Subjects were men and women enrolled in a multicenter randomized trial designed to determine if azithromycin, taken daily for one year, decreased the frequency of AECOPDs. 33 Eligibility criteria included age $ 40 years, a clinical diagnosis of COPD, and an increased risk of experiencing an AECOPD based on criteria defined by Niewoehner et al. 34 Patients had to be free of AECOPDs for a minimum of 4 weeks prior to enrollment. Exclusion criteria included a diagnosis of asthma or bronchiectasis, among others. 33 Acute exacerbations were defined as "a complex of respiratory symptoms (increased or new onset) of more than one of the following: cough, sputum, wheezing, dyspnea, or chest tightness with a duration of at least three days requiring treatment with antibiotics or systemic steroids". 34 