Localizing chronic Q fever: a challenging query

Abstract

Background: Chronic Q fever usually presents as endocarditis or endovascular infection. We investigated whether 18F-FDG PET/CT and echocardiography were able to detect the localization of infection. Also, the utility of the modified Duke criteria was assessed.

Methods: Fifty-two patients, who had an IgG titre of ≥ 1024 against C. burnetii phase I ≥ 3 months after primary infection or a positive PCR ≥ 1 month after primary infection, were retrospectively included. Data on serology, the results of all imaging studies, possible risk factors for developing proven chronic Q fever and clinical outcome were recorded.

Results: According to the Dutch consensus on Q fever diagnostics, 18 patients had proven chronic Q fever, 14 probable chronic Q fever, and 20 possible chronic Q fever. Of the patients with proven chronic Q fever, 22% were diagnosed with endocarditis, 17% with an infected vascular prosthesis, and 39% with a mycotic aneurysm. 56% of patients with proven chronic Q fever did not recall an episode of acute Q fever. Ten out of 13 18F-FDG PET/CT-scans in patients with proven chronic Q fever localized the infection. TTE and TEE were helpful in only 6% and 50% of patients, respectively.

Conclusions: If chronic Q fever is diagnosed, 18F-FDG PET/CT is a helpful imaging technique for localization of vascular infections due to chronic Q fever. Patients with proven chronic Q fever were diagnosed significantly more often with mycotic aneurysms than in previous case series. Definite endocarditis due to chronic Q fever was less frequently diagnosed in the current study. Chronic Q fever often occurs in patients without a known episode of acute Q fever, so clinical suspicion should remain high, especially in endemic regions.

Figure 1

Titres of anti-phase 1 IgG at the time of chronic Q fever diagnosis.

Figure 2

Titres of complement fixation test at the time of chronic Q fever diagnosis. Abbrevations: CFT Complement fixation test.

Figure 3

¹⁸F-FDG PET/CT image demonstrating a mycotic aneurysm. ¹⁸F-FDG PET/CT images (left column coronal sections, right column transverse sections, upper row PET images, lower row PET/CT fusion images) of a patient with proven chronic Q fever demonstrating a mycotic aneurysm and associated abscess adjacent to the left common iliac artery (arrows). Abbrevations: ¹⁸F DG-PET/CT¹⁸F- fluorodeoxyglucose positron emission tomography combined with CT.