Metastatic infectious disease and clinical outcome in Staphylococcus aureus and Streptococcus species bacteremia

Abstract

Early detection of metastatic infection in patients with Gram-positive bacteremia is important as morbidity and mortality are higher in the presence of these foci, probably due to incomplete eradication of clinically silent foci during initial treatment. We performed a prospective study in 115 patients with Staphylococcus aureus or Streptococcus species bacteremia with at least 1 risk factor for the development of metastatic foci, such as community acquisition, treatment delay, persistently positive blood cultures for >48 hours, and persistent fever >72 hours after initiation of treatment. An intensive search for metastatic infectious foci was performed including ¹⁸F-fluorodeoxyglucose-positron emission tomography in combination with low-dose computed tomography scanning for optimizing anatomical correlation (FDG-PET/CT) and echocardiography in the first 2 weeks of admission. Metastatic infectious foci were detected in 84 of 115 (73%) patients. Endocarditis (22 cases), endovascular infections (19 cases), pulmonary abscesses (16 cases), and spondylodiscitis (11 cases) were diagnosed most frequently. The incidence of metastatic infection was similar in patients with Streptococcus species and patients with S. aureus bacteremia. Signs and symptoms guiding the attending physician in the diagnostic workup were present in only a minority of cases (41%). An unknown portal of entry, treatment delay >48 hours, and the presence of foreign body material were significant risk factors for developing metastatic foci. Mean C-reactive protein levels on admission were significantly higher in patients with metastatic infectious foci (74 vs. 160 mg/L). FDG-PET/CT was the first technique to localize metastatic infectious foci in 35 of 115 (30%) patients. As only a minority of foci were accompanied by guiding signs or symptoms, the number of foci revealed by symptom-guided CT, ultrasound, and magnetic resonance imaging remained low. Mortality tended to be lower in patients without complicated infection compared to those with metastatic foci (16% vs. 25%, respectively). Five of 31 patients (16%) without proven metastatic foci died. In retrospect, 3 of these 5 patients likely had metastatic foci that could not be diagnosed while alive. In patients with Gram-positive bacteremia and a high risk of developing complicated infection, a structured protocol including echocardiography and FDG-PET/CT aimed at detecting metastatic infectious foci can contribute to improved outcome.