This study is designed to better understand the effect of a short course of antibiotics on changes in intestinal and nasopharyngeal microbiome on treated children and untreated household contacts. The investigators hypothesize that a short course of antibiotics will lead to decreased bacterial diversity shortly after completion of the antibiotic course, and higher probability of identification of bacterial resistance genes in rectal and nasopharyngeal samples. The investigators hypothesize that a 5-day course of antibiotics (azithromycin, amoxicillin, or co-trimoxazole) will lead to significantly decreased intestinal and nasopharyngeal bacterial diversity among children aged 6-59 months.