Increased Mortality with Accessory Gene Regulator (agr) Dysfunction inStaphylococcus aureusamong Bacteremic Patients
ABSTRACTAccessory gene regulator (agr) dysfunction inStaphylococcus aureushas been associated with a longer duration of bacteremia. We aimed to assess the independent association betweenagrdysfunction inS. aureusbacteremia and 30-day in-hospital mortality. This retrospective cohort study included all adult inpatients withS. aureusbacteremia admitted between 1 January 2003 and 30 June 2007. Severity of illness prior to culture collection was measured using the modified acute physiology score (APS).agrdysfunction inS. aureuswas identified semiquantitatively by using a δ-hemolysin production assay. Cox proportional hazard models were used to measure the association betweenagrdysfunction and 30-day in-hospital mortality, statistically adjusting for patient and pathogen characteristics. Among 814 patient admissions complicated byS. aureusbacteremia, 181 (22%) patients were infected withS. aureusisolates withagrdysfunction. Overall, 18% of patients withagrdysfunction inS. aureusdied, compared to 12% of those with functionalagrinS. aureus(P= 0.03). There was a trend toward higher mortality among patients withS. aureuswithagrdysfunction (adjusted hazard ratio [HR], 1.34; 95% confidence interval [CI], 0.87 to 2.06). Among patients with the highest APS (scores of >28),agrdysfunction inS. aureuswas significantly associated with mortality (adjusted HR, 1.82; 95% CI, 1.03 to 3.21). This is the first study to demonstrate an independent association betweenagrdysfunction and mortality among severely ill patients. The δ-hemolysin assay examiningagrfunction may be a simple and inexpensive approach to predicting patient outcomes and potentially optimizing antibiotic therapy.