Rare urban-acquired human leptospirosis and environmental health investigation in Sydney, Australia

Leptospirosis is a zoonosis caused by exposure to <i>Leptospira</i> excreted into the environment by rodents or other mammals. A notification of a case of leptospirosis in an adult male with no history of travel or exposure to livestock or rodents triggered an environmental health investigation of his workplace, a local golf course. We hypothesised that a water splash in the eye from a creek running through the golf course, which occurred after a period of heavy rainfall, had led to <i>Leptospira</i> exposure, likely on the basis of contamination of the creek water by rodent urine. Testing of environmental water samples detected pathogenic <i>Leptospira</i> DNA in ten of eleven samples, although cultures were negative. However, we had difficulty interpreting this finding as we found <i>Leptospira</i> DNA in ten of 14 environmental samples in inner and eastern Sydney remote from the workplace, and these were not associated with notified human cases. When we reviewed the 53 human leptospirosis cases notified over the twenty-year period 2003-2022 in residents of metropolitan Sydney, of the 49 cases with <i>Leptospira</i> exposure information, 46 had recognised sources of exposure: travel overseas (27) or to tropical northern Australia (5); rural exposure often to livestock and/or rodents (12); work in an abattoir (1); and involvement in a raspberry farm outbreak (1). Only three, including the case described, acquired infection in suburban Sydney. Acquisition of human leptospirosis is a rare event in suburban Sydney; true cases without a travel or occupational exposure history may be under-recognised by clinicians. However, with increasing biodiversity loss and where climate change results in heavier rainfall and more frequent floods, it is likely that human leptospirosis will become more common in urban as well as endemic settings.