Clinical Characteristics and Resistance Patterns of Pseudomonas aeruginosa Isolated from Operations Enduring Freedom and Iraqi Freedom Trauma Patients

Abstract

Background. Wound infections and blood stream infections are the most common infections following combat-related injuries. Multidrug-resistant (MDR) Gram-negative organisms have been increasingly identified in these infections, but the impact of Pseudomonas aeruginosa (PsA) has yet to be evaluated. We describe clinical characteristics, resistance patterns, and outcomes associated with PsA infections in military trauma patients. Methods. All PsA initial unique wound and blood isolates as well as serial isolates (≥7 days from initial isolate from any site) were collected via the Trauma Infectious Disease Outcomes Study (June 2009-February 2014). Antimicrobial susceptibilities (CLSI criteria) were determined using the BD Phoenix Automated Microbiology System and E-test. MDR was defined as resistance to ≥3 classes of aminoglycosides, β-lactams, carbapenems, and/or fuoroquinolones. Results. Of 2,618 trauma admissions, 146 (6%) patients with 374 PsA isolates met inclusion criteria. Forty patients had serial PsA isolation with a median of 2 subsequent isolates (IQR 1-5). All patients were male with a median injury severity score (ISS) of 33. Patients largely had blast-related injuries (132; 90%) with a median hospital stay of 57 days. Overall mortality was 7%. There was a median of 14 days from injury to initial PsA isolation. Culture types were 247 wound, 34 blood, 40 respiratory, 32 urine, and 21 other. Fify-four (37%) patients had fuoroquinolone resistance. Fourteen (10%) patients had MDR PsA recovered. Patients with MDR PsA had a higher median ISS (50 vs. 33, P < 0.01), longer hospital stay (140 vs. 55 days, P < 0.01), and more serial PsA cultures (4 vs. 0, P < 0.01). Initial PsA isolates from five patients and serial isolates from nine other patients were MDR. Tose with the initial MDR PsA had a longer duration from injury to initial PsA isolation (59 vs. 13 days, P < 0.01). Emergence of MDR PsA on serial isolation was associated with higher ISS, longer hospital stay, more ventilator days, and greater number of serial isolates (P < 0.01). Conclusion. PsA is a common pathogen isolated in combat-related wound and bloodstream infections, but uncommonly MDR. Risk factors for MDR PsA were longer duration of hospitalization prior to isolation and recurrent isolation.