Objectives: Multidrug-resistant Pseudomonas aeruginosa and Acinetobacter baumannii are becoming increasingly important nosocomial pathogens worldwide. To study the evolution of non-fermenters in a tertiary care hospital, we undertook a retrospective 10 year (1999-2008) trend analysis of antimicrobial consumption and resistance in non-fermenters causing bacteraemia.
Methods: Antibiotic consumption and resistance were analysed by linear regression. The Pearson correlation coefficient was used for assessing correlation between them.
Results: A total of 69,010 blood cultures were performed, which grew 15,465 isolates (22% positivity rate), of which 1525 isolates (771 isolates of P. aeruginosa and 754 isolates of A. baumannii) were non-fermenters. Overall antibiotic consumption showed an increasing trend, from 158 to 319 defined daily doses (DDDs)/100 bed-days (r(2)= 0.62, P = 0.007). The largest relative increase in antibiotic consumption was seen for carbapenems (r(2)= 0.68, P = 0.022), followed by β-lactam/inhibitor combinations (r(2 )= 0.45, P = 0.033), whereas third-generation cephalosporins, fluoroquinolones and aminoglycosides showed no significant changes. A significant increase in resistance in A. baumannii to fluoroquinolones (r(2 )= 0.63, P = 0.006), aminoglycosides (r(2 )= 0.63, P = 0.011) and carbapenems (r(2 )= 0.82, P = 0.013) and in P. aeruginosa to aminoglycosides (r(2 )= 0.59, P = 0.01) was observed. Carbapenem consumption was associated with the development of resistance in A. baumannii (r = 0.756, P = 0.049), whereas no such association was observed for other antimicrobials among non-fermenters.
Conclusions: Our study highlights the growing problem of high antimicrobial consumption. The increasing prevalence of non-fermenters and the emergence of multidrug-resistant A. baumannii are associated with the consumption of carbapenems. The data cannot prove cause and effect.