Large-scale evaluation of enzyme-linked immunospot assay and skin test for diagnosis of Mycobacterium tuberculosis infection against a gradient of exposure in The Gambia

Tuberculin test using Indian indigenous purified-protein derivative (PPD) shows only moderate agreement with international standard PPD

Background

In India, the prevalence of Latent TB infection (LTBI) is estimated to be around 40%. Various formulations of PPD(Purified protein derivative) are available, for diagnosis of LTBI, which may give variable responses. The commercially available PPD in India is by Arkray Healthcare (TST-Arkray). It is unclear if this product may have a similar sensitivity compared to other internationally accepted tuberculins (TST-Tubersol).

Objectives

To assess the performance of the two TSTs compared to Quantiferon-Gold Plus (QFT-Plus).

Methodology

A blood sample was collected for the QFT-Plus test. Both the TSTs were placed in the right and the left volar aspect of the forearms and 48 hrs later, the subjects came back to the study site for reading.

Results

Among the 512 participants who were recruited, 326 subjects were healthcare professionals and 186 subjects were household contacts of patients with tuberculosis. They were tested with both TST-Tubersol and TST-Arkray, 139(27 %) participants tested positive for TST-Tubersol (≥10 mm), whereas 203 participants (40.1 %)tested positive for TST-Arkray. There was moderate agreement between the two tests with k = 0.58. Also, there was only poor agreement between both the TSTs with QFT Plus(kappa = 0.19 for Tubersol and 0.17 for Arkray). With QFT-Plus as gold standard, the sensitivity, specificity, PPV and NPV of TST-Tubersol, ast an induration cut-off of 10 mm was 46.8 %,76.3 %,31.8 % and 85.8 %. respectively and TST- Arkray; 60.6 %, 64 %, 28.5 % and 87.2 % respectively.

Conclusion

The Indian TST (Arkray Diagnostics) has shown moderate agreement with the internationally accepted Tubersol. Additionally, there was poor agreement between the TSTs and QFT plus test.

Interferon gamma release assays for diagnosis of osteoarticular tuberculosis: A systematic review and meta-analysis

Background

Although the Interferon Gamma Release Assays (IGRA) is often used to identify latent tuberculosis, it also plays a crucial role in diagnosing active extrapulmonary tuberculosis. Some studies have assessed the use of IGRA as a biomarker for osteoarticular tuberculosis (OATB), which is elevated following TB infection. Still, conclusive results about its effectiveness have not been reported.

Method

We searched PubMed, Embase, and Cochran databases. We obtained literature related to the diagnosis of OATB by IGRA, and the retrieval period was from the establishment of the database to June 2021. The bivariate random effect model was used to summarize the sensitivity, specificity, and accuracy of other indicators in diagnosing OATB by IGRA, and the forest plot and receiver operating characteristic (ROC) curve were used for testing.

Results

We included seven studies involving 643 subjects in diagnosing OATB by IGRA. The comprehensive sensitivity and specificity were 0.84 (95% CI, 0.70–0.92) and 0.78 (95% CI, 0.66–0.87), respectively. The area under the curve (AUC) was 0.87.

Conclusion

In blood samples, the diagnostic accuracy of IGRAS is poor in patients with suspected OAT. We conclude that IGRA may not be appropriate for patients with OATB.

Early Clearance of Mycobacterium tuberculosis Is Associated With Increased Innate Immune Responses

BACKGROUND

A proportion of tuberculosis (TB) case contacts do not become infected, even when heavily exposed. We studied the innate immune responses of TB case contacts to understand their role in protection against infection with Mycobacterium tuberculosis, termed "early clearance."

METHODS

Indonesian household contacts of TB cases were tested for interferon-γ release assay (IGRA) conversion between baseline and 14 weeks post recruitment. Blood cell populations and ex vivo innate whole blood cytokine responses were measured at baseline and, in a subgroup, flow cytometry was performed at weeks 2 and 14. Immunological characteristics were measured for early clearers, defined as a persistently negative IGRA at 3 months, and converters, whose IGRA converted from negative to positive.

RESULTS

Among 1347 case contacts, 317 were early clearers and 116 were converters. Flow cytometry showed a resolving innate cellular response from 2 to 14 weeks in persistently IGRA-negative contacts but not converters. There were no differences in cytokine responses to mycobacterial stimuli, but compared to converters, persistently IGRA-negative contacts produced more proinflammatory cytokines following heterologous stimulation with Escherichia coli and Streptococcus pneumoniae.

CONCLUSIONS

Early clearance of M. tuberculosis is associated with enhanced heterologous innate immune responses similar to those activated during induction of trained immunity.

Comparison of tuberculin skin test and interferon gamma release assay in pediatric candidates of heart transplantation and a 2-year follow-up

BACKGROUND

Currently, tuberculin skin test (TST) and interferon gamma release assay (IGRA) are used to find the latent tuberculosis infection (LTBI) cases in the candidates of heart transplantation. Therefore, this study aimed to compare TST and IGRA to diagnose LTBI in pediatric heart transplant candidates.

METHODS

This cross-sectional study was performed on 50 children, who were candidates for heart transplantation, of whom 42 cases underwent heart transplantation in Shahid Rajaie Cardiovascular, Medical, and Research center, Tehran, Iran, from 2016 to 2017.

RESULTS

Participants of the study included 24 male patients (%48) (p-value = 0.67). The mean age of the patients was 8.18 ± 4.27 years (1-16 years). According to the results, IGRA was negative in all patients, and no indeterminate result was reported, while the purified derivative test (PPD) was positive in three (6%) cases. In comparison with QFT, an accuracy of 94% was achieved for TST to diagnose Mycobacterium tuberculosis infection.

CONCLUSIONS

It seems that TST can still be used as an accurate test for screening LTBI in pediatric candidates for heart transplantation.

Prevention and treatment of tuberculosis in solid organ transplant recipients

Introduction: Tuberculosis (TB) in solid organ transplant (SOT) recipients is associated with significant morbidity and mortality. Its management in transplant recipients is difficult and highly complex, given the underlying immunosuppression and the risks of drug-drug interactions imposed by immunosuppressive drugs that are needed to maintain the transplant allograft.Areas covered: We provide a brief review of TB in SOT and discuss the clinical indications, mechanisms of action and drug resistance, drug-drug interactions, and adverse effects of anti-TB drugs. We provide a summary of recent clinical trials, which serve as the foundation for current recommendations. We further include relevant updates on new agents being evaluated for clinical use in TB management.Expert commentary: TB causes significant morbidity in SOT recipients. The drugs used in the treatment for latent TB and active disease in SOT are similar to the regimens used in the general population. However, TB disease in transplant recipients is more difficult to manage because of the potential for hepatotoxicity and the complex drug-drug interactions with immunosuppressive drugs. We believe that alternative regimens suited for the vulnerable transplant population, and more therapeutic drug options are needed given the adverse toxicities associated with currently approved anti-TB drugs.

