The rising daily coronavirus case count in Massachusetts isn't the only warning sign of a new spike in cases for the Boston area.

Traces of COVID-19 are appearing more frequently at the sewage plant that treats wastewater for Boston and many of its suburbs, according to public data shared by the Massachusetts Water Resources Authority.

Sewage from the southern and western suburbs whose water is treated at Deer Island Treatment Plant has levels coronavirus not seen since last April, when the virus was still near its peak, according to the latest data. The northern suburbs' sewage is showing less virus so far, but it's not far behind, and both lines are trending up.