Large quantities of antibiotic-resistant bacteria enter the environment via municipal — and especially hospital — wastewater streams. Although wastewater treatment plants reduce the total number of bacteria, the most hazardous — multiresistant — strains appear to withstand or even to be promoted by treatment processes. This was demonstrated by Eawag researchers in a study carried out in Lake Geneva, near Lausanne.
Treated wastewater from the city of Lausanne — around 90,000 m3 per day — is released into Vidy Bay (Lake Geneva); the discharge point is located 700 m offshore, at a depth of 30 m. The Lausanne region does not have a pharmaceutical industry or intensive animal production. However, the Lausanne treatment plant receives wastewater not only from the region’s 214,000 inhabitants and a number of smaller healthcare centres, but also from a major healthcare facility — the University Hospital of Canton Vaud (CHUV).