title: Coliform bacteria as indicators of diarrheal risk in household drinking water: systematic review and meta-analysis.
abstract: BACKGROUND
  Current guidelines recommend the use of Escherichia coli (EC) or thermotolerant ("fecal") coliforms (FC) as indicators of fecal contamination in drinking water. Despite their broad use as measures of water quality, there remains limited evidence for an association between EC or FC and diarrheal illness: a previous review found no evidence for a link between diarrhea and these indicators in household drinking water.
  
  
  OBJECTIVE
  We conducted a systematic review and meta-analysis to update the results of the previous review with newly available evidence, to explore differences between EC and FC indicators, and to assess the quality of available evidence.
  
  
  METHODS
  We searched major databases using broad terms for household water quality and diarrhea. We extracted study characteristics and relative risks (RR) from relevant studies. We pooled RRs using random effects models with inverse variance weighting, and used standard methods to evaluate heterogeneity and publication bias.
  
  
  RESULTS
  We identified 20 relevant studies; 14 studies provided extractable results for meta-analysis. When combining all studies, we found no association between EC or FC and diarrhea (RR 1.26 [95% CI: 0.98, 1.63]). When analyzing EC and FC separately, we found evidence for an association between diarrhea and EC (RR: 1.54 [95% CI: 1.37, 1.74]) but not FC (RR: 1.07 [95% CI: 0.79, 1.45]). Across all studies, we identified several elements of study design and reporting (e.g., timing of outcome and exposure measurement, accounting for correlated outcomes) that could be improved upon in future studies that evaluate the association between drinking water contamination and health.
  
  
  CONCLUSIONS
  Our findings, based on a review of the published literature, suggest that these two coliform groups have different associations with diarrhea in household drinking water. Our results support the use of EC as a fecal indicator in household drinking water.
authors.affiliation: Division of Epidemiology, University of California, Berkeley, California, United States of America.
authors.forename: Joshua S
authors.initials: JS
authors.lastname: Gruber
authors.affiliation: Division of Epidemiology, University of California, Berkeley, California, United States of America.
authors.forename: Ayse
authors.initials: A
authors.lastname: Ercumen
authors.affiliation: Division of Epidemiology, University of California, Berkeley, California, United States of America.
authors.forename: John M
authors.initials: JM
authors.lastname: Colford
mesh_terms: D003967:Diarrhea / Q000382:microbiology*; D060766:Drinking Water / Q000382:microbiology*; D004755:Enterobacteriaceae / Q000302:isolation & purification*; D004926:Escherichia coli / Q000302:isolation & purification; D005191:Family Characteristics; D005243:Feces / Q000382:microbiology*; D006801:Humans; D015203:Reproducibility of Results; D018570:Risk Assessment / Q000379:methods; D012307:Risk Factors; D060753:Water Quality
chemical_list: D060766:Drinking Water