Background. Coxiella burnetii endocarditis is considered to be a late complication of Q fever in patients with preexisting valvular heart disease (VHD). We observed a large transient aortic vegetation in a patient with acute Q fever and high levels of IgG anticardiolipin antibodies (IgG aCL). Therefore, we sought to determine how commonly acute Q fever could cause valvular vegetations associated with antiphospholipid antibody syndrome, which would be a new clinical entity.Methods. We performed a consecutive case series between January 2007 and April 2014 at the French National Referral Center for Q fever. Age, sex, history of VHD, immunosuppression, and IgG aCL assessed by enzyme-linked immunosorbent assay were tested as potential predictors.Results. Of the 759 patients with acute Q fever and available echocardiographic results, 9 (1.2%) were considered to have acute Q fever endocarditis, none of whom had a previously known VHD. After multiple adjustment, very high IgG aCL levels (>100 immunoglobulin G-type phospholipid units; relative risk [RR], 24.9 [95% confidence interval {CI}, 4.5-140.2]; P = .002) and immunosuppression (RR, 10.1 [95% CI, 3.0-32.4]; P = .002) were independently associated with acute Q fever endocarditis.Conclusions. Antiphospholipid antibody syndrome with valvular vegetations in acute Q fever is a new clinical entity. This would suggest the value of systematically testing for C. burnetii in antiphospholipid-associated cardiac valve disease, and performing early echocardiography and antiphospholipid dosages in patients with acute Q fever.

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