Molecular Detection of Coxiella burnetii in the Sera of Patients with Q Fever Endocarditis or Vascular Infection

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Abstract
In the absence of a specific diagnosis based on serology, chronic Q fever is inevitably fatal. However, diagnosis is often delayed because the test is not widely available. To shorten the diagnostic delay, we adapted a nested-PCR assay with serum as a template and the LightCycler as a thermal cycler, termed LCN-PCR. We retrospectively and prospectively applied this method to samples from 48 patients diagnosed with Q fever endocarditis or vascular infection and to samples from 100 controls with endocarditis caused by other microorganisms. We also prospectively applied this technique to samples from 30 patients treated for a Q fever endocarditis and to samples from 13 patients with a convalescent acute Q fever with ambiguous immunoglobulin G (IgG) phase I titer. LCN-PCR had a specificity of 100%. It was positive only in samples from patients with evolutive Q fever, as none of the samples from patients with a treated chronic Q fever or with a convalescent acute Q fever presented positive results. When performed prospectively on recently stored sera, the sensitivity of LCN-PCR is 64% (7 of 11 samples; P = 0.004), but the efficiency of LCN-PCR was dramatically altered by the storage of specimens at −20°C. High IgG phase I titers decreased the sensitivity of LCN-PCR. A significant difference was observed among LCN-PCR results for sera with IgG phase I titers of ≥1:25,600 compared to sera with IgG phase I titers of P = 0.004). In patient samples with titers below 1:25,600 tested prospectively, sensitivity was 100% (7 of 7). The LCN-PCR assay may be helpful in establishing an early diagnosis of chronic Q fever.