In a series of studies since 2020, a Yale team has shown that measuring COVID-19 RNA in sewage can provide insights into the course of the pandemic. New research based on wastewater data suggests that many more people had been infected with COVID-19 by May 2021 than official case counts indicated.

Since the early weeks of the COVID-19 pandemic in the United States, a group of Yale researchers has diligently tracked the virus via a useful but decidedly unglamorous source: sewage.

Daily measurements from the New Haven wastewater treatment facility have yielded a series of important insights about the pandemic’s course. In one study, a group of Yale researchers including Yale SOM’s Edward H. Kaplan, a professor of operations research, public health, and engineering, and Jordan Peccia, professor of chemical and environmental engineering, demonstrated that the concentration of COVID-19 RNA per milliliter of sewage sludge rises and falls with the rate of infection seen in testing and hospitalization data. In another, they found that testing wastewater can provide an early warning sign of a worsening outbreak, three to five days before hospitalizations begin to surge.

Now they’ve uncovered yet another secret in the sludge. In their latest paper, Kaplan, Peccia, and Yale student coauthors Alessandro Zulli and Marcela Sanchez use wastewater data to calculate the cumulative COVID-19 incidence rate in New Haven and present a formula that would allow other municipalities to do the same. Their results suggest that nearly a third of people in the New Haven area had been infected by May 2021—a finding that is consistent with three other independent statistical estimates, but notably larger than the 12% figure derived from official case counts.

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