A four-year analysis of antimicrobial use and antimicrobial resistance among Gram-negative bacilli in an Italian intensive care unit

Abstract number: 1134_02_262

Bassetti M., Righi E., Fasce R., Costa A., Cantagalli E., Rebesco B., Cruciani M., Mengoli C., Bobbio Pallavicini F., Bassetti D.

Obiectives:

Assess rates of antimicrobial resistance of the common gram-negative isolates in ICU and to evaluate the impact of antibiotic use on the emergence of resistant organisms.

Methods:

Retrospective analysis for a four years period (1999–2002) in a medical and surgical ICU. Duplicate isolates were not considered. A hospital-acquired infections (HAI) was defined, according to CDC definitions. Susceptibility was evaluated for piperacillin (P), piperacillin/tazobactam (PT), cefotaxime (CX), ceftazidime (CZ), ciprofloxacin (CP), gentamicin (GT) and imipenem (IM). We analysed resistance patterns and DDDs per 1000 patient-days. Data were analysed by Chi square for linear trend and logistic regression, with a level of significance defined as p < 0.05.

Results:

1476 clinical strains were isolated from 1237 patients with an HAI. A prevalence of Gram-negatives isolates (>60%) was observed. High resistance rates were observed for almost all the antibiotic tested. Exceptions were IM (100% strains susceptible) and GT (93–99%) toward K. pneumoniae (Kp), IM toward Serratia spp. (90–100%), and GT toward Kp (93–99%). Steady levels of resistance to all the antibiotics tested were observed for P. aeruginosa (Pa) and Serratia spp. By contrast, a significant trend toward an increase in resistance rate to P, CX, CZ, and CP was observed for Kp. A linear and significant trend toward a decrease in resistance rate to PT was observed. Overall, we recorded a continual increase in the antibiotics use from 1999 through 2002. The most remarkable trend in antimicrobial use was represented by huge increases in utilization of broad spectrum penicillins, 3rd generation cephalosporins, IM, and CP. A significant drug-usage vs susceptibility relationship was found with Kp and Proteus spp. (Pr). Increasing use of CX, CZ, P, and CP was associated with decreased susceptibility of Kp to themselves. The increase in the consumption of PT was associated with increasing susceptibility of Kp. Moreover, increasing use of CX and IP were associated with decreased susceptibility of Pr to these drugs. No other significant relationships were found.

Conclusion:

The data demonstrated the correlation between antimicrobial consumption for extended spectrum cephalosporins, quinolones and carbapenems and selection of resistances in Kp, Pr and Pa. In contrast, an increased usage of PT was associated with increasing susceptibility in Kp, suggesting a protective role of PT for ESBL in Kp.