Surveillance of antimicrobial resistance in Streptococcus pneumoniae, Haemophilus influenzae, and Moraxella catarrhalis in the United States in 1996-1997 respiratory season

Abstract A U.S. surveillance study of antimicrobial resistance in respiratory tract pathogens in the respiratory season (1996–1997) is reported that induced 11,368 isolates from 434 institutions in 45 states and the District of Columbia. β-lactamase was produced by 33.4% of Haemophilus influenzae and 92.7% of Moraxella catarrhalis . Of the 9,190 Streptococcus pneumoniae isolates tested, 33.5% were not susceptible to penicillin (MIC ≥ 0.12 μg/mL), with 13.6% having high-level resistance (MICs > 1 μg/mL). For H. influenzae , the most active antimicrobials (based on percent of strains susceptible) were levofloxacin (100%) and ceftriaxone (99.9%); the least active were ampicillin (67.2%) and clarithromycin (58.1%). For M. catarrhalis , the most active drugs were amoxicillin-clavulanate, ceftriaxone, and levofloxacin (100%); the least active was amplicillin. The order of the activity of the drugs against S. pneumoniae were levofloxacin (97.3%) > ceftriaxone (87.1%) > amoxicillin-clavulanate (81.7%) = clarithromycin (80.9%) > cefuroxime (74.5%) > penicillin (66.5%). The activity of the β-lactams and clarithromycin against isolates of S. pneumoniae was closely associated with the resistance to penicillin. Levofloxacin was more active against S. pneumoniae overall, because it exhibited no cross-resistance. These data indicate that the incidence of β-lactamase production in H. influenzae (33.4%) and M. catarrhalis (92.7%) is similar to other recent studies, and that the incidence of penicillin-intermediate and -resistant S. pneumoniae is increasing, particularly the high-level penicillin-resistant (MICs > 1 μg/mL) strains, which were often multi-resistant.