A multicenter study of the antimicrobial susceptibility of community-acquired lower respiratory tract pathogens in the United States, 1992-1994. The Alexander Project.

A multicenter, collaborative study was performed over a three-year period (1992-1994) to determine the antimicrobial susceptibilities of isolates of Haemophilus influenzae, Moraxella catarrhalis, and Streptococcus pneumoniae from community-acquired lower respiratory tract infections. Isolates were collected from five geographically separated medical centers in the United States and sent to a central laboratory for antimicrobial susceptibility testing. Of 350, 536, and 372 isolates of H. influenzae collected from the five centers in 1992, 1993, and 1994, 26.3%, 28.2%, and 30.1%, respectively, were beta-lactamase-positive. All isolates of H. influenzae remained susceptible to ceftriaxone, doxycycline, ciprofloxacin, and ofloxacin over the three-year period. Between 95 and 100% of isolates of H. influenzae remained susceptible to amoxicillin-clavulanic acid cefixime, clarithromycin, and chloramphenicol over this same period. The prevalence of beta-lactamase-positive isolates of M. catarrhalis increased from 92.1% in 1992 to 93.8% in 1993 and to 96.5% in 1994; however, isolates of this species were highly susceptible to amoxicillin-clavulanic acid, the cephalosporins, the macrolides, the fluoroquinolones, chloramphenicol, doxycycline, and trimethoprim-sulfamethoxazole. The prevalence of penicillin-intermediate isolates of S. pneumoniae decreased from 16% in 1992 to 8.2% in 1994, whereas that of penicillin-resistant isolates increased from 5.6% to 10.9% in the same period. Ceftriaxone susceptibility declined from 95.2% to 88.4% over the three years, whereas chloramphenicol susceptibility declined from 98.4% to 90.5% and that of trimethoprim-sulfamethoxazole declined from 85.6% to 68.7%. Macrolide activity remained unchanged.