Changing concepts of "latent tuberculosis infection" in patients living with HIV infection

Beyond latent and active tuberculosis: a scoping review of conceptual frameworks

There is growing recognition that tuberculosis (TB) infection and disease exists as a spectrum of states beyond the current binary classification of latent and active TB. Our aim was to systematically map and synthesize published conceptual frameworks for TB states. We searched MEDLINE, Embase and EMcare for review articles from 1946 to September 2023. We included 40 articles that explicitly described greater than two states for TB. We identified that terminology, definitions and diagnostic criteria for additional TB states within these articles were inconsistent. Eight broad conceptual themes were identified that were used to categorize TB states: State 0: Mycobacterium tuberculosis (Mtb) elimination with innate immune response (n = 25/40, 63%); State I: Mtb elimination by acquired immune response (n = 31/40, 78%); State II: Mtb infection not eliminated but controlled (n = 37/40, 93%); State III: Mtb infection not controlled (n = 24/40, 60%); State IV: bacteriologically positive without symptoms (n = 26/40, 65%); State V: signs or symptoms associated with TB (n = 39/40, 98%); State VI: severe or disseminated TB disease (n = 11/40, 28%); and State VII: previous history of TB (n = 5/40, 13%). Consensus on a non-binary framework that includes additional TB states is required to standardize scientific communication and to inform advancements in research, clinical and public health practice.

Interferon Gamma Release Assay and Tuberculin Skin Test Performance in Pregnant Women Living With and Without HIV

BACKGROUND

HIV and pregnancy may affect latent TB infection (LTBI) diagnostics. Tuberculin skin test (TST) and newer generation QuantiFERON-TB Gold Plus (QFT-Plus) evaluations in pregnant women living with HIV (WLHIV) and without HIV are lacking.

METHODS

In this cross-sectional study, pregnant women underwent TST and QFT-Plus testing during antenatal care in Kenya. We estimated LTBI prevalence and TST and QFT-Plus performances. Diagnostic agreement was assessed with kappa statistic, participant characteristics associated with LTBI and HIV were assessed with generalized linear models, and QFT-Plus quantitative responses were assessed with Mann-Whitney U test.

RESULTS

We enrolled 400 pregnant women (200 WLHIV/200 HIV-negative women) at median 28 weeks gestation (interquartile range 24-30). Among WLHIV (all on antiretroviral therapy), the median CD4 count was 464 cells/mm3 (interquartile range 325-654); 62.5% (125) had received isoniazid preventive therapy. LTBI prevalence was 35.8% and similar among WLHIV and HIV-negative women. QFT-Plus testing identified 3-fold more women with LTBI when compared with TST (32% vs. 12%, P < 0.0001). QFT-Plus positivity prevalence was similar regardless of HIV status, although TB-specific antigen responses were lower in WLHIV than in HIV-negative women with LTBI (median QFT-TB1 1.05 vs. 2.65 IU/mL, P = 0.035; QFT-TB2 1.26 vs. 2.56 IU/mL, P = 0.027). TST positivity was more frequent among WLHIV than among HIV-negative women (18.5% vs 4.6%; P < 0.0001).

CONCLUSIONS

QFT-Plus assay had higher diagnostic yield than TST for LTBI in WLHIV and HIV-negative women despite lower TB-specific antigen responses in WLHIV. Higher TST positivity was observed in WLHIV. LTBI diagnostic performance in the context of pregnancy and HIV has implications for clinical use and prevention studies, which rely on these diagnostics for TB infection entry criteria or outcomes.

Plasma host protein biomarkers correlating with increasing Mycobacterium tuberculosis infection activity prior to tuberculosis diagnosis in people living with HIV

BACKGROUND

Biomarkers correlating with Mycobacterium tuberculosis infection activity/burden in asymptomatic individuals are urgently needed to identify and treat those at highest risk for developing active tuberculosis (TB). Our main objective was to identify plasma host protein biomarkers that change over time prior to developing TB in people living with HIV (PLHIV).

METHODS

Using multiplex MRM-MS, we investigated host protein expressions from 2 years before until time of TB diagnosis in longitudinally collected (every 3-6 months) and stored plasma from PLHIV with incident TB, identified within a South African (SA) and US cohort. We performed temporal trend and discriminant analyses for proteins, and, to assure clinical relevance, we further compared protein levels at TB diagnosis to interferon-gamma release assay (IGRA; SA) or tuberculin-skin test (TST; US) positive and negative cohort subjects without TB. SA and US exploratory data were analyzed separately.

FINDINGS

We identified 15 proteins in the SA (n=30) and 10 in the US (n=24) incident TB subjects which both changed from 2 years prior until time of TB diagnosis after controlling for 10% false discovery rate, and were significantly different at time of TB diagnosis compared to non-TB subjects (p<0.01). Five proteins, CD14, A2GL, NID1, SCTM1, and A1AG1, overlapped between both cohorts. Furthermore, after cross-validation, panels of 5 - 12 proteins were able to predict TB up to two years before diagnosis.

INTERPRETATION

Host proteins can be biomarkers for increasing Mycobacterium tuberculosis infection activity/burden, incipient TB, and predict TB development in PLHIV.

FUNDING

NIH/NIAID AI117927, AI146329, and AI127173 to JMA.