Genetic Resistance to Mycobacterium tuberculosis Infection and Disease

Natural history studies of tuberculosis (TB) have revealed a spectrum of clinical outcomes after exposure to Mycobacterium tuberculosis, the cause of TB. Not all individuals exposed to the bacterium will become diseased and depending on the infection pressure, many will remain infection-free. Intriguingly, complete resistance to infection is observed in some individuals (termed resisters) after intense, continuing M. tuberculosis exposure. After successful infection, the majority of individuals will develop latent TB infection (LTBI). This infection state is currently (and perhaps imperfectly) defined by the presence of a positive tuberculin skin test (TST) and/or interferon gamma release assay (IGRA), but no detectable clinical disease symptoms. The majority of healthy individuals with LTBI are resistant to clinical TB, indicating that infection is remarkably well-contained in these non-progressors. The remaining 5-15% of LTBI positive individuals will progress to active TB. Epidemiological investigations have indicated that the host genetic component contributes to these infection and disease phenotypes, influencing both susceptibility and resistance. Elucidating these genetic correlates is therefore a priority as it may translate to new interventions to prevent, diagnose or treat TB. The most successful approaches in resistance/susceptibility investigation have focused on specific infection and disease phenotypes and the resister phenotype may hold the key to the discovery of actionable genetic variants in TB infection and disease. This review will not only discuss lessons from epidemiological studies, but will also focus on the contribution of epidemiology and functional genetics to human genetic resistance to M. tuberculosis infection and disease.

More significance of TB-IGRA except for the diagnose of tuberculosis

OBJECTIVE

Tuberculosis (TB)-interferon gamma release assay (IGRA) test has the characteristics of short time, high specificity, and high sensitivity, but it lacks the correlation research between TB-IGRA test results and body's immune cells, disease progression and prognosis, which is explored in this study.

DESIGN

A retrospective study was carried out on positive TB-IGRA patients who were infected with TB and diagnosed at our hospital from January 2014 to June 2015. The TB-IGRA, routine blood test, T-cell subgroup data were collected for statistical analysis.

RESULTS

TB-IGRA results were in positive proportion to the lymphocytes, CD4+ T cells and CD4+ CD28+ T cells, whereas negative to the Treg cells. Patient with unilateral pulmonary lesion had higher TB-IGRA than those with bilateral pulmonary lesions. After the stimulation of TB-specific antigen, the proportion of CD4+ IFN-γ+ and CD8+ IFN-γ+ T Tcells were both increased and the CD4+ IFN-γ+ T had positive correlation with the value of TB-IGRA.

CONCLUSIONS

IFN-γ was tested with TB-IGRA in patients with TB by the specific TB T cells and correlated with the lymphocytes, while the lymphocytes also closely related to the host's anti-TB immunity and disease outcome. Hence the result of TB-IGRA could reflect the specific anti-TB immunity ability of the host, disease progression and prognosis. This study further expands the application scope of TB-IGRA technology in the diagnosis of TB and lays a foundation for clinical practice to understand the immunity state of the patients with TB and the application of auxiliary clinical immunity regulators.

G allele at -924 A > G position of FoxP3 gene promoter as a risk factor for tuberculosis

BACKGROUND

Forkhead box protein 3 (FoxP3) is an important factor for development and function of Regulatory T cells (Treg). Studies have found an association between common gene polymorphisms in FoxP3 and some infectious diseases. The aim of this study was to evaluate possible associations between two Single nucleotide polymorphisms (SNPs) in the promoter of the FoxP3 gene to susceptibility to tuberculosis (TB) and the alteration of Foxp3 gene expression.

METHODS

The pattern distribution of genotype at two position, -3279 A > C (rs3761548) and -924 A > G (rs2232365) on the promoter of FoxP3 gene was evaluated using polymerase chain reaction-single specific primer (PCR-SSP) method in 183 tuberculosis patients and 183 healthy control. In addition the quantity of FoxP3 gene expression at mRNA level was identified by the real-time PCR.

RESULTS

The frequency of G allele at -924 A > G was significantly higher was higher in TB patients (59.5%) than control group (39.5%) (P ≤ 0.05). In addition, our data viewed approximately 5- folds more FoxP3 gene expression in female patients with GG genotype in comparison to female healthy cases with the same genotype (P ≤ 0.001). There was no statistically significant differences between the distribution pattern of -3279 A > C polymorphism in patients and healthy individuals along with it effect on the FoxP3 gene expression among both groups (P > 0.05).

CONCLUSIONS

Our outcome suggests that the -924 A > G polymorphism leads to enhance FoxP3 gene expression and susceptibility to tuberculosis in the sex dependent manner. This event may rise the count of Treg cells and modulate the immune response against tuberculosis.

Addressing the Challenges of Tuberculosis: A Brief Historical Account

Tuberculosis (TB) is a highly contagious disease that still poses a threat to human health. Mycobacterium tuberculosis (MTB), the pathogen responsible for TB, uses diverse ways in order to survive in a variety of host lesions and to subsequently evade immune surveillance; as a result, fighting TB and its associated multidrug resistance has been an ongoing challenge. The aim of this review article is to summarize the historical sequence of drug development and use in the fight against TB, with a particular emphasis on the decades between World War II and the dawn of the twenty first century (2000).

Diagnosis of Latent Tuberculosis Infection

For 2015, tuberculosis (TB) incidence in the United States has plateaued at 3.0 per 100,000. This remains the lowest case rate since recording started. On the global level, although the TB epidemic is larger than previously estimated, TB deaths and incidence rate continue to fall. For both low and high incidence countries, accelerating the decline in TB incidence towards elimination goals requires that more emphasis be placed on strengthening systems for detection and treatment of latent TB infection (LTBI) in addition to improving TB care globally. Here, we review the tuberculin skin test and gamma interferon release assays currently available for the detection of LTBI.

Chemokines additional to IFN-γ can be used to differentiate among Mycobacterium tuberculosis infection possibilities and provide evidence of an early clearance phenotype

Current diagnostic tests for tuberculosis (TB) remain limited in their ability to discriminate between active TB (ATB) and latent TB infection (LTBI). Early clearance (EC) of TB by individuals exposed to Mycobacterium tuberculosis is a debated phenomenon for which evidence is lacking. We measured and compared secreted chemokines in the plasma fraction from 48 ATB, 38 LTBI, 162 presumed EC and 39 healthy controls (HC) using the QuantiFERON^®-TB Gold In-Tube assay. Single chemokine markers were limited in their ability to discriminate between ATB and LTBI: IFN-γ showed 16.7% sensitivity; CCL2 showed moderate sensitivity (70.8%) and specificity (74.4%); CXCL10 showed high sensitivity (87.5%) and specificity (78.9%). Compared to IFN-γ alone, IFN-γ combined with CXCL10 significantly improved (p < 0.001) the sensitivity and specificity to discriminate between ATB and HC (97.9% sensitivity and 94.9% specificity) and between ATB and LTBI (89.6% sensitivity and 71.1% specificity). Levels of CCL2 were very significantly lower (p < 0.0001) in EC compared to HC groups and hence CCL2 is a useful marker for EC. This study demonstrated the potential application of profiling using multiple chemokines for differentiating among the various M. tuberculosis infection possibilities. We also present evidence to support the EC phenomenon based on the decrease of CCL2 levels.

Comparison of QuantiFERON-TB gold in tube test versus tuberculin skin test for screening of latent tuberculosis infection in Saudi Arabia: A population-based study

OBJECTIVES:

To compare QuantiFERON-TB gold in tube (QFT-GIT) test with tuberculin skin test (TST) in detecting latent tuberculosis infection (LTBI) among a general population in Saudi Arabia.

METHODS:

A population-based cross-sectional study was conducted between July 2010 and March 2013 among individuals randomly selected from the list of those receiving care at primary healthcare centers in three provinces of Saudi Arabia; Central, Western, and Eastern provinces. Those younger than 5 years, immunocompromised, had a current or previous history of active TB, LTBI, or who were receiving anti-TB medications were excluded. Informed consent was obtained before the study questionnaire was completed. Participants were then evaluated for LTBI using QFT-GIT test followed immediately by TST.

