Surveillance of Resistance Among Major Pathogens Causing Respiratory Tract Infections in the United States

Abstract

Several major North American monitoring programs have revealed disturbing patterns of antimicrobial resistance among respiratory tract pathogens. There is a widespread variability in the resistance trends identified, depending on the geographic region where the specimen was collected and various patient characteristics, such as age and site of infection. The latest results from the surveillance programs demonstrate that the prevalence of pneumococcal penicillin nonsusceptibility in the United States as a whole is either static (macrolides) or decreasing (penicillins). However, mechanisms of macrolide resistance are changing in the United States, with decreasing strains expressing lower-level resistance (minimal inhibitory concentrations, 1-16 μg/mL), whereas strains with high-level combined erm(B)- and mef(A)-encoded resistance are becoming more common. Resistance levels among Streptococcus pyogenes to macrolides remain generally low, however, with wide geographical variations and considerable variation of the proportions of isolates containing mef(A) and erm(A), which suggests major genetic clones are spreading in certain regions. Finally, amoxicillin resistance in Haemophilus iqfluenzae is declining.