Coverage and fidelity of the Xpert MTB/RIF™ implementation in a high-burden area for pulmonary tuberculosis in Colombia

Introducción.

La prueba Xpert MTB/RIF™ es una prueba molecular rápida para el diagnóstico de la tuberculosis y la resistencia a la rifampicina. Desde el 2010 es la recomendada por la Organización Mundial de la Salud (OMS) y, aunque fue introducida en Colombia en el 2012, se desconocen los resultados de su uso.

Objetivo.

Describir la cobertura y la fidelidad en el uso de la prueba Xpert MTB/RIF™ en pacientes con tuberculosis pulmonar en una ciudad con alta carga de la enfermedad en Colombia.

Materiales y métodos.

Se hizo un estudio retrospectivo descriptivo de casos del programa de tuberculosis en Cali entre el 2013 y el 2019. La cobertura se estimó como el total de pruebas empleadas en los casos registrados en el programa. La fidelidad se midió con base en los protocolos internacionales de uso de la Xpert MTB/RIF™. Además, se hizo un análisis de correspondencias múltiples entre la prueba y las variables sociodemográficas.

Resultados.

Se incluyeron 6.328 pacientes con tuberculosis pulmonar, de los cuales 181 eran resistentes a los fármacos. La cobertura total de la Xpert MTB/RIF™ durante el periodo de estudio fue de 10,3 % (n=655), con una variación anual entre 0,2 y 23 %. La fidelidad fue de 46,8 % para los grupos de mayor riesgo de tuberculosis multirresistente (TB-MDR). El uso de la prueba se relacionó con la condición de ser hombre, afrocolombiano, y tener entre 41 y 60 años de edad.

Conclusiones.

La cobertura de la prueba Xpert MTB/RIF™ en Cali es baja y su uso no responde a la priorización recomendada para su implementación. Se requieren estrategias para promover su uso adecuado, de manera que contribuya a la meta de poner fin a la tuberculosis.

Does Isoniazid Preventive Therapy Provide Better Treatment Outcomes in HIV-Infected Individuals in Northern Ethiopia? A Retrospective Cohort Study

Objectives

Early antiretroviral therapy (ART), isoniazid preventive therapy (IPT), and isoniazid-rifapentine (3HP) are effective strategies for preventing tuberculosis (TB) among people living with HIV (PLHIV). The study aimed to determine the effect of IPT on the TB incidence, follow-up CD4⁺ T cells, and all-cause mortality rate. Participants. Eligible patients on ART (n = 1, 863) were categorized into one-to-two ratios of exposed groups to IPT (n = 621) and nonexposed groups to IPT (n = 1, 242). Exposed groups entered the cohort at their first prescription of IPT, and unexposed groups entered into the study at the first prescription of ART and then followed until the occurrence of the outcome or date of administrative censoring (June 30, 2017). The outcome endpoints were TB incidence, follow-up CD4⁺ T cells, and all-cause mortality rate.

Results

The follow-up CD4⁺ T cells for the exposed and nonexposed groups were 405.74 and 366.95 cells/mm (World Health Organization (WHO), 2017), respectively, a statistically significant finding (t ₁₈₆₁ = -3.770, p < 0.0001; Cohen's d = 0.186). Nine percent of the exposed patients (620 incidence of TB per 100,000 person-years (PYs)) and 21.9% of the nonexposed patients (3160 incidence of TB per 100,000 PYs) developed TB. Mortality rate (per 100,000 PYs) was 440 for the exposed and 1490 for the unexposed patients. Statistically significant determinants of the all-cause mortality were unscheduled follow-up (AHR = 1.601; 95% CI: 1.154-2.222) and unable to work properly (AHR = 2.324; 95% CI: 1.643-3.288).

Conclusion

This study demonstrates the effect of IPT in reducing incidence of TB and all-cause mortality rate and improving follow-up CD4⁺ T cells. Promoting IPT use can help to achieve the TB eradicating national agenda in Ethiopia.

Global dynamics of a tuberculosis model with fast and slow progression and age-dependent latency and infection

In this paper, a mathematical model describing tuberculosis transmission with fast and slow progression and age-dependent latency and infection is investigated. It is assumed in the model that infected individuals can develop tuberculosis by either of two pathogenic mechanisms: direct progression or endogenous reactivation. It is shown that the transmission dynamics of the disease is fully determined by the basic reproduction number. By analyzing corresponding characteristic equations, the local stability of a disease-free steady state and an endemic steady state of the model is established. By using the persistence theory for infinite dimensional system, it is proved that the system is uniformly persistent when the basic reproduction number is greater than unity. By constructing suitable Lyapunov functionals and using LaSalle's invariance principle, it is verified that the global dynamics of the system is completely determined by the basic reproduction number.

Subclinical tuberculosis among adults with HIV: clinical features and outcomes in a South African cohort

BACKGROUND

Subclinical tuberculosis is an asymptomatic disease phase with important relevance to persons living with HIV. We describe the prevalence, clinical characteristics, and risk of mortality for HIV-infected adults with subclinical tuberculosis.

