Clinical Evaluation of Gen-Probe's Amplified Mycobacterium Tuberculosis Direct Test for Rapid Diagnosis of Mycobacterium tuberculosis in Egyptian Children at Risk for Infection

Abstract

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. 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. 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-Guérin 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. 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%. 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.