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Measurement of SARS-CoV-2 RNA in Wastewater Tracks Community Infection Dynamics

Our take —

Over a ten-week period starting in March 2020, wastewater sludge from New Haven, Connecticut was collected and monitored for SARS-CoV-2. RNA found in wastewater was compared to the number of positive cases and hospitalizations in clinical settings. Viral RNA detection in wastewater preceded hospital admissions by 1 to 4 days, and due to delays in the reporting of test results, viral RNA detection in wastewater preceded positive test results by 6 to 8 days. Taken together with other evidence, it appears that wastewater data continue to show promise for outbreak detection and epidemic monitoring.

Study design

Ecological

Study population and setting

Primary sewage sludge from the New Haven, Connecticut Metropolitan Area was monitored daily for SARS-CoV-2 by tracking RNA concentrations between March 19, 2020 and June 1, 2020. Samples were collected from a wastewater treatment facility that accepts wastewater from approximately 200,000 individuals across four cities (New Haven, Hamden, East Haven, and Woodbridge). The wastewater data were compared with clinical SARS-CoV-2 positive tests results by date of specimen collection, test positivity by date of collection, positive test results by reporting data, and COVID-19 hospital admissions to Yale New Haven Hospital for residents of the four cities. Viral RNA was measured using qRT-PCR.

Summary of Main Findings

Copies of viral RNA in the wastewater were found at concentrations between 1.7 x 103 ml-1 to 4.6 x 105 ml-1 during this time period. Concentration threshold values for qRT-PCR in wastewater samples were all below 40, with 97% of them being less than 38, indicating that these samples would very likely be judged positive for SARS-CoV-2 in a clinical setting. During the 10-week study period, viral detection in the wastewater sludge corresponded with the number of cases seen in clinical settings with a lag. Viral RNA detection in wastewater sludge was 0 to 2 days ahead of positive test results by date of sample collection, 1 to 4 days ahead of hospital admissions, and 6 to 8 days ahead of the date of when a test result was yielded for a positive sample.

Study Strengths

Because this study compared the presence of SARS-CoV-2 in wastewater sludge samples to SARS-CoV-2 in clinical settings, the authors had the ability to estimate lead times between the presence of virus in the community and when COVID-19 may pose a public health challenge.

Limitations

This study was conducted in the context of delayed test reporting. The same lag and lead times would therefore be unlikely to apply in the context of rapid, real-time testing or regular testing of both symptomatic and asymptomatic individuals.

Value added

These data add to the body of evidence on the utility of wastewater monitoring for the purpose of SARS-CoV-2 surveillance and early detection of outbreaks at the population-level.

This review was posted on: 20 October 2020