Munich River Surfers Show Higher Leptospira Seroreactivity Than Controls

After four regular surfers on Munich’s Eisbach River were hospitalized with severe leptospirosis during 2021–2024, researchers conducted a controlled cross-sectional study from September to November 2024. They enrolled 102 surfers and 100 controls with serologic data and collected questionnaires, blood samples, and 15 environmental water and soil samples. The primary assessment was Leptospira IgG seroreactivity, with PCR used to test blood and environmental samples.

Seroreactivity, including borderline results, was found in 10 of 102 surfers (9.8%) and 3 of 100 controls (3.0%; relative risk 3.27; 90% CI 1.13–9.41; one-sided p=0.041). All IgG-positive samples were negative by microscopic agglutination testing, and blood PCR was negative. One of 15 environmental samples—a soil sample near the surfers’ exit point—tested positive for Leptospira DNA. Most seroreactive participants reported no compatible symptoms in the preceding year.

The results support an association between regular urban freshwater surfing and serologic evidence of exposure, but do not establish when or where exposure occurred or indicate active infection. The small number of seroreactive participants, possible travel-related exposure, and early-release status limit interpretation; the authors also note that recreational water exposure was not systematically recorded in regional surveillance.