School of Environment, Tsinghua University, Beijing, China.
Civil and Environmental Engineering, University of California, Irvine, USA.
Sci Total Environ. 2021 Mar 25;762:143056. doi: 10.1016/j.scitotenv.2020.143056. Epub 2020 Oct 15.
The COVID-19 pandemic has had a profound impact on human society. The isolation of SARS-CoV-2 from patients' feces on human cell line raised concerns of possible transmission through human feces including exposure to aerosols generated by toilet flushing and through the indoor drainage system. Currently, routes of transmission, other than the close contact droplet transmission, are still not well understood. A quantitative microbial risk assessment was conducted to estimate the health risks associated with two aerosol exposure scenarios: 1) toilet flushing, and 2) faulty connection of a floor drain with the building's main sewer pipe. SARS-CoV-2 data were collected from the emerging literature. The infectivity of the virus in feces was estimated based on a range of assumption between viral genome equivalence and infectious unit. The human exposure dose was calculated using Monte Carlo simulation of viral concentrations in aerosols under each scenario and human breathing rates. The probability of COVID-19 illness was generated using the dose-response model for SARS-CoV-1, a close relative of SARS-CoV-2, that was responsible for the SARS outbreak in 2003. The results indicate the median risks of developing COVID-19 for a single day exposure is 1.11 × 10 and 3.52 × 10 for toilet flushing and faulty drain scenario, respectively. The worst case scenario predicted the high end of COVID-19 risk for the toilet flushing scenario was 5.78 × 10 (at 95th percentile). The infectious viral loads in human feces are the most sensitive input parameter and contribute significantly to model uncertainty.
新冠疫情对人类社会产生了深远的影响。从患者粪便中分离出 SARS-CoV-2 后，人们担心病毒可能会通过粪便传播，包括暴露于厕所冲水时产生的气溶胶和室内排水系统。目前，除了密切接触飞沫传播之外，其他传播途径仍未得到很好的理解。本研究采用定量微生物风险评估方法，估计两种气溶胶暴露情景（1）厕所冲水，以及（2）地漏与建筑物主污水管之间的故障连接，与健康相关的风险。SARS-CoV-2 数据来自新兴文献。根据病毒基因组当量和感染单位之间的一系列假设，估计粪便中病毒的感染力。使用每个情景下气溶胶中病毒浓度和人体呼吸率的蒙特卡罗模拟，计算人体暴露剂量。使用 2003 年 SARS 爆发的 SARS-CoV-1（与 SARS-CoV-2 密切相关的病毒）的剂量-反应模型生成 COVID-19 患病的概率。结果表明，单次暴露导致 COVID-19 发病的中位数风险分别为 1.11×10和 3.52×10，对于厕所冲水和地漏故障情景。最坏情况下，预测的厕所冲水情景下 COVID-19 风险最高值为 5.78×10（第 95 百分位数）。粪便中感染性病毒载量是最敏感的输入参数，对模型不确定性有显著影响。
