Clinical characteristics that portend a positive Xpert Ultra test result in patients with pleural tuberculosis.

BACKGROUND: The performance of Xpert-MTB/RIF, including the newer Xpert Ultra test, for the diagnosis of pleural TB is poor (~28 - 38%). There are no data on patient characteristics that portend a positive Xpert-Ultra test in pleural fluid. These characteristics could be useful for selecting patients for Xpert-Ultra testing, thus maximising benefits of a positive test, while minimising cost. OBJECTIVES: To determine the clinical, radiological, microbiological and biochemical characteristics associated with Xpert-Ultra positivity in patients with suspected pleural tuberculosis. METHODS: We performed a subgroup analysis of a prospective observational cohort (N=165 patients with suspected pleural TB) evaluating same-day diagnostic tools for pleural tuberculosis. Forty-nine patients with confirmed pleural tuberculosis (culture and/or histology) were included in the final analysis. RESULTS: Of the 49 participants, 17 (35%) were female and 9 (18.4%) were HIV-infected. In the multivariate analysis including demographic, radiological and pleural fluid test characteristics, there were no independent predictors of Xpert-Ultra positivity. However, when pleural fluid test results were excluded, and when only rapidly ascertainable pre-test factors (demographic and radiologic variables) were considered, the multivariable analysis showed that only a chest X-ray (CXR) suggestive of active TB (cavities, consolidation and hilar lymphadenopathy) was associated with Xpert-Ultra positivity (p=0.021). Notably, only 22% (n=11/49) of the participants had a CXR suggestive of active TB and of these, 73% (n=8/11) had a positive Xpert-Ultra result. CONCLUSION: CXR features suggestive of active TB are significantly associated with a positive Xpert-Ultra test result on pleural fluid. These data inform clinical practice in resource-poor settings.

Diagnostic accuracy of induced sputum LAM ELISA for tuberculosis diagnosis in sputum-scarce patients.

OBJECTIVE: To examine whether a lipoarabinomannan (LAM) enzyme-linked immunosorbent assay (ELISA) that offers diagnostic utility using urine in patients with tuberculosis (TB) and human immunodeficiency virus (HIV) co-infection can be used in induced sputum to diagnose sputum-scarce patients with suspected TB. DESIGN: LAM was measured in induced sputum samples obtained from 61 consecutively recruited sputum-scarce TB suspects in a tertiary hospital respiratory clinic in South Africa. Liquid culture positivity for Mycobacterium tuberculosis was used as the reference standard. Receiver operating characteristic analysis was used to assess alternative LAM concentration cut-offs. RESULTS: A total of 87% (53/61) of study patients had a valid M. tuberculosis culture result; 49% (23/53) were HIV-infected and 17% (9/53) were culture-positive for M. tuberculosis. Induced sputum smear microscopy and LAM ELISA had an overall sensitivity of 56% (95%CI 27-81); however, the specificity of LAM ELISA was 48% (95%CI 34-62), while the positive and negative predictive values were respectively 18% (95%CI 8-36) and 84% (95%CI 65-94). An optimal rule-in cut-off selected by receiver operating characteristic (LAM concentration >5.73 ng/ml) increased test specificity to 98% and reduced sensitivity to 22%. Normalisation of the assay for sample total protein or cell count did not improve diagnostic accuracy. CONCLUSIONS: In this proof-of-concept study, the ELISA was not clinically useful for TB diagnosis using induced sputum.

Are interferon-γ release assays useful for diagnosing active tuberculosis in a high-burden setting?

