Treatment of persistent focalized Q fever: time has come for an international randomized controlled trial.

Q fever is a worldwide zoonosis due to Coxiella burnetii, responsible for endocarditis and endovascular infections. Since the 1990s, the combination hydroxychloroquine + doxycycline has constituted the curative and prophylactic treatment in persistent focalized Q fever. This combination appears to have significantly reduced the treatment's duration (from 60 to 26 months), yet substantial evidence of effectiveness remains lacking. Data are mostly based on in vitro and observational studies. We conducted a literature review to assess the effectiveness of this therapy, along with potential alternatives. The proposed in vitro mechanism of action describes the inhibition of Coxiella replication by doxycycline through the restoration of its bactericidal activity (inhibited in acidic environment) by alkalinization of phagolysosome-like vacuoles with hydroxychloroquine. So far, the rarity and heterogeneous presentation of cases have made it challenging to design prospective studies with statistical power. The main studies supporting this treatment are retrospective cohorts, dating back to the 1990s-2000s. Retrospective studies from the large Dutch outbreak of Q fever (>4000 cases between 2007 and 2010) did not corroborate a clear benefit of this combination, notably in comparison with other regimens. Thus, there is still no consensus among the medical community on this issue. However insufficient the evidence, today the doxycycline + hydroxychloroquine combination remains the regimen with the largest clinical experience in the treatment of 'chronic' Q fever. Reinforcing the guidelines' level of evidence is critical. We herein propose the creation of an extensive international registry, followed by a prospective cohort or ideally a randomized controlled trial.