A predictive risk map for human leptospirosis guiding further investigations in brown rats and surface water.

Leptospirosis is a zoonosis caused by the spirochete spp. It is often not clear why certain areas appear to be hotspots for human leptospirosis. Therefore, a predictive risk map for the Netherlands was developed and assessed, based on a random forest model for human leptospirosis incidence levels with various environmental factors and rat density as variables. Next, it was tested whether misclassifications of the risk map could be explained by the prevalence of spp. in brown rats. Three recreational areas were chosen, and rats (≥25/location) were tested for spp. Concurrently, it was investigated whether spp. prevalence in brown rats was associated with DNA concentration in surface water, to explore the usability of this parameter in future studies. Approximately 1 L of surface water sample was collected from 10 sites and was tested for spp. Although the model predicted the locations of patients relatively well, this study showed that the prevalence of spp. infection in rats may be an explaining variable that could improve the predictive model performance. Surface water samples were all negative, even if they had been taken at sites with a high spp. prevalence in rats.