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SARS-CoV-2 RNA concentrations in primary municipal sewage sludge as a leading indicator of COVID-19 outbreak dynamics

Our take —

This study, published as a preprint and thus not yet peer-reviewed, shows nearly perfect correlation between trends in viral SARS-CoV-2 RNA measured in sewage sludge in New Haven, Connecticut, and both trends in hospital admissions and community cases testing positive for COVID-19. These results are may be useful for surveillance activities, particularly early warning systems. Further work must be done to validate these findings, and ensure they are generalizable to other settings.

Study design


Study population and setting

The study was conducted in the metropolitan area of New Haven, Connecticut from March 19 to May 1, 2020, with daily primary sludge collected from the East Shore Water Pollution Abatement Facility, which serves an estimated 200,000 people. The study also used Yale New Haven admission data and community SARS-CoV-2 testing data from the Connecticut Department of Public Health.

Summary of Main Findings

SARS-CoV-2 was found in all sludge samples, however 96.5% of all SARS-CoV-2 viral RNA tested samples had concentrations that were less than the detection threshold indicated for this method. Among samples testing positive, the viral RNA level peaked 3 days before hospital admissions, and 7 days before COVID-19 case counts. When shifting the viral RNA data forward by 3 days, there was high correlation with hospital admissions (R=0.996), and when shifted forward by 7 days, there was a high correlation with COVID-19 case counts (R=0.994).

Study Strengths

The study integrated multiple data sources to understand how viral RNA in sewage was associated with COVID outcomes in the community over time. By using sewage sludge rather than wastewater, there is a higher solid content of the material, which often leads to increased detection compared to wastewater.


Further validation of using sewage sludge viral RNA data as a proxy for COVID-19 cases must be done, and while the correlation coefficient provides evidence of a linear relationship between the two, further statistics should be calculated. These results also may not be generalizable to other areas given they sampled from one city. In addition, this study was conducted during the stay-at-home order in Connecticut, and may not be as applicable when the stay-at-home order is lifted as people travel again.

Value added

This study provides promising results that sewage sludge analysis could be useful for COVID-19 disease surveillance activities, especially when testing capacity may be limited.