Value of the tuberculin skin testing and of an interferon-gamma release assay in haemodialysis patients after exposure to M. tuberculosis

Pulmonary Tuberculosis and Management of Contact Patients in a Department of Nephrology and Kidney Transplantation

OBJECTIVES

To describe the investigation, follow-up, management and outcomes in a cohort of chronic kidney disease and kidney transplant recipients exposed to a case of pulmonary tuberculosis.

METHODS

Contacts were investigated following a concentric circles approach and followed-up according to their level of priority. In those with an evidence of latent tuberculous infection, treatment decision was based on the level of exposure, individual vulnerability, as well as the results of an interferon-gamma release assay.

RESULTS

130 patients with chronic kidney disease and 180 kidney transplant recipients were identified as contacts and followed-up over a two-year period.Only few vulnerable high-priority contacts received an anti-tuberculosis treatment, including the 2 (100%)highly exposed patients in circle 1, 11/78(14.1%)chronic kidney disease patients and 4/142 (2.8%) kidney transplant recipients in circle 2, and10/52 (19.2%) chronic kidney disease patients and 2/36 (5.6%) kidney transplant recipients in circle 3;all having a positive interferon-gamma release assay result. No incident case of tuberculosis disease occurred.

CONCLUSIONS

These findings suggest that latent tuberculosis treatment, as recommended in European guidelines, might be reasonably avoided in vulnerable high-priority contacts of circle 2 with a negative interferon-gamma release assay in countries with low prevalence of tuberculosis.

Discordance in latent tuberculosis (TB) test results in patients with end-stage renal disease

OBJECTIVES

This natural experiment was designed to assess the impact of exposure to an active case of tuberculosis (TB) on a group of immunosuppressed individuals, with end-stage renal disease over an extended follow-up.

STUDY DESIGN

Close contacts of people with sputum smear-positive Mycobacterium tuberculosis are at high risk of infection, particularly immunosuppressed individuals. An infectious TB healthcare worker worked in a renal dialysis unit for a month before diagnosis, with 104 renal dialysis patients, was exposed for ≥8 h.

METHODS

Patients were informed and invited for screening 8-10 weeks postexposure. They either underwent standard two-step assessment with tuberculin skin test (TST) and QuantiFERON^®-TB Gold (Cellestis GmbH; QFN) interferon-gamma release assay (IGRA) or after consent, enrolled in a study where these two tests were performed simultaneously with T-SPOT^®-TB (Oxford Immunotec Ltd; TSPOT). Patients within the study were followed up for 2 years from exposure, with QFN and TSPOT repeated at months 3 and 6 from the first testing.

RESULTS

Of 104 exposed individuals, 75 enrolled in the study. There was a high degree of discordance among QFN, TSPOT and TST. This was seen at both the first time point and also over time in subjects who were retested. No patients had active TB at the baseline testing. None received treatment for latent TB infection. Over the following 2 years, no one developed TB disease.

CONCLUSION

This study suggests that there is a low risk of progression to active TB in low-incidence countries even in high-risk groups. This plus the degree of the test result discordance emphasises the complexities of managing TB in such settings as it is unclear which of these tests, if any, provides the best diagnostic accuracy.

Accurate diagnosis of latent tuberculosis in children, people who are immunocompromised or at risk from immunosuppression and recent arrivals from countries with a high incidence of tuberculosis: systematic review and economic evaluation

BACKGROUND

Tuberculosis (TB), caused by Mycobacterium tuberculosis (MTB) [(Zopf 1883) Lehmann and Neumann 1896], is a major cause of morbidity and mortality. Nearly one-third of the world's population is infected with MTB; TB has an annual incidence of 9 million new cases and each year causes 2 million deaths worldwide.

OBJECTIVES

To investigate the clinical effectiveness and cost-effectiveness of screening tests [interferon-gamma release assays (IGRAs) and tuberculin skin tests (TSTs)] in latent tuberculosis infection (LTBI) diagnosis to support National Institute for Health and Care Excellence (NICE) guideline development for three population groups: children, immunocompromised people and those who have recently arrived in the UK from high-incidence countries. All of these groups are at higher risk of progression from LTBI to active TB.

