Increase of leptospirosis in dengue-negative patients after a hurricane inPuerto Rico in 1966

Leptospirosis has rarely been reported in Puerto Rico, although in the peri od from 1948 to 1952, 208 cases of leptospirosis and an island-wide seropre valence of antibody to Leptospira of 14% were documented. In Puerto Rico in October 1996, following rainfall and a period of flooding generated by Hur ricane Hortense, serum specimens of 4 patients with suspected dengue fever that were negative for dengue tested positive for Leptospira-specific IgM a ntibodies in a dipstick assay. Subsequently, we used an island-wide dengue laboratory-based surveillance system to determine the increase in leptospir osis after hurricane-generated floods. All anti-dengue IgM-negative patient s (n = 142) with disease onset from August 8 to October 6, 1996 from prehur ricane and posthurricane groups were investigated for leptospirosis. Labora tory-confirmed leptospirosis cases were defined as microscopic agglutinatio n test titers greater than or equal to 1 : 400 to 1 or more serovars, or po sitive immunohistochemistry in autopsy tissues. Four (6%) of 72 prehurrican e and 17 (24%) of 70 posthurricane patients had laboratory-confirmed cases of leptospirosis (relative risk [RR] = 4.4, 95% confidence interval [CI] = 1.6-12.4). The mean age of case-patients was 34 years (range = 13-64). Eigh teen (86%) of 21 confirmed case-patients were males, including one patient who died (31 years old). Patients were located in 18 (38%) of 48 municipali ties that submitted serum samples. Clinical features significantly associat ed with leptospirosis were eye pain (RR = 1.5, 95% CI = 1.3-1.9), joint pai n (RR = 1.4, 95% CI = 1. 1-1.6), diarrhea (RR = 1.7, 95% CI = 1.2-2.5), and jaundice (RR = 3.3, 95% CI = 1.5-7.2). This study demonstrates the utility of a dengue laboratory-based surveillance system for the detection of an i ncrease of leptospirosis, which most likely would have gone unrecognized. L eptospirosis is treatable with antibacterial agents; knowledge of this diag nosis may significantly reduce morbidity and mortality.