Epidemiology, diagnosis, and treatment of Q fever

Acute Q fever is the generic name for febrile diseases such as pneumonia and bronchitis mainly occurring after transtracheal infection of Coxiella burnetii, an obligate intracellular parasite of Coxiella belonging to the Rickettsia family, in a broad sense, and difficult to differentiate from other respiratory infections by clinical features alone. In addition to respiratory ailments, diseases including hepatitis and fever of unknown origin are also observed. In many cases, acute Q fever is transient and febrile, showing influenza-like symptoms such as fever, malaise, and arthralgia mainly in summer, and is self-limiting with a good prognosis. Because it may lead to chronic Q fever and a poor prognosis in the form of endocarditis, it is desirable to progressively treat patients upon strong suspicion or definite diagnosis of the disease. Definite diagnosis is currently based on a significant increase in serum antibody titer, but many cases take a long time to achieve a sufficient increase in antibody titer, so it must be determined several times. The results of PCR using respiratory tract specimens in the acute phase are also very useful for diagnosis, but development of a rapid, highly sensitive, simple diagnostic method is much desired. In treatment, β-lactam antibiotics with low cell penetration are ineffective and tetracyclines is the drug of first-choice. Macrolides, new-quinolones, and rifampicin are also effective, but treatment must be continued one or two weeks after fever subsides in a few days after treatment is started.