Correspondence Azithromycin is effective in patients with chronic bronchitis

concluded that azithromycin is more effective than the comparator antibiotics in patients with community-acquired pneumonia but not in patients with acute exacerbation of chronic bronchitis. The latter conclusion is based on a metaanalysis of 13 randomized controlled trials that did not show statistically significantly better efficacy of azithromycin (OR for treatment failure 0.64, 95% CI 0.31–1.32). The results of the 13 trials were heterogeneous. Examination of the source of heterogeneity indicates one trial as an outlier. This trial had different features to the remaining 12 trials. Removal of this trial from the meta-analysis would restore homogeneity. Meta-analysis of the remaining 12 trials shows statistically significantly better efficacy of azithromycin (OR = 0.47, 95% CI 0.30–0.74). An important criterion for performing meta-analysis is whether the studies are measuring the same underlying