Variation in the observed effect of Xpert MTB/RIF testing for tuberculosis on mortality: a systematic review and analysis of trial design considerations

Background: 

Most studies evaluating the effect of Xpert MTB/RIF testing for tuberculosis (TB) concluded that it did not reduce overall mortality compared to usual care. We conducted a systematic review to assess whether key study design and execution features contributed to earlier identification of patients with TB and decreased pre-treatment loss to follow-up, thereby reducing the potential impact of Xpert MTB/RIF testing.

Methods: 

We searched the Cochrane Central Register of Controlled Trials (CENTRAL), MEDLINE, and Scopus for literature published from 1st January 2009 to February 2019. We included all primary intervention studies that had evaluated the effect of Xpert MTB/RIF on mortality compared to usual care in participants with presumptive pulmonary TB. We critically reviewed features of included studies across: Study setting and context, Study population, Participant recruitment and enrolment, Study procedures, and Study follow-up.

Results: 

We included seven randomised and one non-randomised study.  All included studies demonstrated relative reductions in overall mortality in the Xpert MTB/RIF arm ranging from 6% to 40%. However, mortality reduction was reported to be statistically significant in two studies. Study features that could explain the lack of observed effect on mortality included: the higher quality of care at study sites; inclusion of patients with a higher pre-test probability of TB leading to higher than expected empirical rates; performance of additional diagnostic testing not done in usual care leading to increased TB diagnosis or empiric treatment initiation; the recruitment of participants likely to return for follow-up; and involvement of study staff in ensuring adherence with care and follow-up.

Conclusion: 

Most studies of Xpert MTB/RIF were designed and conducted in a manner that resulted in more patients being diagnosed and treated for TB, minimising the potential difference in mortality Xpert MTB/RIF testing could have achieved compared to usual care.