Human specific microbial source tracking (MST) markers which are highly specific to human waste contamination offer the advantage of better association with human pathogens than traditional microbial indicators. However, the performance of these MST markers may vary across different geographical regions. The magnitude of MST markers also plays an important role in interpreting the health risks. This study aims to (i) validate the specificity and sensitivity of human markers for tropical urban catchments; (ii) identify the threshold concentrations of MST markers, i.e. human polyomaviruses (HPyVs), Bacteroides thetaiotaomicron (B. theta) and Methanobrevibacter smithii (M. smithii), that correspond to the acceptable gastrointestinal (GI) illness risks associated with swimming using the QMRA approach; and (iii) validate the threshold concentrations of MST markers using the surveillance data obtained from the tropical urban environment. Among the three MST markers, HPyVs showed the highest specificity (100%) to sewage samples, followed by M. smithii (97%) and B. theta (90%). All MST markers showed 100% sensitivity towards sewage contamination, with B. theta present in highest abundance in sewage, followed by HPyVs and M. smithii. This study demonstrates a risk-based framework to identify the threshold concentrations of MST markers associated with GI illness risks in environmental waters by considering two main influencing factors (i.e. decay and dilution factors). This study successfully validated the B. theta threshold concentration range (581 to 8073 GC/100mL) with field data (370 to 6500 GC/100mL) in estimating GI illness risks with an Enterococcus model. Field data showed that the MST markers at threshold concentrations were able to classify the safe level in more than 83% of the samples, according to GI illness risks from Enterococcus and adenovirus. The study also highlighted the lack of associations between MST markers and GI illness risks from norovirus. With comprehensive information on specificity, sensitivity and threshold concentrations of MST markers, increasing confidence can be placed on identifying human source contamination and evaluating the health risks posed in environmental waters in Singapore.

人类特定微生物源跟踪 (MST) 标记对人类废物污染具有高度特异性，与传统微生物指标相比，它具有与人类病原体更好地关联的优势。然而，这些 MST 标记的性能可能因不同的地理区域而异。MST 标记的量级在解释健康风险方面也起着重要作用。本研究旨在 (i) 验证热带城市集水区人类标记的特异性和敏感性；(ii) 确定 MST 标记物的阈值浓度，即人类多瘤病毒 (HPyVs)、Bacteroides thetaiotaomicron ( B. theta ) 和Methanobrevibacter smithii ( M. smithii))，对应于使用 QMRA 方法游泳相关的可接受的胃肠 (GI) 疾病风险；(iii) 使用从热带城市环境中获得的监测数据验证 MST 标记的阈值浓度。在三个 MST 标记中，HPyVs 对污水样品的特异性最高 (100%)，其次是M. smithii (97%) 和B. theta (90%)。所有 MST 标记都对污水污染表现出 100% 的敏感性，其中B. theta在污水中的丰度最高，其次是 HPyVs 和M. smithii. 本研究展示了一个基于风险的框架，通过考虑两个主要影响因素（即衰减和稀释因素）来确定环境水域中与胃肠道疾病风险相关的 MST 标记物的阈值浓度。本研究成功地验证了B. theta阈值浓度范围（581 至 8073 GC/100mL）和现场数据（370 至 6500 GC/100mL），用于估计肠球菌模型的GI 疾病风险。现场数据显示，根据肠球菌的胃肠道疾病风险，阈值浓度的 MST 标记能够对超过 83% 的样本进行安全水平分类和腺病毒。该研究还强调了 MST 标记物与诺如病毒引起的胃肠道疾病风险之间缺乏关联。有了关于 MST 标记物的特异性、敏感性和阈值浓度的全面信息，可以增加对识别人源污染和评估新加坡环境水域中构成的健康风险的信心。