ABSTRACT
BACKGROUND: Chlamydia pneumoniae causes a variety of respiratory infections and is involved in cardiovascular diseases. Diagnosis of C. pneumoniae infection currently relies on antibody detection by microimmunofluorescence (MIF), which has limited use, and is the retrospective diagnosis for acute infection. OBJECTIVE: Find an effective early diagnosis of acute upper respiratory infection, or use in combination with MIF to accurately diagnose the infection by C. pneumoniae. MATERIAL AND METHOD: Direct immunofluorescence (DIF) was developed to detect C. pneumoniae in nasopharyngeal specimens obtained from patients with upper respiratory tract infection, and normal individuals. IgM and IgG antibodies against C. pneumoniae by MIF were determined for evaluation of the detected C. pneumoniae and seroconversion. RESULTS: DIF gave positive results in 29 of 37 (78.4%) samples from 31 patients. Fifteen samples positive by DIF illustrated antibody titers interpreted as acute C. pneumoniae infection, and eight DIF positive samples showed antibody titers of chronic infection. Negative results by both DIF and MIF were found in two patients and 23 of 25 by DIF but 20 of 25 by MIF in normal subjects. Five paired sera subsequently collected from three of the 31 patients illustrated seroconversion 2-4 months after the primary specimen collection, which gave positive results by DIF but negative for antibodies. Significant association was found between C. pneumoniae detection by DIF and antibodies by MIF when analysis was done in the group of patients and normal subjects (p < 0.001; Pearson chi-square test). CONCLUSION: DIF could be an alternative assay for early diagnosis of C. pneumoniae infection, and may be used in combination with MIF for accurate diagnosis of acute C. pneumoniae infection.