RESULTS:

Of the 1369 subjects included in the final analysis, QFT-GIT was positive in 124 (9.1%) and TST was positive in 127 (9.3%). Positive concordance was observed in 49 (3.6%) subjects while negative concordance was observed in 1167 (85.2%) subjects. The overall agreement between the two tests was 88.8% with a significant kappa (κ) test (κ = 0.332, P < 0.001). Concordance was significantly higher in younger age, female gender, single status, students, primary education, living in middle-sized families, and never smoked.

CONCLUSIONS:

The overall agreement of TST and QFT-GIT for the detection of LTBI among a Saudi general population was 88.8%. QFT-GIT is probably comparable to TST for detecting LTBI in an intermediate TB burden country with high at birth bacille calmette guerin vaccination coverage. Further prospective studies are needed to compare the ability of both tests to predict TB disease.

First evaluation of QuantiFERON-TB Gold Plus performance in contact screening

Identifying latently infected individuals is crucial for the elimination of tuberculosis (TB). We evaluated for the first time the performance of a new type of interferon-γ release assay, QuantiFERON-TB Plus (QFT-Plus), which includes an additional antigen tube (TB2), stimulating both CD4+ and CD8+ T-cells in contacts of TB patients.

Contacts were screened for latent TB infection by tuberculin skin test, QFT-Plus and QuantiFERON-TB Gold in Tube (QFT-GIT).

In 119 TB contacts, the overall agreement between QFT-Plus and QFT-GIT was high, with a Cohen's κ of 0.8. Discordant results were found in 12 subjects with negative QFT-GIT and positive QFT-Plus results. In analyses of markers of TB exposure and test results, the average time spent with the index case was the strongest risk factor for positivity in each of these tests. The difference in interferon-γ production between the two antigen tubes (TB2−TB1) was used as an estimate of CD8+ stimulation provided by the TB2. TB2−TB1 values >0.6 IU·mL−1 were significantly associated with proximity to the index case and European origin.

QFT-Plus has a stronger association with surrogate measures of TB exposure than QFT-GIT in adults screened for latent TB infection. Interferon-γ response in the new antigen tube used an indirect estimate of specific CD8+ response correlates with increased Mycobacterium tuberculosis exposure, suggesting a possible role in identifying individuals with recent infection.

The Use of Interferon Gamma Inducible Protein 10 as a Potential Biomarker in the Diagnosis of Latent Tuberculosis Infection in Uganda

Background

In the absence of a gold standard for the diagnosis of latent tuberculosis (TB) infection (LTBI), the current tests available for the diagnosis of LTBI are limited by their inability to differentiate between LTBI and active TB disease. We investigated IP-10 as a potential biomarker for LTBI among household contacts exposed to sputum positive active TB cases.

Methods

Active TB cases and contacts were recruited into a cohort with six months’ follow-up. Contacts were tested for LTBI using QuantiFERON^®-TB Gold In-Tube (QFN) assay and the tuberculin skin test (TST). Baseline supernatants from the QFN assay of 237 contacts and 102 active TB cases were analysed for Mycobacterium tuberculosis (MTB) specific and mitogen specific IP-10 responses.

Results

Contacts with LTBI (QFN⁺TST⁺) had the highest MTB specific IP-10 responses at baseline, compared to uninfected contacts (QFN^-TST^-) p<0.0001; and active cases, p = 0.01. Using a cut-off of 8,239 pg/ml, MTB specific IP-10 was able to diagnose LTBI with a sensitivity of 87.1% (95% CI, 76.2–94.3) and specificity of 90.9% (95% CI, 81.3–96.6). MTB specific to mitogen specific IP-10 ratio was higher in HIV negative active TB cases, compared to HIV negative latently infected contacts, p = 0.0004. Concentrations of MTB specific IP-10 were higher in contacts with TST conversion (negative at baseline, positive at 6-months) than in those that were persistently TST negative, p = 0.001.

Conclusion

IP-10 performed well in differentiating contacts with either latent or active TB from those who were uninfected but was not able to differentiate LTBI from active disease except when MTB specific to mitogen specific ratios were used in HIV negative adults. In addition, IP-10 had the potential to diagnose ‘recent TB infection’ in persons classified as having LTBI using the TST. Such individuals with strong IP-10 responses would likely benefit from chemoprophylaxis.

Role of QuantiFERON(®)-TB Gold In-Tube in tuberculosis contact investigation: experience in a tuberculosis unit

BACKGROUND

Interferon-γ release assays (IGRAs) are increasingly used for the diagnosis of latent tuberculosis infection (LTBI). Because of the lack of a gold standard for the diagnosis of LTBI, IGRAs are compared to the tuberculin skin test (TST) and yield conflicting results. We assessed the usefulness of an IGRA test, QuantiFERON(®)-TB Gold In-Tube (QFT-G-IT), for diagnosing LTBI compared with TST in the setting of a contact screening study.

METHODS

A prospective comparison between the QFT-G-IT and the TST in TB contact subjects in a low TB burden area was conducted sequentially between January 2006 and December 2012.

RESULTS

A moderate concordance between the two tests (κ = 0.44 for TST cut-off of 5 mm and κ = 0.56 for TST cut-off of 15 mm) was found. A better agreement was shown in younger contacts and in non-vaccinated contacts when using a TST of 15 mm. Independent risk factors for a TST(+)/QFT-G-IT(-) discordance were history of BCG vaccination and age between 31 and 59 years. Discordance was also more frequent using a TST cut-off value of 5 mm. QFT-G-IT(+)/TST(-) was infrequent and was found in older contacts.

CONCLUSIONS

Based on our data, we cannot recommend the use of QFT-G-IT as the only test to rule out LTBI, especially in older patients.

Broad adaptive immune responses to M. tuberculosis antigens precede TST conversion in tuberculosis exposed household contacts in a TB-endemic setting

Background

The identification of Mycobacterium^-tuberculosis (Mtb) infected individuals remains a challenge due to an insufficient understanding of immune responses detected with the current diagnostic tests for latent tuberculosis i.e. the tuberculin skin test (TST) or IFN–γ release assays (IGRAs) and an inability to distinguish infection stages with current immunologic assays. Further classification based on markers other than IFN–γ may help to define markers of early Mtb infection.

Methods

We assessed the TST status of Mtb^-exposed household contacts at baseline and at 6 months. Contacts were classified into those with initial positive TST (TST⁺); those with baseline negative TST but TST conversion at 6 months (TST converters, TSTC) and those with persistently negative TST (PTST⁻). We assessed their short^- and long^-term immune responses to PPD and ESAT–6/CFP–10 (EC) via IFN–γ ELISPOT and a multiplex cytokine array in relation to TST status and compared them to those of TB cases to identify immune profiles associated with a spectrum of infection stages.

Results

After 1 and 6 days stimulation with EC, 12 cytokines (IFN–γ, IL–2, IP–10, TNF–α, IL–13, IL–17, IL–10, GMCSF, MIP–1β, MCP–3, IL–2RA and IL–1A) were not different in TSTC compared to TST⁺ suggesting that robust adaptive Mtb^-specific immune responses precede TST conversion. Stratifying contacts by baseline IFN–γ ELISPOT to EC in combination with TST results revealed that IP–10 and IL–17 were highest in the group of TST converters with positive baseline ELISPOT, suggesting they might be markers for recent infection.

Conclusion

We describe a detailed analysis of Mtb^-specific biomarker profiles in exposed household contacts in a TB endemic area that provides insights into the dynamic immune responses to Mtb infection and may help to identify biomarkers for ‘at^-risk’ populations beyond TST and IGRA.

