Xpert MTB/RIF Ultra versus Xpert MTB/RIF for the diagnosis of tuberculous meningitis: a prospective, randomised, diagnostic accuracy study

Abstract

Background: Xpert MTB/RIF Ultra (Xpert Ultra) might have higher sensitivity than its predecessor, Xpert MTB/RIF (Xpert), but its role in tuberculous meningitis diagnosis is uncertain. We aimed to compare Xpert Ultra with Xpert for the diagnosis of tuberculous meningitis in HIV-uninfected and HIV-infected adults.

Methods: In this prospective, randomised, diagnostic accuracy study, adults (≥16 years) with suspected tuberculous meningitis from a single centre in Vietnam were randomly assigned to cerebrospinal fluid testing by either Xpert Ultra or Xpert at baseline and, if treated for tuberculous meningitis, after 3-4 weeks of treatment. Test performance (sensitivity, specificity, and positive and negative predictive values) was calculated for Xpert Ultra and Xpert and compared against clinical and mycobacterial culture reference standards. Analyses were done for all patients and by HIV status.

Findings: Between Oct 16, 2017, and Feb 10, 2019, 205 patients were randomly assigned to Xpert Ultra (n=103) or Xpert (n=102). The sensitivities of Xpert Ultra and Xpert for tuberculous meningitis diagnosis against a reference standard of definite, probable, and possible tuberculous meningitis were 47·2% (95% CI 34·4-60·3; 25 of 53 patients) for Xpert Ultra and 39·6% (27·6-53·1; 21 of 53) for Xpert (p=0·56); specificities were 100·0% (95% CI 92·0-100·0; 44 of 44) and 100·0% (92·6-100·0; 48 of 48), respectively. In HIV-negative patients, the sensitivity of Xpert Ultra was 38·9% (24·8-55·1; 14 of 36) versus 22·9% (12·1-39·0; eight of 35) by Xpert (p=0·23). In HIV co-infected patients, the sensitivities were 64·3% (38·8-83·7; nine of 14) for Xpert Ultra and 76·9% (49·7-91·8; ten of 13) for Xpert (p=0·77). Negative predictive values were 61·1% (49·6-71·5) for Xpert Ultra and 60·0% (49·0-70·0) for Xpert. Against a reference standard of mycobacterial culture, sensitivities were 90·9% (72·2-97·5; 20 of 22 patients) for Xpert Ultra and 81·8% (61·5-92·7; 18 of 22) for Xpert (p=0·66); specificities were 93·9% (85·4-97·6; 62 of 66) and 96·9% (89·5-91·2; 63 of 65), respectively. Six (22%) of 27 patients had a positive test by Xpert Ultra after 4 weeks of treatment versus two (9%) of 22 patients by Xpert.

Interpretation: Xpert Ultra was not statistically superior to Xpert for the diagnosis of tuberculous meningitis in HIV-uninfected and HIV-infected adults. A negative Xpert Ultra or Xpert test does not rule out tuberculous meningitis. New diagnostic strategies are urgently required.

Funding: Wellcome Trust and the Foundation for Innovative New Diagnostics.

Figure 1

Trial profile Xpert Ultra=Xpert MTB/RIF Ultra. Xpert=Xpert MTB/RIF.

Figure 2

Positive mycobacterial tests in individuals with at least one confirmatory test for tuberculous meningitis 168 positive mycobacterial tests (25 positive by Xpert Ultra, 21 by Xpert, 77 by Ziehl–Neelsen smear, and 45 by MGIT) from 82 patients with a diagnosis of definite tuberculous meningitis. MGIT=mycobacteria growth indicator tube. Xpert Ultra=Xpert MTB/RIF Ultra. Xpert=Xpert MTB/RIF.

Figure 3

Comparison of the diagnostic sensitivities of Xpert Ultra and Xpert between baseline and testing after 4 weeks of antituberculosis treatment Data shown for 49 patients (27 Xpert Ultra, 22 Xpert) undergoing both baseline and follow-up CSF sampling. All cases with a positive nucleic acid amplification test at follow-up testing (n=8) were positive at baseline testing. Xpert Ultra=Xpert MTB/RIF Ultra. Xpert=Xpert MTB/RIF.