Macroscopic agglutination tests that utilize killed antigens are widely available. This test is useful in screening for recent or recurrent infection. Silver impregnation and fluorescent antibody techniques permit identification of leptospires in infected tissue or body fluids. Spirochetes may also be demonstrated by phase-contrast or darkfield microscopy, however, the skill required and the high frequency of artifacts found with these tests limit their use. Unlike other pathogenic spirochetes, leptospires are easily cultured on commercially available media.
Media containing rabbit serum or bovine serum albumin and long-chain fatty acids are suitable.
Repeated blood cultures in the 1stwk of infection with very small inocula of blood are recommended. They can be recovered from the blood or CSF during the first 10 days of illness and from urine after the 2ndwk. Prolonged incubation is thus required. The diagnosis is most often established by serologic testing. A microscopic slide-agglutination test utilizing killed antigen is the most useful screening test.