Infectious Disease Division, International Centre for Diarrhoeal Disease Research, Bangladesh (icddr,b), Dhaka, Bangladesh.
Center for Global Safe Water, Sanitation, and Hygiene, Emory University, Atlanta, GA, USA.
Int J Hyg Environ Health. 2020 Sep;230:113619. doi: 10.1016/j.ijheh.2020.113619. Epub 2020 Sep 15.
Despite wide usage of on-site sanitation, there is limited field-based evidence on the removal or release of pathogens from septic tanks and other primary treatment systems, such as anaerobic baffled reactors (ABR). In two low-income areas in Dhaka, we conducted a cross-sectional study to explore pathogen loads discharged from commonly used on-site sanitation-systems and their transport in nearby drains and waterways.
We collected samples of drain water, drain sediment, canal water, and floodwater from April-October 2019. Sludge, supernatant, and effluent samples were also collected from septic tanks and ABRs. We investigated the presence and concentration of selected enteric pathogens (Shigella, Vibrio cholerae (V. cholerae), Salmonella Typhi (S. Typhi), Norovirus Genogroup-II (NoV-GII), and Giardia) and presence of Cryptosporidium in these samples using quantitative polymerase chain reaction (qPCR).The equivalent genome copies (EGC) of individual pathogens were estimated in each sample by interpolation of the mean Ct value to the corresponding standard curve and the dilution factor for each sample type. Absolute quantification was expressed as log EGC per 100 mL for the water samples and log EGC per gram for the sediment samples.
Among all samples tested (N = 151), 89% were contaminated with Shigella, 68% with V. cholerae and NoV-GII, 32% with Giardia, 17% with S. Typhi and 6% with Cryptosporidium. A wide range of concentration of pathogens [range: mean log concentration of Giardia = 0.74 EGC/100 mL in drain ultrafiltration samples to mean log concentration of NoV-GII and Giardia = 7.11 EGC/100 mL in ABR sludge] was found in all environmental samples. The highest pathogen concentrations were detected in open drains [range: mean log concentration = 2.50-4.94 EGC/100 mL], septic tank effluent [range: mean log concentration = 3.32-4.65 EGC/100 mL], and ABR effluent [range: mean log concentration = 2.72-5.13 EGC/100 mL].
High concentrations of pathogens (particularly NoV-GII, V.cholerae and Shigella) were frequently detected in environmental samples from two low-income urban neighbourhoods of Dhaka city. The numerous environmental exposure pathways for children and adults make these findings of public health concern. These results should prompt rethinking of how to achieve safe sanitation solutions that protect public health in dense low-income areas. In particular, improved management and maintenance regimes, further treatment of liquid effluent from primary treatment processes, and appropriate application of onsite, decentralised and offsite sanitation systems given the local context.
尽管现场卫生设施得到广泛应用，但关于化粪池和其他初级处理系统（如厌氧折流板反应器（ABR））中病原体的去除或释放，仍缺乏现场证据。在达卡的两个低收入地区，我们进行了一项横断面研究，以探索常用现场卫生设施系统排放的病原体负荷及其在附近排水渠和水道中的传输情况。
我们于 2019 年 4 月至 10 月期间采集了排水渠水、排水沉积物、运河水和洪水样本。还从化粪池和 ABR 收集了污泥、上清液和废水样本。我们使用定量聚合酶链反应（qPCR）检测了所选肠道病原体（志贺氏菌、霍乱弧菌（V. cholerae）、伤寒沙门氏菌（S. Typhi）、诺如病毒基因群-II（NoV-GII）和贾第虫）的存在和浓度，以及这些样本中的隐孢子虫。通过将平均 Ct 值内插到相应的标准曲线和每个样本类型的稀释因子，估算每个样本中个体病原体的等效基因组拷贝（EGC）。绝对定量表示为每 100 毫升水样的 log EGC 和每克沉积物的 log EGC。
在所测试的所有样本中（N=151），89%的样本受到志贺氏菌污染，68%的样本受到霍乱弧菌和 NoV-GII 污染，32%的样本受到贾第虫污染，17%的样本受到伤寒沙门氏菌污染，6%的样本受到隐孢子虫污染。所有环境样本中均发现病原体浓度范围广泛[范围：贾第虫的平均对数浓度=0.74 EGC/100 毫升在排水超滤样品中，NoV-GII 和贾第虫的平均对数浓度=7.11 EGC/100 毫升在 ABR 污泥中]。在所有环境样本中，最高的病原体浓度检测到在开放排水渠[范围：平均对数浓度=2.50-4.94 EGC/100 毫升]、化粪池废水[范围：平均对数浓度=3.32-4.65 EGC/100 毫升]和 ABR 废水[范围：平均对数浓度=2.72-5.13 EGC/100 毫升]中。
在达卡市两个低收入城市社区的环境样本中，经常检测到高浓度的病原体（特别是 NoV-GII、霍乱弧菌和志贺氏菌）。儿童和成人存在许多环境暴露途径，这些发现引起了公共卫生关注。这些结果应促使重新考虑如何实现安全卫生解决方案，以保护贫困人口稠密地区的公共卫生。特别是在当地背景下，需要改进初级处理过程中液体废水的管理和维护制度，进一步处理，以及适当应用现场、分散和场外卫生设施系统。
