Box 2.

Diagnostic tests for leptospirosis

Isolation of leptospires
  • Blood culture for leptospirosis: gold standard test, requires samples during the first week of illness. Labour intensive and time consuming, requires high levels of biosafety levels, low diagnostic yield. Used for identification of serovar, and for determining antibiotic sensitivity.

  • Polymerase-chain reaction (PCR): useful for early diagnosis (first week of acute illness). High sensitivity and specificity. Useful for genomic classification.

  • Dark-ground microscopy of body fluids: low sensitivity, obsolete now.

Serological methods
Antibodies are usually detectable by day 6-10 of illness and peak within 3-4 weeks. Comparison of acute and convalescent have high sensitivity and specificity. Can be used for genus or serogroup identification.
  • Microscopic agglutination test: serological reference standard. However, requires experienced observers to reduce inter-observer variation. Time consuming and hazardous as live cultures are required to provide antigen. Available only in reference laboratories.

  • IgM enzyme-linked immunosorbent assay (ELISA): easily available. Sensitivity and specificity depend on regional patterns of seropositivity.