In March 2020, the Austrian ski town of Ischgl—known for 239 kilometers of uninterrupted runs and an exuberant après-ski scene—suddenly became infamous as the site of the one of the first COVID-19 superspreading events. Hundreds of infected skiers took the virus home and seeded outbreaks all around Europe.

As the pandemic progressed, however, Ischgl was on the vanguard for a more positive reason: Health officials and scientists in the state of Tyrol were among the first to monitor levels of the pandemic coronavirus in sewage—and base health policy decisions on them. Because the region is so dependent on tourism, officials were eager to know whether the virus was truly on the decline so they could lift key restrictions. They also wanted to catch the earliest possible signals that it might be coming back. Wastewater analysis, which picks up fragments of virus shed in feces, was invaluable, says Stefan Wildt, a wastewater expert at the state’s department of water management. Following Tyrol’s lead, a national program has recently expanded to cover more than half of Austria’s population.