Department of Civil Engineering, University of Ottawa, Ottawa K1N 6N5, Canada.
City of Ottawa (Engineering Services), Ottawa K1J 1K6, Canada.
Sci Total Environ. 2024 Dec 15;956:177351. doi: 10.1016/j.scitotenv.2024.177351. Epub 2024 Nov 5.
Wastewater-based surveillance (WBS) is increasingly used for monitoring disease targets in wastewaters around the world. This study, performed in Ottawa, Canada, identifies a decrease in SARS-CoV-2 wastewater measurements during snowmelt-induced sewer flushing events. Observations first revealed a correlation between suppressed viral measurements and periods of increased sewage flowrates, air temperatures above 0 °C during winter months, and solids mass flux increases. These correlations suggest that high sewage flowrates from snowmelt events or intense precipitation events lead to the scouring of previously settled solids in sewers and the subsequent entrainment of these solids into the transported wastewaters. Collection of WBS samples during flushing events hence contains a heterogeneous mixture of solids, including resuspended solids with varying degrees of decay. Therefore flushing events can present a challenge for accurately measuring disease target viral signals when using solids-based analytical methods. This study demonstrates that resuspended solids entrained in the wastewaters during flushing events retain PMMoV signal while the SARS-CoV-2 signal is significantly reduced due to the slower decay rate of pepper mild mottle virus (PMMoV) compared to SARS-CoV-2 within wastewaters. Hence current normalization methods using PMMoV are shown to be ineffective in correcting for flushing events and the associated resuspension of settled solids, as the PMMoV signal of settled solids within sewers does not account for the differential decay rates experiences by SARS-CoV-2 signal in settled solids. Instead, this study identifies RNA to PMMoV correction factor as an effective approach to correct for flushing events and to realign SARS-CoV-2 signal with COVID-19 hospital admission rates within communities. As such, the study highlights the key physicochemical parameters necessary to identify flushing events that affect SARS-CoV-2 WBS measurements and introduces a novel RNA to PMMoV correction factor approach for solids-based analysis of SARS-CoV-2 during flushing events, enhancing the accuracy of WBS data for public health decision-making.
污水监测（WBS）在全球范围内越来越多地用于监测污水中的疾病靶标。本研究在加拿大渥太华进行，发现冬季融雪期间污水冲刷事件会导致 SARS-CoV-2 污水测量值下降。最初的观察结果表明，病毒测量值降低与污水流量增加、冬季月份空气温度高于 0°C 以及固体通量增加有关。这些相关性表明，融雪事件或强降水事件导致污水中先前沉降的固体被冲刷，并随后将这些固体带入输送的污水中。因此，在冲刷事件期间采集的污水监测样本包含了固体的不均匀混合物，包括具有不同降解程度的再悬浮固体。因此，在使用基于固体的分析方法时，冲刷事件可能会对准确测量疾病靶标病毒信号带来挑战。本研究表明，在冲刷事件中，污水中夹带的再悬浮固体保留了 PMMoV 信号，而 SARS-CoV-2 信号由于其在污水中的降解速率较慢，信号显著降低。因此，当前使用 PMMoV 的归一化方法在纠正冲刷事件和相关的沉降固体再悬浮方面效果不佳，因为污水中沉降固体的 PMMoV 信号并不能说明 SARS-CoV-2 信号在沉降固体中经历的不同降解速率。相反，本研究确定了 RNA 到 PMMoV 的校正因子，作为一种有效的方法来纠正冲刷事件，并使 SARS-CoV-2 信号与社区内的 COVID-19 住院率重新对齐。因此，该研究强调了确定影响 SARS-CoV-2 WBS 测量的冲刷事件所需的关键物理化学参数，并提出了一种基于 RNA 到 PMMoV 的校正因子方法，用于在冲刷事件期间对 SARS-CoV-2 进行基于固体的分析，提高了 WBS 数据在公共卫生决策中的准确性。
