Ciprofloxacin resistance in Staphylococcus aureus: a 12-year experience in a major Canadian health centre

Abstract number: P1736

Kowalewska-Grochowska K., Armstrong G.

Objective: To observe an evolution of a ciprofloxacin resistance pattern in Staphylococcus aureus isolated from a patient population served by a large Canadian hospital over 12 years.

Method:Staphylococcus aureus isolated from clinical specimens collected between 1994 and 2005 was used as the representative organism in this retrospective study. Microbiology laboratory database was reviewed for three sentinel years (1994, 1999 and 2005) regarding patient age, gender and specimen source. Organism identification and resistance to ciprofloxacin was determined by either/or: BioMerrieux VITEK, Becton Dickinson Phoenix, Kirby Bauer disk diffusion, AB Biodisk E-test, Becton Dickinson Pasco and/or Dade Behring MicroScan, using resistance criteria from Clinical and Laboratory Standards Institute(CLSI). Repeat specimens of the same sample type collected within one month were excluded from analysis. Microsoft Excel was used for data analysis.

Results: The 5280 pathogenic S. aureus strains from 4089 patients were distributed uniformly throughout three sentinel periods of the study. The most common specimen source for all three periods was surface/wound swab, followed by sputum and fluid/aspirate. Overall ciprofloxacin resistance rates were 3.13% for 1994; this was followed by an increase to 8.82% for 1999 and to 17.9% for 2005. Resistance rates were highest in sputum isolates for 1994 (7%), and urine isolates for 1999 and 2005 (13.3 and 31.1% respectively). In every sentinel period, highest resistance rates were seen elderly (over 60 years of age); males with resistant S. aureus far outnumbered the females.

Conclusions: Overall ciprofloxacin resistance rates increased over a 12 year surveillance period. The unexpected plateau of this increase between 1999 and 2005 was most likely due to change in prescribing habits caused by new region-wide antibiotic control initiative. In view of popularity of quinolones in clinical practice we advise a targeted approach by restricting these drugs in elderly males to further limit development of resistance.