Predictors of Enteric Pathogens in the Domestic Environment from Human and Animal Sources in Rural Bangladesh

Abstract

Fecal indicator organisms are measured to indicate the presence of fecal pollution, yet the association between indicators and pathogens varies by context. The goal of this study was to empirically evaluate the relationships between indicator Escherichia coli, microbial source tracking markers, select enteric pathogen genes, and potential sources of enteric pathogens in 600 rural Bangladeshi households. We measured indicators and pathogen genes in stored drinking water, soil, and on mother and child hands. Additionally, survey and observational data on sanitation and domestic hygiene practices were collected. Log₁₀ concentrations of indicator E. coli were positively associated with the prevalence of pathogenic E. coli genes in all sample types. Given the current need to rely on indicators to assess fecal contamination in the field, it is significant that in this study context indicator E. coli concentrations, measured by IDEXX Colilert-18, provided quantitative information on the presence of pathogenic E. coli in different sample types. There were no significant associations between the human fecal marker (HumM2) and human-specific pathogens in any environmental sample type. There was an increase in the prevalence of Giardia lamblia genes, any E. coli virulence gene, and the specific E. coli virulence genes stx1/2 with every log₁₀ increase in the concentration of the animal fecal marker (BacCow) on mothers' hands. Thus, domestic animals were important contributors to enteric pathogens in these households.

Figure 1

Pathogens associated with human and animal origin in different reservoirs investigated in this paper. ^aAtypical enteropathogenic E. coli (EPEC) is transmitted by humans and animals, typical is transmitted by humans only. ^bSTEC: Shiga toxin- producing E. coli. ^cEnterotoxins found in enterotoxigenic E. coli (ETEC) can be from humans and animals but species-specific adhesion factors confer host specificity. ^dOutside of human and animal sources, indicator E. coli can also occur naturally in the environment. ^eBacCow is specific to animals. ^fAggR gene in enteroaggregative E. coli (EAEC) only found in strains isolated from humans. ^gEnteroinvasive E. coli (EIEC) has been found in humans and primates; primates are not relevant to this study.

Figure 2

Prevalence ratios and 95% confidence intervals indicating the average increase in prevalence of norovirus GII, Giardia lamblia, and E. coli virulence genes for a 1 log₁₀ increase in (a). MPN E. coli/sample matrix and (b) gene copies of BacCow/sample matrix. ◆ indicates too few samples were positive to model. Pathogens and virulence genes associated with human or human and animal sources are underlined in blue and orange, respectively. CH: child hands, MH: mother hands, SW: stored water, S: soil. ECVG: E. coli virulence gene, EHEC: Enterohemorrhagic E. coli, EPEC: Enteropathogenic E. coli, EAEC: Enteroaggregative E. coli, STEC: Shiga toxin-producing E. coli, ETEC: Enterotoxigenic E. coli, EIEC: Enteroinvasive E. coli.

Figure 3

Adjusted prevalence ratios and 95% confidence intervals indicating the prevalence of norovirus GII, Giardia lamblia, and E. coli virulence genes in households with fecal piles or cow patties above and below a threshold value. For cow, goat/sheep, and nonpoultry birds, the threshold value was zero. For chicken/nonchicken poultry the threshold value was 5 (>5 versus ≤5). Feces types with a p-value < 0.2 in bivariate models between outcomes and exposures were included in the adjusted models (models adjusted for the presence of other feces types in households if these were associated with the outcome pathogen in a bivariate model at p-value < 0.2). Pathogens and virulence genes associated with human or human and animal sources are underlined in blue and orange, respectively. Prevalence ratios for EIEC were omitted due to their large confidence intervals. CH: child hands, MH: mother hands, SW: stored water, S: soil. ECVG: E. coli virulence gene, EHEC: enterohemorrhagic E. coli, EPEC: enteropathogenic E. coli, EAEC: enteroaggregative E. coli, STEC: Shiga toxin-producing E. coli, ETEC: enterotoxigenic E. coli, EIEC: enteroinvasive E. coli.