Q fever pneumonia in children in Japan.

The prevalence of Q fever pneumonia among children with atypical pneumonia from whom only an acute-phase serum sample was available was traced by using an indirect immunofluorescence (IF) test, nested PCR, and isolation. Twenty (34.5%) of 58 sera were found to have both polyvalent and immunoglobulin M antibodies to the phase II antigen of Coxiella burnetii by the IF test. Q fever pneumonia was present in 23 (39.7%) of 58 patients as determined by both the nested PCR and isolation and in 20 patients as determined by the IF test. The sensitivities for nested PCR and isolation were 100%, and that for the IF test was 87%. Our results indicate that nested PCR was faster and more sensitive than isolation and the IF test in the diagnosis of acute Q fever when a single acute-phase serum was available. These findings suggest that C. burnetii is an important cause of atypical pneumonia in children in Japan.