Occult Staphylococcus aureus bacteremia in adult emergency department patients: rare but important.

Background: We sought to elaborate the epidemiology and outcomes of adult patients with occult Staphylococcus aureus bacteremia who were inadvertently discharged from the emergency department (ED) before positive blood culture results were obtained.
Methods: Between 2001 and 2010, 759 true occult bacteremia cases were identified, including 65 patients with S. aureus bacteremia. Sixty-two patients were enrolled (case group) and analyzed using two 1:2 case-control strategies. Control group I patients were selected from among 997 S. aureus bacteremia patients directly admitted from the ED. Control group II patients were selected from 694 ED patients with occult bacteremia other than S. aureus. Cox regression analyses were used to assess the independent effect of occult S. aureus bacteremia on patient mortality.
Results: There was no significant difference between the case group and control group I with respect to organ failure, septic shock, intensive care unit (ICU) admission proportion, length of ICU stay, and 30-day mortality. However, compared with control group II, the case group had significantly higher rates of hospital admission, organ failure, septic shock, ICU admission, and 30-day mortality. Age, endocarditis, and S. aureus infection were independent predictors of mortality among adult occult bacteremia patients.
Conclusions: Among patients with occult bacteremia, S. aureus infections had significantly greater adverse impacts on a variety of outcome variables than other bacterial infections. Because S. aureus bacteremia is frequently associated with endovascular or deep-seated infection, it is imperative that first-line clinicians perform prudent evaluations of cases with nonapparent infection foci before discharging febrile patients from EDs.