Antimicrobial use and other risk factors for infections with antimicrobial-resistant bacteria and fungi bacteria and fungi in an intensive care unit

Introduction: Resistant infections are especially problematic in the intensive care unit (ICU), but risk factors remain unclear. We hypothesized that the risk factors for resistant Gram-negative rods (rGNR), resistant Gram-positive cocci (rGPC), and secondary fungal infections differed. Materials and Methods: A single-center cohort study of patients with ICU-acquired infections from 1997 to 2017 was performed. Inclusion was conditioned on the presence of rGNR, rGPC, or fungi. Risk factors studied included demographics, medical comorbidities, Acute Physiology and Chronic Health Evaluation (APACHE) II score, and previous antimicrobial exposure. Results: Four thousand three hundred and nineteen ICU-acquired infections were identified. One thousand nine hundred and ninety-eight were considered resistant and 2321 were considered nonresistant. Identification of any resistant organism was significantly associated with female sex, nontrauma diagnosis, APACHE II score, liver disease, chronic steroid use, history of any prior infection, and history of a resistant infection, but not days of prior antimicrobial use. Infections with rGNR were associated with days of therapeutic antimicrobials given for a previous infection, but not total prior antimicrobial days during hospitalization. rGPC infections were associated with both previous infections treated with antimicrobials and total prior antimicrobial days during hospitalization. Fungal infections were not associated with any measure of prior antimicrobial exposure. Controlling for the severity of illness and demographics, resistant infections were not associated with mortality compared to nonresistant infections. Conclusions: The likelihood of rGNR infection is closely linked to recent antimicrobial exposure, while rGPC infection appears to be associated with prior antimicrobial exposure. Fungal infections may not be associated with prior antimicrobial exposure. These findings suggest disparate mechanisms of dysbiosis for different classes of resistant pathogens.