Study of the sewage from a municipality in southern Minas Gerais, Brazil: correlation of physical and chemical variables, COVID-19 cases, and SARS-CoV-2 RNA concentration

ABSTRACT Wastewater-based epidemiology is an important public health tool with great applicability when facing the COVID-19 pandemic, since infected individuals are able to excrete SARS-CoV-2 particles. In this context, this study aimed to correlate the number of cases of COVID-19 with physical and chemical variables and the presence of the virus in raw sewage samples from a sewage treatment plant (STP) in the municipality of Lavras, Minas Gerais, Brazil, collected between the 19th and 25th epidemiological weeks. The samples were concentrated by electronegative membrane adsorption method and SARS-CoV-2 RNA was extracted, detected, and quantified by RT-qPCR using oligonucleotides and probes for the N gene. Moreover, the variables pH, total suspended solids, and chemical oxygen demand were evaluated. COVID-19 cases were obtained from epidemiological bulletins made available by the municipal government. From the 24th epidemiological week on, a reduction in viral concentration (copies L-1) was observed concomitantly with the pandemic response countermeasures initiated by the municipality. A strong and significant positive correlation (p<0.05) between viral load and number of confirmed cases was obtained through Spearman’s test. However, there was no correlation between the presence of the virus and the physical and chemical characteristics of the sewage. Therefore, it is suggested that further research be carried out in order to track SARS-CoV-2 concentrations in wastewater, thus corroborating with the fight against the pandemic and the achievement of epidemiological surveillance systems based on sewage monitoring.

摘要 基于废水的流行病学（Wastewater-based epidemiology）是一项重要的公共卫生工具，在应对新型冠状病毒肺炎（COVID-19）大流行时具有极高应用价值，因为感染个体可排出新型冠状病毒（SARS-CoV-2）颗粒。本研究旨在将巴西米纳斯吉拉斯州拉夫拉斯市某污水处理厂（STP）原污水样本中的COVID-19确诊病例数、理化指标与病毒检出情况进行关联分析，样本采集于第19至25流行病学周期间。样本采用负电性膜吸附法进行浓缩，通过针对N基因的寡核苷酸与探针，利用反转录实时荧光定量聚合酶链反应（RT-qPCR）对SARS-CoV-2核糖核酸（RNA）进行提取、检测与定量。此外，本研究还对pH值、总悬浮固体及化学需氧量三项理化指标进行了测定。COVID-19病例数据取自该市市政部门公开的流行病学通报。自第24流行病学周起，病毒拷贝浓度（copies·L⁻¹）出现下降，这与该市启动的大流行应对防控措施同步发生。通过斯皮尔曼相关性检验可知，病毒载量与确诊病例数之间存在显著的强正相关关系（p<0.05）。然而，病毒检出情况与污水的理化特征之间未发现显著相关性。因此，本研究建议开展更多相关研究以追踪废水中SARS-CoV-2的浓度，从而为抗击新冠大流行及完善基于污水监测的流行病学监测体系提供科学支撑。