Background: Fluoroquinolones are now recommended for the treatment of respiratory tract infections due to Streptococcus pneumoniae, particularly when the isolates are resistant to beta-lactam antibiotics. Although pneumococci with reduced susceptibility to fluoroquinolones have been identified, their prevalence has not been determined in a defined population.
Methods: We performed susceptibility testing on 7551 isolates of S. pneumoniae obtained from surveillance in Canada in 1988 and from 1993 to 1998. Pneumococci with reduced susceptibility to fluoroquinolones (defined as a minimal inhibitory concentration of ciprofloxacin of at least 4 microg per milliliter) were further characterized. We also examined antibiotic prescriptions dispensed in Canadian retail pharmacies.
Results: Between 1988 and 1997, fluoroquinolone prescriptions increased from 0.8 to 5.5 per 100 persons per year. The prevalence of pneumococci with reduced susceptibility to fluoroquinolones increased from 0 percent in 1993 to 1.7 percent in 1997 and 1998 (P=0.01). Among adults, the prevalence increased from 1.5 percent in 1993 and 1994 combined to 2.9 percent in 1997 and 1998 combined. The prevalence was higher in isolates from older patients (2.6 percent among those 65 years of age or older vs. 1.0 percent among those 15 to 64 years of age, P<0.001) and among those from Ontario (1.5 percent, vs. 0.4 percent among those from the rest of Canada; P< 0.001). Fluoroquinolone use was greatest among the elderly and in Ontario. The 75 isolates (17 serotypes) of pneumococci with reduced susceptibility to fluoroquinolones were submitted by 40 laboratories in eight provinces. Reduced susceptibility to fluoroquinolones was associated with resistance to penicillin.
Conclusions: The prevalence of pneumococci with reduced susceptibility to fluoroquinolones is increasing in Canada, probably as a result of selective pressure from the increased use of fluoroquinolones.