DATA SOURCES

Electronic databases including MEDLINE, EMBASE, The Cochrane Library and Current Controlled Trials were searched from December 2009 up to December 2014.

REVIEW METHODS

English-language studies evaluating the comparative effectiveness of commercially available tests used for identifying LTBI in children, immunocompromised people and recent arrivals to the UK were eligible. Interventions were IGRAs [QuantiFERON(®)-TB Gold (QFT-G), QuantiFERON(®)-TB Gold-In-Tube (QFT-GIT) (Cellestis/Qiagen, Carnegie, VA, Australia) and T-SPOT.TB (Oxford Immunotec, Abingdon, UK)]. The comparator was TST 5 mm or 10 mm alone or with an IGRA. Two independent reviewers screened all identified records and undertook a quality assessment and data synthesis. A de novo model, structured in two stages, was developed to compare the cost-effectiveness of diagnostic strategies.

RESULTS

In total, 6687 records were screened, of which 53 unique studies were included (a further 37 studies were identified from a previous NICE guideline). The majority of the included studies compared the strength of association for the QFT-GIT/G IGRA with the TST (5 mm or 10 mm) in relation to the incidence of active TB or previous TB exposure. Ten studies reported evidence on decision-analytic models to determine the cost-effectiveness of IGRAs compared with the TST for LTBI diagnosis. In children, TST (≥ 5 mm) negative followed by QFT-GIT was the most cost-effective strategy, with an incremental cost-effectiveness ratio (ICER) of £18,900 per quality-adjusted life-year (QALY) gained. In immunocompromised people, QFT-GIT negative followed by the TST (≥ 5 mm) was the most cost-effective strategy, with an ICER of approximately £18,700 per QALY gained. In those recently arrived from high TB incidence countries, the TST (≥ 5 mm) alone was less costly and more effective than TST (≥ 5 mm) positive followed by QFT-GIT or T-SPOT.TB or QFT-GIT alone.

LIMITATIONS

The limitations and scarcity of the evidence, variation in the exposure-based definitions of LTBI and heterogeneity in IGRA performance relative to TST limit the applicability of the review findings.

CONCLUSIONS

Given the current evidence, TST (≥ 5 mm) negative followed by QFT-GIT for children, QFT-GIT negative followed by TST (≥ 5 mm) for the immunocompromised population and TST (≥ 5 mm) for recent arrivals were the most cost-effective strategies for diagnosing LTBI that progresses to active TB. These results should be interpreted with caution given the limitations identified. The evidence available is limited and more high-quality research in this area is needed including studies on the inconsistent performance of tests in high-compared with low-incidence TB settings; the prospective assessment of progression to active TB for those at high risk; the relative benefits of two-compared with one-step testing with different tests; and improved classification of people at high and low risk for LTBI.

STUDY REGISTRATION

This study is registered as PROSPERO CRD42014009033.

FUNDING

The National Institute for Health Research Health Technology Assessment programme.

Comparison of interferon gamma release assay & tuberculin skin tests for diagnosis of latent tuberculosis in patients on maintenance haemodialysis

Background & objectives:

Tuberculosis (TB) is a common infection in patients on haemodialysis. There is a definite role of treatment of latent TB (LTB) in these patients. However, diagnosis of LTB in these patients by tuberculin skin test (TST) is unreliable. There is suggestion that interferon gamma release assay (IGRA) will be more reliable test for diagnosis of LTB in this setting. Thus, we evaluated value of IGRA and TST for the diagnosis of LTB in patients on dialysis in an Indian setting.

Methods:

Patients with end stage kidney disease on dialysis were included. Patients with active TB were excluded. Each patient was subjected to TST (induration of ≥10 mm was taken as positive) and QuantiFERON TB Gold In-Tube test (QFT-GIT) for diagnosis of LTB.

