Household and personal factors are sources of heterogenity in intestinal parasite clearance among Mexican children 6–15 months of age supplemented with vitamin A and zinc

• Gut parasite clearance heterogeneity evaluated among supplemented children.
• Vitamin A-zinc effects on Giardia or Ascaris clearance lower with no piped water access.
• Zinc efficacy on E. histolytica clearance greater when mothers <6 years of education.
• Clearance heterogeneity is due to exposure risk differences and baseline immune responses.

A randomised, double-blind, placebo-controlled trial was carried out among Mexico children aged 6–15 months to determine how household characteristics modify vitamin A and zinc supplementation efficacy on Ascaris lumbricoides, Giardia intestinalis and Entamoeba histolytica/E. dispar infection durations. Children assigned to receive vitamin A every 2 months, a daily zinc supplement, a combined vitamin A-zinc supplement or a placebo were followed for 1 year. Parametric hazard models were fit to infection durations stratified by personal and household factors. Children supplemented with vitamin A and zinc combined from households lacking piped water and children in all three treatment arms from households with dirt floors had longer G. intestinalis and A. lumbricoides infection durations than their counterparts, respectively. Shorter E. histolytica/E.dispar durations were found among zinc-supplemented children of mothers who had <6 years of education and no indoor bathrooms. Heterogeneity in supplementation efficacy among children may reflect differences in exposure risk and baseline immune responses.

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