Antimicrobial Resistance in Respiratory Tract <i>Streptococcus pneumoniae</i> Isolates: Results of the Canadian Respiratory Organism Susceptibility Study, 1997 to 2002

<jats:title>ABSTRACT</jats:title> <jats:p> A total of 6,991 unique patient isolates of <jats:italic>Streptococcus pneumoniae</jats:italic> were collected from October 1997 to June 2002 from 25 medical centers in 9 of the 10 Canadian provinces. Among these isolates, 20.2% were penicillin nonsusceptible, with 14.6% being penicillin intermediate (MIC, 0.12 to 1 μg/ml) and 5.6% being penicillin resistant (MIC, ≥2 μg/ml). The proportion of high-level penicillin-resistant <jats:italic>S. pneumoniae</jats:italic> isolates increased from 2.4 to 13.8% over the last 3 years of the study, and the proportion of multidrug-resistant <jats:italic>S. pneumoniae</jats:italic> isolates increased from 2.7 to 8.8% over the 5-year period. Resistant rates (intermediate and resistant) among non-β-lactam agents were as follows: macrolides, 9.6 to 9.9%; clindamycin, 3.8%; doxycycline, 5.5%; chloramphenicol, 3.9%; and trimethoprim-sulfamethoxazole, 19.0%. Rates of resistance to non-β-lactam agents were higher among penicillin-resistant strains than among penicillin-susceptible strains. No resistance to vancomycin or linezolid was observed; however, 0.1% intermediate resistance to quinupristin-dalfopristin was observed. The rate of macrolide resistance (intermediate and resistant) increased from 7.9 to 11.1% over the 5 years. For the fluoroquinolones, the order of activity based on the MICs at which 50% of isolates are inhibited (MIC <jats:sub>50</jats:sub> s) and the MIC <jats:sub>90</jats:sub> s was gemifloxacin > clinafloxacin > trovafloxacin > moxifloxacin > grepafloxacin > gatifloxacin > levofloxacin > ciprofloxacin. The investigational compounds ABT-773 (MIC <jats:sub>90</jats:sub> , 0.008 μg/ml), ABT-492 (MIC <jats:sub>90</jats:sub> , 0.015 μg/ml), GAR-936 (tigecycline; MIC <jats:sub>90</jats:sub> , 0.06 μg/ml), and BMS284756 (garenoxacin; MIC <jats:sub>90</jats:sub> , 0.06 μg/ml) displayed excellent activities. Despite decreases in the rates of antibiotic consumption in Canada over the 5-year period, the rates of both high-level penicillin-resistant and multidrug-resistant <jats:italic>S. pneumoniae</jats:italic> isolates are increasing in Canada. </jats:p>