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C.N. Ta, D.F. Sahm, A. Ingerman; Levofloxacin Susceptibility in Multi–Drug–Resistant S. pneumoniae Isolates from the Nationwide TRUST Surveillance Study, 2000–2004 . Invest. Ophthalmol. Vis. Sci. 2006;47(13):3573.
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Since the early 1990s, pneumococcal resistance to many common antibiotics has risen steadily in the United States. Because resistant organisms can survive and acquire resistance to multiple antibiotics, the prevalence of multi–drug–resistant Streptococcus pneumoniae (MDRSP) strains has increased as well. Levofloxacin has been available to treat systemic infections for >9 years and is the new–generation fluoroquinolone most widely used as oral/IV therapy for systemic infections. Levofloxacin is also commonly used to treat ophthalmic infections. We assessed changes in levofloxacin susceptibility over time in MDRSP isolates collected in TRUST, an annual surveillance study that monitors antimicrobial susceptibility in isolates collected from >200 institutions in all 50 states.
TRUST (Tracking Resistance in the U.S. Today) is an annual surveillance of antimicrobial resistance designed to detect changes in antimicrobial susceptibility patterns. Antimicrobial minimum inhibitory concentrations (MICs) in MDRSP isolates (resistant to >2 classes of antimicrobials) were determined by broth microdilution. Levofloxacin MIC susceptible breakpoint: <2.0 µg/mL.
In four respiratory seasons (2000–2004), 22,794 S. pneumoniae isolates were collected by institutions participating in TRUST; 99% of these isolates were levofloxacin–susceptible. Multi–drug resistance (resistance to >2 drug classes) was identified in 4,704 S. pneumoniae isolates (21% of all isolates); 98% of these MDRSP isolates were susceptible to levofloxacin. 601 MDRSP isolates were 4–drug resistant and 294 isolates were 5–drug resistant (cephalosporin, macrolides, penicillin, tetracycline, and trimethoprim/sulfamethoxazole); 98% of both 4– and 5–drug resistant MDRSP isolates remained levofloxacin–susceptible. MDRSP susceptibility to levofloxacin changed <1% from year to year.
Despite >9 years of levofloxacin use, susceptibility of MDRSP to levofloxacin remains high.
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