Early clearance of Mycobacterium tuberculosis: a new frontier in prevention

Early clearance (EC) is the successful eradication of inhaled Mycobacterium tuberculosis before an adaptive immune response develops. Evidence for EC comes from case contact studies that consistently show that a proportion of heavily exposed individuals do not develop M. tuberculosis infection. Further support for the existence of this phenotype comes from genetic loci associated with tuberculin reactivity. In this review we discuss aspects of the innate response that may underpin EC and hypotheses that can be tested through field laboratory link studies in M. tuberculosis case contacts. Specifically, we consider mechanisms whereby alveolar macrophages recognize and kill intracellular M. tuberculosis, and how other cell types, such as neutrophils, natural killer T cells, mucosa-associated invariant T cells and cd T cells may assist. How EC may be impaired by HIV infection or vitamin D deficiency is also explored. As EC is a form of protective immunity, further study may advance the development of vaccines and immunotherapies to prevent M. tuberculosis infection.

Immunogenic Mycobacterium africanum strains associated with ongoing transmission in The Gambia

In West Africa, Mycobacterium tuberculosis strains co-circulate with M. africanum, and both pathogens cause pulmonary tuberculosis in humans. Given recent findings that M. tuberculosis T-cell epitopes are hyperconserved, we hypothesized that more immunogenic strains have increased capacity to spread within the human host population. We investigated the relationship between the composition of the mycobacterial population in The Gambia, as measured by spoligotype analysis, and the immunogenicity of these strains as measured by purified protein derivative–induced interferon-γ release in ELISPOT assays of peripheral blood mononuclear cells. We found a positive correlation between strains with superior spreading capacity and their relative immunogenicity. Although our observation is true for M. tuberculosis and M. africanum strains, the association was especially pronounced in 1 M. africanum sublineage, characterized by spoligotype shared international type 181, which is responsible for 20% of all tuberculosis cases in the region and therefore poses a major public health threat in The Gambia.

Latent TB infection diagnosis in population exposed to TB subjects in close and poor ventilated high TB endemic zone in India

Background

The present study was designed to investigate the utility of Quantiferon TB gold (QFT-G) and Tuberculin skin test (TST) for diagnosis of latent TB infection (LTBI) in high crowding TB endemic zone of Nagpur, India and their comparison with associated risk factors.

Methods

Out of 342 eligible participants, QFT-G and TST were performed in 162 participants.

Results

The prevalence of LTBI observed according to QFT-G and TST was 48% and 42% respectively, with an agreement of 52.47%. QFT-G positivity was associated with age while TST positivity was associated with body mass index (BMI). Duration of exposure emerged as a key risk factor significantly associated with both the tests.

Conclusion

The prevalence of LTBI was quite high in the studied zone as detected by both the evaluated tests and thus, the combination of both the tests will be best predictive for LTBI in such high TB endemic regions.

Evaluation of gamma interferon immune response elicited by the newly constructed PstS-1(285-374):CFP10 fusion protein to detect Mycobacterium tuberculosis infection

The PstS1 antigen is highly immunogenic, principally when combined with CFP10 during both latent and active TB infection. In the present study, a selected pstS1 gene fragment was cloned, fused with CFP10, and expressed in Escherichia coli. The product [PstS-1(285-374):CFP10] was compared to the recombinant fused RD1 (region of deletion 1) protein (ESAT-6:CFP10) in detecting Mycobacterium tuberculosis infection in 108 recent contacts of pulmonary tuberculosis (TB) cases, considering a positive tuberculin skin test (TST) to be the baseline. The release of gamma interferon (IFN-γ) in 22-h whole-blood and 5-day lymphocyte stimulation assays primed with each antigen was determined. All contacts were clinically followed for up to 1 year, and 87% of the tuberculin skin test-positive (TST(positive)) patients accepted preventative treatment. Concerning the IFN-γ response to PstS-1(285-374):CFP10 in the 22-h and 5-day assays, a slight increase in contact-TST(positive) detection was observed (23/54 and 26/54) compared to the level seen with the RD1 protein (18/54 and 24/54) whereas in the TST(negative) group, similarly lower numbers (≤5/48) of responders were achieved for both antigens, except for RD1 in the 5-day assay (8/48). By combining the IFN-γ responders to both antigens in the 5-day assays, slightly higher increases in positivity were found in the TST(positive) (32/54) and TST(negative) (10/48) groups. Two of 12 untreated TST(positive) contacts progressed to active TB and were concordantly positive in all assays, except for one contact who lacked positivity in the RD1 5-day assay. We demonstrated for the first time that PstS-1(285-374):CFP10 slightly increased contact positivity and detection of active disease progression, suggesting its potential application as a TB infection marker.

Recombinant ESAT-6-CFP10 Fusion Protein Induction of Th1/Th2 Cytokines and FoxP3 Expressing Treg Cells in Pulmonary TB

BACKGROUND

Early secretory antigenic target 6 (ESAT-6) and culture filtrate protein 10 (CFP-10) are Mycobacterium tuberculosis (Mtb)-specific antigens that are secreted by actively metabolising bacteria and contribute to the virulence of the bacteria. Their ability to induce Treg and Th2 responses, particularly during the first two weeks of treatment, has not been comprehensively examined to date. The purpose of this work was to characterise Th1, Th2 and Treg responses to rESAT-6-CFP10 fusion protein in TB patients before and during the intensive phase of treatment and in healthy M.bovis BCG vaccinated donors.

METHODS

Forty-six newly diagnosed, HIV-negative, smear-positive pulmonary TB patients and 20 healthy donors were recruited in the UK and Ghana. Their peripheral blood mononuclear cells (PBMC) were used in ex vivo ELISPOT and in vitro cultures to identify immunological parameters of interest.

RESULTS

The study confirmed that protective immune responses to rESAT-6-CFP10 are impaired in active TB but improved during treatment: circulating antigen-specific IL-4-producing T-cells were increased in untreated TB but declined by two weeks of treatment while the circulating antigen-specific IFN-γ producing T cells which showed a transient rise at one week of treatment, persisted at baseline levels at two months of treatment. In vitro T cell proliferation and IFN-γ production were reduced, while IL-4 and CD4(+)FoxP3(+)CD25(hi) cell expression were increased in response to rESAT-6-CFP10 fusion protein in untreated TB. These responses were reversed during early treatment of TB.

CONCLUSIONS

These observations support further investigations into the possible utility of these parameters as markers of active disease and favourable treatment outcomes.

The performance of quantiferon-TB gold in-tube (QFT-IT) test compared to tuberculin skin test (TST) in detecting latent tuberculosis infection (LTBI) in the presence of HIV coinfection in a high TB-burden area with BCG-vaccinated population

OBJECTIVES

To compare quantiferon-TB gold "in tube" (QFT-IT) with the conventional tuberculin skin test (TST) for the diagnosis of latent tuberculosis infection (LTBI) in HIV-infected adults in a setting highly endemic for tuberculosis with BCG vaccinated population in Bangalore, Karnataka, India.

PATIENTS AND METHODS

The study population (100 BCG-vaccinated adults) was divided into 4 groups: HIV patients with TB patient contact, HIV patients with past history of TB, TB patients (positive control), and healthy volunteers (negative control).

RESULTS

Overall agreement between TST and QFT-IT was 52.4% (κ = 0.22). Increasing the TST cutoff value from 5 mm to 10 mm among HIV-positive groups resulted in better agreement 62.5% in Group 1 and 81.2% in Group 2.

DISCUSSION

In a setting with high TB prevalence, the TST gives increased false positives in HIV-positive groups if 5 mm is used as the cutoff value. This could be minimized by increasing the cutoff to 10 mm.

CONCLUSION

The 2-step approach (initial testing of all cases with TST and confirmation of only those positive in TST by testing with QFT-IT) will be economical and help in treating LTBI cases in lower middle income countries like India.

