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Objective: Fluoroquinolones are bacteriocidal drugs that are widely used to treat severe urinary and respiratory tract infections. Studies show that resistance to fluoroquinolones is continuously increasing both in Europe and the United States. The purpose of this study was to measure the frequency of fluoroquinolone resistance in the most prevalent Gram negative rods and look at the correlation with fluoroquinolone use over the last 8 years.

Materials and methods: All strains of Escherichia coli, Klebsiella sp., Proteus sp. and Pseudomonas aeruginosa identified from clinical specimens at the Department of Clinical Microbiology at the Landspitali University Hospital (LUH) during the time period 1.11.2006 to 31.1.2007. Antibiotic susceptibility testing was performed by disc diffusion tests and all strains were tested for ciprofloxacin susceptibility. Antibiotic resistance data for the last years were collected from the reports of the Department of Clinical Microbiology, but ciprofloxacin susceptibility was usually only tested for specimens from hospitalised patients and when there was resistance to two or more antimicrobial agents. Data on antibiotic use/sales was obtained from the State Epidemiologist at the Directorate of Health.

Results: Of the 1861 strains tested, 104 fluoroquinolone resistant strains were identified during the study period, including 91 E. coli (87%), 8 Klebsiella sp. (8%) and 5 P. aeruginosa (5%). No fluoroquinolone resistant Proteus sp. was identified. There was a significant positive correlation between fluoroquinolone use and the frequency of resistant strains of E. coli and Enterobacteriaceae. The frequency of resistant E. coli strains was 6% and it differed significantly between age groups (p >0.001) and sex, 6% for females and 11% for males (p = 0.015). The ratio of fluoroquinolone resistant E. coli was highest in the LUH and homes for the elderly.

Conclusion: The frequency of fluoroquinolone resistance is increasing fast in Iceland but is still one of the lowest compared to the other European countries. The frequency is highest in the oldest age groups where the use of the quinolones is the greatest and there was a significant correlation between the quinolone use and the frequency of resistance in E. coli and Enterobacteriaceae. The results highlight the importance of prudent fluoroquinolone use and the need to monitor fluoroquinolone use and resistance.

Table I. The number of strains identified for each species according to age group, sex and the origin of specimens.

Table II. The number of fluoroquinolone resistant strains for each species according to age group and sex (% of resistant strains)

Table III. The ratio proportion of fluoroquinolone resistant strains in theaccording to type of different health care institutions.

Table IV. Fluoroquinolone use and the frequency of fluoroquinolone resistant strains in the years 1998 to 2006 (number of strains tested in parenthesis)

Picture 1. The proportion of strains resistant to antibiotics.

(AMP=ampicillin, MEL=mecillinam, AMC=amoxicillin/clavulanic acid, CXM=cefuroxime, CAZ=ceftazidime, CN=gentamicin, W=trimethoprim, SXT=trimethoprim/sulfamethoxazole, F=nitrofurantoin, CIP=ciprofloxacin)

Picture 2. Comparison of the frequency of resistace to other antibiotics among fluoroquinolone sensitive and resistant E. coli. (AMP=ampicillin, MEL=mecillinam , AMC=amoxicillin/clavulanic acid, CXM=cefuroxime, CAZ=ceftazidime, CN=gentamicin, W=trimethoprim, SXT=trimethoprim/sulfamethoxazole, F=nitrofurantoin, CIP=ciprofloxacin)

Picture 3. The ratio of fluoroquinolone resistant E. coli and the use of fluoroquinolones 1998 to 2006.

Picture 4. The ratio of fluoroquinolone resistant P. aeruginosa and fluoroquinolone use 1998 to 2006.

Picture 5. Number of prescriptions for fluoroquinolones according to age groups.