Tracking virus presence in sewage to help monitor pandemic: researchers

The detection of the presence of SARS-CoV-2 RNA in sewage samples has raised the possibility of using environmental water surveillance to monitor virus activity in infected areas, researchers have said.

Similar environmental surveillance for the polio virus has played a critical role in the eradication of wild polio virus globally.

In their paper titled “SARS-CoV-2 detection in sewage samples: Standardization of method & preliminary observations”, published recently in the Indian Journal of Medical Research, researchers claim to have undertaken the study to standardise the methodology for detection of SARS-CoV-2 from sewage and explore the feasibility of establishing supplementary surveillance for COVID-19.

Researchers have now suggested that SARS-CoV-2 detection in waste waters could be used to understand the epidemiology of COVID-19.

“Decreasing concentration or absence of virus at previously SARS-CoV-2-positive sewage sampling sites may indicate successful implementation of COVID-19 control strategies and it may provide evidence of the presence or absence of SARS-CoV-2-infected populations and confirmation of COVID-19-free zones,” the study noted.

Intestinal infection

The study was conducted by ICMR-National Institute of Virology, (Mumbai Unit) and Division of Epidemiology and Communicable Diseases, ICMR, Delhi, and said though COVID spreads mainly via the droplets of respiratory secretions, it was also detected in stool samples of patients, indicating active infection of the gastrointestinal tract.

For the study, sewage samples were collected from six sites in Mumbai using the grab sample method and processed using polyethylene glycol (PEG)-dextran phase separation method for virus concentration. Real-time RT-PCR assay was used to detect the presence of SARS-CoV-2 RNA.

“A total of 20 sewage samples collected from six different wards in Mumbai city, before the spread of SARS-CoV-2 infections and during May 11-22, 2020, were processed using the phase separation method. The WHO two-phase PEG-dextran method was modified during standardization. SARS-CoV-2 was found to concentrate in the middle phase only. All samples collected before March 16, 2020 were SARS-CoV-2 negative. Viral RNA was detected in sewage samples collected during the ongoing COVID-19 pandemic in all the six wards,” the study said.

The study concluded that PEG-dextran phase separation method was effectively used to concentrate SARS-CoV-2 from domestic waste waters to detection levels. It would be feasible to initiate sewage surveillance for the virus to generate data about the viral transmission in various epidemiologic settings.

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