Scientists say that measuring coronavirus levels in wastewater could help them estimate the number of infections in communities. The method could be used around the world to identify where the virus is spreading and reduce the need for mass testing. Small studies carried out in Europe and Australia suggest that signs of the coronavirus can be found in sewage waste material carried away from homes and other buildings in a system of pipes. Those findings have led some scientists to consider wide wastewater testing to estimate the number of infected people in a given area.