CXCL9 and respiratory tract infectious disorder: An episode of respiratory infection with CXCL9 concentrations greater than the 25th, 50th, and 75th percentile had adjusted HRs for CLAD of 1.8 (95% CI 1.1–2.8), 2.4 (95% CI 1.4–4.0) and 4.4 (95% CI 2.4–8.0), respectively.