ABSTRACT
BACKGROUND: Chlamydia pneumoniae has recently been established as an important cause of acute respiratory tract infections such as pneumonia and bronchitis in humans. We introduced a 'touchdown' PCR method for detection of C. pneumoniae from sputum. METHODS: A total of 474 patients with respiratory infection were enrolled in the study. The sputum samples were tested for C. pneumoniae by the 'touchdown' PCR and cultured for Chlamydia. The sputum samples were pretreated with 5% NaOH for mucolysis. In 'touchdown' PCR, the first round PCR amplified DNA from both C. pneumoniae and Chlamydia psittaci, while the second round specifically targeted C. pneumoniae, allowing the two species to be differentiated. RESULTS: The 'touchdown' PCR could detect 10-2 inclusion forming unit (IFU) in the 1st round and 10-3 IFU in the second round PCR. None of the C. trachomatis serovars, C. psittaci and other organisms tested was amplified. 'Touchdown' PCR detected C. pneumoniae DNA in 24 (5%) of the 474 sputum samples. Nine patients with C. pneumoniae had community acquired pneumonia. Another nine patients had pulmonary tuberculosis of which three had coexisting pneumonia. Two patients had lung cancer, another two had chronic bronchitis, one had pharyngitis, and one person was a normal healthy individual. CONCLUSIONS: The sputum preparation with 5% NaOH and the 'touchdown' PCR method are effective in the detection of C. pneumoniae. C. pneumoniae is one of the most common causative agents for pulmonary infection.