Evaluation of two enzyme-linked immunosorbent assay methods for detection of immunoglobulin M antibodies in acute leptospirosis

Leptospirosis is a common zoonosis of worldwide distribution. Diagnosis of leptospirosis is usually accomplished by serology, but the microscopic agglutination test (MAT) generally requires paired sera for detection of seroconversion and is considered too complex for routine use. A number of rapid assays have been developed in recent years. In the present study, 2 immunoglobulin (Ig) M enzyme-linked immunosorbent assay (ELISA) methods were evaluated for the early diagnosis of acute leptospirosis in Barbados. A total of 103 patients admitted to the Queen Elizabeth Hospital for diagnosis of suspected leptospirosis were investigated. A case of leptospirosis was confirmed by a 4-fold rise in titer between 2 sera tested by MAT, an initial titer of : 800 in the MAT, or by isolation of leptospires from blood or urine. A total of 48 cases of leptospirosis were confirmed. In 33 cases, both commercial assays were positive in the first sample, taken at admission, a mean of 6.7 days after onset of symptoms, whereas seroconversion was detected in a further 9 cases. Both assays were negative in 5 cases, and the remaining case gave discordant results in the 2 assays. False-positive IgM results were detected in 4 patients without leptospirosis. The sensitivity of the 2 assays was 89.6 and 97.5%, respectively, and specificities were 92.7 and 96.4%, respectively. The positive predictive values were 87.8 and 95.5%, and the negative predictive values were 90.7 and 89.5%, respectively. Either of these assays can be used for early diagnosis of leptospirosis, particularly in laboratories that cannot perform more specialized leptospiral serology.