Biogeography and temperature response of Vibrio cholerae nonO1/nonO139 in Eastern Austrian inland bathing waters

Non-toxigenic Vibrio cholerae (NTVC) are naturally thriving in various aquatic environments, including rivers, lakes, and coastal waters. Although unable to produce cholera toxin, they cause severe infections, including wound and bloodstream infections or gastrointestinal illness. Over the past three decades, a well-documented rise in NTVC infections has been reported in countries of the Northern hemisphere, linked to climate change induced rising water temperatures in coastal ecosystems. In contrast, information on the occurrence of NTVC in continental inland water-bodies is scarce, and no rise in cases has been observed. The aim of our study was thus to elucidate the biogeography and temperature response of NTVC populations in inland bathing sites in Eastern Austria, an ecoregion that has been regularly afflicted with NTVC cases in the past decades. NTVC abundance was assessed in 46 water bodies with culture-based and qPCR methods and related to geographical and environmental key-parameters. Statistical modeling identified a clear geographical gradient, with temperature, and conductivity as key-drivers of NTVC abundance. Easy-to-determine geographical and environmental thresholds were established to enable bathing-site operators and health authorities to quickly assess NTVC occurrence and potential exposure risk. The temperature response of the NTVC populations in nine selected ponds, revealed that a 1-log rise in culturable NTVC numbers and a 0.5 log rise of NTVC quantified by qPCR is obtained by a temperature increase of 6°C, a realistic and currently unfolding climate change scenario for the European continent. Improved surveillance systems linking NTVC abundance, environmental data and clinical cases would be required to protect an increasingly vulnerable population.