The impact of antimicrobial resistance: changing epidemiology of community-acquired respiratory-tract infections.

Current surveillance data and mechanisms of resistance for the three most common bacteria infecting the respiratory tract are reviewed. Many pathogens, once susceptible to available antimicrobials, are now demonstrating high levels of resistance to commonly prescribed antimicrobial agents for the treatment of respiratory-tract infections. The three most common respiratory-tract pathogens, Streptococcus pneumoniae, Haemophilus influenzae, and Moraxella catarrhalis, all exhibit high-level resistance to one or a number of agents, including penicillin, ampicillin, erythromycin, tetracycline, and first-generation cephalosporins. To determine the prevalence of resistance in these organisms, surveillance programs have begun tracking the emergence of antimicrobial resistance in the United States and worldwide. Data recovered from several national surveillance studies should help guide decisions about empirical therapeutic treatment.