Distribution of Antibodies to Coxiella burnetii in Patients with Unknown Fever and Atypical Pneumonia

ABSTRACT

Coxiella burnetii is the causative agent of Q fever worldwide in human and animals. While several clinical cases of Q fever were reported in Korea till the middle of 1990s, nobody has reported a case thereafter. However possibilities for an outbreak have still been raised. In this study, antibody titers to C. burnetii in patients with unknown fever and atypical pneumonia were tested by an indirect immunofluorescence method using the phase II antigen. In addition, the validity of a PCR method in indentifying C. burnetii directly from human sera was tested. Among the 560 specimens from atypical pneumonia patients, 23 sera (4.29%) reacted positively to the phase II antigen of C. burnetii. IgG antiphase II antigen titers were 116 in 16, 132 in 2, 164 in 2, 1128 in 2, and > or =1256 in one serum. IgM and IgA antibodies anti-phase II antigen were detected in 6 and 3 sera at 116, respectively. And each two sera had IgM antibodies at 132 and 164. Anti-phase II antigen IgG antibody titers in the patients with unknown fever were 116 in 5, 132 in 2, 1128 in 1, and 1256 in 3 sera. However, IgM antibody wasn't detected in this group. Of the 202 sera from abattoir workers, 5 (2.47%) reacted with phase II antigen. Among 448 sera of healthy controls, anti-phase II antigen IgG titer of 116 was found in 7 and 132 in 1 and 164 in 3 sera. In the case of IgM titer, two sera were reactive at 116 and 132, each. Significant differences among the test groups were not noted in the present study. The PCR assay to detect C. burnetii com-1 and plasmid genes did not show reliable specificity and sensitivity for the diagnosis of Q fever. So, the usefulness of the PCR for laboratory diagnosis of Q fever still remains controversial.