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. 2021 Jan 19;8(4):ofab025.
doi: 10.1093/ofid/ofab025. eCollection 2021 Apr.

Performance of GeneXpert MTB/RIF for Diagnosing Tuberculosis Among Symptomatic Household Contacts of Index Patients in South Africa

Kavindhran Velen  1 , Laura J Podewils  2 , N Sarita Shah  3 , James J Lewis  4   5 , Tiro Dinake  1 , Gavin J Churchyard  1   6 , Mary Reichler  7 , Salome Charalambous  1   6
Affiliations

Performance of GeneXpert MTB/RIF for Diagnosing Tuberculosis Among Symptomatic Household Contacts of Index Patients in South Africa

Kavindhran Velen et al. Open Forum Infect Dis. .

Abstract

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.

Keywords: GeneXpert MTB/RIF; TB disease; household contacts; mycobacterial culture.

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Figures

Figure 1.
Figure 1.
Flow diagram of Xpert MTB/RIF and mycobacterial growth indicator tube (MGIT) culture testing results. HH, household; MTB, Mycobacterium tuberculosis.
Figure 2.
Figure 2.
Distribution of time to culture positivity for each of the 33 culture-positive tuberculosis cases.
See this image and copyright information in PMC

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