Global assessment of exposure to faecal contamination through drinking water based on a systematic review

Abstract

Objectives: To estimate exposure to faecal contamination through drinking water as indicated by levels of Escherichia coli (E. coli) or thermotolerant coliform (TTC) in water sources.

Methods: We estimated coverage of different types of drinking water source based on household surveys and censuses using multilevel modelling. Coverage data were combined with water quality studies that assessed E. coli or TTC including those identified by a systematic review (n = 345). Predictive models for the presence and level of contamination of drinking water sources were developed using random effects logistic regression and selected covariates. We assessed sensitivity of estimated exposure to study quality, indicator bacteria and separately considered nationally randomised surveys.

Results: We estimate that 1.8 billion people globally use a source of drinking water which suffers from faecal contamination, of these 1.1 billion drink water that is of at least 'moderate' risk (>10 E. coli or TTC per 100 ml). Data from nationally randomised studies suggest that 10% of improved sources may be 'high' risk, containing at least 100 E. coli or TTC per 100 ml. Drinking water is found to be more often contaminated in rural areas (41%, CI: 31%-51%) than in urban areas (12%, CI: 8-18%), and contamination is most prevalent in Africa (53%, CI: 42%-63%) and South-East Asia (35%, CI: 24%-45%). Estimates were not sensitive to the exclusion of low quality studies or restriction to studies reporting E. coli.

Conclusions: Microbial contamination is widespread and affects all water source types, including piped supplies. Global burden of disease estimates may have substantially understated the disease burden associated with inadequate water services.

Keywords: E. coli; agua para consumo humano; cara de enfermedad; charge de morbidité; coliforme termotolerante; coliformes thermo-tolérants; disease burden; drinking water; eau potable; seguridad del agua; sécurité de l'eau; thermotolerant coliform; water safety.

Figure 1

Analytical approaches used to estimate global exposure to unsafe drinking-water.

Figure 2

Relationship between proportion of samples contaminated with faecal indicator bacteria and the proportion with lev els greater than or equal to 10 per 100 ml, showing fitted quadratic model. Circles are proportional to the number of samples tested at a given type of water source within each study.]

Figure 3

Proportion of the population exposed to faecally contaminated drinking water from improved sources or with access only to unimproved sources by region and globally for 2012. FIB: faecal indicator bacteria; HI: high income; LMI: low or middle income; Am: Americas; EasMed: Eastern Mediterranean; Euro: Europe; SEA: South-East Asia; West_Pac: western Pacific. Confidence intervals do not account for uncertainty in the relationship between presence (≥1 per 100 ml) and levels of contamination (≥10 per 100 ml) nor do they account for uncertainty in estimation from surveys and censuses.]