Immunoglobulin G Anticardiolipin Antibodies and Progression to Q Fever Endocarditis

Background. Immunoglobulin G (IgG) anticardiolipin (aCL) antibodies are associated with valvulopathy and endocarditis in patients with lupus and other diseases. During acute Q fever, high IgG aCL prevalence has been reported, but the clinical significance remains unknown. Methods. To test if increased IgG aCL at acute Q fever diagnosis is associated with an increased risk of progression to endocarditis, all patients diagnosed in the French National Referral Center for Q fever from January 2007 to December 2011 were included and followed regularly until January 2013 in a 5-year prospective cohort study. Q fever endocarditis was defined according to recently updated criteria. Results. Seventy-two patients were followed for a median time of 31 months (interquartile range, 18-47 months). Of these, 13 patients with valvulopathy without antibiotic prophylaxis progressed to endocarditis. IgG aCL levels were highly prevalent (57%) and significantly higher in the presence of a valvulopathy (P =.005). Using Cox regression analysis, highly increased levels of IgG aCL (adjusted hazard ratio [AHR], 12.95; 95% confidence interval, 2.85-58.95; P =.001) and high levels of phase II immunoglobulin M (IgM; AHR, 6.59; 95% CI, 1.37-31.62; P =.018) were the only independent predictors of progression to endocarditis. Conclusions. Rapid progression from acute Q fever to endocarditis is associated with high levels of IgG aCL and high levels of phase II IgM, findings that should be critical in the prevention of endocarditis.