Discovery of V. cholerae in Copenhagen sewage

We report the unexpected discovery of a persistance low abundance of Vibrio cholerae of a single wastewater treatment plant in Copenhagen, Denmark at least since 2015. Remarkably, no environmental or locally transmitted clinical case of V. cholerae has been reported in Denmark for more than 100 years. This presence was initially overlooked during routine metagenomic analyses because of the low abundance and large mixing of false-positive reads. We, however, have recovered a near-complete genome out of 100+ sewage samples taken over the past 8 years. The recovered genome lacks the gene responsible for cholerae toxin production. Our finding illustrates the importance, challenges and effectiveness of wastewater-based pathogen surveillance.