[Infection by Coxiella burnetii (Q fever)]

In spite of being described over 60 years, Q fever is still a little known disease. The exact prevalence is also unknown, but probably the number of cases of Q fever is underestimated. There is much variation in the clinical presentation, including severe forms with a poor prognosis. Acute cases often present as an asymptomatic infection, flu-like syndrome, pneumonia or hepatitis. Presumably, host factors play an important role in the development of chronic disease, which may present as endocarditis with negative blood culture. The diagnosis of Q fever should be considered in cases of fever of unknown origin, especially if the subject has been in contact with mammals suspicious to be infected. The best methods of microbiological diagnosis are those that allow direct detection of bacteria (cell culture and PCR), although these procedures should be performed in laboratories with adequate biosafety measures, and with specialized personnel. For serologícal diagnosis, the reference method is indirect immunofluorescence (IIF), which is very sensitive and specific. In suspected cases of acute Q fever, diagnosis should be confirmed by serum titers (IgG and/or IgM), obtained by immunofluorescence above the cutoff calculated for each geographic area, or by seroconversion.