Evaluation of the xpert MTB/RIF assay at a tertiary care referral hospital in a setting where tuberculosis and hiv infection are highly endemic

Abstract

Background: There were 1.45 million deaths from tuberculosis (TB) in 2011. A substantial proportion of active pulmonary TB cases in countries where tuberculosis, human immunodeficiency virus (HIV) infection, and AIDS are highly endemic remain undiagnosed because of the reliance on sputum-smear microscopy. This study evaluated the performance of the Xpert MTB/RIF assay at a tertiary care referral center in Zambia, a country where the burden of TB and HIV infection is high.Methods: A total of 881 adult inpatients admitted to University Teaching Hospital in Lusaka who were able to produce sputum were enrolled and analyzed in the study, irrespective of admission diagnosis. Sputum specimens were analyzed by fluorescence smear microscopy, the Xpert MTB/RIF assay, mycobacterial growth indicator tube (MGIT) culture, and MGIT drug-susceptibility testing. The sensitivity and specificity of the Xpert MTB/RIF assay were evaluated using culture as the gold standard.Results: Culture-confirmed TB was found in 201 of 881 patients (22.8%). The specificity of the Xpert MTB/RIF assay was 95.0% (95% confidence interval [CI], 92.4%-96.8), and the sensitivity was 86.1% (95% CI, 80.3-90.4%). In sputum smear-negative, culture-positive cases, the assay was 74.7% sensitive (95% CI, 64.6%-82.8%), identifying 71 additional TB cases that were not detected by smear microscopy. A total of 18 of 111 patients with TB who were tested (16.2%) had multidrug-resistant (MDR) TB. The sensitivity and specificity of the Xpert MTB/RIF assay for detecting culture-confirmed, rifampicin-resistant TB was 81.3% (95% CI, 53.7-95.0%) and 97.5% (95% CI, 90.4-99.6%), respectively.Conclusions: The Xpert MTB/RIF assay performs better than smear microscopy in an inpatient setting in a country where TB and HIV infection are highly endemic. Assessment of its usefulness and cost-effectiveness for increased detection of TB cases missed by sputum smear and for concomitant screening for MDR TB among adult inpatients attending tertiary care referral centers in other countries with a high burden of TB and HIV infection is warranted. © 2012 Published by Oxford University Press on behalf of the Infectious Diseases Society of America. All rights reserved.