An epidemic of a pertussis-like illness caused by Chlamydia pneumoniae

Background. Between June and July, 1994, we encountered an epidemic of a pe rtussis-like illness in adolescents in a junior high school located in a ru ral area of Japan. The purposes of this study were to record the clinical m anifestations and to identify an etiology, Patients and methods. We interviewed patients and parents and we performed physical examinations on patients with cough during the epidemic. The chest radiographs were also reviewed by us. To identify an etiology we performed culture and serologic studies for a variety of bacteria, Mycoplasma, chlam ydiae and viruses. Polymerase chain reaction (PCR) for Chlamydia pneumoniae was carried out on throat swab specimens, Results. Of a total of 230 students 136 (59%) had severe cough illnesses. O ne developed pneumonia, 9 had bronchitis and the remaining 126 (93%) presen ted upper respiratory tract infections (URI), The mean duration of cough in cases with URI was 17.4 days and that in cases with bronchitis and pneumon ia was 30.4 days. Serology and/or cultures for Bordetella pertussis, Bordet ella parapertussis, Mycoplasma pneumoniae, Chlamydia trachomatis, Chlamydia psittaci or viruses were negative. Detection of C. pneumoniae infection wa s carried out in 46 patients with pneumonia, bronchitis or URI by serology and PCR, The patient with pneumonia, 7 of 7 patients with bronchitis and 32 (84%) of 38 patients with URI were documented to be infected by C. pneumon iae either by serology, PCR or both tests. Conclusion. An epidemic of a pertussis-like illness in a junior high school population was caused by C. pneumoniae.