Analysis of sewage sludge for a period of 10 weeks in the New Haven, Connecticut, metropolitan area in the U.S., during the COVID-19 outbreak period March 19 to June 1 once again demonstrates the utility of viral RNA monitoring of municipal wastewater for SARS-CoV-2 infection surveillance at a population-wide level. In this case, the sewage samples collected and analysed helped monitor about 200,000 residents in the metropolitan area.
Pre-empting records
Analysis of the sludge samples allowed researchers to track the rise and fall of positive cases and hospital admissions days before they were officially known or recorded. Based on the RNA concentrations in the sludge, the researchers were able to know the swing in cases up to two days before samples could be collected, one–four days before hospital admissions and six–eight days before positive results were reported. The results were published in the journal Nature Biotechnology.
While the researchers collected and analysed primary sewage sludge that form when raw wastewater discharges into treatment facilities, in places that lack primary wastewater treatment, monitoring of raw wastewater streams would be necessary, they write.
Infection dynamics
Based on the results, a team of researchers led by Dr Jordan Peccia and Dr Saad Omer from Yale University, New Haven, write: “In communities facing a delay between specimen collection and the reporting of test results, immediate wastewater results can provide considerable advance notice of infection dynamics.”
Utility of wastewater
The results come in the wake of uncertainty and poor understanding of the utility of wastewater SARS-CoV-2 concentrations for tracking the progression of COVID-19 infections. This despite the evidence that SARS-CoV-2 RNA is present in the stools of COVID-19 patients and hence in sewage, and of increased RNA concentrations in sewage being correlated with increased number of cases reported days later.
Besides delay in seeking a test and reporting of test results, symptoms may take a few days to present once infection sets in. Samples were collected every day and the concentration of viral RNA in the sewage samples were compared with publicly available infection data. They analysed the numbers and percentages of positive SARS-CoV-2 tests by specimen collection date, the numbers of positive SARS-CoV-2 tests by reporting date, and COVID-19 hospital admissions.
“Sludge results were not a leading indicator compared to positive test results or percentage of positive tests by date of specimen collection. However, they led hospitalizations by one–four days and test results by report date by about one week. Thus, in communities where test reporting is delayed, sludge results, if analysed and reported on the same day as sampling, can provide substantial advance notice of infection dynamics,” they write.
Primary sludge handling approaches can be different in treatment plants and this could affect the levels of detectable virus. “Given the uncertainties in sludge data and epidemiological data, we did not attempt to correlate absolute numbers of sludge SARS-CoV-2 RNA concentrations and COVID-19 cases,” they note.
