Risk Factors Associated With Carbapenem-Resistant Pseudomonas aeruginosa

Pseudomonas aeruginosa infections resistant to carbapenem antimicrobials have increased. Traditional risk factors for non-carbapenem resistance include intensive care unit stay, mechanical ventilation, previous hospitalization, and major comorbidities. As microbes evolve, our understanding of their risk factors for resistance also should evolve.

We conducted a retrospective study of adult inpatients and outpatients with a positive Pseudomonas aeruginosa culture during 2014. Cultures were obtained from system laboratories and medical records were reviewed through our electronic medical record. Pearson's chi-squared test with Yates correction and 2-sample t-tests were performed on categorical and continuous variables, respectively. Binary regression was used for multivariable modeling.

Patients (N=1,763), of mean age 68.0 years and body mass index (BMI) 30.4 kg/m2, were more likely to be women (51.3%) and were predominately white (89.3%). Resistance to imipenem or meropenem (14.0%) on univariable analysis was associated with several variables of interest. Non-white race (odds ratio [OR] =1.67; P=0.009), respiratory cultures (OR=1.95; P=0.003), recent institutional transfer (OR=2.50; P<0.0001), vasopressor use (OR=1.98; P=0.001), central line placement (OR=1.55; P=0.036), and peripherally inserted central catheter placement (OR=1.74; P=0.002) remained significant predictors of carbapenem resistance in multivariable modeling.

Demographic and traditional risk factors, as well as respiratory cultures, were predictive of carbapenem resistance and may guide initial antibiotic treatment. Use of "last resort" antibiotics for Pseudomonas aeruginosa based solely on patient chronic conditions may not be necessary. Fortunately, <1% of strains were resistant to all drugs tested. Ongoing efforts to face drug-resistant organisms are warranted.