Occurrence, virulence profiles and quantitative microbial risk assessment of WHO priority pathogens isolated from hand-dug wells used for domestic purposes in Southwestern Nigeria

Graphical abstract showing hand-dug wells in Ife-East LGA as a silent reservoir of selected WHO priority pathogens, with a quantitative microbial risk assessment indicating unacceptable infection risk for K. pneumoniae. Groundwater from hand-dug wells is a major source of drinking water in many Nigerian communities but is highly vulnerable to microbial contamination. This study assessed the occurrence, selected virulence attributes, and infection risk associated with third-generation cephalosporin- and carbapenem-resistant Klebsiella pneumoniae, Enterobacter spp., Acinetobacter baumannii and Pseudomonas aeruginosa in hand-dug wells in Ife East Local Government Area, southwestern Nigeria. A cross-sectional survey of 296 wells was conducted using membrane filtration technique, culture-based isolation, phenotypic biofilm detection, polymerase chain reaction screening of virulence genes, and quantitative microbial risk assessment. Overall, 23.6% (70/296) of wells were contaminated, with K. pneumoniae being most prevalent (13.5%), followed by P. aeruginosa (4.4%), A. baumannii (3.0%) and Enterobacter spp. (3.0%). Pathogen concentrations ranged from 1 × 102 to 4.2 × 104 cfu/100 mL. Among 71 isolates, 67.6% were biofilm producers and 60.6% harboured at least one virulence gene. Quantitative microbial risk assessment for K. pneumoniae indicated a daily infection probability of approximately 78% and a high annual infection risk. Hand-dug wells in Ife East LGA represent significant reservoirs of WHO-priority pathogens, underscoring the need for improved well protection, routine water quality monitoring and strengthened water, sanitation, and hygiene interventions.