We furthermore find that BALF CXCL9 concentrations during respiratory infections increase CLAD risk in a dose-response manner: a single episode of respiratory infection with CXCL9 >25th, 50th, and 75th percentiles had HRs for CLAD of 1.8, 2.4, and 4.4, respectively. Here, CXCL9 is linked to respiratory tract infectious disorder.