Background: On 21 November 2005, a 32-year-old male resident of New York was hospitalized with suspected leptospirosis. He had participated in an endurance-length swamp race on 4-5 November 2005 outside of Tampa, Florida.
Methods: We interviewed racers to assess illness, medical care, and race activities. A suspected case was defined as fever plus > or = 2 signs or symptoms of leptospirosis occurring in a racer after 4 November 2005. Individuals with suspected cases were referred for treatment as needed and were asked to submit serum samples for microscopic agglutination testing (MAT) and for rapid testing by the dot enzyme-linked immunosorbent assay dipstick immunoglobulin M immunoassay.
Results: The Centers for Disease Control and Prevention and participating state health departments interviewed 192 (96%) of 200 racers from 32 states and Canada. Forty-four (23%) of 192 racers met the definition for a suspected case. The median age of the patients was 37 years (range, 19-66 years), and 128 (66.7%) were male. Fourteen (45%) of the 31 patients with suspected cases who were tested had their cases confirmed by serological testing (a single sample with MAT titer > or = 400), including the index case patient. Organisms of a potential novel serovar (species Leptospira noguchii) were isolated in culture from 1 case patient. Factors associated with increased risk of leptospirosis included swallowing river water (odds ratio [OR], 3.4; 95% confidence interval [CI], 1.6-7.0), swallowing swamp water (OR, 2.4; 95% CI, 1.1-5.2), and being submerged in any water (OR, 2.3; 95% CI, 1.1-4.7).
Conclusions: This report describes a leptospirosis outbreak that resulted in a high rate of symptomatic infection among adventure racers in Florida. The growing popularity of adventure sports may put more people at risk for leptospirosis, even in areas that have not previously been considered areas of leptospirosis endemicity.