CAMBRIDGE – As novel coronavirus cases climb, Cambridge-based tech startup Biobot is looking at an early clue lurking underground—sewage.

The company is analyzing the amount of COVID-19 in local wastewater, working with hundreds of communities across the country.

By testing wastewater, the company has found it is able to detect COVID levels in an area about a week before human testing catches up, since the virus is present in, shall we say, a person’s excrement, before symptoms appear.

Biobot cofounder and President Newsha Ghaeli explained how one county uses its data to create a “heat map” of COVID clusters.

“What they can do,” said Ghaeli, “is in real time they’re routing their mobile testing vans to the communities that, that week, have the highest viral load in wastewater.”

Biobot piloted this approach in early March with the Massachusetts Water Resources Authority, which covers an area that has accounted for about 45% of the state’s COVID cases. According to MWRA’s latest data, the eastern part of the Commonwealth is experiencing a spike not seen since April.

Biobot was looking at opioid levels in wastewater before its current work tracking COVID-19. For example, Ghaeli said one city figured out most of its opioid consumption was in the form of prescription painkillers, not heroin—information that helped create a strategy.

“They shifted their resources behind, like, medication drop-off units, educational material around the adverse effects of prescription opioids,” said Ghaeli. “And they decreased overdoses by 40%.”

Until this summer, Biobot was offering its COVID services free – but now, it’s charging local governments, schools, universities and other groups. So far, the company has generated data representing about 10% of the country.