Increased incidence of human leptospirosis and the effect of temperature and precipitation, the Netherlands, 2005 to 2023

BackgroundThe incidence of leptospirosis, a zoonotic infection transmitted mainly by rodents, has increased in humans over the past decade in the Netherlands. Previous studies, mostly from countries with tropical climates, suggest that temperature and rainfall influence leptospirosis incidence.AimWe aimed to identify factors that could explain the increasing leptospirosis incidence in the Netherlands, including temperature and precipitation.MethodsEpidemiological data of leptospirosis cases notified from 2005 to 2023 to the national surveillance system were analysed to identify changes over the years. Negative binomial regression models were used to assess associations between weather variables and leptospirosis incidence.ResultsFrom 2005 to 2023, 1,164 cases were notified. The annual number of cases increased 2.7-fold in the period of 2019-2023 compared with 2005-2009, and the number of autochthonous cases 4.1-fold. Data from 1,158 cases were included in the analyses, and 596 (51.5%) of these cases were autochthonous. Most cases were male (n = 927; 80.1%), needed hospital treatment (n = 861; 74.4%) and acquired the infection through contact with surface water and/or soil (n = 611, 72.6%). Higher mean winter (incidence rate ratio (IRR) = 1.27; 95% confidence interval (CI): 1.18-1.36) and summer (IRR = 1.38; 95% CI: 1.18-1.61) temperatures were significantly associated with increased leptospirosis incidence.ConclusionLeptospirosis incidence has increased over the past decades and may continue to increase due to climate change. Prevention should aim at advising the appropriate preventive measures to avoid exposure to <i>Leptospira</i> and increasing awareness about leptospirosis among clinicians to allow for timely diagnosis and treatment.