Risk of acquiring drug-resistant (MDR) Gram-negative isolates with previous exposure to antibiotic

Introduction

Prior antimicrobial therapy is one of the most important factors leading to the acquisition of MDR organisms. Formulating antibiotic policy and choice of empirical antibiotic selection will be helped by knowing the association of MDR Gram-negative organisms with a previous exposure of particular antibiotic.

Methods

Prospective observational study during January 2008 to June 2009 in a 50-bed ICU in a tertiary care hospital. Specimens sent after 2 days of the start of the antibiotic and no more than 90 days from the stop date have been included in the study. Analyses were based on those specimens that resulted in detection of MDR Gram-negative organism. Observed relative risk (RR) of an antibiotic class was computed with respect to an MDR infection. RR was computed as the ratio of the risk of the event (acquiring the infection) occurring in the exposed group vs in the nonexposed group. A logistic regression model was used where multiple antibiotics were applied.

Results

A total of 1,072 specimens from 500 patients met the criteria as specified above. Of these, 423 (39.4%) specimens resulted in detection of MDR bacteria, 186 (17.4%) resulted in detection of non-MDR bacteria and no bacteria were detected in the remaining 463 (43.2%) specimens. Of the total 423 cases of MDR acquisitions, ESBL Enterobacteriaceae (151 or 35%), MDR Acineto (89 or 21%) and MDR Pseudo (58 or 14%). Risk of isolating ESBL Enterobacteriaceae was highly significant with the prior exposure to third-generation cephalosporin (RR = 5.8 and P < 0.001). Risk of isolating MDR Acinetobacter spp. was highly significant with the exposure to piperacillin-tazobactam (RR = 2.7 and P < 0.001). Risk of isolating MDR Pseudomonas spp. was significant with the exposure to Group 2 carbapenem (RR = 2.2 and P > 0.001). Group 1 carbapenem, aminoglycosides have not been found to have significant association with any individual MDR organisms.

Conclusions

Previous exposure to antibiotics leads to increased acquisition of MDR organisms. There is a significant association of isolating different MDR organisms with previous exposure to a particular class of antibiotic.

Figure 1

Observed relative risk of MDR infections for different antibiotic classes.