CAMBRIDGE, Mass. (AP) — U.S. coronavirus cases are up, leading a smattering of school districts, especially in the Northeast, to bring back mask recommendations and requirements. Their return comes for the first time since the omicron winter surge ebbed and as the United States approaches 1 million deaths from the virus. Districts in Maine, New Jersey and Pennsylvania have brought masks back in schools, with a few in Massachusetts also recommending them. The uptick in cases is a vast undercount because testing has dropped considerably and most tests are being taken at home and are not reported to health departments.