An 82-year-old man with non-Hodgkin’s lymphoma in remission and a history of congestive heart failure and hypertension presents with one week of generalized malaise and intermittent fevers. Vitals show a temperature of 101oF, blood pressure of 130/60 mmHg, and heart rate of 100. His exam is notable for an erythematous and tender chest port site, with no murmurs. Blood cultures drawn upon presentation show gram-positive cocci speciated to Staphylococcus aureus. What are the next steps in management of this patient?
S. aureus bacteremia (SAB) is a common infectious cause of morbidity and mortality worldwide, causing both community-acquired and hospital-acquired bacteremia. In the U.S. alone, it accounts for 23% of all bloodstream infections and is the bacterial pathogen most strongly associated with death.1 Mortality rates are approximately 42% in those with methicillin-resistant S. aureus (MRSA) bacteremia and 28% in those with methicillin-sensitive S. aureus (MSSA) bacteremia.2
Recognizing the severity of SAB, the Infectious Disease Society of America (IDSA) published treatment guidelines in 2011 to help direct the clinical care of this disease process.3 However, the majority of the recommendations are based on observational studies and expert opinion, as less than 1,500 patients have been enrolled in randomized controlled trials specifically targeted to investigate the treatment of SAB.4
Review of the Data
A clinically significant SAB usually is defined as the isolation of S. aureus from a venous blood culture with associated symptoms and signs of systemic infection.5 As SAB contamination is rare and can be associated with multiple complications, including metastatic infections, embolic stroke, recurrent infection, and death, any finding of a positive blood culture must be taken seriously.4
SAB treatment is multifaceted and should focus on the removal of any nidus of infection, such as a catheter or a prosthetic device, the use of prolonged antimicrobial therapy, and the evaluation of potential complications. In a retrospective study, Johnson et al showed that failure to remove the source is one of the strongest independent predictors of relapse in patients with SAB.6 However, 10% to 40% of patients have no identifiable focus, which increases the impetus to evaluate for complications.7-8 Overall, approximately one-third of patients with SAB develop metastatic complications, either from hematogenous seeding or local extension of infection.9
In addition to advanced age and such comorbid conditions as cirrhosis, the strongest predictor of complications is a positive blood culture at 48 to 96 hours after an initial positive blood culture, as shown in a large prospective cohort study by Fowler et al.7,10-11 Additional independent risk factors (see Table 1) include community acquisition (likely due to prolonged duration of bacteremia), skin examination suggesting the presence of acute systemic infection, and persistent fever at 72 hours after the first positive blood culture. Patients with even one of these risk factors are at high risk for a complicated course (which occurs in about 35%). In a case-control study, Chihara et al showed that S. aureus bacteruria in the absence of urinary tract pathology or recent urinary tract instrumentation might be associated with threefold increased mortality compared with those without bacteriuria, even after adjustment for comorbid conditions.12