Although interferon-γ release assays (IGRAs) are intended for diagnosing latent tuberculosis (TB), we hypothesised that in a high-burden setting: 1) the magnitude of the response when using IGRAs can distinguish active TB from other diagnoses; 2) IGRAs may aid in the diagnosis of smear-negative TB; and 3) IGRAs could be useful as rule-out tests for active TB. We evaluated the accuracy of two IGRAs (QuantiFERON®-TB Gold In-tube (QFT-GIT) and T-SPOT®.TB) in 395 patients (27% HIV-infected) with suspected TB in Cape Town, South Africa. IGRA sensitivity and specificity (95% CI) were 76% (68-83%) and 42% (36-49%) for QFT-GIT and 84% (77-90%) and 47% (40-53%) for T-SPOT®.TB, respectively. Although interferon-γ responses were significantly higher in the TB versus non-TB groups (p<0.0001), varying the cut-offs did not improve discriminatory ability. In culture-negative patients, depending on whether those with clinically diagnosed TB were included or excluded from the analysis, the negative predictive value (NPV) of QFT-GIT, T-SPOT®.TB and chest radiograph in smear-negative patients varied between 85 and 89, 87 and 92, and 98% (for chest radiograph), respectively. Overall accuracy was independent of HIV status and CD4 count. In a high-burden setting, IGRAs alone do not have value as rule-in or -out tests for active TB. In smear-negative patients, chest radiography had better NPV even in HIV-infected patients.

High prevalence of smoking among patients with suspected tuberculosis in South Africa.

There is growing evidence that tobacco smoking is an important risk factor for tuberculosis (TB). There are no data validating the accuracy of self-reported smoking in TB patients and limited data about the prevalence of smoking in TB patients from high-burden settings. We performed a cross-sectional analysis of 500 patients with suspected TB in Cape Town, South Africa. All underwent comprehensive diagnostic testing. The accuracy of their self-reported smoking status was determined against serum cotinine levels. Of the 424 patients included in the study, 56 and 60% of those with active and latent TB infection (LTBI), respectively, were current smokers. Using plasma cotinine as a reference standard, the sensitivity of self-reported smoking was 89%. No statistically significant association could be found between smoking and active TB or LTBI. In Cape Town, the prevalence of smoking among patients with suspected and confirmed TB was much higher than in the general South African population. Self-reporting is an accurate measure of smoking status. These results suggest the need to actively incorporate tobacco cessation programmes into TB services in South Africa.

Comparison of same day versus delayed enumeration of TB-specific T cell responses.

BACKGROUND/OBJECTIVE: Flexibility in sample processing may improve test utility of the quantitative antigen-specific T cell assay (T-SPOT.TB). We investigated whether delayed sample processing with and without the use of T-Cell Xtend, a proprietary reagent, impacted upon test accuracy. METHODS: Blood samples obtained from 363 sequentially recruited tuberculosis suspects or treated patients were processed immediately (day 0) and at different times after receipt of the sample [approximately 24-h (day 1) or approximately 32-h (day 2)] with and without adding T-Cell Xtend. RESULTS: T-Cell-Xtend-independent median ELISPOT counts (spot forming cells per million peripheral blood mononuclear cells) were significantly higher at day 1 versus day 0 (114 vs. 100; n=66; p=0.03); inter-time-point agreement between the results was 95.45% and the conversion/reversion rate was 4.55%. By contrast, counts on day 0 without T-Cell Xtend versus day 1 with T-Cell Xtend were similar (56 vs. 56; n=215), inter-time-point agreement between the results was 97.17%, and the conversion/reversion rate was 2.83%. Counts performed at day 2 with T-Cell Xtend were not significantly different from day 0. These findings were independent of HIV status. CONCLUSION: There was high agreement between results when samples were processed immediately and after a 24-h delay. However, although the use of T-Cell Xtend appeared to reduce the number of conversions/reversions this reduction was not statistically significant. Larger studies are required to clarify these findings.

Quantitative lung T cell responses aid the rapid diagnosis of pulmonary tuberculosis.

