Q fever is an ubiquitous zoonosis caused by C burnetii
. Infected aerosols generated by farm animals are the usual source of human infection.2
Our patient reported frequent contact with farm animals, specifically goats. C burnetii
is an obligate intracellular bacterium that may cause acute and chronic infections in humans. Although most acute infections (60%) are asymptomatic, frequently observed symptoms include isolated fever, atypical pneumonia and hepatitis.3
Recovery is spontaneous in most cases. However, acute Q fever may evolve to chronic infection, that is, an infection persisting for more than 6 months, in 1 to 5% of patients.4
Such a progression occurs most frequently in patients with a valve disease, a vascular prosthesis or aneurysm, immunocompromised patients or in pregnant women.5
Serologically, chronic Q fever is characterised by an IgG titre to phase I antigen greater than 1:800. Clinically, chronic Q fever presents as endocarditis, vascular infections, osteoarticular infections and chronic hepatitis.6
Infective aneurysms and infection of vascular prostheses account for 9% of chronic Q fever cases.7
The risk of progression from acute to chronic infection is estimated to be 40% in patients with valvular defects,5
but it is as yet undetermined in patients with arterial diseases.
The delay between acute and chronic infection is variable. In 2007, Landais et al8
demonstrated that 50% of patients developed chronic Q fever within 3 months of acute infection, and 75% within 6 months. Here, the development of chronic Q fever may have been facilitated by the use of corticosteroids for polymyalgia rheumatica. Indeed, exacerbation of chronic Q fever with corticosteroid therapy has been previously reported.9
Despite the severity of chronic Q fever, its diagnosis is often delayed due to the absence of specific clinical symptoms and because the initial infection is often asymptomatic.10
Q fever is mainly diagnosed through serology with the reference method being the indirect immunofluorescence assay.11
In our laboratory in Marseille (Southern France), the French National Reference Centre for Rickettsial Diseases, we use a microimmunofluorescence technique. Chronic Q fever was defined by a cut-off titre of phase I antigen-specific IgG greater than 1:800. The serological diagnosis of chronic Q fever should encourage the search for valve disease by echocardiography. Transthoracic echocardiography is recommended in the first instance; however, in the case of a normal transthoracic echocardiograph, transoephageal echocardiography should be performed in order to detect a bicuspid aortic valve or mitral regurgitation12
if the antibody titre increases. Indeed minor valvulopathies, such as minor valvular insufficiency, mitral valve prolapse or a bicuspid aortic valve, are a predisposing factor for Q fever endocarditis.13
If a valvular lesion is ruled out, abdominal and pelvic CT should be performed to search for an arterial aneurysm.14
(). The diagnosis of an aneurysm infection can be established by serology with the same profile as endocarditis.6
The documentation of cardiac or arterial abnormalities is crucial to improve the management and prognosis of chronic Q fever. The management of chronic Q fever is complex. Prolonged antibiotic therapy with both doxycycline (200 mg per day) and hydroxychloroquine (600 mg per day) should be administered for a minimum of 18 months.10
Strategy and management of chronic Q fever diagnosis.
vascular infection has a poor prognosis. An early diagnosis is necessary to enable early treatment and avoid severe complications. In a recent study of 30 cases of C burnetii
infected aortic aneurysms or vascular grafts, vascular surgery was significantly associated with recovery but the associated mortality rate was high (25%). Because rupture of infected aneurysms is the main complication of C burnetii
aortic infections, surgery is required in most C burnetii
It is recommended that serological testing be performed 3 and 6 months following the diagnosis of acute Q fever to allow for the early detection of chronic infection. Delays in diagnosis have been shown to have a significant negative impact on prognosis.8
When phase I antigen-specific antibody titres are increasing rapidly and when echocardiography is negative, we suggest performing a CT scan to identify any arterial aneurysms.
- Radiologic examinations, notably echocardiography and CT, have as important a place in chronic Q fever diagnosis as serology because management of Q fever infection depends on the presence or absence of valve disease or vascular infection.
- These vascular infections have a poor prognosis, which is why early management of this infection is fundamental, especially because diagnosic delays have a significant impact on prognosis.