Results:

A total of 185 patients were included; 129 (69.7%) were males and mean age was 36.7 ± 12.3 yr. Past history of TB was present in 18 (9.7%) patients. One hundred and thirty four (72.4%) patients had scar of BCG vaccination. QFT-GIT test was positive in 66 (36%), TST in 32 (17%) and both in 13 (7%) patients. Of the 66 patients positive with QFT-GIT, only 13 (19.6%) were positive for TST. Of the 32 patients positive with TST, only 13 (40.6%) were positive with QFT-GIT; 100 (54%) patients were negative for both the tests. Overall, 85 (45.9%) patients were positive for either of the two tests. Poor agreement was shown between the two methods. On logistic regression analysis, odds of QFT-GIT to be positive in patients with BCG vaccination was 1.23 and with history of TB 0.99, both being insignificant. odds of tuberculin skin test to be positive in patients with BCG vaccination was 1.04 and with history of TB 0.99, both again being insignificant.

Interpretation & conclusions:

Our findings showed that more number of patients (36%) on haemodialysis were positive for QuantiFERON Gold In-Tube test as compared to TST (17%). There was poor agreement between the two tests. No significant effect of BCG vaccination and history of TB in past was observed on both tests.

Detecting latent tuberculosis in compromised patients

PURPOSE OF REVIEW

The detection of latent tuberculosis infection (LTBI) in different categories of compromised patients is reviewed with focus on the role of strategies incorporating immunodiagnostic tests and analysis of epidemiological and clinical risk factors.

RECENT FINDINGS

The development of active tuberculosis (TB) is increased in compromised patients and is closely related to determinants for disease reactivation or newly acquired TB infection. A targeted detection of LTBI in these high-risk groups should be performed especially if preventive treatment is planned. The performance of immunodiagnostic tests is highly variable among different groups of immunocompromised individuals. Findings of cross-sectional studies indicate a better diagnostic accuracy of interferon-γ release assays over the tuberculin skin test. The critical issue is that in low-incidence countries, the positive and negative predictive values of any of immunodiagnostic tests were very poor. A targeted testing process involving analysis of TB risk factors increases the predictive positive values of immunodiagnostic tests and may improve LTBI detection.

SUMMARY

The LTBI detection in immunocompromised patients is a challenge. The development of new immunological biomarkers and integrated clinical and epidemiological strategies are needed to identify LTBI in compromised individuals and to plan preventive chemotherapies in those at risk of developing active TB.

The use of Quantiferon-TB gold in-tube test in screening latent tuberculosis among Saudi Arabia dialysis patients

BACKGROUND AND AIM

Screening for tuberculosis (TB) is a key strategy for controlling infection. This study aimed to detect latent TB among dialysis patients.

METHODS

This is a prospective study conducted in King Saud University, Riyadh involving hemodialysis (HD) and peritoneal dialysis (PD) patients aged ≥18 years. Patients were screened for latent TB infection (LTBI) using both TBskin test (TST) and QuantiFERONTB Gold In-Tube test (QFT-GIT). All participants were followed-up clinically and radiologically every 3 months for 2 years.

RESULTS

A total of 243 (181 HD and 62 PD) patients were included and 112(46.1%) were males. 45.3% showed positive QFT in HD patients with sensitivity of 91.7%, specificity of 71.4%, positive predictive value (PPV) of 19.5%, and negative predictive value (NPV) of 91.1%. TST results in HD showed that positive TST was 17.4%, sensitivity was 63.2%, specificity was 95.5%, PPV was 51.5%, and NPV was 91.1%. Five (8.1%) showed positive QFT in PD patients with sensitivity of 7.7%, specificity of 91.8%, PPV of 6.6%, and NPV of 92.3%. TST results in PD showed that positive TST was 9.8%, sensitivity was 35.7%, specificity was 97.9%, PPV was 55.8%, and NPV was 93.3%. Previous TB infection was significantly correlated with QFT only in HD patients, but significantly associated with TST in both HD and PD patients. Also in HD, QFT was significantly associated with TST (P = 0.043).

CONCLUSIONS

Due to high variability of QFT-GIT sensitivity, we recommend its use for its NPV and to use either TST or QFT in screening latent TB.