In the study, published last week in the journal Nature Biotechnology, researchers began taking daily samples from a New Haven-area wastewater treatment plant, which serves multiple towns in Connecticut including New Haven, East Haven, Hamden and parts of Woodbridge.

The study’s results, which span 10 weeks from March 19 to June 1, found that testing sewers for Covid-19 — collecting samples from the “primary sewage sludge” of settled solids — produces transmission trends that are “very similar” to those of contact tracing, but come about “six to eight” days earlier.