Hurricane-related leptospirosis in dengue-negative patients, Puerto Rico, 1996

Leptospirosis (Lepto) is rarely reported in Puerto Rico (PR), but after a hurricane and widespread floods (September 1996), serum samples of four patients with renal failure, collected in the island wide surveillance for dengue fever, tested negative by IgM ELISA (Den-neg), and positive in a rapid Leptospira IgM dipstick assay (DST). To determine the increase of lepto in PR after hurricane-generated floods, we applied the DST to specimens from 143 Den-neg patients, with disease onset from 8/7 to 9/12/96 (Pre-hurricane), or 9/13 to 10/6/96 (Post-hurricane) . DST positive sera, and a random 1 : 3 sample of DST negative sera were retested by the microscopic agglutination test (MAT). Organ tissues from one fatality were examined by immunohistochemistry (IHC). Laboratory confirmed lepto was defined as an MAT titer ≥ 1: 400 to one or more serovars or positive IHC. Five (6.9%) of 72 Pre-hurricane, and 19 (26.8%) of 71 Post-hurricane patients tested positive by DST. Four and 17,respectively, were confirmed (Relative risk = 4.31; 95 % confidence interval = 1.53 -12.18, p <0.005). Their mean age was 34.3 years (range: 13-64). Eighteen (85.7 %) of 21 confirmed cases were male, including 2 fatal cases (20, 31 years; onset 8/15, 9/20/96). Case fatality rate = 9.5 %. Residences of patients were located in 18 of the 78 municipalities. Preliminary record review revealed exposure to flood waters in 4 of 5 cases. This study demonstrates the utility of laboratory-based surveillance systems, in conjunction with rapid laboratory tests, for the detection of emerging public health problems. Lepto is treatable with antimicrobial agents, and knowledge of this diagnosis may significantly reduce morbidity and mortality.