Laboratory diagnosis of leptospirosis

Leptospirosis is a worldwide zoonosis caused by pathogenic Leptospira species, for which humans are accidental hosts. It is endemic in the tropical urban areas including our country, where seasonal epidemics are becoming increasingly common. Laboratory tests are necessary to confirm the diagnosis of clinically suspected leptospirosis due to its varied symptomatology. Moreover, leptospirosis must always be considered during the differential diagnosis of other tropical febrile illnesses. Laboratory analysis depends on the samples available and temporal stage of the illness. A confusing array of laboratory tests is described for the detection of this spirochete and antibodies. The conventional tests include direct microscopy, culture and the most widely used reference standard method -the microscopic agglutination test. In addition a variety of newer serological tests and those based on molecular techniques have been described. This review has attempted to describe the basis of these techniques and discussed the relative advantages and drawbacks of these assays with special emphasis on the selection of the most appropriate specimen and test, and the correct interpretation of the test result.