A double-blind, cluster-randomized, placebo-controlled study in Niger investigated the mass distribution of azithromycin in different age groups of children. The study focused on the selection of macrolide resistance determinants in the intestine and nasopharynx. Resistance was observed in children aged 1 to 59 months. Children aged 1 to 59 months without previous resistance to antibiotics in the nasopharynx were also examined. The study demonstrated the selection of resistant determinants in the intestine in children after the distribution of azithromycin.