Evaluation of two immunodiagnostic tests for early rapid diagnosis of leptospirosis in Sri Lanka: a preliminary study.

BACKGROUND: Leptospirosis is often treated based on clinical diagnosis. There is a need for rapid laboratory diagnosis for this condition. The aim of this study was to compare the diagnostic accuracy of two rapid IgM based immunodiagnostic assays with the microscopic agglutination test (MAT), in acute leptospirosis infection. METHODS: MAT, IgM based immunochromatographic test (Leptocheck-WB) and IgM ELISA were performed using acute sera of patients clinically suspected to have leptospirosis (n = 83). Bayesian latent class modeling was used to compare the accuracy of these tests. RESULTS: Percentage positivity for MAT, Leptocheck-WB, and IgM ELISA were 48.1, 55.3, and 45.7 % respectively. Bayesian latent class modeling showed a combined positivity rate of leptospirosis of 44.7 %. The sensitivity of MAT, Leptocheck-WB and IgM ELISA were 91.4, 95 and 81.1 %, and specificity were 86.7, 76.4 and 83.1 %, respectively. CONCLUSIONS: Leptocheck-WB has high sensitivity, and, because it is quick and easy to perform, would be a good screening test for acute leptospirosis infection. IgM ELISA has good specificity, and is comparable with MAT; given that it is easier to perform and more widely available than MAT, it would be a more appropriate confirmatory test for use in hospitals with limited access to a specialized laboratory.

Diagnosis of Leptospirosis: Comparison between Microscopic Agglutination Test, IgM-ELISA and IgM Rapid Immunochromatography Test.

BACKGROUND: Leptospirosis is diagnosed on clinical grounds, and confirmed by microscopic agglutination test (MAT). IgM-ELISA (Serion-Virion) and immunochromatography test (Leptocheck-WB) are two immunodiagnostic assays for leptospirosis. Their sensitivity, specificity and applicability in Sri Lanka have not been systematically evaluated. METHODS: Clinically diagnosed leptospirosis patients (n = 919) were recruited from three hospitals in the Western Province of Sri Lanka, during June 2012 to December 2013. MAT, IgM-ELISA and Leptocheck-WB were performed on all patient sera. MAT titer of ≥ 400 in single sample, four-fold rise or seroconversion ≥ 100 in paired samples were considered as positive for MAT. For diagnostic confirmation, MAT was performed during both acute and convalescent phases. Anti-leptospiral IgM ≥ 20 IU/ml and appearance of a band in the test window were considered as positive for IgM-ELISA and Leptocheck-WB test respectively. Patients with an alternative diagnosis (n = 31) were excluded. Data analysis was performed using two methods, i) considering MAT as reference standard and ii) using Bayesian latent class model analysis (BLCM) which considers each test as imperfect. RESULTS: MAT, IgM-ELISA and Leptocheck-WB positivity were 39.8%, 45.8% and 38.7% respectively during the acute phase. Acute-phase MAT had specificity and sensitivity of 95.7% and 55.3% respectively, when compared to overall MAT positivity. IgM-ELISA and Leptocheck-WB had similar diagnostic sensitivity when compared with acute-phase MAT as the gold standard, although IgM-ELISA showed higher specificity (84.5%) than Leptocheck-WB (73.3%). BLCM analysis showed that IgM-ELISA and Leptocheck-WB had similar sensitivities (86.0% and 87.4%), while acute-phase MAT had the lowest sensitivity (77.4%). However, acute-phase MAT had high specificity (97.6%), while IgM-ELISA and Leptocheck-WB showed similar but lower specificity (84.5% and 82.9%). CONCLUSIONS: Both IgM-ELISA and Leptocheck-WB shows similar sensitivities and specificities. IgM-ELISA may be superior to MAT during the acute phase and suitable for early diagnosis of leptospirosis. Leptocheck-WB is suitable as a rapid immunodiagnostic screening test for resource limited settings.