Estimating the minimum number of SARS-CoV-2 infected cases needed to detect viral RNA in wastewater: To what extent of the outbreak can surveillance of wastewater tell us?

• Published in: Environmental research Vol. 195; p. 110748
• Main Authors: Hong, Pei-Ying, Rachmadi, Andri Taruna, Mantilla-Calderon, David, Alkahtani, Mohsen, Bashawri, Yasir M., Al Qarni, Hamed, O'Reilly, Kathleen M., Zhou, Jianqiang
• Format: Journal Article
• Language: English
• Published: Netherlands Elsevier Inc 01.04.2021; The Authors. Published by Elsevier Inc
• Subjects: activated sludge; COVID-19; Detection sensitivity; Disease Outbreaks; epidemiology; genes; hospitals; Humans; Log reduction; monitoring; nucleocapsid; Reverse transcription quantitative PCR; RNA; RNA, Viral - genetics; SARS-CoV-2; septic systems; Severe acute respiratory syndrome coronavirus 2; total organic carbon; viruses; Wastewater; wastewater treatment; Wastewater-based epidemiology; water quality; COVID-19; Detection sensitivity; Log reduction; Reverse transcription quantitative PCR; Wastewater-based epidemiology
• ISSN: 0013-9351; 1096-0953; 1096-0953
• DOI: 10.1016/j.envres.2021.110748

There is increasing interest in wastewater-based epidemiology (WBE) of SARS-CoV-2 RNA to serve as an early warning system for a community. Despite successful detection of SARS-CoV-2 RNA in wastewaters sampled from multiple locations, there is still no clear idea on the minimal number of cases in a community that are associated with a positive detection of the virus in wastewater. To address this knowledge gap, we sampled wastewaters from a septic tank (n = 57) and biological activated sludge tank (n = 52) located on-site of a hospital. The hospital is providing treatment for SARS-CoV-2 infected patients, with the number of hospitalized patients per day known. It was observed that depending on which nucleocapsid gene is targeted by means of RT-qPCR, a range of 253–409 positive cases out of 10,000 persons are required prior to detecting RNA SARS-CoV-2 in wastewater. There was a weak correlation between N1 and N2 gene abundances in wastewater with the number of hospitalized cases. This correlation was however not observed for N3 gene. The frequency of detecting N1 and N2 gene in wastewater was also higher than that for N3 gene. Furthermore, nucleocapsid genes of SARS-CoV-2 were detected at lower frequency in the partially treated wastewater than in the septic tank. In particular, N1 gene abundance was associated with water quality parameters such as total organic carbon and pH. In instances of positive detection, the average abundance of N1 and N3 genes in the activated sludge tank were reduced by 50 and 70% of the levels detected in septic tank, suggesting degradation of the SARS-CoV-2 gene fragments already occurring in the early stages of the wastewater treatment process. [Display omitted] •253 to 409 positive cases out of 10,000 persons are required prior to detecting SARS-CoV-2 RNA in wastewater.•N1 and N2 gene abundance exhibit weak positive correlation with number of patients.•N1 gene provides better sensitivity and correlation for use as monitoring marker.•Abundance of N1 gene associated with total organic carbon and pH.•N1 and N3 genes were reduced by > 50% in partially treated wastewater but N2 genes abundance increased.