Increasing incidence of iliopsoas abscesses with MRSA as a predominant pathogen

Objectives: Iliopsoas abscesses (IPAs) are rare infections involving purulence within the muscles of the iliopsoas compartment, seldom due to Methicillin-resistant Staphylococcus aureus (MRSA) historically. This study was designed to evaluate the clinical characteristics and outcomes of patients with IPAs. Methods: A retrospective analysis of the demographics, clinical presentation, microbiologic data and treatment modalities among patients with IPAs from 1993 to 2007 at The Johns Hopkins Hospital was performed. Results: Among 61 patients with IPAs, infection rates increased from 0.5 cases/10,000 admissions (1993-2004) to 6.5 cases/10,000 admissions (2005-2007) (P < 0.001). An adjacent infectious focus was identified in 80% of patients, from skeletal (48%), intra-abdominal (23%), vascular (5%), genitourinary (3%), and cutaneous sources (2%). During 2005-2007, MRSA became a predominant pathogen, accounting for 25% of all cases and 37% of cases with a definitive microbiologic diagnosis (P = 0.006). Patients with IPAs >2 cm were more likely to undergo drainage, with trends toward longer hospitalizations, longer antibiotic courses, and increased odds of securing a definitive microbiologic diagnosis. Conclusions: Since 2005, rates of IPA have dramatically increased, with MRSA now the leading cause of infection. Knowledge of common pathogens should guide antimicrobial therapy including empiric coverage for MRSA in institutions with similar populations, especially if culture data are not available.