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Chlorinated drinking water exposure enriches antimicrobial resistance pathways in the infant gut microbiome: a randomized trial

K. Parkin, Claus T Christophersen, Valerie Verhasselt, Debra J. Palmer, M. Cooper, S. L. Prescott, D. Silva, D. Martino

Communications Medicine, 2026

197 participants

Abstract

Water chlorination is essential for controlling harmful microbes in drinking water; however, the antimicrobial effects of chlorine-based disinfectants present in tap water may influence early-life gut microbial ecology. To investigate the functional and compositional impact of chlorinated drinking water on the gut microbiome of infants. The waTer qUality and Microbiome Study (TUMS) was an Australian-based double-blinded, randomised controlled trial. Six-month-old infants (n = 197) received either de-chlorinated drinking water via benchtop filtration (treatment, n = 99), or regular chlorinated water (control, n = 98) for twelve months. Tap water and stool samples were collected at baseline and at end of intervention. Metagenomic sequencing was used for faecal microbiome analysis. Primary outcomes were differences in gut microbiota between groups, secondary outcomes included incidence of allergic sensitization and respiratory conditions. At baseline, 170 stool samples (83 control, 87 intervention) were collected, with 130 samples obtained at the end of the intervention (65 control, 65 intervention). Overall community structure was similar between groups after the intervention, including beta diversity (0.56% variance explained; p = 0.84), richness (−4.25, 95% CI; −14.85 to 6.35, p = 0.43) or Shannon Index (−0.14, 95% CI; −0.32 to 0.04, p = 0.12). The chlorinated water group showed enrichment of antibiotic resistance MetaCyc groups and pathways (adjusted p < 0.05). Stratified…

How strong is the evidence?

Evidence Hub reads this as a randomized trial, done in people. Its evidence level is 2 of 5 (High · randomized trial). Randomized trials of a reasonable size are the strongest single-study design. Reported size: 197 participants or records.

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