Direct diagnosis ofMycobacterium tuberculosis in blood samples of HIV infected patients by polymerase chain reaction.

We have developed a simple, economical and reproducible method for processing blood samples from HIV infected patients for diagnosis of tuberculosis. The procedure was validated on 55 samples selected for tuberculosis based on clinical criteria. 52 patients had radiological changes indicative of pulmonary tuberculosis of which only 28 were positive for AFB in sputum (sensitivity 54%) and 27 for tuberculin (sensitivity 52%). 26 HIV positive patients who showed positive X-ray did not react to tuberculin. The genus PCR probe missed 3 samples (sensitivity 94%) compared to X-ray.M.tuberculosis was detected in the blood of all X-ray positive cases by PCR using TB400 probe (sensitivity 100%) and another probe forM. tuberculosis, IS6110, missed 6 of them (sensitivity 88% compared to X-ray and 89% compared to TB400). It is proposed that this simple sample processing method could be used to screen all blood samples quickly for mycobacteremia using the genus PCR and only those positive for mycobacteria need to be tested forM.tuberculosis. This would save the scarce resources and time by reducing significantly the number of samples to be screened for species confirmation.