Compliance with follow-up cultures in Staphylococcus aureus bacteremia: Opportunity for quality improvement

Background: Treatment failure in uncomplicated Staphylococcus aureus bacteremia (SAB) occurs in 20-30% of cases. Published guidelines recommend follow-up blood cultures (cx) to document clearance of SAB within 72 hrs of treatment initiation. We hypothesized that not all patients (pts) with SAB would have follow-up blood cultures done and that pts without documented clearance would have higher in-hospital mortality.

Methods: We performed a retrospective cohort study of adult pts with their first episode of SAB from 2008-2012 at a large academic medical center. Pts were excluded if they left AMA, were discharged to hospice, or had a blood cx’s obtained ≤72 hours from discharge or death. We used logistic regression to study the association between SAB clearance (≥1 negative cx collected >1 hour after the last positive cx) and mortality. We estimated the causal risk difference of documenting SAB clearance versus failure to do so using the g-computation approach.

Results: We identified 1,437 pts with SAB; 873 pts met study inclusion criteria. Study pts median age = 57 (IQR: 46-67) yrs, were predominantly male (60.1%, n=525), Caucasian (60.1%, n=525) and the median Charlson score = 2.0 (IQR: 1.0-5.0). The median length of stay = 14.0 (8.0-25.0) days and 48.8% (n=426) had an ICU admission. 88.4% of SAB were healthcare-associated. 45.0% (n=393) of pts had a central venous catheter. 33.1% (n=289) were hemodialysis pts, 11.1% (n=97) had endocarditis and 6.4% (n=56) had pneumonia. The mean duration of SAB = 1.1 (±4.6) days and duration of antibiotics = 10.2 (±12.5) days. Failure to perform follow-up cx to confirm clearance occurred in 11.5% (n=100) of pts. In-hospital mortality was greater in pts without documented clearance [27/100 (27%) w/o vs. 67/773 (8.7%) w/ clearance]. Failure to document SAB clearance (OR = 5.4, 95% CI: 2.7, 10.0), Charlson comorbidity score (OR = 1.3, 95% CI: 1.1, 1.4), ICU admission (OR = 8.1, 95% CI: 4.2, 15.7) and pneumonia (OR = 2.6, 95% CI: 1.1, 5.9) were independent predictors of mortality. The estimated causal risk difference of mortality per 100 SAB pts without documented clearance was 18.9% (95% CI: 17.4%, 20.5%) compared to those with documented clearance.

Conclusion: A lack of repeat cultures to document clearance of SAB occurred in 11.5% of pts and was independently associated with poor outcomes.