CHATTANOOGA (AP) — The city of Chattanooga plans to keep testing local wastewater for the prevalence of COVID-19 into 2021 after a study in May that showed thousands more cases of the virus than what was reported by local health officials, the Chattanooga Times Free Press reported.

Throughout May, the city's wastewater treatment center sent samples to Massachusetts-based Biobot. At first, Biobot did not detect any coronavirus traces, despite several dozen cases in the community. Then on May 26, Biobot projected 12,500 coronavirus infections in the county. At the time, the Hamilton County Health Department was reporting 717 infections.

Dr. William Schaffner, an infectious disease specialist at Vanderbilt University Medical Center, said that confirms what experts already know about the virus — "that we really have more infections than we think."

But he said not all of those projected cases may be people with active infections.

"People can, even after they recover, have a positive nasal swab test, but that's just fragments of the virus. The virus is not active," Schaffner said. "What could be measured at the central wastewater treatment plant could be a measure of current, active infections as well as people who are still putting into the wastewater virus fragments from their illness two weeks ago."

Chattanooga was one of about 350 cities that participated in the initial study, said Maura Sullivan, chief operating officer for the city.

The city will work with Biobot into 2021 to continue testing wastewater through a contract for around $23,900, Sullivan said.

Samples will be sent every two weeks and city leaders expect to get results between three and seven days later, said Jeff Rose, director of wastewater systems.