title: Water distribution system deficiencies and gastrointestinal illness: a systematic review and meta-analysis.
abstract: BACKGROUND
  Water distribution systems are vulnerable to performance deficiencies that can cause (re)contamination of treated water and plausibly lead to increased risk of gastrointestinal illness (GII) in consumers.
  
  
  OBJECTIVE
  It is well established that large system disruptions in piped water networks can cause GII outbreaks. We hypothesized that routine network problems can also contribute to background levels of waterborne illness and conducted a systematic review and meta-analysis to assess the impact of distribution system deficiencies on endemic GII.
  
  
  METHODS
  We reviewed published studies that compared direct tap water consumption to consumption of tap water re-treated at the point of use (POU) and studies of specific system deficiencies such as breach of physical or hydraulic pipe integrity and lack of disinfectant residual.
  
  
  RESULTS
  In settings with network malfunction, consumers of tap water versus POU-treated water had increased GII [incidence density ratio (IDR) = 1.34; 95% CI: 1.00, 1.79]. The subset of nonblinded studies showed a significant association between GII and tap water versus POU-treated water consumption (IDR = 1.52; 95% CI: 1.05, 2.20), but there was no association based on studies that blinded participants to their POU water treatment status (IDR = 0.98; 95% CI: 0.90, 1.08). Among studies focusing on specific network deficiencies, GII was associated with temporary water outages (relative risk = 3.26; 95% CI: 1.48, 7.19) as well as chronic outages in intermittently operated distribution systems (odds ratio = 1.61; 95% CI: 1.26, 2.07).
  
  
  CONCLUSIONS
  Tap water consumption is associated with GII in malfunctioning distribution networks. System deficiencies such as water outages also are associated with increased GII, suggesting a potential health risk for consumers served by piped water networks.
authors.affiliation: Division of Epidemiology, School of Public Health, University of California, Berkeley, Berkeley, California, USA.
authors.forename: Ayse
authors.initials: A
authors.lastname: Ercumen
authors.forename: Joshua S
authors.initials: JS
authors.lastname: Gruber
authors.forename: John M
authors.initials: JM
authors.lastname: Colford
mesh_terms: D060766:Drinking Water / Q000382:microbiology*; D005767:Gastrointestinal Diseases / Q000453:epidemiology* / Q000382:microbiology; D006801:Humans; D015994:Incidence; D018508:Water Purification / Q000592:standards*; D014881:Water Supply / Q000032:analysis*
chemical_list: D060766:Drinking Water