Identification of human and animal fecal contamination in drinking water sources in the Kathmandu Valley, Nepal, using host-associated Bacteroidales Quantitative PCR Assays

Abstract

This study identified the sources of fecal contamination in the groundwater of different land covers. A total of 300 groundwater samples were collected in the Kathmandu Valley, Nepal, in the dry (n = 152) and wet (n = 148) seasons of 2016. Fecal indicator bacteria were initially enumerated, and then fecal contamination sources were identified using human (BacHum), ruminant (BacR), and pig-associated (Pig2Bac) Bacteroidales quantitative polymerase chain reaction assays. Sixty-six percent (197/300) of the tested groundwater samples had Escherichia coli concentrations higher than the World Health Organization threshold for drinking ( < 1 most probable number/100 mL). The fecal contamination of the groundwater was of human (22%, 55/250), ruminant (11%, 28/250), and pig (3%, 8/250) origin. Deep tube wells were less likely to be positive for E. coli and fecal markers compared to shallow dug wells. The human fecal marker was more likely to be detected in sources from built-up as compared to agricultural areas (Adjusted odds ratio (AOR) = 3.60, p = 0.002). Likewise, the ruminant fecal marker was more likely to be detected in sources from agricultural as compared to built-up areas (AOR = 2.90, p = 0.018). These findings suggest the preparation of mitigation strategies for controlling fecal pollution based on land cover and well types.