Relevance of latent TB infection in areas of high TB prevalence

About one-third of the world population has latent TB infection (LTBI), the majority of which is distributed in 22 high-burden countries. Early diagnosis and treatment of active TB remains the top priority in resource-poor countries with high TB prevalence. Notwithstanding, because LTBI contributes significantly to the pool of active TB cases later on, its diagnosis and treatment is essential, especially in high-risk groups. The lack of a gold standard and several limitations of currently available tools, namely the tuberculin skin test and interferon-γ release assays, are major constraints for LTBI diagnosis. In areas with high TB prevalence, interferon-γ release assays have not shown superiority over the conventional tuberculin skin test and are yet to be systematically studied. Decisions regarding LTBI treatment with isoniazid preventive therapy should be made, keeping in mind the high prevalence of isoniazid resistance in these settings. Although efforts to shorten the LTBI treatment duration are encouraging, most trials have focused on adherence and toxicity. Future trials on short-duration regimens in high-burden settings should address drug efficacy issues as well. LTBI management, therefore, should comprise a targeted screening approach and individualization of LTBI treatment protocols. In addition, efforts should focus on airborne infection control measures in high-burden countries. A high prevalence of drug-resistant TB, the HIV epidemic, and delays in the diagnosis of active TB cases are other major concerns in areas of high TB prevalence. There is ample space for further research in these countries, whose outcomes may strengthen future national guidelines.

Predictive value of interferon-γ ELISPOT assay in HIV 1-infected patients in an intermediate tuberculosis-endemic area

The tuberculin skin test for diagnosing latent tuberculosis (TB) has some limitations for HIV-infected patients, especially in BCG vaccinated countries. The objective of this study was to identify the incidence rate of new TB cases among HIV-infected patients in an intermediate TB-endemic area and to examine its correlation with the ELISPOT assay. We prospectively followed up 124 patients with HIV-1 infection to monitor development of active TB disease after performing an ELISPOT assay (T-SPOT. TB test, Oxford Immunotec, Ltd., Abingdon, UK). A total of 120 patients were followed for a median of 947 days; four patients with active TB at enrollment were excluded. Eleven patients developed active TB during 238 person-years, giving a high incidence rate of 4621/100,000 person-years. Patients with positive ELISPOT responses had a higher TB incidence rate than those with negative ELISPOT responses; however this was not statistically significant [20% (6/30) vs. 6.02% (5/83), p=0.052]. A Cox regression analysis showed that the independent risk factors associated with progression of TB were low CD4(+) T cell counts, previous history of TB treatment, and positive ELISPOT results. Advanced HIV-infected patients who showed a positive TB ELISPOT assay had a higher rate of progression to TB in the intermediate TB-endemic area.

Latent tuberculosis infection screening for laboratory personnel using interferon-γ release assay and tuberculin skin test in Korea: an intermediate incidence setting

BACKGROUND

Though recent reports have indicated a higher prevalence of latent tuberculosis infection (LTBI) in laboratory personnel than in other healthcare workers, these studies included only a limited number of laboratory personnel.

METHODS

We have thus focused on the laboratory personnel, who had a high level of exposure to specimens from patients with TB. We recruited 173 laboratory personnel and performed QuantiFERON-TB Gold In-Tube test (QFT-G) and tuberculin skin test (TST).

RESULTS

QFT-G was positive in 21.4% of the enrolled laboratory personnel, and TST was positive in 33.3%. The agreement between the two tests was fair (κ = 0.234). In multivariate analyses, household contactwith TBpatients (P = 0.013), the laboratory sections of microbiology (P = 0.045) and chemistry/immunology (P = 0.014) were shown to be significantly associated with positive QFT-G results.

CONCLUSION

Our data show a high prevalence of TST and QFT-G positivity in laboratory personnel and emphasize the importance of LTBI screening for laboratory personnel. In BCG-vaccinated populations with an intermediate incidence setting, QFT-G seems to be superior to TST as a screening tool for the detection of LTBI. Further study, including results of follow-up tests will be helpful for confirmation of our findings.

Innate and adaptive immune responses during acute M. tuberculosis infection in adult household contacts in Kampala, Uganda

Contacts of active pulmonary tuberculosis (TB) patients are at risk for Mycobacterium tuberculosis (MTB) infection. Because most infections are controlled, studies during MTB infection provide insight into protective immunity. We compared immune responses of adult household contacts that did and did not convert the tuberculin skin test (TST). Innate and adaptive immune responses were measured by whole blood assay. Responses of TST converters (TSTC) were compared with persistently TST negative contacts (PTST-) and contacts who were TST+ at baseline (TST+). TLR-2, TLR-4, and IFN-γR responses to IFN-γ did not differ between the groups, nor did γδ T cell responses. T cell responses to MTB antigens differed markedly among TSTC, PTST-, and TST+ contacts. Thus, no differences in innate responses were found among the three household contact groups. However, adaptive T cell responses to MTB antigens did differ before and during MTB infection among PTST-, TSTC, and TST+ contacts.

Interferon gamma and interferon gamma inducible protein-10 in detecting tuberculosis infection

OBJECTIVE

This study aimed to compare the levels of TB-antigen specific Interferon gamma (IFN-γ) and IFN-γ inducible protein (IP)-10 in culture of whole blood samples from healthy controls (HC) and healthy household contacts (HHC).

METHODOLOGY

A total of 386 study subjects, which included 186 HC and 200 HHC, were recruited. QuantiFERON-TB Gold in-tube (QFT-IT) assay was employed to measure IFN-γ levels. IP-10 levels were measured in the supernatants collected from QFT-IT tubes. Tuberculin skin test was also performed.

RESULTS

The levels of TB antigen specific IFN-γ and IP-10 were significantly higher in HHC compared to HC. There was no significant difference observed between positivity of QFT-IT and IP-10 in HC and HHC. The positivity of TST was significantly lower in subjects <17 year, when compared to IP-10 (p<0.005). The reduced cut-off point 0.22IU/ml significantly increased the positivity of QFT-IT among children with high risk for latent TB infection (LTBI).

CONCLUSIONS

Measurement of TB antigen specific IFN-γ and IP-10 can be potential markers for the detection of LTBI.

MCP1 SNPs and pulmonary tuberculosis in cohorts from West Africa, the USA and Argentina: lack of association or epistasis with IL12B polymorphisms

The monocyte chemotactic protein-1 (MCP-1) is a chemokine that plays an important role in the recruitment of monocytes to M. tuberculosis infection sites, and previous studies have reported that genetic variants in MCP1 are associated with differential susceptibility to pulmonary tuberculosis (PTB). We examined eight MCP1 single nucleotide polymorphisms (SNPs) in a multi-ethnic, case-control design that included: 321 cases and 346 controls from Guinea-Bissau, 258 cases and 271 controls from The Gambia, 295 cases and 179 controls from the U.S. (African-Americans), and an additional set of 237 cases and 144 controls of European ancestry from the U.S. and Argentina. Two locus interactions were also examined for polymorphisms in MCP1 and interleukin 12B (IL12B), another gene implicated in PTB risk. Examination of previously associated MCP1 SNPs rs1024611 (-2581A/G), rs2857656 (-362G/C) and rs4586 (+900C/T) did not show evidence for association. One interaction between rs2857656 and IL12B SNP rs2288831 was observed among Africans but the effect was in the opposite direction in Guineans (OR = 1.90, p = 0.001) and Gambians (OR = 0.64, p = 0.024). Our data indicate that the effect of genetic variation within MCP1 is not clear cut and additional studies will be needed to elucidate its role in TB susceptibility.

