Exacerbations of chronic obstructive pulmonary disease (COPD) due to pathogenic microorganisms are a major cause of morbidity and mortality. Three major classes of pathogenic microorganisms have been implicated in exacerbations of COPD: aerobic bacteria, viruses, and atypical bacteria. Sputum cultures and bronchoscopic protected-specimen brush cultures are positive for aerobic bacteria in half the exacerbations of COPD. NontypeableHaemophilus influenzae, Streptococcus pneumoniae, and Moraxella catarrhalisare the most frequently isolated bacterial pathogens. Viral infections are associated with one third of exacerbations.Chlamydia pneumoniaeinfection is associated with 5verbar;Xpercnt;to 10verbar;Xpercnt; of exacerbations whereasMycoplasmainfection has been seen only rarely in this setting. As many as half of bacterial exacerbations of COPD are now caused by pathogens that are resistant to aminopenicillins (e.g., amoxicillin). An approach to empiric antibiotic therapy of acute exacerbations on the basis of stratifying exacerbations and patients and choosing antibiotic therapy accordingly is outlined.
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