Evaluation of an in-house ELISA using the intermediate species Leptospira fainei for diagnosis of leptospirosis.

Leptospirosis is recognized as an emerging zoonotic disease generally affecting urban slums in developing countries and tropical regions. A combination of non-specific symptoms, low awareness among the medical community and a lack of readily available diagnostic tests have made leptospirosis an underdiagnosed disease. In this study, we tested an in-house ELISA with formalin-treated and boiled bacteria from the intermediate species Leptospira fainei as an antigen to detect Leptospira-specific IgM antibodies. A total of 819 serum samples, tested by a microscopic agglutination test (MAT) as a reference test, were used to evaluate the ELISA. Compared with positive and negative sera, the ELISA showed 94 % sensitivity and 99 % specificity. Positive and negative likelihood ratios were 94 and 0.06, respectively. No cross-reactivity was observed in sera from subjects with dengue and syphilis infections. The kappa value was 0.92 (95 % confidence interval 0.88-0.96), which indicated excellent agreement between the MAT and ELISA. The overall performance of this in-house ELISA suggests applicability as a rapid screening test for the diagnosis of leptospirosis in resource-limited settings and in hospitals and laboratories where a MAT is not available.