Among 515 patients with DLI tested for leptospirosis, 115 (22%) had a positive immunoglobulin M (IgM) leptospirosis rapid diagnostic test (LRDT) result.§ Because anti-Leptospira IgM antibodies can persist ≥12 months postinfection (5), the team performed testing to confirm the LRDT results and assess whether a leptospirosis outbreak occurred during the dengue outbreak. The gene discussed is CD40LG; the disease is dengue disease.