IL18 and Q fever: Previously, we published that cytokine production (TNF-α, IL-1β, IL-1Ra, IL-4, IL-5, IL-6, IL-10, IL-12p70, IL-23, IL-18) in C. burnetii-stimulated diluted blood did not distinguish seropositive controls from chronic Q fever patients, whereas the ratio of IFN-γ/IL-2 production appeared to accurately identify chronic Q fever patients with 79% sensitivity and 96% specificity [23].