Trend analysis of antibiotic resistance and minimum inhibitory concentration distribution from 1997 to 2007 among Pseudomonas aeruginosa, Escherichia coli and Klebsiella pneumoniae in European ICUs

Introduction

The aim of this study was to analyse trends in antibiotic susceptibility and minimum inhibitory concentration (MIC) distribution in European ICUs based on data from the Mystic surveillance study initiated in 1997 [1].

Methods

Twenty-eight ICUs in Belgium, Croatia, Finland, Germany, Spain, Sweden and the UK contributed with nonrepeat isolates of Pseudomonas aeruginosa (n = 3,241), Escherichia coli (n = 3,306), and Klebsiella pneumoniae (n = 1,660). Only non-repeat isolates taken on clinical indication were included. Two models were used for trend analysis: Model A: changes in susceptibility (S), intermediate (I) and resistance (R) using the EUCAST breakpoints [2] described by the logistic regression model p_R = 1/(1 + exp(-a_R - b_R × year)) and Model B: changes in MIC distribution 2logMIC = a_M + b_M × year. The parameters b_R and b_M describe the time dependence, and the hypotheses b_R = 0 and b_M = 0 can be tested. Year was used as the independent variable in both models.

Results

Resistance (I+R%) rates in 2007 and trend analysis ((+ increase, - decrease), (P values for changes in susceptibility/MIC distribution from 1997 to 2007)): P. aeruginosa: imipenem 43% ((+/+), <0.001/<0.001)) (Figures 1 and 2), meropenem 27% ((+/+), (0.01/0.04)), ceftazidime 32% ((+/+), (0.035/<0.001)), ciprofloxacin 32% ((-/-) (0.39/0.79)), gentamicin 22% ((-/-),(0.002/0,019)); E. coli: imipenem 0.6% ((-/-) (<0.013/<0.001)), meropenem 0% ((+/-) (0.66/<0.001)), cefotaxime 9% ((-/+), (0.61/0.17)), ciprofloxacin 25% ((+/+), (<0.001/0.07)), gentamicin 14% ((+/+), (0.14/0.44)); and K. pneumoniae: imipenem 0% ((-/-) (<0.001/<0.001)), meropenem 0.5% ((-/-) (0.89/<0.001)), cefotaxime 13% ((-/-), (<0.001/0.3)), ciprofloxacin 17% ((+/-), (0.017/0.78)), gentamicin 21% ((+/-), (0.16/0.61)).

Figure 1

(abstract P302)

Figure 2

(abstract P302)

Conclusion

Significantly (P < 0.05) increasing resistance rates (I+R%) and increasing MICs (2log MIC) were found among P. aeruginosa to carbapenems and ceftazidime. For other species-antibiotic combinations there were either low (<1%) resistance rates or not the same significant changes demonstrated with the two trend models. This study showed that trend analysis based on MIC distributions was not more sensitive than trend analysis based on changes in susceptibility (I+R). High (>27%) resistance rates were seen for all tested drugs against P. aeruginosa while low (<1%) resistance rates were only shown for carbapenems against E. coli and K. pneumoniae.