Table_2_Longitudinal wastewater-based surveillance of SARS-CoV-2 during 2023 in Ethiopia.XLS

IntroductionAlthough wastewater-based epidemiology (WBE) successfully functioned as a tool for monitoring the coronavirus disease 2019 (COVID-19) pandemic globally, relatively little is known about its utility in low-income countries. This study aimed to quantify severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) RNA in wastewater, estimate the number of infected individuals in the catchment areas, and correlate the results with the clinically reported COVID-19 cases in Addis Ababa, Ethiopia.
MethodsA total of 323 influent and 33 effluent wastewater samples were collected from three Wastewater Treatment Plants (WWTPs) using a 24-h composite Moore swab sampling method from February to November 2023. The virus was captured using Ceres Nanotrap® Enhancement Reagent 2 and Nanotrap® Microbiome A Particles, and then nucleic acids were extracted using the Qiagen QIAamp Viral RNA Mini Kit. The ThermoFisher TaqPath™ COVID-19 kit was applied to perform real-time reverse transcriptase polymerase chain reaction (qRT-PCR) to quantify the SARS-CoV-2 RNA. Wastewater viral concentrations were normalized using flow rate and number of people served. In the sampling period, spearman correlation was used to compare the SARS-CoV-2 target gene concentration to the reported COVID-19 cases. The numbers of infected individuals under each treatment plant were calculated considering the target genes’ concentration, the flow rate of treatment plants, a gram of feces per person-day, and RNA copies per gram of feces.
ResultsSARS-CoV-2 was detected in 94% of untreated wastewater samples. All effluent wastewater samples (n = 22) from the upflow anaerobic sludge blanket (UASB) reactor and membrane bioreactor (MBR) technology were SARS-COV-2 RNA negative. In contrast, two out of 11 effluents from Waste Stabilization Pond were found positive. Positive correlations were observed between the weekly average SARS-CoV-2 concentration and the cumulative weekly reported COVID-19 cases in Addis Ababa. The estimated number of infected people in the Kality Treatment catchment area was 330 times the number of COVID-19 cases reported during the study period in Addis Ababa.
DiscussionThis study revealed that SARS-CoV-2 was circulating in the community and confirmed previous reports of more asymptomatic COVID-19 cases in Ethiopia. Additionally, this study provides further evidence of the importance of wastewater-based surveillance in general to monitor infectious diseases in low-income settings.
ConclusionWastewater-based surveillance of SARS-CoV-2 can be a useful method for tracking the increment of COVID-19 cases before it spreads widely throughout the community.

引言
尽管基于污水的流行病学（wastewater-based epidemiology, WBE）已在全球范围内成功作为监测新型冠状病毒肺炎（coronavirus disease 2019, COVID-19）大流行的工具，但目前对其在低收入国家的应用价值尚了解甚少。本研究旨在定量检测污水中的严重急性呼吸综合征冠状病毒2（severe acute respiratory syndrome coronavirus 2, SARS-CoV-2）核糖核酸（RNA），估算集水区内的感染人数，并将检测结果与埃塞俄比亚亚的斯亚贝巴的临床报告COVID-19病例进行关联分析。

方法
2023年2月至11月，采用24小时混合摩尔拭子采样法，从3座污水处理厂（Wastewater Treatment Plants, WWTPs）采集了323份进水污水样本与33份出水污水样本。研究使用Ceres Nanotrap®增强试剂2与Nanotrap®微生物组A颗粒捕获病毒，随后采用凯杰QIAamp病毒RNA迷你试剂盒提取核酸。使用赛默飞TaqPath™ COVID-19试剂盒开展实时逆转录聚合酶链反应（real-time reverse transcriptase polymerase chain reaction, qRT-PCR），以定量检测SARS-CoV-2 RNA。通过污水处理厂的处理流量与服务人口数对污水病毒浓度进行标准化处理。采样期间，采用斯皮尔曼相关性分析比较SARS-CoV-2靶基因浓度与报告的COVID-19病例数。结合靶基因浓度、污水处理厂处理流量、每人每日粪便排泄量及每克粪便中的RNA拷贝数，计算各污水处理厂集水区内的感染人数。

结果
94%的未处理污水样本中检测到SARS-CoV-2。采用上流式厌氧污泥床（upflow anaerobic sludge blanket, UASB）反应器与膜生物反应器（membrane bioreactor, MBR）工艺的污水处理厂的所有出水样本（n=22）均呈SARS-CoV-2 RNA阴性。与之相反，稳定塘处理工艺的11份出水样本中有2份呈阳性。亚的斯亚贝巴的周平均SARS-CoV-2浓度与累计周报告COVID-19病例数呈正相关。研究期间，卡利蒂污水处理厂集水区的估算感染人数是当地报告COVID-19病例数的330倍。

讨论
本研究证实SARS-CoV-2在社区中传播，印证了此前关于埃塞俄比亚存在大量无症状COVID-19病例的报道。此外，本研究进一步证明了基于污水的监测在低收入地区监测传染病的重要性。

结论
基于污水的SARS-CoV-2监测可作为一种有效方法，在COVID-19在社区广泛传播前追踪病例数的增长。