METHODS

Untreated adults with HIV presenting for outpatient care in Durban, South Africa were screened for tuberculosis-related symptoms and had sputum tested by acid-fast bacilli smear and tuberculosis culture. Active tuberculosis and subclinical tuberculosis were defined as having any tuberculosis symptom or no tuberculosis symptoms with culture-positive sputum. We evaluated the association between tuberculosis disease category and 12-month survival using Cox regression, adjusting for age, sex, and CD4 count.

RESULTS

Among 654 participants, 96 were diagnosed with active tuberculosis disease and 28 with subclinical disease. The median CD4 count was 68 (interquartile range 39-161) cells/mm3 in patients with active tuberculosis, 136 (72-312) cells/mm3 in patients with subclinical disease, and 249 (125-394) cells/mm3 in those without tuberculosis disease (P < 0.001). The proportion of smear positive cases did not differ significantly between the subclinical (29%) and active tuberculosis groups (14%, P 0.08). Risk of mortality was not increased in individuals with subclinical tuberculosis relative to no tuberculosis (adjusted hazard ratio 0.84, 95% confidence interval 0.26-2.73).

CONCLUSIONS

Nearly one-quarter of tuberculosis cases among HIV-infected adults were subclinical, which was characterized by an intermediate degree of immunosuppression. Although there was no significant difference in survival, anti-tuberculous treatment of subclinical cases was common.

TRIAL REGISTRATION

Prospectively registered on ClinicalTrials.gov , NCT01188941 (August 26, 2010).

Global dynamics of an epidemiological model with age of infection and disease relapse

In this paper, an epidemiological model with age of infection and disease relapse is investigated. The basic reproduction number for the model is identified, and it is shown to be a sharp threshold to completely determine the global dynamics of the model. By analysing the corresponding characteristic equations, the local stability of a disease-free steady state and an endemic steady state of the model is established. By means of suitable Lyapunov functionals and LaSalle's invariance principle, it is verified that if the basic reproduction number is less than unity, the disease-free steady state is globally asymptotically stable, and hence the disease dies out; if the basic reproduction number is greater than unity, the endemic steady state is globally asymptotically stable and the disease becomes endemic.

Evaluation of the tuberculosis surveillance system in the Ashaiman municipality, in Ghana

Introduction

Tuberculosis (TB) was the leading cause of death from an infectious illness globally with an estimated 10.4 million new cases and 1.4 million deaths in 2015. In Ghana, from the 2013 TB prevalence survey conducted by the National Tuberculosis Control Programme, the incidence is estimated as 165 per 100,000 population and a mortality rate of 7.5 per 1,000 infected people. The Tuberculosis surveillance system is part of the general framework of the Integrated Disease Surveillance and Response. This evaluation was to assess whether the system is meeting its set objectives, assess its usefulness and describe its attributes.

Methods

The TB surveillance system of the Ashaiman municipality was evaluated using Centre for Disease Control and Prevention updated guidelines for evaluating public health surveillance systems 2006. Records review from 2014 to 2016 was done to assess objectives of the system and surveillance data source of 2016 was used to assess attributes. Interviews were conducted at the various levels using semi-structured questionnaire and data analysis done with Epi info 7 and Microsoft Excel to run frequencies and percentages.

Results

The surveillance system is well structured with standardized data collection tools. The system was found to be useful, though it just partially met its objectives. It was also found to be simple, flexible and fairly stable with average timeliness. It had low acceptability and is not geographically representative. It had low sensitivity of 45/100,000 and a low predictive value positive of 6.6%.

Conclusion

The surveillance system was found to be useful but partially met its objectives. There is the need to improve the sensitivity, predictive value positive timeliness and acceptability.

Combined use of Quantiferon and HBHA-based IGRA supports tuberculosis diagnosis and therapy management in children

OBJECTIVES

Interferon-γ release assays (IGRA) are designed for diagnosis of tuberculosis (TB) infection, and do not discriminate latent TB infection (LTBI) from active TB. Heparin-binding hemagglutinin antigen (HBHA) emerged as a promising antigen for TB diagnosis when used in IGRA format. Aim of this study was to prospectively evaluate the performance of an HBHA-based IGRA to support TB diagnosis and TB therapy monitoring in children with TB infection or active TB disease.

METHODS

Following clinical, microbiological and radiological assessment, children (0-14 years old) were tested by the QuantiFERON TB-Gold In tube (QFT) assay and an aliquot of whole-blood was stimulated with HBHA and IFNγ evaluated only in QFT-positive subjects.

RESULTS

Among the 550 children tested, 486 (88.4%) scored negative and 64 (11.6%) positive. None of the QFT-negative had active TB. Among the QFT-positive, 45 were with LTBI and 19 active TB. HBHA-IGRA scored positive in 41/45 children (91.1%) with LTBI and in 6/19 active TB children (31.6%) at diagnosis (p = 0.001); remarkably, 5 of these 6 children with active TB scoring HBHA-positive were asymptomatic. Moreover, following TB-specific therapy, most of the non-HBHA-responding children, gained an HBHA-positive response.

CONCLUSIONS

HBHA-based IGRA is a useful support in TB diagnosis and TB-therapy monitoring in children.

"Tuberculosis in advanced HIV infection is associated with increased expression of IFNγ and its downstream targets"

BACKGROUND

Tuberculosis (TB) is the major cause of death in Human Immunodeficiency Virus (HIV)-infected individuals. However, diagnosis of TB in HIV remains challenging particularly when HIV infection is advanced. Several gene signatures and serum protein biomarkers have been identified that distinguish active TB from latent infection. Our study was designed to assess if gene expression signatures and cytokine levels would distinguish active TB in advanced HIV.