Mycobacteria and biological response modifiers: two sides of the relationship

With increasing use of biological response modifiers (BRMs) for various systemic inflammatory diseases there is a need to be vigilant about complications with the use of these therapies. It is important to have appropriate screening for the infections in patients requiring BRMs. However, many studies have reported benefits of certain BRMs in the treatment of infections such as tuberculosis as adjuncts. Continued research and technical advances in immunogenetics helps understand complex mechanisms in the usage of the BRMs. This article summarizes the different aspects of the relationship between mycobacterial infections and the use of various BRMs for inflammatory conditions.

Diagnosing latent tuberculosis in high-risk individuals: rising to the challenge in high-burden areas

A key challenge to greater progress in tuberculosis (TB) control is the reservoir of latent TB infection (LTBI), which represents a huge long-lived reservoir of potential TB disease. In parts of Africa, as many as 50% of 15-year-olds and 77%-89% of adults have evidence of LTBI. A second key challenge to TB control is the human immunodeficiency virus (HIV)-associated TB epidemic, and Africa alone accounts for one-quarter of the global burden of HIV-associated TB. HIV co-infection promotes both reactivation TB from LTBI and rapidly progressive primary TB following recent exposure to Mycobacterium tuberculosis. Preventing active TB and tackling latent infection in addition to the Directly Observed Treatment, Short-Course (DOTS) strategy could improve TB control in high-burden settings, especially where there is a high prevalence of HIV co-infection. Current strategies include intensified case finding (ICF), TB infection control, antiretroviral therapy (ART), and isoniazid preventive therapy (IPT). Although ART has been widely rolled out, ICF and IPT have not. A key factor limiting the rollout and effectiveness of IPT and ICF is the limitations of existing tools to both diagnose LTBI and identify those persons most at risk of progressing to active TB. In this review, we examine the obstacles and consider current progress toward the development of new tools to address this pressing global problem.

Risk factors associated with positive QuantiFERON-TB Gold In-Tube and tuberculin skin tests results in Zambia and South Africa

Introduction

The utility of T-cell based interferon-gamma release assays for the diagnosis of latent tuberculosis infection remains unclear in settings with a high burden of tuberculosis.

Objectives

To determine risk factors associated with positive QuantiFERON-TB Gold In-Tube (QFT-GIT) and tuberculin skin test (TST) results and the level of agreement between the tests; to explore the hypotheses that positivity in QFT-GIT is more related to recent infection and less affected by HIV than the TST.

Methods

Adult household contacts of tuberculosis patients were invited to participate in a cross-sectional study across 24 communities in Zambia and South Africa. HIV, QFT-GIT and TST tests were done. A questionnaire was used to assess risk factors.

Results

A total of 2,220 contacts were seen. 1,803 individuals had interpretable results for both tests, 1,147 (63.6%) were QFT-GIT positive while 725 (40.2%) were TST positive. Agreement between the tests was low (kappa = 0.24). QFT-GIT and TST results were associated with increasing age (adjusted OR [aOR] for each 10 year increase for QFT-GIT 1.15; 95% CI: 1.06–1.25, and for TST aOR: 1.10; 95% CI 1.01–1.20). HIV positivity was less common among those with positive results on QFT-GIT (aOR: 0.51; 95% CI: 0.39–0.67) and TST (aOR: 0.61; 95% CI: 0.46–0.82). Smear positivity of the index case was associated with QFT-GIT (aOR: 1.25; 95% CI: 0.90–1.74) and TST (aOR: 1.39; 95% CI: 0.98–1.98) results. We found little evidence in our data to support our hypotheses.

Conclusion

QFT-GIT may not be more sensitive than the TST to detect risk factors associated with tuberculous infection. We found little evidence to support the hypotheses that positivity in QFT-GIT is more related to recent infection and less affected by HIV than the TST.

Latent tuberculosis in children: diagnosis and management

Control of tuberculosis in children often escapes attention because of the paucibacillary nature of the illness. However, they contribute much of the morbidity, mortality and future reservoir of the disease which reiterates the importance of risk-factor based screening for latent infection and appropriate treatment. We review the modalities and importance of diagnosis and treatment of latent tuberculosis infection in children. At this time, the role for interferon-gamma release assays in low-income, high-burden settings is rather limited but further research in the coming years might clear their role in children. An important emerging area of research is the development of an improved skin test for TB that uses specific mycobacterial antigens rather than tuberculin, thus is more feasible and useful in resource limited settings.

Interleukin 12B (IL12B) genetic variation and pulmonary tuberculosis: a study of cohorts from The Gambia, Guinea-Bissau, United States and Argentina

We examined whether polymorphisms in interleukin-12B (IL12B) associate with susceptibility to pulmonary tuberculosis (PTB) in two West African populations (from The Gambia and Guinea-Bissau) and in two independent populations from North and South America. Nine polymorphisms (seven SNPs, one insertion/deletion, one microsatellite) were analyzed in 321 PTB cases and 346 controls from Guinea-Bissau and 280 PTB cases and 286 controls from The Gambia. For replication we studied 281 case and 179 control African-American samples and 221 cases and 144 controls of European ancestry from the US and Argentina. First-stage single locus analyses revealed signals of association at IL12B 3′ UTR SNP rs3212227 (unadjusted allelic p = 0.04; additive genotypic p = 0.05, OR = 0.78, 95% CI [0.61–0.99]) in Guinea-Bissau and rs11574790 (unadjusted allelic p = 0.05; additive genotypic p = 0.05, OR = 0.76, 95% CI [0.58–1.00]) in The Gambia. Association of rs3212227 was then replicated in African-Americans (rs3212227 allelic p = 0.002; additive genotypic p = 0.05, OR = 0.78, 95% CI [0.61–1.00]); most importantly, in the African-American cohort, multiple significant signals of association (seven of the nine polymorphisms tested) were detected throughout the gene. These data suggest that genetic variation in IL12B, a highly relevant candidate gene, is a risk factor for PTB in populations of African ancestry, although further studies will be required to confirm this association and identify the precise mechanism underlying it.

Pathogenesis, immunology, and diagnosis of latent Mycobacterium tuberculosis infection

Phagocytosis of tubercle bacilli by antigen-presenting cells in human lung alveoli initiates a complex infection process by Mycobacterium tuberculosis and a potentially protective immune response by the host. M. tuberculosis has devoted a large part of its genome towards functions that allow it to successfully establish latent or progressive infection in the majority of infected individuals. The failure of immune-mediated clearance is due to multiple strategies adopted by M. tuberculosis that blunt the microbicidal mechanisms of infected immune cells and formation of distinct granulomatous lesions that differ in their ability to support or suppress the persistence of viable M. tuberculosis. In this paper, current understanding of various immune processes that lead to the establishment of latent M. tuberculosis infection, bacterial spreading, persistence, reactivation, and waning or elimination of latent infection as well as new diagnostic approaches being used for identification of latently infected individuals for possible control of tuberculosis epidemic are described.