BACKGROUND: The diagnosis of smear-negative pulmonary tuberculosis (TB) is problematic. There are limited data on the profile of alveolar TB antigen-specific T cells, and their utility for the rapid immunodiagnosis of pulmonary TB is unclear. METHODS: Antigen-specific interferon gamma (IFNgamma) responses to the RD-1 antigens ESAT-6 and CFP-10 (T-SPOT.TB and QuantiFERON-TB-Gold-In-Tube), heparin-binding haemagglutinin and purified protein derivative were evaluated, using alveolar lavage cells, in 91 consecutively recruited South African patients suspected of having TB. RESULTS: Of 85 evaluable patients (29% HIV+), 24, 11, 48 and 2 had definite TB, probable TB, non-TB and an uncertain diagnosis, respectively. Between 34% (T-SPOT.TB) and 41% (QuantiFERON-TB-Gold-In-Tube) of all test results were inconclusive. Failure of the positive control was significantly higher with the QuantiFERON-TB-Gold-In-Tube than with T-SPOT.TB (85% vs 46% of inconclusive results; p = 0.001). Using staphylococcal enterotoxin B, compared with phytohaemagglutinin, substantially reduced failure of the positive control (25% to 3%; p = 0.02). In evaluable samples, when the definite and non-TB groups were used for outcome analysis, the percentage sensitivity, specificity, positive predictive value and negative predictive value for T-SPOT.TB (> or = 20 spots/million alveolar mononuclear cells) and QuantiFERON-TB-Gold-In-Tube (0.35 IU/ml) were 89, 94, 89 and 94% (n = 55) and 55, 86, 77 and 69% (n = 46), respectively. Rapid diagnosis of TB was achieved more frequently with T-SPOT.TB than with smear microscopy (14/24 (58%) vs. 7/24 (29%) of definite TB cases; p = 0.02). Heparin-binding haemagluttinin and purified protein derivative alveolar lymphocyte IFNgamma responses had poor performance outcomes. CONCLUSION: Provided evaluable results are obtained, the RD-1, but not the heparin-binding haemagglutinin or purified protein derivative, alveolar lymphocyte IFNgamma ELISPOT response is a useful rapid immunodiagnostic test for TB. However, test utility in high-burden settings may be limited by the high proportion of inconclusive results.

Utility of quantitative T-cell responses versus unstimulated interferon-{gamma} for the diagnosis of pleural tuberculosis.

The clinical utility of antigen-specific interferon (IFN)-gamma release assays (IGRAs) using pleural mononuclear cells, for the diagnosis of tuberculosis (TB), requires clarification. We compared the diagnostic utility of unstimulated pleural IFN-gamma levels with several pleural antigen-specific T-cell IGRAs (early secretory antigenic target-6 and culture filtrate protein-10 (T-SPOT.(R)TB, QuantiFERON(R)-TB Gold In-tube), purified protein derivative (PPD) and heparin-binding haemagglutinin (HBHA)) in 78 South African TB suspects. Test results were compared against a clinical score and a reference standard. Out of 74 evaluable subjects 48, seven and 19 had definite, probable and no TB, respectively. 11 (15%) out of 74 pleural samples (nine (19%) out of 48 of the definite TB cases) had total cell counts that were inadequate for T-cell processing. In the remaining 63 samples, the sensitivity, specificity, positive predictive value and negative predictive value of different diagnostic methods were as follows. Maximal bioclinical score: 54, 89, 92 and 43%, respectively; T-SPOT.(R)TB: 86, 60, 84 and 64%, respectively; QuantiFERON(R)-TB Gold In-tube: 57, 80, 87 and 44%, respectively; HBHA-specific IGRA: 59, 31, 64 and 27%, respectively; PPD-specific IGRA: 81, 40, 76 and 46%, respectively; and pleural fluid unstimulated IFN-gamma: 97, 100, 100 and 94%, respectively. Unstimulated IFN-gamma was the most accurate test for distinguishing TB from non-TB effusions in a high-burden setting. The antigen-specific T-cell IGRAs were limited by suboptimal accuracy and the inability to isolate sufficient mononuclear cells to perform the assay.