A confirmed case was defined as a suspected case with a positive real-time PCR result for leptospirosis, and a probable case was defined as a suspected case with detection of leptospirosis-specific immunoglobulin M (IgM) antibodies by enzyme linked immunosorbent assay (ELISA).* Microagglutination testing, the reference standard serologic test for leptospirosis, was considered for probable cases but was not possible because of shipping difficulties. The gene discussed is CD40LG; the disease is leptospirosis.