Use

The test is used to confirm the presence of the infectious agent Coxiella burnetii, which causes Q fever, in symptomatic patients. It is recommended to test acute and convalescent sera. Acute Q fever is demonstrated by a four-fold rise in phase II IgG titers between two samples collected 3-6 weeks apart. Phase I IgG titers can increase during seroconversion, but in acute infection, the Phase I IgG titer should remain lower than the Phase II titer. A single convalescent serum sample with a Phase II IgG titer greater than 1:128 in a patient who has been sick for more than one week suggests probable acute Q fever. Chronic Q fever is best indicated by a Phase I IgG titer greater than the Phase II titer.