Goodness-of-fit models for case–control study to identify risk factors for chronic Q fever, the Netherlands. A) All chronic Q fever cases (n = 105); area under the curve (c-statistic) 0.77 (95% CI 0.71–0.83); p<0.001. B) Proven and probable chronic Q fever cases (n = 72); c-statistic 0.86 (95% CI 0.81–0.92); p<0.001. C) Proven chronic Q fever cases (n = 44); c-statistic 0.91 (95% CI 0.85–0.97); p<0.001. Patient risk factors included in the model (no. observations): A) valvular surgery (18); vascular prosthesis (15); aneurysm (12); nonhematologic malignancy (16); age, continuous, mean 63.9 y; B) valvular surgery (18); vascular prosthesis (15); aneurysm (12); renal insufficiency (12); age, continuous, mean 67.3 y; C) valvular surgery (10); vascular prosthesis (14); aneurysm (9); renal insufficiency (9); age, continuous, mean 68.4.