The Impact of Chlorinated Drinking Water Exposure on Gut Microbiota Development in Infants: a Randomised Controlled Trial.

Abstract

Background: Early gut microbiota disruptions can increase the risk for dysbiosis and predispose to chronic diseases. While chlorinated drinking water is generally considered safe, the antimicrobial effects of chlorine-based disinfectants may negatively impact the developing infant microbiota, which is particularly vulnerable during this critical period. This study investigates the specific effects of chlorinated water on the gut microbiome in infants. Methods: The waTer qUality and Microbiome Study (TUMS) is a double-blinded, randomized controlled trial (RCT). Six-month old infants (n=197) received either de-chlorinated drinking water (via benchtop filtration), or regular tap water for twelve months. Stool samples were collected at six-months (baseline) and at eighteen-months of age. Metagenomic sequencing was used for faecal microbiome analysis. Samples of participant tap water was also collected pre- and post-intervention. Results: Participants were balanced for sex, delivery method, and breast-feeding status at time of recruitment between the control (n=98) and treatment (n=99) groups. We collected a total of 170 baseline stool samples (83 in the control group and 87 in the treatment group), and 130 follow-up stool samples (65 in the control group and 65 in the treatment group). Interindividual variation was higher at six-months compared to eighteen months. No significant differences in overall community structure (beta diversity (p=0.35), richness (p=0.98) or Shannon Index (p=0.45)) were found between treatment groups. However, 55 genera were differentially abundant at follow-up (adjusted p-value < 0.01), primarily within the Firmicutes phylum. Analysis of metabolic pathways revealed the chlorinated water group showed significantly higher abundance of antibiotic resistance genes mostly attributable to Escherichia and Klebsiella species. Conclusion: Water chlorination induces predominantly minor changes in infant gut microbiome composition; but appears to increase the abundance of antibiotic-resistant genes. While water chlorination remains a vital public health tool for ensuring safe drinking water, our findings underscore the need for continued research into the potential for increased antibiotic resistance, and suggest there may be value in exploring alternative disinfectant strategies.