Risk factors for multidrug-resistant bacteria in patients with post-operative peritonitis requiring intensive care.

Objectives: This prospective non-interventional study investigated the risk factors for multidrug-resistant bacteria (MDRB) in patients with post-operative peritonitis (POP), to provide guidance for empirical antimicrobial therapy.

Methods: All consecutive patients, >15 years old, admitted to a surgical intensive care unit (ICU) between September 2006 and January 2009 for a first episode of POP were included. Antibiotic susceptibilities of microorganisms recovered from blood cultures and peritoneal fluid were determined by disc diffusion. Amoxicillin/clavulanic acid, ticarcillin/clavulanic acid, piperacillin/tazobactam, cefotaxime, ceftazidime, cefepime, imipenem, gentamicin, amikacin and ciprofloxacin were tested against Gram-negative bacteria, and oxacillin, amoxicillin, vancomycin, gentamicin and erythromycin were tested against aerobic Gram-positive bacteria. Results were reported as susceptible or resistant.

Results: MDRB were isolated from 20/115 (17%) patients. In univariate analysis, use of antimicrobial therapy during the 3 months prior to hospitalization and a long duration between hospital admission or first operation and relaparotomy were significantly associated with MDRB recovery. In multivariate analysis, only antimicrobial treatment in the 3 months preceding hospitalization and duration between first operation and relaparotomy were independent risk factors for MDRB [odds ratio (OR) = 5.80, 95% confidence interval (95% CI) = 1.99-16.91 and OR = 1.10, 95% CI = 1.02-1.19, respectively]. No MDRB were found when the delay between the first operation and relaparotomy was <5 days. POP severity, non-surgical and surgical complications, hospital and ICU length of stay, and mortality were similar in patients with and without MDRB.

Conclusions: Our results suggest that broad-spectrum antibiotics should be used in ICU patients with POP who have received antimicrobial therapy in the 3 months prior to hospitalization, or with >5 days between the first operation and relaparotomy.