METHODS

We conducted a case-control study of whole blood RNA-Seq and plasma cytokine/chemokine analysis in HIV-infected with CD4+ T cell count of ≤ 100 cells/μl, with and without active TB. Next, the overlap of the differentially expressed genes (DEG) with the published signatures was performed and then receiver operator characteristic (ROC) analysis was done on small gene discriminators to determine their performance in distinguishing TB in advanced HIV. ELISA was performed on plasma to evaluate cytokine and chemokine levels.

RESULTS

Hierarchical clustering of the transcriptional profiles showed that, in general, HIV-infected individuals with TB (TB-HIV) clustered separately from those without TB. IPA indicated that the TB-HIV signature was characterized by an increase in inflammatory signaling pathways. Analysis of overlaps between DEG in our data set with published TB signatures revealed that significant overlap was seen with one TB signature and one TB-IRIS signature. ROC analysis revealed that transcript levels of FcGR1A (AUC = 0.85) and BATF2 (AUC = 0.82), previously reported as consistent single gene classifiers of active TB irrespective of HIV status, performed successfully even in advanced HIV. Plasma protein levels of IFNγ, a stimulator of FcGR1A and BATF2, and CXCL10, also up-regulated by IFNγ, accurately classified active TB (AUC = 0.98 and 0.91, respectively) in advanced HIV. Neither of these genes nor proteins distinguished between TB and TB-IRIS.

CONCLUSIONS

Gene expression of FcGR1A and BATF2, and plasma protein levels of IFNγ and CXCL10 have the potential to independently detect TB in advanced HIV. However, since other lung diseases were not included in this study, these final candidates need to be validated as specific to TB in the advanced HIV population with TB.

Symptom screening for active tuberculosis in pregnant women living with HIV

This is a protocol for a Cochrane Review (Diagnostic test accuracy). The objectives are as follows: To assess the accuracy of the four-symptom screen (cough, fever, night sweats, or weight loss) for identifying active TB in pregnant PLHIV who are screened in an outpatient or community setting. To investigate potential sources of heterogeneity of the accuracy of the four-symptom screen between studies including: ART status, CD4 cell count, gestational age, pregnancy stage (pregnancy vs. postpartum), screening test definition of cough (any cough vs. cough greater than 2 weeks).To describe the accuracy of single symptoms included within the four-symptom screen, additioal symptoms or symptom combinations, for identifying active TB in pregnant PLHIV. For example, additional symptoms may include failure to gain weight or fatigue.

Effect of Pregnancy on Interferon Gamma Release Assay and Tuberculin Skin Test Detection of Latent TB Infection Among HIV-Infected Women in a High Burden Setting

BACKGROUND

Peripartum immunologic changes may affect latent tuberculosis infection (LTBI) diagnostic performance among HIV-infected women.

METHODS

HIV-infected women were serially tested with tuberculin skin test (TST) and interferon gamma release assay [QuantiFERON TB Gold In-tube (QFT)] in pregnancy and 6 weeks postpartum in Kenya. Prevalence, sensitivity and agreement, and correlates of QFT/TST positivity were assessed. Quantitative QFT mitogen and Mycobacterium tuberculosis antigen (Mtb-Ag) responses were compared by peripartum stage. Incidence of test conversion at 6 weeks postpartum was evaluated in baseline TST-/QFT- women.

RESULTS

Among 100 HIV-infected women, median age was 26 years, median CD4 was 555 cells per cubic millimeter, and 88% were on antiretrovirals. More women were QFT+ than TST+ in both pregnancy (35.4% vs. 13.5%, P = 0.001) and postpartum (29.6% vs. 14.8%, P < 0.001). Among 18 consistently QFT+ women, 8 (44%) converted from TST- to TST+, with improved test agreement postpartum (56.9%, κ = 0.20 to 82.4%, κ = 0.60). Three initially QFT-/TST- women had test conversion (TST+ and/or QFT+), suggesting new infection (incidence 13.4/100 person-years). Mean QFT mitogen (4.46 vs. 7.64 IU/mL, P < 0.001) and Mtb-Ag (1.03 vs. 1.54 IU/mL, P = 0.03) responses were lower among all women retested in pregnancy vs. postpartum, and specifically among persistently QFT+ women (Mtb-Ag: 3.46 vs. 4.48 IU/mL, P = 0.007). QFT indeterminate rate was higher in pregnancy (16%) compared with postpartum (0%) because of lower mitogen response.

CONCLUSIONS

QFT identified >2-fold more women with LTBI compared with TST in pregnancy and postpartum. Lower QFT Mtb-Ag and mitogen responses in pregnancy compared with postpartum suggest that pregnancy-associated immunologic changes may influence LTBI test performance.

Clinical Correlates and Drug Resistance in HIV-Infected and -Uninfected Pulmonary Tuberculosis Patients in South India

OBJECTIVES

To examine demographics, clinical correlates, sputum AFB (acid fast bacilli) smear grading DOTS (Directly Observed Therapy Short Course) uptake, and drug resistance in a cohort of newly-diagnosed, smear positive pulmonary tuberculosis (TB) patients with respect to HIV status at baseline, and compare smear conversion rates, side effects and mortality after two months.

