescent-phase sera (n = 128) were collected >or=15 days after onset (median = 29.1). By a traditional method (two-by-two contingency table), the sensitivities for detection of leptospirosis cases were 93.2% by LDS, 92.5% by DST, 86.5% by ELISA, and 79.0% by IHA. Specificity was 98.8% by DST, 97% by ELISA and MAT, 95.8% by IHA, and 89.6% by LDS. With a latent class analysis (LCA) model that included all the rapid tests and the clinical case definition, sensitivity was 95.5% by DST, 94.5% by LDS, 89.9% by ELISA, and 81.1% by IHA. The sensitivity and specificity estimated by the traditional methods were quite close to the LCA estimates. However, LCA allowed estimation of the sensitivity of the MAT (98.2%), which traditional methods do not allow. For acute-phase sera, sensitivity was 52.7% by LDS, 50.0% by DST, 48.7% by MAT and ELISA, and 38.5% by IHA. The sensitivity for convalescent-phase sera was 93.8% by MAT, 84.4% by DST, 83.6% by LDS, 75.0% by ELISA, and 67.2% by IHA. A good overall correlation with the MAT was obtained for each of the assays, with the highest concordance being with the DST (kappa value, 0.85; 95% confidence interval [CI], 0.8 to 0.90). The best correlation was between ELISA and DST (kappa value, 0.86; 95% CI, 0.81 to 0.91). False-positive LDS results were frequent (>or=20%) in sera from individuals with Epstein-Barr virus, human immunodeficiency virus, and periodontal disease and from healthy volunteers. The ease of use and significantly high sensitivity and specificity of DST and ELISA make these good choices for diagnostic testing.

Human infection caused by Leptospira fainei

We report a human case of leptospirosis in which the spirochete was detected by dark-field microscopy examination of cerebrospinal fluid (CSF) and isolated from both CSF and blood. Leptospira fainei was identified by sequencing the 16S rDNA gene, which had been amplified by polymerase chain reaction. This case confirms the role of L. fainei as a human pathogen and extends its distribution to southern Europe.

Evaluation of a passive microcapsule agglutination test for the screening of human leptospirosis

Microcapsules, absorbed with two mixed antigens--each composed of 3 sonicated leptospira serovars--were developed in the past as a microcapsule agglutination test (MCA-LS) for the screening of clinical leptospirosis. For this study, fifty serum samples, taken at an earlier and at a later stage of illness from 25 Italian in-patients with clinical symptoms of leptospirosis, were tested with both the MCA-LS one-dilution test and the microscopic agglutination (MA) test, the confirmatory test for leptospirosis, with 18 leptospira strains circulating in Italy. Compared with MA, MCA-LS showed a sensitivity of 91.7%, and a specificity of 92.3%, including leptospirosis not sustained by the diagnostic strains used in the MCA-LS kit.

Evaluation of an immunoenzymatic test (ELISA) for the diagnosis of leptospirosis in Italy

An enzyme-linked immunosorbent assay (ELISA) was assessed to detect in humans IgM and IgG against the main serogroups/serovars of Leptospira present in Italy. Sonicated antigens from strain Wijnberg, serogroups Icterohaemorrhagiae and Riccio 2, serogroup Australis, were used in ELISA and the results were compared to microagglutination test (MAT). IgM were confirmed to be the predominant class of antibodies; the total sensitivity obtained by Wijnberg/ELISA with the sera of patients infected by different serogroups was 81.5% in relation to MAT, better sensitivity was achieved by the use of Riccio 2/ELISA; no reaction occurred with the control sera. Cross-reactivity was noted with some sera of patients with Lyme disease (IgM) and with few sera of patients with autoimmune disease (IgM and IgG). To improve the sensitivity of the ELISA both antigens Wijnberg and Riccio 2 must be employed in the immunoenzymatic assay, since serogroup Australis must be considered as a new emerging serogroup causing human leptospirosis in our country.