Clinical evaluation of Gen-Probe's amplified mycobacterium tuberculosis direct test for rapid diagnosis of Mycobacterium tuberculosis in Egyptian children at risk for infection

Context.-Diagnostic detection of tuberculosis (TB) has improved considerably. Available, standardized, nucleic acid-based amplification techniques have been shown to yield reliable results within 4 to 7 hours of sample processing. Objective.-To study the diagnostic performance of Gen-Probe's technique for direct detection of Mycobacterium tuberculosis in comparison with BACTEC 460 TB culture for both positive and negative Ziehl-Neelsen smears in Egyptian children at risk for TB infection. Design.-We prospectively evaluated 50 children from families with a positive history of TB. All patients were referred from outpatient clinics of the Mansoura University Children's Hospital, Egypt. The children had a positive tuberculin skin test with an induration diameter of more than 10 mm and had scars from a bacille Calmette-Guerin vaccination within the past 2 years. Three consecutive sputum samples were taken from each patient. The samples were examined to detect M tuberculosis by means of the Gen-Probe technique, direct smear microscopy, and bacterial culture by BACTEC 460 TB. Results.-Of the 50 cases, 30 (60%) had sputum samples that were positive for TB by BACTEC 460 TB culture, and 29 cases (58%) were positive by the Gen-Probe technique. Sensitivity and specificity of Ziehl-Neelsen smears was 83.3% and 100%, respectively, with overall accuracy of 90%. Sensitivity and specificity of the Gen-Probe technique were 96.7% and 100%, respectively, with overall accuracy of 98%. Conclusions.-The results of this study suggest that the Gen-Probe technique is an accurate method for rapid detection of M tuberculosis complexes in respiratory samples from children at risk for TB. It can be used for diagnosis of smear-negative cases that are suspect for TB.