Beyond borders: A systematic review and meta-analysis of human-specific faecal markers across geographical settings

Human fecal waste is a global health risk associated with diarrheal diseases, responsible for approximately 1.2 million deaths annually. Microbial Source Tracking (MST) is a molecular method that evaluates environmental sources of fecal contamination, aiding quantification of this contamination and associated health risks. However, reported variations in global human gut microbiomes and geographic performance of human-specific fecal markers suggest that current MST targets may not have broad applicability across populations. This systematic review quantified the performance of human-specific fecal markers to identify those suitable for use across various geographic regions. We evaluated data from primary research articles, published before 18^th October 2023, identified through PubMed, Scopus, and Web of Science using PRISMA guidelines. 103 studies published between 1995 and 2023, spanning 34 countries, 6 continents, and 4 climate zones met inclusion criteria, with quantifiable performance metrics (sensitivity, specificity or accuracy) and a geographic testing location. Extracted data was analyzed to establish marker performance across geographic locations, climate zones, and development status. Over 80% were conducted in High-Income Countries (HICs) and >50% in temperate zones, primarily in the USA (43%), Australia (24%), and Spain (19%). Bacteroides HF183 was the most commonly tested (n = 45 studies). However, no target consistently demonstrated sensitivity, specificity, and/or accuracy >80% across different settings. Consequently, a decision tree is presented supporting selection of appropriate human-specific markers for regional-specific baseline studies. This provides critical information to support new MST research, particularly in Low- and Middle-Income Countries (LMICs), assisting with informed decision and method selection for assessing risks of faecal derived pathogens.