Group B (past asymptomatic infection) and group C (past symptomatic infection) subjects showed varying degrees of IFNγ recall responses to C. burnetii (both p < 0.0001 compared to group A controls by one-way ANOVA with Holm-Šídák multiple comparisons test), with no significant difference between the two groups (p = 0.9). Here, IFNG is linked to infection.