Antimicrobial susceptibilities of Streptococcus pyogenes isolated from respiratory and skin and soft tissue infections: United States LIBRA surveillance data from 1999

This study evaluated current levels of antimicrobial resistance and associated demographic trends among clinical isolates of Streptococcus pyogenes in the United States as part of the LIBRA surveillance initiative. In 1999, 2,742 isolates of S. pyogenes (2,039 respiratory; 405 skin and soft tissue; 148 blood) were collected from 324 clinical laboratories and centrally tested for antimicrobial susceptibility by the broth microdilution method. All isolates were susceptible to penicillin (MIC 90, ≤0.06 μg/mL), ceftriaxone (MIC 90, ≤0.03 μg/mL), vancomycin (MIC 90, 0.5 μg/mL), levofloxacin (MIC 90, 1 μg/mL), and moxifloxacin (MIC 90, 0.25 μg/mL). Twenty-four (0.9%) azithromycin-intermediate (MIC, 1 μg/mL) and 170 (6.2%) azithromycin-resistant (MIC, ≥2 μg/mL) isolates were identified. Regionally, azithromycin resistance varied by levofloxacin) demonstrated potent in vitro activity against all isolates of S. pyogenes tested, including those from skin and soft tissue infections. Given the higher rates of macrolide resistance reported in other countries and the seriousness of invasive infections, continued antimicrobial surveillance of S. pyogenes in the United States would be prudent.