The vast brown rivers of sludge that gush into the sewage treatment plants across Germany may hold a key to early detection of any new wave of the coronavirus, scientists tell CNN. Fred Pleitgen writes for CNN that the Helmholtz Center for Environmental Research is leading a trial that’s sampling wastewater from plants serving some of the largest urban areas and trying to find evidence of the coronavirus. The ultimate goal is for almost all sewage plants to install these coronavirus early warning systems so as to track the spread of Covid-19.