When analyzing time-to-first AECOPD using a model that included treatment group (ie, azithromycin versus placebo) and log-transformed MBL concentration stratified by clinic, treatment group was significant (P , 0.0001) and log-transformed MBL concentration was not (P = 0.629). The hazard ratio for a one-unit increase in log-transformed MBL concentration was 1.02 (95% CI 0.94-1.12). For the rate per person-year of AECOPDs, a negative-binomial analysis of a model that included treatment group and log-transformed MBL concentration found that treatment group was significant (P = 0.010) but log-transformed MBL concentration was not (P = 0.470). The coefficient for log-transformed MBL concentration in this model was 0.031 (95% CI, −0.053 to +0.115).