In case of acute Q fever, the receiver operating characteristics analysis showed that the presence of aCL antibodies were significantly associated with acute Q fever complications such as acute Q fever endocarditis (area under the curve [AUC], 0.67; 95% CI, 0.58-0.76; P < .001), thrombosis (AUC, 0.72; 95% CI, 0.60-0.85; P = .002), hemophagocytic syndrome (AUC, 0.78; 95% CI, 0.67-0.89; P = .003), meningitis (AUC, 0.68; 95% CI, 0.56-0.79; P = .01), and alithiasic cholecystitis (AUC, 0.75; 95% CI, 0.60-0.90; P = .05) (eTable 13 in the Supplement). Here, ACLY is linked to hemophagocytic syndrome.