Analysis of ciprofloxacin activity against Streptococcus pneumoniae after 10 years of use in the United States

As the most commonly used fluoroquinolone in the United States since 1987, ciprofloxacin has exerted the greatest selective pressure on S. pneumoniae and provides a valuable marker to evaluate the actual and potential emergen ce of fluoroquinolone resistance in this species. Analysis of susceptibilit y results obtained with 5,640 strains collected from throughout the United States showed that only 16 (0.3%) of the isolates demonstrated MICs of grea ter than or equal to 4 mu g/ml. The prevalence of this phenotype was signif icantly higher (P < 0.05) among penicillin-resistant populations, among iso lates from patients >64 years old, and among respiratory isolates. However, >99% of strains had MICs of <4 mu g/ml regardless of the risk group examin ed, and the MIC population distributions were the same for each risk group. These findings demonstrate that the phenotype of a MIC of greater than or equal to 4 mu g/ml remains uncommon after 10 years of ciprofloxacin use; ho wever, these findings are no reason to become complacent with regard to app ropriate use of fluoroquinolones and the need to carefully track resistance trends. Equally important is careful analysis of data that result from sur veillance in terms of risk factors acid other associated trends so that res istance and susceptibility, and their consequences, are neither over- nor u nderestimated.