Enzyme-linked immunospot assay for interferon-gamma to support the diagnosis of tuberculosis in diabetic patients

Screening for Latent Tuberculosis Infection in Adults: Updated Evidence Report and Systematic Review for the US Preventive Services Task Force

Importance

Latent tuberculosis infection (LTBI) can progress to active tuberculosis disease, causing morbidity and mortality.

Objective

To review the evidence on benefits and harms of screening for and treatment of LTBI in adults to inform the US Preventive Services Task Force (USPSTF).

Data Sources

PubMed/MEDLINE, Cochrane Library, and trial registries through December 3, 2021; references; experts; literature surveillance through January 20, 2023.

Study Selection

English-language studies of LTBI screening, LTBI treatment, or accuracy of the tuberculin skin test (TST) or interferon-gamma release assays (IGRAs). Studies of LTBI screening and treatment for public health surveillance or disease management were excluded.

Data Extraction and Synthesis

Dual review of abstracts, full-text articles, and study quality; qualitative synthesis of findings; meta-analyses conducted when a sufficient number of similar studies were available.

Main Outcomes and Measures

Screening test accuracy; development of active tuberculosis disease, transmission, quality of life, mortality, and harms.

Results

A total of 113 publications were included (112 studies; N = 69 009). No studies directly evaluated the benefits and harms of screening. Pooled estimates for sensitivity of the TST were 0.80 (95% CI, 0.74-0.87) at the 5-mm induration threshold, 0.81 (95% CI, 0.76-0.87) at the 10-mm threshold, and 0.60 (95% CI, 0.46-0.74) at the 15-mm threshold. Pooled estimates for sensitivity of IGRA tests ranged from 0.81 (95% CI, 0.79-0.84) to 0.90 (95% CI, 0.87-0.92). Pooled estimates for specificity of screening tests ranged from 0.95 to 0.99. For treatment of LTBI, a large (n = 27 830), good-quality randomized clinical trial found a relative risk (RR) for progression to active tuberculosis at 5 years of 0.35 (95% CI, 0.24-0.52) for 24 weeks of isoniazid compared with placebo (number needed to treat, 112) and an increase in hepatotoxicity (RR, 4.59 [95% CI, 2.03-10.39]; number needed to harm, 279). A previously published meta-analysis reported that multiple regimens were efficacious compared with placebo or no treatment. Meta-analysis found greater risk for hepatotoxicity with isoniazid than with rifampin (pooled RR, 4.22 [95% CI, 2.21-8.06]; n = 7339).

Conclusions and Relevance

No studies directly evaluated the benefits and harms of screening for LTBI compared with no screening. TST and IGRAs were moderately sensitive and highly specific. Treatment of LTBI with recommended regimens reduced the risk of progression to active tuberculosis. Isoniazid was associated with higher rates of hepatotoxicity than placebo or rifampin.

Diabetes is associated with lower tuberculosis antigen-specific interferon gamma release in Tanzanian tuberculosis patients and non-tuberculosis controls

BACKGROUND

Diabetes is increasingly common in TB endemic regions and plays a role as a possible risk factor for increased progression from latent TB infection (LTBI) to active TB disease. Although the pathophysiological mechanisms are not fully understood, the immune system is weakened in diabetes patients and therefore the validity of interferon gamma release assays (IGRA) may be compromised. The aim of the present study was to assess the association between diabetes and Mycobacterium tuberculosis (Mtb) antigen-specific interferon gamma (IFN-γ) release in a TB endemic area among culture-confirmed TB patients and non-TB controls.

METHODS

Culture-confirmed pulmonary TB patients (n = 187) and healthy non-TB neighbourhood controls (n = 190) from Mwanza, Tanzania were tested for the presence of circulating T cells recognizing Mtb antigens using an IGRA. The diabetes status of all participants was assessed using a standard oral glucose tolerance test. The impact of diabetes on the performance of the IGRA was estimated using robust linear and logistic regression.

