We demonstrated, by measuring a broad panel of cytokines, that ex-vivo C. burnetii-specific IFN-γ production is higher and interleukin (IL)-2 production is lower in chronic Q fever patients than in patients with past Q fever (Schoffelen et al., 2014), and concluded that a high IFN-γ/IL-2 ratio has a high specificity to discriminate between these two groups. This evidence concerns the gene IFNG and Q fever.