Performance of GeneXpert MTB/RIF for diagnosing tuberculosis among symptomatic household contacts of index patients in South Africa

Background We describe the performance of GeneXpert MTB/RIF (Xpert) for diagnosing tuberculosis (TB) among symptomatic household contacts (HHCs) of rifampicin-resistant and drug-sensitive index cases. Methods We conducted a cross-sectional study among HHCs of recently diagnosed (<2 weeks) smear-positive and Xpert-positive index cases in the Bojanala District, South Africa. The HHCs were screened for TB symptoms; persons with ≥1 TB symptom provided 1 sputum for smear microscopy, Xpert, and mycobacterial growth indicator tube (MGIT) culture. Diagnostic test performance of Xpert was determined using MGIT as the reference standard. Results From August 2013 to July 2015, 619 HHCs from 216 index cases were enrolled: 60.6% were female, median age was 22 years (interquartile range, 9-40), and 126 (20.4%) self-reported/tested human immunodeficiency virus positive. A total of 54.3% (336 of 619) of contacts had ≥1 TB symptom (cough, fever, night sweats, weight loss), 297 of 336 (88.4%) of which provided a sputum; 289 (97.3%) had complete testing and 271 were included in the analysis. In total, 42 (6.8%) of 619 HHCs had microbiologically confirmed TB. The MGIT identified 33 HHCs as positive for Mycobacterium tuberculosis; of these, 7 were positive on Xpert resulting in a sensitivity of 21.2% (95% confidence interval [CI], 9.0-38.9), specificity of 98.3% (95% CI, 95.6-99.5), positive predictive value of 63.6% (95% CI, 30.8-89.1), and negative predictive value of 90.0 (95% CI, 85.7-93.4). Conclusions Among symptomatic HHCs investigated for TB, Xpert performed suboptimally compared with MGIT culture. The poor performance of Xpert for diagnosing TB suggests that a more sensitive test, such a Xpert Ultra or culture, may be needed to improve yield of contact investigation, where feasible.