Role of different classes of antimicrobials on the risk of acquisition of resistant micro-organisms in critically ill medical patients

Abstract number: P1276

Martínez J.A., Vila J., Delgado E., Monte M.R., Alquezar A., Castro P., Trilla A., Codina C., Vaselka P., Nicolás J.M.

Objective: To assess the role of different classes of antibiotics on the risk of acquisition of resistant micro-organisms in critically ill medical patients.

Methods: From March 2006 to May 2007, all patients admitted to an 8-bed medical intensive care unit (MICU) were subjected to swabbing of nares, pharynx and rectum, and culture of respiratory secretions on admission and thrice weekly thereafter. Acquisition of a resistant microorganism was defined as the isolation, after 48 hours of MICU stay, of a strain of meticillin-resistant Staphylococcus aureus, vancomycin-resistant enterococci, enteric Gram-negative bacilli resistant to third-generation cephalosporins, Pseudomonas aeruginosa resistant to at least one class of antipseudomonals or any other non-fermenter from patients whose admission cultures were either negative or positive for a susceptible isolate of the same species. The first acquired resistant microorganism defined the outcome. Recorded clinical variables included demographics, severity scores, underlying conditions and exposure to any procedure or drugs during MICU stay. Analysis was restricted to patients with a length of stay greater than 2 days and performed by using a logistic regression procedure.

Results: Out of 293 patients evaluated, 72 (25%) acquired a resistant microorganism, including a Gram-positive in 8 (3%), P. aeruginosa in 19 (6%), other non-fermenters in 12 (4%), Escherichia coli in 16 (5%), Klebsiella spp. in 6 (2%), and an enteric ampC-bearing organism in 11 (4%). The primary site of colonisation involved the rectum in 57 cases (79%). Of 270 (92%) patients exposed to antimicrobials, 204 (76%) received an antipseudomonal regimen, including ceftazidime in 33 (12%), piperacillin-tazobactam in 62 (23%), meropenem in 93 (34%) and a quinolone in 106 (39%, ciprofloxacin in 33 and levofloxacin in 73). Multivariate analysis selected age (OR 1.02, 95% CI 1–1.04), use of ceftazidime for >3 d (OR 3.8, 95% CI 1.3–11), mechanical ventilation for >3 d (OR 7.9, 95% CI 2–31) and exposure to a nasogastric tube (OR 15, 95% CI 2.8–79) as the best predictors for the acquisition of resistant organisms, whereas location in two particular rooms was protective (OR 0.3, 95% CI 0.1–0.8).

Conclusions: Currently, in critical care settings characterised by an almost universal exposure to antimicrobials, ceftazidime use may represent the antimicrobial exposure associated with the highest risk for the acquisition of resistant bacteria.