INTRODUCTION
URTIs, upper respiratory tract infections
UPPER RESPIRATORY TRACT INFECTIONS
Human airway microbiota forms a complex, balanced ecosystem and serves as the gatekeeper for respiratory health (Globally, inappropriate antibiotic prescribing is common, and the majority of such prescriptions are for patients with upper respiratory tract infections (URTIs), which are self-limiting and of viral origin in most cases (Azithromycin, a macrolide antibiotic, is widely used in URTIs because of the broad antibacterial spectrum, including Gram-positive bacteria (The exposure to elevated levels of outdoor PMIn this randomized controlled study, we focused on the airway microbiota dynamic variation in the healthy adults. The 16S rRNA gene sequencing was applied to the induced sputum samples collected before administration of the drugs (3-day azithromycin and placebo) and at 4 time points over 60 days postdosing. We aim to track the process of variation and re-establishment of biodiversity, microbial interactions, and community composition of the airway microbiota after a 3-day azithromycin administration. We also estimated the potential influence of outdoor environmental factors (e.g., humidity, concentration of PM