Seasonal differences in enteric pathogen occurrence across multiple drinking water sources in Kathmandu Valley, Nepal

ABSTRACT

Schematic overview of the study showing five drinking water sources in Kathmandu Valley (tap, well, stone spout, jar, and tanker water) analyzed using microfluidic qPCR for enteric pathogens. Results indicate seasonal differences in pathoge n prevalence, with higher concentrations and clustering of fecal indicators in winter samples compared with summer samples.

Residents of Nepal's Kathmandu Valley face chronic water shortages and rely on multiple water sources to meet their daily needs. However, inconsistent operational monitoring across these sources increases the likelihood of disease outbreaks. To assess the water quality status across multiple water sources, 86 samples were collected in 2018 during the winter (n = 22) and summer (n = 64) from five source types: water tankers, jar, tap, well, and stone-spouts and screened for 22 pathogens using microfluidic quantitative Polymerase Chain Reaction (mf-qPCR). Two fecal indicator bacteria and five enteric pathogens were detected. Contamination patterns showed seasonal variations, with 95% of winter samples and 55% of summer samples testing positive for pathogens. Winter samples exhibited higher concentrations of fecal indicators than summer samples. Campylobacter jejuni appeared exclusively in summer, while Adenovirus and Giardia lamblia were detected only during winter. Nonmetric multidimensional scaling showed significant clustering by season (p < 0.001), while source type was not associated with community composition. Winter samples clustered with adv4041, ftsZ, uidA, and eaeA, showing consistently higher relative abundances whereas summer samples exhibited sporadic and sparse gene distribution. These findings highlight seasonal differences in pathogen exposure risks that should be accounted for when designing surveillance and intervention measures.