[Clinical manifestation of Q fever and tuberculosis, similarly caused by intracellular parasites].

Q fever is a generic term for pneumonia, bronchitis, etc. caused by infection with Coxiella burnetii, a rickettsia-related species of bacteria, in humans. Q-fever is a transient and acute febrile illness that takes a course similar to influenza, and its clinical picture greatly differs from that of tuberculosis that takes a chronic course. The reason for this is thought to be because the generation time of C. burnetii is extremely short (several tens of minutes) compared with Mycobacterium tuberculosis, though those are similar intracellular parasites. Q fever is fourth- or fifth-ranked among the community-acquired pneumonias in the United States and Europe but has a good prognosis with 1-2% of mortality even in the cases that follow a natural course without treatment. Meanwhile, there is a chronic type that follows a protracted course or has a poor prognosis. Therefore, cases definitely diagnosed with Q fever or strongly suspected of Q fever should seek aggressive treatment. Q fever is definitely diagnosed by confirming significant increase in serum antibody titer, but the patients should be followed because in many cases it takes a long time before serum antibody titer increases. Beta-lactams are ineffective against C. burnetii, an obligate intracellular parasite. Although tetracyclines, macrolides, quinolones, rifampicin, etc. are used effectively in the treatment of Q fever, many cases appear to improve by beta-lactam administration because the illness often takes a natural course.