Diagnosis of chlamydia pneumoniae respiratory infection by cell culture compared with nested touchdown polymerase chain reaction and microimmunoflourescence

ABSTRACT

Chlamydia pneumoniae is a common cause of respiratory tract infection and community acquired pneumonia. This work was designed to evaluate different diagnostic methods with different types of samples for diagnosis of C. pneumoniae infection. The study included 50 subjects, classified into two groups; the patients group included 40 patients; 25 males and 15 females presented with different pulmonary lesions, their ages ranged from 17 to 70 years with mean+/-SD of 47.75 +/-14.3 and 10 age and sex matched apparently healthy individuals served as controls. All patients and control were subjected to the following investigations; Hep-2 cell culture followed by detection of C. pneumoniae by immunofluorescence, polymerase chain reaction [PCR] to detect C. pneumoniae DNA and microimmunofluorescence [MIF] to detect C. pneumoniae antibodies [IgG and IgM]. The study results showed that 28 patients were diagnosed positive for C. pneumoniae by PCR compared with 17 positive by Hep-2 cell culture and 17 positive by MIF. There were 8 patients showed positive results by the three methods, 9 were positive by Hep-2 cell culture and PCR techniques, 8 were positive by PCR and MIF techniques, three were positive by PCR only and one patient showed positive IgM antibodies. All the 17 culture positive samples in this study were detected by PCR which emphisizes the high sensitivity of PCR. In addition, 11 of the culture negative samples were positive by PCR and 8 of these were confirmed by MIF technique. Three cases that were positive by PCR could not be confirmed by MIF. When we used the results of cell culture technique as a gold standard test and compared with those of PCR and MIF the sensitivity of PCR was 100%, while the sensitivity of MIF was 47.1%. The specificity of PCR was low 52.2% while that of MIF was 60.9%. The positive predective value, negative predective value, and accuracy of PCR were 60.7%, 100% and 72.5% respectively while those of MIF were 47.1% 60.9% and 55%. The positive results of C. pneumoniae infection were increased in sputum samples than nasopharyngeal swabs 60% versus 40% by cell culture and 90 % versus 70 % by PCR. From this study, we can conclude that although cell culture is frequently taken as the gold standard test in microbiological practice; this may not be valid with organisms that are difficult to grow as C. pneumoniae. MIF is of value as a complement to the C. pneumonia detection methods to distinguish acute infection from pre-existing infection. When sputum samples can be obtained, are superior to nasopharyngeal swabs. As a final point, PCR is a rapid and sensitive technique, and we suggest that PCR can be used along with another diagnostic method for prompt diagnosis