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

A U.S. surveillance study of antimicrobial resistance in respiratory tract pathogens in the respiratory season (1996-1997) is reported that included 11,368 isolates from 434 institutions in 45 states and the District of Columbia. beta-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 > or = 0.12 microgram/mL), with 13.6% having high-level resistance (MICs > 1 microgram/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 ampicillin. 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 beta-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 beta-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 microgram/mL) strains, which were often multi-resistant.