New approaches in the diagnosis and treatment of latent tuberculosis infection

With nearly 9 million new active disease cases and 2 million deaths occurring worldwide every year, tuberculosis continues to remain a major public health problem. Exposure to Mycobacterium tuberculosis leads to active disease in only ~10% people. An effective immune response in remaining individuals stops M. tuberculosis multiplication. However, the pathogen is completely eradicated in ~10% people while others only succeed in containment of infection as some bacilli escape killing and remain in non-replicating (dormant) state (latent tuberculosis infection) in old lesions. The dormant bacilli can resuscitate and cause active disease if a disruption of immune response occurs. Nearly one-third of world population is latently infected with M. tuberculosis and 5%-10% of infected individuals will develop active disease during their life time. However, the risk of developing active disease is greatly increased (5%-15% every year and ~50% over lifetime) by human immunodeficiency virus-coinfection. While active transmission is a significant contributor of active disease cases in high tuberculosis burden countries, most active disease cases in low tuberculosis incidence countries arise from this pool of latently infected individuals. A positive tuberculin skin test or a more recent and specific interferon-gamma release assay in a person without overt signs of active disease indicates latent tuberculosis infection. Two commercial interferon-gamma release assays, QFT-G-IT and T-SPOT.TB have been developed. The standard treatment for latent tuberculosis infection is daily therapy with isoniazid for nine months. Other options include therapy with rifampicin for 4 months or isoniazid + rifampicin for 3 months or rifampicin + pyrazinamide for 2 months or isoniazid + rifapentine for 3 months. Identification of latently infected individuals and their treatment has lowered tuberculosis incidence in rich, advanced countries. Similar approaches also hold great promise for other countries with low-intermediate rates of tuberculosis incidence.

Tuberculosis case-contact research in endemic tropical settings: design, conduct, and relevance to other infectious diseases

The study of the contacts of patients with tuberculosis has a long history. Where tuberculosis is endemic, regular recruitment of tuberculosis cases and their household contacts can be done for research and strategic intervention. This recruitment provides a platform whereby host, pathogen, and environmental factors related to tuberculosis can be investigated and new interventions can be assessed. We describe the types of study possible within a tuberculosis case-contact study platform and its essential components, including recruitment and follow-up of the patients with tuberculosis, their household contacts and community controls, assessments and sampling, and data management and processing. Sample handling and storage, local engagement, ethical challenges, and the strengths and weaknesses of study design are all important issues in case-contact research. A case-contact study platform is a powerful research tool to answer fundamental questions in tuberculosis and has relevance to the study of other major infectious diseases.

Decay kinetics of an interferon gamma release assay with anti-tuberculosis therapy in newly diagnosed tuberculosis cases

Background

Qualitative and quantitative changes in IGRA response offer promise as biomarkers to monitor Tuberculosis (TB) drug therapy, and for the comparison of new interventions. We studied the decay kinetics of TB-specific antigen T-cell responses measured with an in-house ELISPOT assay during the course of therapy.

Methods

Newly diagnosed sputum smear positive TB cases with typical TB chest radiographs were recruited. All patients were given standard anti-TB treatment. Each subject was followed up for 6 months and treatment outcomes were documented. Blood samples were obtained for the ESAT-6 and CFP-10 (EC) ELISPOT at diagnosis, 1-, 2-, 4- and 6-months. Qualitative and quantitative reversion of the ELISPOT results were assessed with McNemar test, conditional logistic regression and mixed-effects hierarchical Poisson models.

Results

A total of 116 cases were recruited and EC ELISPOT was positive for 87% (95 of 109) at recruitment. There was a significant decrease in the proportion of EC ELISPOT positive cases over the treatment period (p<0.001). Most of the reversion occurred between the start and first month of treatment and at completion at 6 months. ESAT-6 had higher median counts compared to CFP-10 at all time points. Counts for each antigen declined significantly with therapy (p<0.001). Reverters had lower median SFUs at the start of treatment compared to non-Reverters for both antigens. Apart from the higher median counts for non-Reverters, no other risk factors for non-reversion were found.

Conclusions

TB treatment induces qualitative and quantitative reversion of a positive in-house IGRA in newly diagnosed cases of active TB disease. As this does not occur reliably in the majority of cured individuals, qualitative and quantitative reversion of an IGRA ELISPOT has limited clinical utility as a surrogate marker of treatment efficacy.

Commercial interferon gamma release assays compared to the tuberculin skin test for diagnosis of latent Mycobacterium tuberculosis infection in childhood contacts in the Gambia

BACKGROUND

We compared the performance of tuberculin skin test (TST), Quantiferon-TB Gold in-tube (QFT-GIT), and T-SPOT.TB in diagnosing latent tuberculosis (LTBI) among childhood TB contacts in a TB endemic setting with high BCG coverage. We evaluated the performance of interferon gamma release assays (IGRAs) and TST when combined in an algorithm.

METHODS

Childhood contacts of newly diagnosed TB patients were tested with TST, QFT-GIT, and T-SPOT. The level of exposure in contacts was categorized according to whether they slept in the same room, same house, or a different house as the index case. For the evaluation of combined test performance, prior estimates for prevalence of latent TB were used in Bayesian models that assumed conditional dependence between tests.

RESULTS

A total of 285 children were recruited. Overall, 26.5%, 33.0%, and 33.5% were positive for TST, T-SPOT, or QFT-GIT, respectively. All 3 tests responded to the gradient of sleeping proximity to the index case. Neither TST nor IGRA results were confounded by BCG vaccination. There was moderate agreement (kappa = 0.40-0.68) between all 3 tests. Combination of either IGRA with TST increased sensitivity (by 9.3%-9.6%) especially in contacts in the highest exposure category but was associated with loss of specificity (9.9%-11.3%).

CONCLUSION

IGRAs and TST are similar in their diagnostic performance for LTBI. An approximate 10% sensitivity benefit for using the TST and an IGRA in combination is associated with a slightly greater specificity loss. Testing strategies combining an IGRA and TST with an "or" statement may be useful only in situations where there is a high pretest probability of latent infection.

A statistical method was used for the meta-analysis of tests for latent TB in the absence of a gold standard, combining random-effect and latent-class methods to estimate test accuracy

OBJECTIVE

Because of the lack of a gold standard, the diagnostic performance of tests for the detection of latent tuberculosis infection (LTBI) is not known. However, statistical methods can be used to estimate the accuracy from the studies reporting the concordance among the tests.

STUDY DESIGN AND SETTING

We developed a random-effect latent-class model to estimate performance characteristics of three LTBI diagnostic tests: tuberculin skin test (TST, at 10-mm cutoff), QuantiFERON-TB gold (QFG), and TSPOT-TB from the studies evaluating agreement among the tests.

RESULTS

Nineteen studies were included. QFG had a sensitivity of 0.642 (95% confidence interval [CI]: 0.593-0.691) and specificity of 0.996 (95% CI: 0.989-1.000), TSPOT-TB had a sensitivity of 0.500 (95% CI: 0.334-0.666) and specificity of 0.906 (95% CI: 0.882-0.929), and TST had a sensitivity of 0.709 (95% CI: 0.658-0.761) and specificity of 0.683 (95% CI: 0.522-0.844). Results were not sensitive to the inclusion of any single study. When only the three studies that reported on TSPOT were removed, estimates for the other two tests varied minimally.

CONCLUSIONS

Statistical methods can help estimate the accuracy of LTBI tests. Although the specificities were close to their reported values in the literature, the estimates for sensitivities were low; a finding that should be carefully evaluated.

Immunogenicity of antigens from the TbD1 region present in M. africanum and missing from "modern" M. tuberculosis: a cross- sectional study

Background

Currently available tools cannot be used to distinguish between sub-species of the M. tuberculosis complex causing latent tuberculosis (TB) infection. M. africanum causes up to half of TB in West- Africa and its relatively lower progression to disease suggests the presence of a large reservoir of latent infection relative to M. tuberculosis.

Methods

We assessed the immunogenicity of the TbD1 region, present in M. africanum and absent from "modern" M. tuberculosis, in an ELISPOT assay using cells from confirmed M. africanum or M. tuberculosis infected TB patients without HIV infection in the Gambia.

