Performance of stool Xpert MTB/RIF Ultra for detection of Mycobacterium tuberculosis among adults living with HIV: a multicentre, prospective diagnostic study

Abstract

Background: When people living with HIV develop pulmonary tuberculosis, it often manifests without detectable acid-fast bacilli on sputum microscopy. We aimed to assess the diagnostic accuracy of stool Xpert MTB/RIF Ultra (hereafter, Ultra) for Mycobacterium tuberculosis detection among adults with HIV.

Methods: This multicentre, prospective diagnostic accuracy study was done in outpatient and inpatient health centres in Eswatini, Mozambique, and Uganda. We enrolled adults aged 15 years and older with HIV with presumptive tuberculosis. We evaluated the diagnostic accuracy of stool Ultra using the simple one-step processing method against a composite microbiological reference standard (CMRS) including three WHO-recommended tuberculosis diagnostic tests (urine tuberculosis biomarker-based lateral-flow lipoarabinomannan [TB-LAM], sputum Ultra, and sputum culture), and stratified by CD4 cell count. We compared sputum versus stool Ultra performance against a composite reference standard of TB-LAM and sputum culture (CMRS2). We also calculated the diagnostic yield among all tested. This study is registered with ClinicalTrials.gov, NCT05047315.

Findings: Between Dec 2, 2021, and Aug 14, 2024, 677 participants were enrolled (247 [36%] men and 430 [64%] women). Tuberculosis was microbiologically confirmed in 119 participants by the CMRS: 39 (33%) had a positive test with sputum Ultra, 30 (25%) had a positive test with culture, and 84 (71%) had a positive test with urine TB-LAM. The sensitivity of stool Ultra compared with CMRS was 23·7% (28/118 [95% CI 16·4-32·4]) and the specificity was 94·0% (504/536 [91·7-95·9]). The sensitivity of stool Ultra in participants with CD4 counts less than or equal to 200 cells per μL was 45·5% (10/22 [24·4-67·8]) compared with 21·3% (17/80 [12·9-31·8]) in those with CD4 counts greater than 200 cells per μL. Against the CMRS2, we observed no differences in sensitivity between sputum and stool Ultra on the basis of CD4 cell count. Stool Ultra resulted in additional cases detected of 23% (30/133) compared with sputum Ultra, 29% (38/133) compared with sputum culture, and 33% (44/133) compared with TB-LAM. The overall diagnostic yield for all treated for stool Ultra was 9% (60/677), for TB-LAM was 12% (84/677), for sputum Ultra was 6% (39/677), and for sputum culture was 4% (30/677).

Interpretation: These results suggest stool Ultra could be used as an additional test for tuberculosis diagnosis among people with HIV, particularly among those with CD4 counts less than 200 cells per μL.

Funding: EDCTP2 and EDCTP3 Programmes supported by the EU.

Figure 1:. Trial profile

CMRS=composite microbiological reference standard. CMRS2=CMRS of sputum culture and urine TB-LAM. NTM=non-tuberculous mycobacteria. TB=LAM=tuberculosis biomarker-based lateral-flow lipoarabinomannan. Ultra=Xpert MTB/RIF Ultra.

Figure 2:. Diagnostic performance of stool Ultra compared with CMRS, sputum Ultra, sputum culture, and urine TB-LAM

*Participants with sputum and stool Ultra trace result were recategorised as negative. †Participants with sputum and stool Ultra trace results or with tuberculosis treatment history were recategorised as negative. CMRS=composite microbiological reference standard. TB-LAM=tuberculosis biomarker-based lateral-flow lipoarabinomannan. FN=false negatives. FP=false positives. TN=true negatives. TP=true positives. Ultra=Xpert MTB/RIF Ultra.

Figure 3:. Venn diagrams showing the distribution of positive test results

(A) Distribution of positive results detected by the index text (stool Ultra) and the three microbiological reference tests of sputum Ultra, sputum culture, and urine TB-LAM (n=133), excluding participants missing a valid result for any of the assays. (B) Distribution of positive results detected by only the three reference tests of sputum Ultra, sputum culture, and urine TB-LAM (n=106), excluding participants missing a valid result for any of the assays. TB-LAM=tuberculosis biomarker-based lateral-flow lipoarabinomannan. Ultra=Xpert MTB/RIFT Ultra.

Figure 4:. Diagnostic yield among all tested of stool Ultra, sputum culture, sputum Ultra, and urine TB-LAM

Diagnostic yield among all tested is defined as the proportion of people in whom a diagnostic test identifies tuberculosis among all people for whom testing is attempted. TB-LAM=tuberculosis biomarker-based lateral-flow lipoarabinomannan. Ultra=Xpert MTB/RIF Ultra.