A series of crucial setbacks in Covid-19 testing has made it difficult to keep up with the virus’ rapid spread, and has inspired some researchers to look to wastewater to help fill in the gap of measuring how prevalent SARS-CoV-2 is in a given community.

In a paper posted Tuesday to the preprint server medRxiv, researchers collected samples in late March from a wastewater treatment plant serving a large metropolitan area in Massachusetts and found that the amount of SARS-CoV-2 particles in the sewage samples indicated a far higher number of people likely infected with Covid-19 than the reported cases in that area.