Human fecal and pathogen exposure pathways in rural Indian villages and the effect of increased latrine coverage

Abstract

Efforts to eradicate open defecation and improve sanitation access are unlikely to achieve health benefits unless interventions reduce microbial exposures. This study assessed human fecal contamination and pathogen exposures in rural India, and the effect of increased sanitation coverage on contamination and exposure rates. In a cross-sectional study of 60 villages of a cluster-randomized controlled sanitation trial in Odisha, India, human and domestic animal fecal contamination was measured in community tubewells and ponds (n = 301) and via exposure pathways in homes (n = 354), using Bacteroidales microbial source tracking fecal markers validated in India. Community water sources were further tested for diarrheal pathogens (rotavirus, adenovirus and Vibrio cholerae by quantitative PCR; pathogenic Escherichia coli by multiplex PCR; Cryptosporidium and Giardia by immunomagnetic separation and direct fluorescent antibody microscopy). Exposure pathways in intervention and control villages were compared and relationships with child diarrhea examined. Human fecal markers were rarely detected in tubewells (2.4%, 95%CI: 0.3–4.5%) and ponds (5.6%, 95%CI: 0.8–10.3%), compared to homes (35.4%, 95%CI: 30.4–40.4%). In tubewells, V. cholerae was the most frequently detected pathogen (19.8%, 95%CI: 14.4–25.2%), followed by Giardia (14.8%, 95%CI: 10.0–19.7%). In ponds, Giardia was most often detected (74.5%, 95%CI: 65.7–83.3%), followed by pathogenic E. coli (48.1%, 95%CI: 34.8–61.5%) and rotavirus (44.4%, 95%CI: 34.2–54.7%). At village-level, prevalence of fecal pathogen detection in community drinking water sources was associated with elevated prevalence of child diarrhea within 6 weeks of testing (RR 2.13, 95%CI: 1.25–3.63) while within homes, higher levels of human and animal fecal marker detection were associated with increased risks of subsequent child diarrhea (P = 0.044 and 0.013, respectively). There was no evidence that the intervention, which increased functional latrine coverage and use by 27 percentage points, reduced human fecal contamination in any tested pathway, nor the prevalence of pathogens in water sources. In conclusion, the study demonstrates that (1) improved sanitation alone may be insufficient and further interventions needed in the domestic domain to reduce widespread human and animal fecal contamination observed in homes, (2) pathogens detected in tubewells indicate these sources are microbiologically unsafe for drinking and were associated with child diarrhea, (3) domestic use of ponds heavily contaminated with multiple pathogens presents an under-recognized health risk, and (4) a 27 percentage point increase in improved sanitation access at village-level did not reduce detectable human fecal and pathogen contamination in this setting.

Identification of Human and Animal Fecal Contamination in Drinking Water Sources in the Kathmandu Valley, Nepal, Using Host-Associated Bacteroidales Quantitative PCR Assays

“…In addition, the use of raw animal waste as fertilizer on agricultural farms is a common practice [15]. Fecal contamination from animals was found to be more prevalent than human contamination in the domestic environment, including source and stored drinking water and soil in rural India and Bangladesh [16][17][18].…”

The Landscape of Enteric Pathogen Exposure of Young Children in Public Domains of Low-Income, Urban Kenya: The Influence of Exposure Pathway and Spatial Range of Play on Multi-Pathogen Exposure Risks

“…However, PCR detection of microbial source tracking (MST) markers in Indian households was associated with diarrhea symptoms in one study. (21) MST markers may occur in the environment more frequently than infectious pathogens, and it is unclear whether MST presence is a reliable proxy for pathogen dose. Validating health outcomes associated with exposure doses in Kisumu children was outside the scope of this study, but is critical to understanding the importance of public exposure pathways in pediatric enteric infections.…”

“…Different types of pathogens have been frequently detected in households of India and Tanzania and public play areas in Kenya, revealing that exposure to pathogens in private and public settings is likely. (21–23) Our group has further shown that soil and surface water from public areas where children play in Kisumu are often contaminated simultaneously by multiple types of pathogens,(23) revealing that children ingesting soil or water at some public sites could ingest multiple types pathogens. Only one report to our knowledge has examined exposure from the perspective of ingesting multiple types of pathogens, rather than presence/absence of an indicator.…”

Oral cholera vaccines: exploring the farrago of evidence

“…6 So far, only the WHO region of the Americas has been certified as free of indigenous measles transmission, 7 but importations of measles into the Americas still cause local and costly outbreaks. 8 Although all other WHO regions have established goals to eliminate measles by 2020 and the GVAP includes indicators related to achieving measles and rubella regional elimination, GVAP progress reports 9 and a 2017 midterm review 10 of the Measles & Rubella Initiative Strategic Plan for 2012-2020 11 both suggest that progress remains off track.…”

“…7 Trials in India have shown similar problems, and a rural sanitation programme failed to show evidence of prevention of diarrhoea and soil-transmitted helminth infections or reduction in faecal contamination of water sources. [8][9][10] Modelling studies have suggested that in areas with poor sanitation, isolated efforts for water quality improvement are likely to be met with low success. 11 Further, considering the high endemicity of cholera in low-income and middle-income countries (LMICs), single-pathway interventions are likely to be inadequate in the control of diarrhoeal diseases, and cholera in particular because of environmental persistence of vibrios, which might not be eradicated even with stringent implementation of such interventions.…”