Table 1.

Criteria for diagnosis of chronic Q fever, according to the Dutch Q fever consensus group [3]

Classification	Definition
Proven	• Positive C. burnetii in tissue or blood in absence of acute Q fever infection OR
	• IFA phase I IgG titer ≥1:1,024 with definite endocarditis according to the revised Duke criteria* OR
	• IFA phase I IgG titer ≥1:1,024 with vascular infection diagnosed with PET/CT, CT, MRI or ultrasound testing
Probable	IFA phase I IgG titer ≥1:1,024 with one of the following manifestations:
	• Valvular deviation that does not meet the definition of endocarditis according to the Duke criteria
	• Aneurysm, valvular- or vascular prosthesis without an infection on PET/CT, CT, MRI or ultrasound testing
	• Suspicion of osteomyelitis or hepatitis as an expression of chronic Q fever
	• Pregnancy
	• Clinical symptoms of chronic infection (e.g. fever, weight loss, night sweating)
	• Granulomatous infection
	• Immunodeficiency
Possible	Solely a phase I IgG ≥1:1,024¥, without any of the manifestations mentioned in the categories proven and probable.

*A set of clinical criteria for the diagnosis of infective endocarditis.

^¥Phase I IgG antibody titer ≥1:1,024 is within the JBZ measured between 9 - 18 months after acute Q fever diagnosis.