Persistence of DNA in a cured patient and positive culture in cases with low antibody levels bring into question diagnosis of Q fever endocarditis.

We evaluated the performance of tools for diagnosing Q fever cardiovascular infection. We retrospectively analyzed 162 cardiovascular samples from 125 patients who were tested serologically by immunofluorescence, quantitative PCR (qPCR), 16S rRNA gene amplification, culture, and immunohistochemistry, and we assessed the viability of Coxiella burnetii by measuring the transcription of the 16S rRNA gene. The qPCR technique was significantly more sensitive than 16S rRNA gene amplification (P < 0.0001), cell culture (P = 0.0002), and immunohistochemistry (P < 0.0001). The sensitivity of these techniques was reduced when applied to patients who had been previously treated. The severity of infection appears to be correlated with phase I IgG levels. We report for the first time 4 cases of endocarditis with positive qPCR and/or culture assay result from patients with a low phase I IgG (IgG I) titer (<800), and we have identified the longest (16 years) persistence of DNA described in a heart valve from a patient cured after being previously treated for endocarditis. The active transcription of the 16S rRNA gene was found in 19/59 tested samples, with a positive predictive value of 100% for a positive culture. In conclusion, the diagnosis of Q fever cardiovascular infection should not be excluded in patients with low titers of phase I IgG when they present with valvulopathy. We recommend testing cardiovascular samples using 3 or 4 different biopsy sections by qPCR evaluation for patients with IgG I titers of ≥200.