Researchers at Yale say the coronavirus shows up in stool days before a person shows symptoms.

Researchers say they think sewage can predict COVID-19 outbreaks.

For two months, they have tested sludge at New Haven's wastewater treatment plant.

Yale Engineering and a state lab found coronavirus levels in sewage nearly match the official testing numbers but they show up a week earlier.

"There's a delay of about a week from you getting sick to becoming tested, and then that data being reported," said Dr. Jordan Peccia, of Yale School of Engineering.

That extra week can give a critical early warning to a coming spike in infections.

"This is something that could be used as a surveillance method, to be able to monitor the amount of activity that's going on in the community without having to test everybody," said Dr. Doug Brackney, of Connecticut Agricultural Experiment Station.

For now, the testing is just in New Haven, but it could be expanded across the state. Connecticut is on the leading edge of this research.

One study found about half of COVID-19 infections show up in human feces. It is still not clear if the virus can be transmitted that way.