Objective: To determine the frequency of MDR-PA and characterize the epidemiology of P. aeruginosa infections in SICU patients.
Methods: This was a retrospective cohort study of healthcare-associated infections caused by antimicrobial-resistant P. aeruginosa during 2006 through 2008 (study period). A case was defined as any adult SICU patient who acquired a P. aeruginosa infection during the study period. MDR-PA was defined as P. aeruginosa resistant to ≥3 of the following five sentinel antimicrobials: imipenem, cefepime, amikacin, ciprofloxacin, and piperacillin. Cases were ascertained through review of medical records and microbiology line listings. Data were recorded in a comprehensive, standardized questionnaire and included detailed clinical, epidemiologic, and microbiological information, device usage, and outcomes. Relative risks (RR) and 95% confidence interval (CI) were determined. Independent correlates for MDR-PA infections were identified through logistic regression analyses.
Results: 42 patients met the case definition. Of these 42 patients, 29 (73%) acquired BSIs and 11 (26%) respiratory tract infections. Of the 42 isolates, 13 (31%) were resistant to just two of the five sentinel agents (low grade resistance). Only 2 (4.8%) isolates met the case definition for MDR-PA; these 2 isolates originated in patients with previously documented low-grade resistance. On univariate analysis, correlates for low-grade resistance included having a BSI (p <0.01), exposure to antimicrobials (p <0.01), chronic liver disease (p <0.001), or hemodialysis (p <0.01). Independent correlates for low-grade resistance were chronic liver disease (adjusted odds ratio [AOR]: 12.0, CI (2.3-80) or prior exposure to ≥1 antimicrobial agents (AOR: 15.4, CI: 1.9-329). In contrast, there was no statistical association between MDR-PA and antimicrobial use or other risk factors.
Conclusions: Using a panel of key antimicrobial agents and a strict case definition, we demonstrated that rates of infection caused by MDR-PA were relatively low among SICU patients. These data also suggest that while low-grade resistance among P. aeruginosa isolates is associated with antimicrobial use, progression to multi-drug resistance is likely dependent on additional risk factors.