Fast but Faithful? Performance Characteristics of Rapid Test Compared with Enzyme-Linked Immunosorbent Assay for Serodiagnosis of Leptospirosis

Background: Leptospirosis is a rapidly re-emerging zoonotic disease, especially in tropical countries such as India. We assessed the frequency and epidemiological profile of leptospirosis in cases of acute febrile illness and also evaluated the diagnostic performance of a rapid test. Subjects and Methods: Observational cross-sectional study conducted at a tertiary care teaching hospital in Delhi. Three hundred and seventy patients presenting with fever of acute onset for <2 weeks were enrolled. Specific IgM antibody to Leptospira interrogans was tested by an Enzyme-Linked Immunosorbent Assay (ELISA) and a rapid test on the serum samples obtained from the study subjects. ELISA was used as the reference standard to assess the diagnostic performance of the rapid test. Results: In the present study, among AFI cases, the frequency of leptospirosis was 47 (12.7%). The majority of leptospirosis cases were among cases younger than 10 years of age (72.7%), with females (61.7%) affected more than males. In comparison with IgM ELISA, the immunochromatography-based IgM rapid test had a sensitivity and specificity of 6.38% and 98.45%, respectively, with a low level of agreement between the two (kappa value of 0.075). Conclusion: As the rapid test used in the present study has a low sensitivity, it cannot be suggested as a screening tool for leptospirosis diagnosis.