DESIGN

A prospective study among 54 HIV positive and 41 HIV negative pulmonary TB patients. Data were collected via face-to-face interviews, review of medical records, and lab tests.

RESULTS

HIVTB co-infected patients, though more symptomatic at baseline, showed more improvement in their symptoms compared to HIV-uninfected TB patients at follow-up. The HIV co-infected group had more prevalent perceived side effects, and sputum smear positivity was marginally higher compared to the HIV negative group at follow-up. Mortality was higher among the HIV-infected group. Both groups had high rates of resistance to first-line anti-tubercular drugs, particularly isoniazid. There was no significant difference in the drug resistance patterns between the groups.

CONCLUSIONS

Prompt initiation and provision of daily regimens of ATT (Anti-Tubercular treatment) along with ART (Anti-Retroviral treatment) via ART centers is urgently needed in India. As resistance to ART and/or ATT is directly linked to medication non-adherence, the use of counseling, regular reinforcement, early detection and appropriate intervention strategies to tackle this complex issue could help prevent premature mortality and development of resistance in HIV-TB co-infected patients. The high rate of isoniazid resistance might preclude its use in India as prophylaxis for latent TB in HIV infected persons as per the World Health Organization (WHO) guideline.

Incidence and correlates of tuberculosis IGRA conversion among HIV-infected postpartum women

SETTING

Prevention of maternal-to-child transmission program at a tertiary care hospital in Nairobi, Kenya. The risk of acquiring Mycobacterium tuberculosis infection among peripartum human immunodeficiency virus (HIV) infected women is poorly defined.

OBJECTIVE

To determine the incidence of and co-factors for interferon-gamma release assay (IGRA) conversion among postpartum HIV-infected women using T-SPOT.TB.

DESIGN

We used data and cryopreserved peripheral blood mononuclear cells from a historical cohort of HIV-infected women enrolled at 32 weeks' gestation and followed for 1 year postpartum between 1999 and 2005.

RESULTS

Of 89 women initially IGRA-negative during pregnancy, 11 (12.4%) became positive, 53 (59.5%) remained negative and 25 (28.1%) were indeterminate at 1 year postpartum. Mean interferon-gamma (IFN-γ) response among converters increased from ~1 to >50 spot-forming cells/well (P = 0.015). IGRA conversion was significantly associated with partner HIV infection, flush toilets, maternal illness and cough during follow-up, but not maternal CD4 count or HIV viral load.

CONCLUSION

The high rates of IGRA conversion seen among HIV-infected postpartum women in our study are similar to those of other groups at high risk for M. tuberculosis infection. This has important implications for M. tuberculosis infection screening strategies and provision of preventive therapy for the health of women and their infants.

Macrophage takeover and the host-bacilli interplay during tuberculosis

Macrophages are key type of antigen-presenting cells that arbitrate the first line of defense against various intracellular pathogens. Tuberculosis, both pulmonary and extrapulmonary, is an infectious disease of global concern caused by Mycobacterium tuberculosis. The bacillus is a highly successful pathogen and has acquired various strategies to downregulate critical innate-effector immune responses of macrophages, such as phagosome-lysosome fusion, autophagy, induction of cytokines, generation of reactive oxygen and nitrogen species and antigen presentation. In addition, the bacilli also subvert acquired immunity. In this review, we aim to provide an overview of different antimycobacterial immune functions of macrophage and the strategies adopted by the bacilli to manipulate these functions to favor its survival and replication inside the host.

Interferon-gamma release assay versus tuberculin skin test for latent tuberculosis infection among HIV patients in Brazil

Setting

Patients HIV+ attending in a reference clinic, Southern Brazil.

Objective

To compare the interferon-gamma-release assay (IGRA – QuantiFERON^® TB Gold In-Tube) with the tuberculin skin test (TST – PPD-Rt 23) for latent tuberculosis infection (LTBI) in patients with HIV.

Design

Cohort study. Patients were simultaneously submitted to the TST and blood collection for the IGRA.

Results

A total of 140 subjects were included. Nine (6.4%) were IGRA+/TST+, 12 (8.6%) were IGRA+/TST−, 4 (3%) were IGRA−/TST+, and 115 (82%) IGRA−/TST−. There was poor agreement between tests (kappa = 0.2), and no correlation between these results and CD4+ T lymphocyte counts. During follow-up, one patient with negative results on both tests died from sepsis, and another with discordant results (IGRA+/TST−) exhibited TST seroconversion. Compared to the TST, IGRA showed a sensitivity and specificity of 69% and 90%, respectively. The IGRA detected 8% more positive results than the TST. All patients were followed up for 2 years.

Conclusion

The higher accuracy of the IGRA would result in LTBI treatments being administered to patients who would have otherwise been overlooked, decreasing the number of active tuberculosis cases. The long-term survival of HIV carriers requires further evaluation.

