Four months into monitoring the presence of COVID-19 in sewage across Minnesota, researchers at the University of Minnesota Medical School’s Duluth Campus say the levels of viral particles in the wastewater reflects increasing cases across the state and has even given them early signs of outbreaks.

Since people infected with COVID-19 shed the virus in their feces, samples taken of raw sewage at an area’s wastewater treatment plant give researchers a snapshot of the amount of virus in that community. Medical school assistant professors Glenn Simmons Jr. and Richard Melvin are collecting samples from almost two dozen wastewater plants in the state with the hopes of figuring out a formula to determine how many cases of COVID-19 an area has based on the amount of viral particles in its wastewater, as the News Tribune reported in May.