Validity of a commercially available IgM ELISA test for diagnosing acute leptospirosis in high endemic districts of Sri Lanka

Background
Lack of point of care diagnostics is a major challenge for control of human leptospirosis. Immunoglobulin M enzyme linked immunosorbent assays (IgM ELISA) have been widely used for the diagnosis of leptospirosis. The purpose of the present study was to determine the validity of IgM ELISA in the diagnosis of leptospirosis in a Sri Lankan context.

Methods
Confirmed cases of leptospirosis from the 2008 Sri Lankan outbreak of leptospirosis and a group of leptospirosis excluded febrile patients were selected for the validation study. Disease confirmation and exclusion was carried out using either paired sample MAT (optimized for the region) or qPCR or both. A commercially available IgM ELISA kit was used and the procedure performed according to the manufacturers’ instruction in the Department of Microbiology, Faculty of Medicine, University of Peradeniya.

Results
The study sample included 88 confirmed cases of leptospirosis and a comparison group of 71 acute fever patients.  Of the 88 confirmed cases selected, 53 reacted in IgM ELISA and of the comparison group, 38 gave a positive reaction. *MAT was carried out among acute and convalescent samples where the acute sample was obtained within the first 10 days of illness and the convalescent sample after the day 14. A regionally optimized MAT panel with 21 serovars were used for MAT

Sensitivity and specificity of IgM ELISA, as a point of care diagnostic test for patients in this sample with acute leptospirosis, was 60.23% (95% CI 49.78, 69.82) and 46.48% (95% CI (35.36, 57.96) respectively. Diagnostic accuracy of the test was 54.09% (95% CI 46.34, 61.65 %). The ROC (Receiver-operator characteristic curve) curve for the IgM ELISA showed a value of .669 for area under the curve. Optimal cut off points were not detected due to the poor test parameters in this sample.

Conclusion
This study shows the poor diagnostic capabilities of IgM ELISA during the acute phase of leptospirosis in high endemic settings

DOI: http://dx.doi.org/10.4038/sljid.v4i2.6952

Sri Lankan Journal of Infectious Diseases 2014; Vol.4(2):83-89