The incremental role of FDG PET/CT in the investigation of patients with Staphylococcus aureus bacteremia

Objectives Staphylococcus aureus is a leading cause of bacteremia, especially in the nosocomial and healthcare associated settings. Staphylococcus aureus bacteremia (SAB) with an unknown focal source of infection is associated with high risk of mortality. FDG-PET/CT has a significant role in the assessment of various infectious conditions such as osteomyelitis, metastatic foci of endocarditis, vascular graft infections and fever of unknown origin, all relevant to the investigation of SAB. This prospective study aims at evaluating the role of FDG PET/CT in the assessment of patients with SAB and its potential impact on patient management.

Methods Consenting adult patients with clinically-significant SAB were consecutively included. Patients were recruited on day 10-14 after the first positive blood culture. Studies were interpreted by two nuclear medicine physicians aware of the patient’s clinical history, for the presence, intensity and localization of foci of abnormal FDG uptake. Additional investigations were ordered at treating physicians' discretion following and according to PET/CT results.

Results Thirteen patients (10 M; age 38-94 years) with SAB underwent FDG PET/CT. In six of thirteen patients (46%) foci of increased FDG uptake (SUVmax range 3.7-10.9), suggestive of infection were detected including discitis/osteomyelitis (n=2), prosthetic hip joint infection (n=1), infected hemodyalisis shunt graft (n=1), infected superficial femoral artery pseudoaneurysm (n=1) and septic trombophlebitis of the brachial vein (n=1). In 3 of the 6 patients PET/CT detected previously unknown sites of infection. In the additional 3 patients PET/CT confirmed clinically suspected sites and excluded additional metastatic infectious foci. These 6 patients received antibiotic for a prolonged 6 week duration. Seven of the 13 patients (54%) had no FDG-avid foci on PET/CT. Two of these patients had vegetations on cardiac echocardiography and were treated for 4 and 6 weeks antibiotic treatment respectively in spite of the lack of FDG uptake. In 5 of the seven patients follow up did not identify the source of SAB as well and the initially prescribed short term antibiotic treatment was not modified.

Conclusions PET/CT identified and characterized increased FDG uptake compatible with infection in about half of the patients with SAB. Two patients with endocarditis vegetations were not detected by PET/CT. FDG imaging was negative and correctly excluded a focal source or complication of SAB in the remaining 5 cases. In combination with echocardiography FDG-PET/CT may thus be a potentially useful tool to correctly diagnose and alter the therapeutic management of patients with SAB.