RESULTS

Compared to normal glucose tolerance, diabetes was associated with reduced levels of Mtb-specific IFN-γ. Increasing levels of fasting blood glucose (B - 0.3, 95% confidence interval - 0.6 to - 0.03, p = 0.033) was negatively associated with IFN-γ. Although TB patients had higher specific and lower unspecific mitogen IFN-γ responses compared to non-TB controls, the association between diabetes and IFN-γ did not depend on TB status.

CONCLUSION

Diabetes is associated with lower levels of Mtb antigen-specific IFN-γ, and the validity of IFN- γ tests for LTBI may be questionable in individuals with diabetes.

Algorithmic approach by endobronchial ultrasound-guided transbronchial needle aspiration for isolated intrathoracic lymphadenopathy: a study in a tuberculosis-endemic country

BACKGROUND/PURPOSE

Isolated intrathoracic lymphadenopathy (IT-LAP) is clinically challenging because of the difficult anatomic location and wide range of associated diseases, including tuberculosis (TB). Although sampling via endobronchial ultrasound-guided transbronchial needle aspiration (EBUS-TBNA) for histopathology is a major development, there is still room for improvement. This study aimed to investigate an algorithmic approach driven by EBUS-TBNA and conventional bronchoscopy to streamline the management of IT-LAP.

METHODS

Eighty-three prospectively enrolled patients with IT-LAP were subjected to an EBUS-TBNA diagnostic panel test (histopathology, cytology, and microbiology) and underwent conventional bronchoscopy for bronchoalveolar lavage. The results were structured into an algorithmic approach to direct patient treatment, workup, or follow-up.

RESULTS

The diagnostic yields of EBUS-TBNA based on histopathology were similar for each disease entity: 77.8% for malignancy, 70.0% for TB, 75.0% for sarcoidosis, 80.0% for anthracosis, and 70.0% for lymphoid hyperplasia (p = 0.96). The incidence of malignancy was 10.8% for total IT-LAP patients, and 12.0% and 33.7% for patients with TB and sarcoidosis, respectively. Thirty-five (42.2%) patients were symptomatic. The leading diagnosis was sarcoidosis (60%), followed by TB (20%), malignancy (11.4%), lymphoid hyperplasia (5.7%), and anthracosis (2.9%). By logistic regression analysis, granulomatous disease (odds ratio: 13.45; 95% confidence interval: 4.45-40.67, p < 0.001) was an independent predictor of symptoms. Seven (8.4%) and three (3.6%) IT-LAP patients diagnosed active TB and suggestive of TB with household contact history, respectively, were all placed on anti-TB treatment.

CONCLUSION

The algorithmic approach streamlines patient management. It enables early detection of malignancy, correctly places nonmalignant patients on an appropriate treatment regimen, and particularly identifies candidates at high risk of TB reactivation for anti-TB chemoprophylaxis.

T-SPOT.TB assay usage in adults and children

The diagnosis and treatment of TB infection is one of the public health priorities. Until recently, diagnosis of TB infection has been based on the tuberculin skin test (TST). However, this is neither 100% sensitive nor specific for the diagnosis of TB infection owing to its many drawbacks. More recently, T-cell-based IFN-γ release assays (IGRAs) have been developed. In this article, we review the clinical performance of one of the IGRAs, T-SPOT.TB assay, for the diagnosis of TB infection in adults and children. We discuss the principle of the assay, its utility in active TB diseases, latent TB infection and the performance of the test in specialized subgroups of patients, such as immunocompromised individuals. When compared with the TST, the T-SPOT.TB assay has better specificity in bacillus Calmette-Guérin-vaccinated individuals, and data suggest that T-SPOT.TB may be more sensitive than the TST. Data in groups at high risk of progression to disease support the idea that T-SPOT.TB performs better than the TST. In addition, application of T-SPOT.TB by using bodily fluids such as cerebrospinal fluid, bronchoalveolar lavage fluid and pleural fluid may offer new diagnostic approaches in extrapulmonary TB disease. Although IGRAs cannot distinguish active TB disease from latent TB infection, these assays perform better than the TST for the detection of TB infection.