American researchers measured the levels of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) genetic material in waste and sewage water. The researchers from Yale University provided an outline of the spread of the infection in the community. Their study titled, “Measurement of SARS-CoV-2 RNA in wastewater tracks community infection dynamics,” is published in the latest issue of the journal Nature Biotechnology.
What was this study about?
Globally, over 31.44 million have been infected with the SARS-CoV-2 virus. Of these, over 967,000 have lost their lives. The virus is highly infectious and spreads rapidly within the community.
At present, all public health organizations and governments are attempting to contain the spread of the infection within the community by adopting several measures to break the chain of its transmission. To monitor the spread of the infection among populations, testing symptomatic individuals is the crucial measure, the authors wrote. The tests measure the presence of SARS-CoV-2 RNA and keep a count of the positive cases around the world.
Scenario in the United States
In the USA and several other nations, the spread of infection is outpacing testing capacity, and the testing system is missing many asymptomatic individuals, the researchers wrote. Further, the symptoms may take up to 2 weeks to appear. The time between the appearance of symptoms and testing could result in further spread.
Sewage monitoring
Due to the problems with testing systems, an alternative to measuring the spread of the disease in the community could be monitoring sewage systems. Authors write that monitoring the sewage in a community’s collection or treatment system could help detect disease prevalence at community levels and has been shown to be useful in the surveillance of the polio virus. They speculate that similar benefits may be seen with surveillance of COVID-19 because stool of COVID-19 patients carry SARS-CoV-2 RNA, and it is seen in raw wastewater. In regions with higher SARS-CoV-2 RNA levels in raw wastewater the cases of COVID-19 cases are also higher.
The researchers wrote that there is no concrete evidence that shows the utility of wastewater SARS-CoV-2 concentrations in tracking the progression of COVID-19 infections. This study was conducted to check if the viral RNA concentrations in wastewater could be correlated with hospitalization data in a metropolitan region in the USA over a period of around ten weeks, which marked the first wave of the SARS-CoV-2 infection pandemic.
What was done?
The researchers explained that the raw wastewater is usually discharged into the treatment facilities where solids are settled and collected into a matrix called primary sewage sludge. The researchers analyzed this primary sludge. The sludge contains several viruses, including the coronavirus.
Samples of the sludge were collected between March 19, 2020, and June 1, 2020, in the New Haven, Connecticut, metropolitan area. The wastewater treatment facility served nearly 200,000 residents. From the sludge, the team quantitatively compared SARS-CoV-2 RNA concentrations (measured with reverse transcription-polymerase chain reaction qRT–PCR) with the 4 reported measures of the outbreak. For measuring the outbreak, four parameters are usually reported, they wrote. These are:
- “SARS-CoV-2 positive test results by date of specimen collection.”
- “The percentage of positive SARS-CoV-2 test results (test positivity) by date of specimen collection.”
- “The number of local hospital admissions of patients with COVID-19.”
- “SARS-CoV-2 positive test results by reporting date.”
Virus RNA copies ranged from 1.7 × 103 ml−1 to 4.6 × 105 ml−1 of primary sludge, they wrote. Concentration threshold (Ct) values were below 40, and 97 percent of the samples had Ct value less than 38.
What was found?
The results revealed that all the five measures – four parameters of reporting and the measure of viral RNA in primary sludge during the more than the 10 weeks of the study, rose and fell. The sludge results rose in the first week (March 19–25, 2020), which was not corroborated with reported testing or hospital admissions data. Overall the lag between sludge positivity and case rise was around 0 to 2 days, they noted. Results showed the lag periods as follows:
- Sludge positivity rose 0–2 days ahead of SARS-CoV-2 positive test results by date of specimen collection
- Sludge positivity rose 0–2 days ahead of the percentage of positive tests by date of specimen collection
- Sludge positivity rose 1–4 days ahead of local hospital admissions
- Sludge positivity rose 6–8 days ahead of SARS-CoV-2 positive test results by reporting date
Conclusions and implications
Jordan Peccia, the Thomas E. Golden, Jr. Professor of Chemical & Environmental Engineering, lead author of the study said, “If you take our smoothed curve for SARS-CoV-2 RNA in sewage sludge and overlay it on the smoothed curves from testing, the trends are very similar - but we’re 5 to 7 days ahead of it... So not only can we use the sewage sludge virus curve to do some forms of epidemiology, but it's also a significant leading indicator.”
The authors of the study wrote in conclusion, “Our data show the utility of viral RNA monitoring in municipal wastewater for SARS-CoV-2 infection surveillance at a population-wide level.” They suggested this as a measure of community spread in populations facing a delay in specimen collection and the reporting of test results. Immediate measurement of the wastewater viral RNA samples can “provide considerable advance notice of infection dynamics,” they wrote.
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