基於污水流行病學建置SARS-CoV-2採樣點選擇方法與效益評估

Abstract

新冠肺炎 (Coronavirus disease 2019, Covid-19) 的大流行嚴重衝擊著世界各國，其影響層面包含經濟、生命、社會等。此病毒傳染力強以及潛伏期長的特性，使得疫情的防範備受考驗。為此，如何在感染初期發現感染患者，儘早實施隔離等公衛措施成了各國矚目的焦點。正因如此，污水流行病學 (Wastewater-Based Epidemiology, WBE) 的概念再次興起，各國也先後實施污水監測計畫，以提早發現社區中的感染個體並追蹤疫情動態。然而，目前國內外針對污水監測尚未建立起一套完善的監測指引，同時也缺乏監測點效益評估方法，因而無法確定監測點設置後，是否能在疫情初期時儘早發現感染源並在疫情爆發後追蹤感染動態，以充分發揮其污水監測能力。 本研究以下水道管網建置完整的淡水區為案例地區，並以污水流行病學實施的各個階段為評估基礎，考量污水中病原體的產生、病毒於污水中的傳輸、採樣與分析之三大要件，建立一套監測點效益評估方法。在監測適宜性的評估中，本研究以排便習慣之機率分布作為病原體產生之關鍵，輔以下水道之水力模型模擬病毒訊號於污水中的傳輸，藉此評估採樣點監測之有效空間與適宜時間。溯源空間適宜性的評估是以土地利用之人口流動強度為篩選依據，排除人口流動性高的下游集污空間以減低無法找到感染源之機率。最終的溯源效益分析是基於二元搜尋的架構，考量溯源分區大小與單次採樣分析所需的時長，估算完成溯源所需花費的總時間。 監測適宜性評估的結果顯示，在低盛行率與高盛行率的時期皆以上午7至10點為最佳採樣時間。低盛行率時，監測點所涵蓋之有效監測空間無論是人孔或是人口數僅佔整個案例地區的10~22%，顯示此監測點無法有效監測其集污區，須於上游無效監測區額外增設監測點位，以增加污水監測面積。 溯源空間適宜性評估的結果顯示，高人口流動性之下游集污區佔整體集污區人孔數之36.98%、總人口數之29.16%，代表部分地區無法發揮污水流行病學之溯源能力，協助定位潛在感染空間。溯源效益評估的結果使決策者得以了解完成溯源所需花費的時間，以及溯源至最終分區時可能的人口數與人孔數。更具體地來說，上述的結果，反映了溯源之空間定位、人口定位能力。

The Covid-19 pandemic has had a significant impact around the world, with economic, life, and society. The highly infectious property and long incubation period of this virus make the prevention of the epidemic challenging. As a result, the concept of Wastewater-Based Epidemiology (WBE) has re-emerged and several countries have launched relative wastewater surveillance programs to detect and track the infected individuals in the community. However, a comprehensive set of monitoring guidelines for wastewater monitoring has not yet been established both domestically and internationally. Besides, there are still lacking of relative methods for evaluating the effectiveness of monitoring sites. Therefore, at this stage, the ability of wastewater surveillance system remains a mystery. To establish a method for evaluating the effectiveness of monitoring sites, this study takes Tamsui District as a case study area, taking into account the three major elements of WBE, the virus shedding in feces, the virus transport in sewer network, sampling and analyzing. When assessing the adequacy of wastewater monitoring, this study take the probability of defecation as the key factor, and hydraulic modeling for simulating the virus transportation in wastewater, to evaluate the effective area and proper time for sampling. The evaluation of suitability space for infection tracking is based on the relation between land-use type and the intensity of population movement. The downstream of these high population flow areas is excluded to reduce the possibility of not point out the source of infection. The benefit of source tracking is based on the framework of binary search, which consider the size of each tracking area and the time required for a single sampling analysis to estimate the total time required to complete source tracking. The results of the monitoring suitability assessment show that the best sampling time is between 7 and 10 a.m. during both low and high prevalence periods. During low prevalence, the effective monitoring space surveilled by the monitoring sites, both in terms of manholes and population, only account for 10-22% of the entire upstream area, indicating that the monitoring sites could not effectively monitor the sewershed. Thus additional monitoring sites are needed in the ineffective monitoring zone to increase the wastewater monitoring coverage. The results of the spatial suitability assessment for traceability show that the catchment areas with highly population flow properties account for 36.98% of the total manholes and 29.16% of the total population. This represents a portion of the area where the source tracking ability of WBE could not be utilized to help locate potential infection sites. The results of the traceability assessment allow decision makers to understand the time required to complete infection tracking, and the potential population and number of manholes when converges to the final district. More specifically, these results reflect the spatial and demographic locating capability of infection tracking.