A standard screening test for the early and rapid diagnosis of leptospirosis

PURPOSE : To perform dark field microscopy (DFM) for detection of Leptospira and to validate the results using Leptospira IgM antibody SERION ELISA test. METHODS : After differential centrifugation of Ruys, DFM was done to demonstrate Leptospira in the blood and SERION ELISA was done for Leptospira IgM antibody in single or paired serum samples. One hundred and eleven cases (39 adults and 72 children) of suspected leptospirosis were included in the study. RESULTS : Anicteric cases accounted for 66.7% (26/39) of adults and complications involving brain, liver, kidney and eyes were seen in 33.3% (13/39). In children, 90.3% (65/72) were anicteric and involvement of brain and liver was seen in 9.7% (7/72) cases. On testing 60 single samples of blood from 23 adults and 37 children, DFM exhibited greater sensitivity of 93.3% (56/60) than that of SERION ELISA for Leptospira IgM antibody (33.3%, 20/60). It was observed that the positivity of DFM decreased from 100% (15/15) to 90.9% (10/11) with increase in the duration of infection for more than one week. ELISA for Leptospira IgM, done on 51 paired blood samples, was positive in 64.7% (33/51) cases when both (first and second) samples were tested while in 45.1% (23/51) cases was positive with first sample alone. 58.8%(30/51) cases were positive by testing second sample. DFM results on paired blood samples showed persistence of Leptospira in 92.9% of cases. CONCLUSION : This study shows the validation of DFM results by SERION ELISA for Leptospira IgM antibody, based on which we recommend that DFM can serve as a standard screening test for early and rapid diagnosis of leptospirosis.