Heterogeneity in tuberculosis pathology, microenvironments and therapeutic responses

Tuberculosis (TB) lesions are extremely complex and dynamic. Here, we review the multiple types and fates of pulmonary lesions that form following infection by Mycobacterium tuberculosis and the impact of this spatial and temporal heterogeneity on the bacteria they harbor. The diverse immunopathology of granulomas and cavities generates a plethora of microenvironments to which M. tuberculosis bacilli must adapt. This in turn affects the replication, metabolism, and relative density of bacterial subpopulations, and consequently their respective susceptibility to chemotherapy. We outline recent developments that support a paradigm shift in our understanding of lesion progression. The simple model according to which lesions within a single individual react similarly to the systemic immune response no longer prevails. Host-pathogen interactions within lesions are a dynamic process, driven by subtle and local differences in signaling pathways, resulting in diverging trajectories of lesions within a single host. The spectrum of TB lesions is a continuum with a large overlap in the lesion types found in latently infected and active TB patients. We hope this overview will guide TB researchers in the design, choice of read-outs, and interpretation of future studies in the search for predictive biomarkers and novel therapies.

B cells and antibodies in the defense against Mycobacterium tuberculosis infection

Better understanding of the immunological components and their interactions necessary to prevent or control Mycobacterium tuberculosis (Mtb) infection in humans is critical for tuberculosis (TB) vaccine development strategies. Although the contributory role of humoral immunity in the protection against Mtb infection and disease is less defined than the role of T cells, it has been well-established for many other intracellular pathogens. Here we update and discuss the increasing evidence and the mechanisms of B cells and antibodies in the defense against Mtb infection. We posit that B cells and antibodies have a variety of potential protective roles at each stage of Mtb infection and postulate that such roles should be considered in the development strategies for TB vaccines and other immune-based interventions.

A Description of Mortality Associated with IPT plus ART Compared to ART Alone among HIV-Infected Individuals in Addis Ababa, Ethiopia: A Cohort Study

BACKGROUND

Tuberculosis (TB) is the most common human immunodeficiency virus (HIV) associated opportunistic infection. It is the leading cause of death in HIV-infected individuals in sub-Saharan Africa. Anti-retroviral therapy (ART) and isoniazid preventive therapy (IPT) are the two useful TB preventative strategies available to reduce TB among people living with HIV (PLHIV). Therefore, the aim of this study is to compare mortality associated with IPT taken together with ART, as well as ART alone, among PLHIV.

METHODS

A retrospective cohort study was undertaken at Tikur Anbessa Specialized Hospital (TASH) and Zewditu Memorial Hospital (ZMH) on 185 patients receiving IPT (6 months) plus ART and 557 patients receiving ART alone. Mortality rates (MR) per 100 person-years (PYs) were used to compare mortality rates amongst the groups. Time-to-death and survival probabilities of the patients were determined using the Kaplan Meier Method. The Cox Proportional Hazard Model was employed to estimate the effect of IPT plus ART on survival of PLHIV.

RESULTS

The mortality cases noted in patients treated by IPT plus ART versus ART alone were 18 (4.5 cases/100 PYs) and 116 (10 cases/100 PYs), respectively. In reference to the ART alone, the IPT plus ART reduced the likelihood of death significantly (aHR 0.48; 95% CI 0.38-0.69) and median time to death was about 26 months (IQR 19-34). Moreover, WHO stage IV (aHR 2.42: 95% CI 1.42-4.11), CD4 values ≥350 cells/mm3 (aHR 0.52; 95% CI 0.28-0.94), adherence to ART (aHR 0.12; 95% CI 0.08-0.20), primary levels of education (aHR 2.20; 95% CI 1.07-4.52); and alcohol consumption (aHR 1.71; 95% CI 1.04-2.81) were factors strongly associated with mortality.

CONCLUSION

We found that PLHIV treated by the IPT plus ART had a lower likelihood of mortality and delayed time-to-death when compared to patients treated by ART alone.

Advances in Diagnostic Assays for Tuberculosis

Approximately one-third of the global burden of tuberculosis (TB) remains undiagnosed each year and the vast majority of cases of multidrug-resistant TB remain undetected. Many countries still place heavy reliance on outdated technologies that are blunt and ineffective tools for controlling this epidemic. However, during the past 10 years, there has been substantial progress within the TB diagnostics developmental pipeline. Old technologies have been reviewed and improved and new technologies have been developed and evaluated and are now being implemented. This review summarizes these developments and describes the currently available diagnostic tools. Consideration is given to the requirements of future diagnostic tests and how these should be evaluated not only with regard to their diagnostic accuracy and operational feasibility, but ultimately in terms of whether they impact clinical outcomes cost effectively, especially for those most in need.

Prevalence of latent tuberculosis infection in persons with and without human immunodeficiency virus infection using two interferon-gamma release assays and tuberculin skin test in a low human immunodeficiency virus prevalence, intermediate tuberculosis-burden country

BACKGROUND

The risk of tuberculosis (TB) is higher in human immunodeficiency virus (HIV)-infected patients and intravenous drug users (IDUs). We determined the prevalence and risk factors of latent TB infection (LTBI) in individuals with or without HIV infection, including IDUs, in a country with a low HIV prevalence, an intermediate TB burden, and a high Bacillus Calmette-Guérin (BCG) vaccine coverage using two interferon-gamma release assays (IGRAs) and the tuberculin skin test (TST).

