Serological differentiation between acute (late control) and endocarditis Q fever.

AIMS To differentiate the serological profiles of chronic (endocarditis) Q fever from the late follow up of acute cases. METHODS Twenty patients (10 diagnosed with acute and 10 with endocarditis Q fever) were studied. Those diagnosed with acute infection were followed up from 2.5 to 88 months (mean 35.8 months). Serological variables included indirect immunofluorescence against phase I and II of Coxiella burnetii (IgM, IgG, and IgA), complement fixation and rheumatoid factor (RF). RESULTS All patients with titres of IgA against phase I, after IgG removal, equal to or above 320 and a complement fixation value equal to or above 128 had endocarditis. No patient with acute Q fever had such a serological profile. CONCLUSIONS The combination of IgA against phase I and complement fixation values may be sufficient to differentiate the serological profile of chronic (endocarditis) Q fever from the late follow up of acute cases.