An evaluation study on phenotypical methods and real-time PCR for detection of Mycobacterium tuberculosis in sputa of two health centers in Iran

For further confirmation of the previous in-house real-time PCR and CYP 141 target as a rapid and cheap diagnostic technique and a new target for direct detection of Mycobacterium tuberculosis, we evaluated and compared the results of smear, culture and real-time PCR in sputa that were collected from 2 health centers. Moreover we tried to evaluate the diagnostic accuracy of phenotypical methods for detection of tuberculosis that have been applied in two health centers of Iran.
Thirty two sputa (including 15 smear positive and 17 smear negative) and 53 Sputa (29 smear and culture positive and 24 smear and culture negative specimens) were collected from tuberculosis suspected patients from health center No. 1 and 2 respectively. A Taqman probe was used for direct detection of M. tuberculosis using the specific primers.
Because of the results, data of health center No. 1 was not reliable. The average number of bacteria that was detected in health center No. 2 by real time PCR was 1.2E퍍7.3퍎; 1.4E퍎1.29퍎 and 8.27E퍎1.07퍎 for one to three plus smear result groups, respectively. The overall sensitivity, specificity, positive predictive value (PPV) and negative predictive value (NPV) of real-time PCR were 96.5% (28/29), 95.8% (23/24), (96.6%) and (96%), respectively.
Compared with the results of previous studies and being a good correlation between real-time PCR and phenotypic methods, emphasize that CYP141 is a good target for quantification of M. tuberculosis in sputa and real-time PCR can be a good method for evaluation of smear microscopy. Moreover, further surveillance is needed to evaluate the phenotypical methods and final decisions that are taken in health centers of Iran that can be observed and evaluated by the cheap molecular methods like in-house methods.