Early diagnosis plays a vital role in controlling tuberculosis. The conventional methodology is slow, with results taking several weeks, in addition to having low sensitivity, especially in clinical paucibacillary samples. The objective of this study was to evaluate the use of polymerase chain reaction (PCR) on solid medium culture for a rapid diagnosis of tuberculosis, mainly in cases of negative sputum smears. Forty sputum samples were collected from inpatients with tuberculosis treated for less than 2 days. Bacilloscopy, PCR for sputum, culture on Löwestein-Jensen (LJ) solid medium, and daily PCR from culture were performed on each sample. DNA extracted from the BCG vaccine, which contains attenuated bacillus Calmette-Guérin, was used as the positive control. Smear microscopy showed 68.6% sensitivity, 80% specificity, 96% positive predictive value, and 26.7% negative predictive value, with culture on LJ medium as the gold standard. Culture at day 28 showed 74.3% sensitivity and 100% specificity. PCR of DNA extracted from sputum amplified a 1027-bp fragment of the 16s RNA gene, showing 22.9% sensitivity and 60% specificity. PCR performed with DNA extracted from daily culture showed that, from the 17th to the 40th day, the sensitivity (85.7%) and specificity (60%) were constant. We conclude that a 17-day culture is a good choice for rapid diagnosis and to interfere with the transmission chain of tuberculosis.
Tuberculosis; Mycobacteria; PCR
