Outcomes among Patients with Staphylococcus aureus Bacteremia in the Veterans Affairs Healthcare System

Background: Recent estimates have demonstrated that while morbidity from Staphylococcus aureus (S. aureus) bacteremia (SAB) has decreased, incidence and mortality continue to increase. This study characterizes SAB in the United States Veteran population and compares outcomes for uncomplicated SAB, complicated SAB and SAB with endocarditis.

Methods: Inpatient adult Veterans ≥18 years with at least one S. aureus-positive blood culture (defined index date) between January 2006 and December 2015 were identified from Veterans Health Administration electronic medical records. SAB episodes were classified as uncomplicated (≥ 1 S. aureus-positive blood culture) or complicated (≥ 2 S. aureus-positive blood cultures drawn ≥ 48 hours apart). Endocarditis patients had ≥ 1 S. aureus-positive blood culture and a 1° or 2° ICD-9-CM diagnosis code of 421. We compared demographics, co-morbidities and outcomes between groups.

 

Results: Of 31,161 Veterans with SAB, 27,806 (89.2%) had uncomplicated SAB and 3,355 (10.8%) had complicated SAB. SAB infections were 21% MRSA, 45% MSSA and 34% unknown, which did not differ between groups. Patients were older (66.3% were ≥ 60 years) and commonly had congestive heart failure (25.2%) and diabetes (47.9%). 2,115 (6.8%) of those with SAB had endocarditis (5.6% of those with uncomplicated and 16.3% with complicated SAB). Compared to all patients with SAB, patients with endocarditis were younger (39.9% vs 33.7% were ≤ 60 years, p<0.001), more likely to use IV drugs (5.0% vs 2.8%, p<0.001) and have complicated bacteremia (25.9% vs 10.8%, p<0.001). ICU admission and hospital length of stay were highest in patients with complicated SAB and endocarditis versus uncomplicated SAB (52.6% vs 43.3%, p<0.001 and 50.7% vs 43.3%, p<0.001; 19 vs 12 days, p<0.001 and 16 vs 12 days, p<0.001). In-hospital and 90-day mortality rates correlated with duration of bacteremia (Figure 1).

 

Conclusion: Despite well-established treatments, morbidity and mortality remain high for patients with SAB, especially those with complicated bacteremia and endocarditis. Understanding differences in demographics, comorbidities and outcomes will identify SAB populations that may benefit from optimized antimicrobial therapy regimens.