METHODS

For this prospective, cross-sectional study, HIV-infected and -uninfected patients from a regional hospital and medical center in Taiwan were enrolled. Results of the two IGRAs [QuantiFERON-TB Gold (QFT-G) and QuantiFERON-TB Gold In-Tube (QFT-GIT)] and the TST were compared. Risk factors for positivity were analyzed.

RESULTS

We recruited 233 patients [198 (85%) men; mean age, 39.4 years]. Most patients (74%) were BCG vaccinated. The prevalence of LTBI was estimated to be 22.8% by TST, 15.9% by QFT-G, and 20.6% by QFT-GIT. HIV-infected individuals had fewer positive QFT-GIT [7.0% vs. 28.6%, p < 0.001, adjusted odds ratio (aOR) = 0.28, p = 0.05] and TST results, and more indeterminate QFT-G responses (9.3% vs. 0.7%, p = 0.002). Concordance between IGRAs and TST was very poor in HIV-infected patients (κ < 0.05). Independent risk factors for IGRA positivity were increasing age (QFT-G: aOR = 1.98, p = 0.03; QFT-GIT: aOR = 2.00, p = 0.01) and IDUs (aOR = 4.33, p = 0.05 by QFT-G).

CONCLUSION

HIV-infected persons had a significantly lower response to both IGRAs and TST. High discordance was found between the two generations of IGRAs and between IGRAs and TST. Increasing age, a known risk factor for LTBI, was significantly associated with IGRAs, but not with TST.

Serological diagnostic assays for HIV-associated tuberculosis in sub-Saharan Africa?

In this issue of Clinical and Vaccine Immunology, Siev and colleagues present an evaluation of antibody responses to four immunodominant proteins of Mycobacterium tuberculosis in patients with HIV-associated pulmonary tuberculosis (TB) in South Africa (M. Siev, D. Wilson, S. Kainth, V. O. Kasprowicz, C. M. Feintuch, E. Jenny-Avital, and J. J. Achkar, 21:791-798, 2014, doi:http://dx.doi.org/10.1128/CVI.00805-13). This commentary discusses the enormous need for simple point-of-care assays for tuberculosis (TB) diagnosis in patients with and without HIV coinfection in high-burden settings and considers the potential role of serological assays and the huge challenges inherent in developing and validating such assays.

Antibodies against Mycobacterial proteins as biomarkers for HIV-associated smear-negative tuberculosis

Serology data are limited for patients with sputum smear-negative HIV-associated active tuberculosis (TB). We evaluated the serum antibody responses against the mycobacterial proteins MPT51, MS, and echA1 and the 38-kDa protein via enzyme-linked immunosorbent assay (ELISA) in South African (S.A.) HIV-positive (HIV(+)) smear-negative TB patients (n = 56), U.S. HIV(+) controls with a positive tuberculin skin test (TST(+); n = 21), and S.A. HIV-negative (HIV(-)) (n = 18) and HIV(+) (n = 24) controls. TB patients had positive antibody reactivity against MPT51 (73%), echA1 (59%), MS (36%), and the 38-kDa protein (11%). Little reactivity against MPT51 and echA1 was observed in control groups at low risk for TB, i.e., S.A. HIV(-) (0% and 6%, respectively), and at moderate risk for TB development, i.e., U.S. HIV(+) TST(+) controls (14% and 10%, respectively). By contrast, more reactivity was detected in the S.A. HIV(+) control group at higher risk for TB (25% and 45%, respectively). Our data hold promise that antibody detection against MPT51 and echA1 might have adjunctive value in the detection of HIV(+) smear-negative TB and might reflect increasing Mycobacterium tuberculosis infection activity in asymptomatic HIV(+) individuals.

Tuberculosis among people living with HIV/AIDS in the German ClinSurv HIV Cohort: long-term incidence and risk factors

Background

Tuberculosis (TB) still presents a leading cause of morbidity and mortality among people living with HIV/AIDS (PLWHA), including those on antiretroviral therapy. In this study, we aimed to determine the long-term incidence density rate (IDR) of TB and risk factors among PLWHA in relation to combination antiretroviral therapy (cART)-status.

Methods

Data of PLWHA enrolled from 2001 through 2011 in the German ClinSurv HIV Cohort were investigated using survival analysis and Cox regression.

Results

TB was diagnosed in 233/11,693 PLWHA either at enrollment (N = 62) or during follow-up (N = 171). The TB IDR during follow-up was 0.37 cases per 100 person-years (PY) overall [95% CI, 0.32-0.43], and was higher among patients who never started cART and among patients originating from Sub-Saharan Africa (1.23 and 1.20 per 100PY, respectively). In two multivariable analyses, both patients (I) who never started cART and (II) those on cART shared the same risk factors for TB, namely: originating from Sub-Saharan Africa compared to Germany (I, hazard ratio (HR); [95% CI]) 4.05; [1.87-8.78] and II, HR 5.15 [2.76-9.60], CD4+ cell count <200 cells/μl (I, HR 8.22 [4.36-15.51] and II, HR 1.90 [1.14-3.15]) and viral load >5 log₁₀ copies/ml (I, HR 2.51 [1.33-4.75] and II, HR 1.77 [1.11-2.82]). Gender, age or HIV-transmission risk group were not independently associated with TB.

