18F-FDG PET/CT for Detection of Metastatic Infection in Gram-Positive Bacteremia

The timely detection of metastatic infectious foci in gram-positive bacteremia is crucial, because these foci often require prolonged antibiotic treatment or drainage. The diagnosis of metastatic infectious foci is difficult because localizing symptoms are often absent. We investigated whether F-18-FDG PET/CT was able to detect such foci and whether detection influenced clinical outcome. Methods: One hundred fifteen nonneutropenic patients with gram-positive bacteremia were prospectively included. Patients with positive blood cultures growing Staphylococcus aureus, Streptococcus species, or Enterococcus species were eligible when a risk factor for developing metastatic infectious foci was present. F-18-FDGPET/CT was performed within 2 wk after the first positive blood culture. Abnormal F-18-FDG uptake had to be confirmed by radiologic, microbiologic, or pathologic studies. Results were compared with a matched historical control group of 230 patients in whom no F-18-FDG PET/CT was performed. Results: Significantly more patients were diagnosed with metastatic foci in the study group (67.8% vs. 35.7%). Of the imaging investigations performed, F-18-FDG PET/CT was the first to delineate infectious foci in 35 patients (30%). In the remaining 70%, either symptoms on physical examination or other imaging techniques first revealed infectious foci. The sensitivity, specificity, negative predictive value, and positive predictive value of F-18-FDG PET/CT were 100%, 87%, 100%, and 89%, respectively. Relapse rates decreased from 7.4% to 2.6% among study patients (P = 0.09) and from 8.9% to 1.4% in patients with S. aureus (P = 0.04). Overall mortality after 6 mo decreased from 32.2% to 19.1% in the F-18-FDG PET/CT group (P = 0.014). Conclusion: In the diagnostic work-up of high-risk patients with gram-positive bacteremia, F-18-FDG PET/CT is a valuable technique that results in lower mortality rates. In patients with S. aureus bacteremia, relapse rates decreased significantly after the addition of F-18-FDG PET/CT.