Results

Antigens from the TbD1 region induced IFNγ responses in only 35% patients and did not discriminate between patients infected with M. africanum vs. M. tuberculosis, while PPD induced universally high responses.

Conclusions

Further studies will need to assess other antigens unique to M. africanum that may induce discriminatory immune responses.

In vitro gamma interferon tests for the detection of tuberculosis infection

The QuantiFERON-TB Gold (QFT-G) is a new FDA approved test for diagnosing Mycobacterium tuberculosis infection. This test detects the release of interferon-gamma (IFNgamma) in whole blood from sensitized persons when it is incubated with mixtures of synthetic peptides representing 2 proteins present in M. tuberculosis: early secretory antigenic target-6 (ESAT-6) and culture filtrate protein-10 (CFP-10). These antigens have greater specificity than tests using purified protein derivative (PPD) as the tuberculosis antigen. The CDC recommends that QFT-G may be used in all circumstances in which the TB skin test is currently used, including contact investigations, evaluation of recent immigrants, and sequential-testing surveillance programs for infection control (e.g., those for health-care workers). Advantages of the QFT-G include: no false-positive reactions from previous BCG vaccination; no cross-reactivity with non-tuberculous mycobacterium infections; and, better detection of active tuberculosis.

Annual risk of tuberculous infection using different methods in communities with a high prevalence of TB and HIV in Zambia and South Africa

Background

The annual risk of tuberculous infection (ARTI) is a key epidemiological indicator of the extent of transmission in a community. Several methods have been suggested to estimate the prevalence of tuberculous infection using tuberculin skin test data. This paper explores the implications of using different methods to estimate prevalence of infection and ARTI. The effect of BCG vaccination on these estimates is also investigated.

Methodology/Principal Findings

Tuberculin surveys among school children in 16 communities in Zambia and 8 in South Africa (SA) were performed in 2005, as part of baseline data collection and for randomisation purposes of the ZAMSTAR study. Infection prevalence and ARTI estimates were calculated using five methods: different cut-offs with or without adjustments for sensitivity, the mirror method, and mixture analysis. A total of 49,835 children were registered for the surveys, of which 25,048 (50%) had skin tests done and 22,563 (90%) of those tested were read. Infection prevalence was higher in the combined SA than Zambian communities. The mirror method resulted in the least difference of 7.8%, whereas that estimated by the cut-off methods varied from 12.2% to 17.3%. The ARTI in the Zambian and SA communities was between 0.8% and 2.8% and 2.5% and 4.2% respectively, depending on the method used. In the SA communities, the ARTI was higher among the younger children. BCG vaccination had little effect on these estimates.

Conclusions/Significance

ARTI estimates are dependent on the calculation method used. All methods agreed that there were substantial differences in infection prevalence across the communities, with higher rates in SA. Although TB notification rates have increased over the past decades, the difference in cumulative exposure between younger and older children is less dramatic and a rise in risk of infection in parallel with the estimated incidence of active tuberculosis cannot be excluded.

Differences between tuberculosis cases infected with Mycobacterium africanum, West African type 2, relative to Euro-American Mycobacterium tuberculosis: an update

Mycobacterium africanum (MAF) is a common cause of human pulmonary tuberculosis in West Africa. We previously described phenotypic differences between MAF and Mycobacterium tuberculosis (MTB) among 290 patients. In the present analysis, we compared 692 tuberculosis patients infected with the two most common lineages within the (MTB) complex found in the Gambia, namely MAF West African type 2 (39% prevalence) and Euro-American MTB (55% prevalence). We identified additional phenotypic differences between infections with these two organisms. MAF patients were more likely to be older and HIV infected. In addition, they had worse disease on chest X-ray, despite complaining of cough for an equal duration, and were more likely severely malnourished. In this cohort, the prevalence of MAF did not change significantly over a 7-year period.

Diagnostic performance of an enzyme-linked immunospot assay for interferon-gamma in extrapulmonary tuberculosis varies between different sites of disease

OBJECTIVES

To evaluate diagnostic performance of an enzyme-linked immunospot assay for interferon-gamma (T SPOT-TB) in patients with suspected extrapulmonary tuberculosis (TB).

METHODS

From January 2007 to December 2008, patients with suspected extrapulmonary TB were prospectively enrolled from 2 tertiary care hospitals.

RESULTS

A total of 138 patients with suspected extrapulmonary TB were enrolled; 50 patients had positive culture for Mycobacterium tuberculosis and 39 patients had probable TB. The sites of infection were lymph node (n = 20), pleura (n = 19), bone/joint (n = 15), urinary tract (n = 7), peritoneum (n = 7), meninges (n = 6), disseminated (n = 5), intestine (n = 3), pericardium (n = 2), skin (n = 2), throat (n = 1), neck (n = 1), and genitalia (n = 1). The overall sensitivity and specificity were 79.8% (71/89) and 81.6% (40/49). The sensitivity ranged from 100% for tuberculous meningitis, tuberculous pericarditis, and intestinal TB, 95% for lymphadenitis, to 42.9% for tuberculous peritonitis. The sensitivity of the T SPOT-TB assay was 70.6% in immunocompromised patients and 85.5% in immunocompetent patients (p = 0.09).

CONCLUSIONS

The T SPOT-TB assay can be a useful tool for diagnosing extra-pulmonary TB in immunocompetent and immunocompromised patients, particularly for tuberculous meningitis, pericarditis, lymphadenitis, and intestinal TB.

Variants in toll-like receptors 2 and 9 influence susceptibility to pulmonary tuberculosis in Caucasians, African-Americans, and West Africans

Tuberculosis (TB) is a global public health problem and a source of preventable deaths each year, with 8.8 million new cases of TB and 1.6 million deaths worldwide in 2005. Approximately, 10% of infected individuals develop pulmonary or extrapulmonary TB, suggesting that host defense factors influence development of active disease. Toll-like receptor' (TLR) polymorphisms have been associated with regulation of TLR expression and development of active TB. In the present study, 71 polymorphisms in TLR1, TLR2, TLR4, TLR6, and TLR9 were examined from 474 (295 cases and 179 controls) African-Americans, 381 (237 cases and 144 controls) Caucasians, and from 667 (321 cases and 346 controls) Africans from Guinea-Bissau for association with pulmonary TB using generalized estimating equations and logistic regression. Statistically significant associations were observed across populations at TLR9 and TLR2. The strongest evidence for association came at an insertion (I)/deletion (D) polymorphism (-196 to -174) in TLR2 that associated with TB in both Caucasians (II vs. ID&DD, OR = 0.41 [95% CI 0.24-0.68], p = 0.0007) and Africans (II vs. ID&DD, OR = 0.70 [95% CI 0.51-0.95], p = 0.023). Our findings in three independent population samples indicate that variations in TLR2 and TLR9 might play important roles in determining susceptibility to TB.

Incidence and nature of infectious disease in patients treated with anti-TNF agents

Tumor necrosis factor alpha (TNF-alpha) inhibitors offer a targeted therapeutic strategy that contrasts with the nonspecific immunosuppressive agents traditionally used to treat most inflammatory diseases. These biologic agents have had a significant impact in ameliorating the signs and symptoms of inflammatory rheumatoid disease and improving patient function. From the onset of clinical trials, a central concern of cytokine blockade has been a potential increase in susceptibility to infections. Not surprisingly, a variety of infections have been reported in association with the use of TNF-alpha inhibitor agents. In particular, there is evidence suggesting an increased rate of granulomatous infections in patients treated with monoclonal TNF-alpha inhibitors. This review provides the incidence and nature of infections in patients treated with TNF-alpha inhibitor agents and reminds the clinician of the required vigilance in monitoring patients.