تشخيص سل ريوي توسط روش PCR
Background: Tuberculosis is a major world health problem mainly in the developing countries. Early isolation of infected patients and application of chemotherapy are the main prevention strategies for tuberculosis control. Although acid-fast stained smears and culture of M.tuberculosis are the standard procedures of diagnosis, they are low in sensitivity and time consuming, respectively. Polymerase chain reaction (PCR) technique has simplified and boosted the direct detection of M.tuberculosis in a significantly shorter time than two conventional methods mentioned.
Materials and Methods: In this study, which was conducted in 9 months, 211 clinical samples were collected from patients with suspected M.tuberculosis complex who had referred to NRITLD. They were tested by PCR assay, culture technique and Ziehl-Neelsen staining. Two pair oligonucleotides were used in PCR assay, detecting 245bp of IS6110 sequence. Results of PCR assay were compared with those of culture technique.
Results: One-hundred and forty five samples (68.7%) were sputum and the other 66 samples (31.3%) were bronchoscopy lavage. Twenty-five samples (11.8%) were positive by PCR assay out of which 21 (84%) were culture positive too.176 from 186 samples with PCR negative results were culture negative too. These 10 samples were examined for PCR inhibitor and identification of M.tuberculosis. Twenty percent (2 samples) of these had PCR inhibitor and 20% (2 samples) were not M.tuberculosis complex. Based on this study, after excluding the samples which had PCR inhibitor and non-tuberculosis complex, sensitivity and specificity of PCR assay in comparison with results of culture and Ziehl-Neelsen staining (as a gold standard) were 93.3% and 98.3%, respectively. Positive and negative predictive values were 84% and 94.6%, respectively.
Conclusion: This study showed that there are no significant differences between cultures and PCR methods. For this reason, we can use PCR assay for direct detection of DNA from M.tuberculosis in clinical samples.