Considering the risk of evolution to a chronic disease in people with risk factors, when a patient is diagnosed with acute Q fever, symptomatic or not, these risk factors must be systematically investigated: pregnancy test in women, cardiac ultrasound (asking the cardiologist to look for any valvular abnormality, even minor ones such as mitral prolapsus, aortic bicuspidy, mitral leak), and a search for a cause of immune suppression (HIV, cancer, lymphoma, splenectomy, treatment).
Patients with previous valvular lesions, aneurisms, or vascular grafts, who present with an acute Q fever, have a high risk of chronic Q fever evolution (5). It has been shown that 38% of patients with valvular abnormalities will develop an endocarditis within two years after an acute Q fever (14). This evolution can be prevented by an antibiotic treatment. This study (5) enhances the importance of detecting valvular abnormalities, even minor ones, in a patient with an acute Q fever, and also of diagnosing Q fever in patients with valvular abnormalities. In the general population, between 1% and 2% show valvular abnormalities (14). If one-third of them develop an endocarditis, it means that 0.3% to 0.6% of the patients with an acute
Q fever (symptomatic or not) will have an endocarditis. These figures explain the lack of power of the Swiss cohort (12), which could not show an increase in the risk of endocarditis 12 years after the outbreak (one to two endocarditis cases among 412 Q fever cases during the outbreak).
The evolution of acute Q fever to chronic fatigue syndrome has been described in Australia (15) and in the United Kingdom (16). Ayres et al. (15) interviewed 71 patients five years after the acute phase, and compared them with controls. The patients reported more frequently sweat, dyspnea, blurred vision, and abnormal tiredness. Penttila et al. have demonstrated that the patients with a chronic fatigue syndrome (20%) show moderate abnormalities of their cytokines regulation (16). A geographical variation seems to exist, since none of the 80 patients followed-up in Martigues (southern France) after an acute Q fever developed chronique fatigue syndrome, versus 37% in an English study (17).
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