Outbreak of respiratory tract infections on an islet in Korea: possible Chlamydia pneumoniae infection.

In March 2004, we experienced an outbreak of Chlamydia pneumoniae infection on an islet of Korea. In order to assess the significance of the epidemic, we performed a mass examination of 137 students (7-16 years old; male, 69; female, 58) at a school. The examination consisted of a questionnaire inquiring about respiratory symptoms, a serum antibody test for C. pneumoniae using a microimmunofluorescence (MIF) method and enzyme-linked immunosorbent assay (ELISA), and nasopharyngeal swab tests to detect of the organism by specific PCR and cell culture. The results demonstrated that 72 (58.3%) of the students had respiratory symptoms such as rhinorrhea, a sore throat, and/or cough or fever. The PCR positivity of acute-phase patients was 63% (12/19) and PCR positivity using the culture sample was 94% (18/19). However, the existence of the organism was not confirmed fluorescein isothiocyanate (FITC). ELISA, one of the serological methods utilized, demonstrated, in the same patients, 48% (13/27) positive IgM antibodies at the acute phase of the outbreak, and 16% (3/19) positive IgM antibodies during the convalescent phase. The index value (ID) 3.0 for single-sera IgG was 19% (5/27) and that for IgA was 4% (1/27) at the acute phase; the corresponding percentages in the convalescent phase were 11% (2/19) and 5% (1/19), respectively. However, as regards paired sera, no patient demonstrated a 1.35 ELISA ID value at 2 weeks, or an increased value of 1.0 at 8 weeks after the onset of the outbreak. In the MIF experiment, the percent positivity of unpaired IgM from the acute phase was 58% (11/19). At convalescent phase, this percentage was 47% (9/19); however, the positivity of paired serum IgG was 26% (5/19). In the same sample, the percentage of positive cases demonstrated by both ELISA and MIF approaches for single IgM was 37% (7/19) at the acute phase and 11% (2/19) at the convalescent phase. We were unable to isolate C. pneumoniae by cell culture, but we did obtain sufficient serological and PCR data to consider C. pneumoniae as the causative agent of the outbreak. Meaningful results were acquired in terms of serology, and were compared to the healthy population in Korea. Although it remains necessary to investigate the possibility of co-infection and to determine whether or not this outbreak coincides with the prevalence of influenza, it was unequivocally concluded that this outbreak of C. pneumoniae infection has occurred on an islet of Korea.