Distribution and prevalence of antimicrobial resistance among Gram-negative isolates in intensive care units (ICU) in Belgian hospitals between 1996 and 1999

Objective : to assess the distribution and prevalence of resistance rates among Gram-negative isolates in Belgian intensive care units (ICUs) between 1996 and 1999. Methods : During 1996-1997 and 1998-1999, over a total period of 10 and 9 months respectively, members of the NPRS Belgian Study group collected, on clinical indications, 3029 consecutive initial isolates of Gramnegative bacteria from patients admitted to 26 Belgian hospitals and performed minimal inhibitory concentration (MIC) determinations by means of the E-test. Breakpoints were defined according to the criteria of the NCCLS. Results : The overall distribution of bacterial species was, in decreasing order of frequency : Pseudomonas aeruginosa >E. coli >E. aerogenes >K., pneumoniae >P. mirabilis >S. marcescens >E. cloacae >K. oxytoca >M. morganii >Stenotrophomonas maltophilia >Acinetobacter spp. All together these species and genera constituted about 90% of all isolates. The frequency of resistance for all the initial Gram-negative isolates in 1998-9 were : amoxicillin-clavulanic acid 60%, piperacillin 31%, piperacillin-tazobactam 20%, cefuroxime 58%, ceftriaxone 31%, ceftazidime 17%, aztreonam 23%, cefepime 10%, imipenem 13%, gentamicin 12%, amikacin 12% and ciprofloxacin 21%. Apart for an increase in multiple drug resistance among P. aeruginosa isolates, no significant trends were observed neither in species distribution nor in the overall prevalence of antimicrobial resistance among Gramnegative isolates from Belgian ICUs between 1996-7 and 1998-9. Conclusions : Among Gram-negative isolates in Belgian ICUs, a very high frequency of resistance was seen to amoxicillin-clavulanic acid and cefuroxime, and rather high frequencies of resistance to piperacillin, ceftriaxone and,aztreonam. Taking into account the species distribution and the prevalence of resistance, cefepime, imipenem, amikacin and gentamicin appeared generally suitable for empirical therapeutic use in severe ICU-acquired Gram-negative infections in Belgium. However, the therapeutic strategy should be adapted according to the local ecology of resistance.