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SARS-CoV-2 detection in sewage samples: Standardization of method & preliminary observations

1 ICMR-National Institute of Virology, Mumbai Unit, Mumbai, Maharashtra, India
2 Division of Epidemiology & Communicable Diseases, Indian Council of Medical Research, New Delhi, India

Correspondence Address:
Deepa Kailash Sharma,
ICMR-National Institute of Virology, Mumbai Unit, Haffkine Institute Compound, AD Marg, Parel, Mumbai 400 012, Maharashtra
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/ijmr.IJMR_3541_20

PMID: 33318343

Background & objectives: Since its first recognition in Wuhan, China, in December 2019, the SARS-CoV-2 has spread rapidly across the world. Though SARS-CoV-2 spreads mainly via the droplets of respiratory secretions, it was also detected in stool samples of patients, indicating active infection of the gastrointestinal tract. Presence of SARS-CoV-2 RNA in sewage samples was reported in February 2020, raising the possibility of using environmental water surveillance to monitor SARS-CoV-2 activity in infected areas. The aim of this study was to standardize the methodology for detection of SARS-CoV-2 from sewage and explore the feasibility of establishing supplementary surveillance for COVID-19. Methods: Sewage specimens were collected from six sites in Mumbai, India, using the grab sample method and processed using polyethylene glycol (PEG)-dextran phase separation method for virus concentration. Real-time reverse transcription-polymerase chain reaction (RT-PCR) assay was used to detect the presence of SARS-CoV-2 RNA. Results: 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. Interpretation & conclusions: 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 SARS-CoV-2 to generate data about the viral transmission in various epidemiologic settings

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