Conclusion

In the German ClinSurv HIV cohort, patients originating from Sub-Saharan Africa, with low CD4+ cell count or high viral load at enrollment were at increased risk of TB even after cART initiation. As patients might be latently infected with Mycobacterium tuberculosis complex, early screening for latent TB infection and implementing isoniazid preventive therapy in line with available recommendations is crucial.

IgA response to ESAT-6/CFP-10 and Rv2031 antigens varies in patients with culture-confirmed pulmonary tuberculosis, healthy Mycobacterium tuberculosis-infected and non-infected individuals in a tuberculosis endemic setting, Ethiopia

Little attention has been given to the role of antibodies against Mycobacterium tuberculosis (Mtb) infection. We have compared the levels of IgA and IgG against ESAT-6/CFP-10 and Rv2031c antigens in sera of patients with culture-confirmed pulmonary tuberculosis (PTB), healthy Mtb-infected and non-infected individuals in endemic TB settings. Venous blood samples were collected from 166 study participants; sera were separated and assayed by an enzyme-linked immunosorbent assay (ELISA). QuantiFERON-TB Gold In-Tube (QFTGIT) assay was used for the screening of latent TB infection. The mean optical density (OD) values of IgA against ESAT-6/CFP-10 and Rv2031 were significantly higher in sera of patients with culture-confirmed PTB compared with healthy Mtb-infected and non-infected individuals (P < 0.001). The mean OD values of IgG against ESAT-6/CFP-10 and Rv2031 were also significantly higher in sera of patients with culture-confirmed PTB compared with healthy Mtb-infected and non-infected individuals (P < 0.05). The mean OD values of IgA against both antigens were also higher in sera of healthy Mtb-infected cases compared with non-infected individuals. There were positive correlations (P < 0.05) between the level of IFN-γ induced in QFTGIT assay and the OD values of serum IgA against both antigens in healthy Mtb-infected subjects. This study shows the potential of IgA response against ESAT-6/CFP-10 and Rv2031 antigens in discriminating clinical TB from healthy Mtb-infected and non-infected cases. Nevertheless, further well-designed cohort study is needed to fully realize the full potential of this diagnostic marker.

The biology of mycobacterium tuberculosis infection

Tuberculosis (TB) still poses a major threat to mankind and during the last thirty years we have seen a recrudescence of the disease even in countries where TB was thought to be conquered. It is common opinion that more effective control tools such as new diagnostics, a new vaccine and new drugs are urgently needed to control the global pandemic, though the so far insufficient understanding of the Mycobacterium tuberculosis (Mtb) mechanism of pathogenesis is a major obstacle for the development of these control tools. In this review, we will summarize the recent advancement in the understanding of Mtb biology and on the pathogenesis of Mtb infection with emphasis on latent infection, with the change in paradigm of the last few years where the dichotomy between latent and active disease has been reconsidered in favor of a dynamic equilibrium between the host and the bacilli, encompassing a continuous spectrum of conditions that has been named TB spectrum. Implications for the diagnosis and control of disease in certain population will also be discussed.

Community's knowledge, attitudes and practices about tuberculosis in Itang Special District, Gambella Region, South Western Ethiopia

Background

Tuberculosis (TB) is one of the primary public health problems in developing countries. HIV/AIDS, poverty, undernutrition, over-crowded living conditions and lack of knowledge about the disease have been known to increase the risk of spreading the bacteria and the risk of developing the disease. The objective of this study was to assess the level of TB knowledge, attitudes and practices of rural communities of Itang Special District of the Gambella Regional State of Ethiopia.

Methods

Between November 2011 and January 2012, a community-based cross sectional study was carried out in a randomly selected rural kebeles (i.e. the smallest administrative units) of Itang communities. The study participants were interviewed using pre-tested questionnaire. The overall knowledge, attitudes and practices of the study participants were assessed using the mean score of each outcome as a cut-off value. Having a score above the mean on each of the three target outcomes was equated with having a good level of knowledge, or having favorable attitude and good practices towards TB.

Results

Out of 422 study participants (58.5% males and 41.5% females) only 3.3% mentioned bacteria/germ as a cause of pulmonary TB (PTB) and 9.9% mentioned cough for at least two weeks as the sign of TB. Taking the mean knowledge score as the cut-off value, 57.6% (95% CI: 52.7% to 62.3%) of the study participants had good level of knowledge about TB, 40.8% (95% CI: 36.0% to 45.6%) had favorable attitude towards TB and 45.9% (95% CI: 41.1% to 50.9%) had good practices. Female participants were less likely to have good level of knowledge [adjusted odds ratio (AOR) = 0.33, 95% CI, 0.21 to 0.51, p < 0.001], less likely to have favorable attitude (AOR = 0.23, 95% CI, 0.14 to 0.37) and less likely to have good practices (AOR = 0.37, 95% CI, 0.24 to 0.57, p < 0.001) compared to male participants.

Conclusion

Majority of the study participants had no correct information about the causative agent of TB and the main symptom of PTB. Moreover, low level of overall knowledge, attitudes and practices about TB was associated with female participants. Hence, TB control strategy in the present study area should include community awareness raising component.

Shortening the 'short-course' therapy- insights into host immunity may contribute to new treatment strategies for tuberculosis

Achieving global control of tuberculosis (TB) is a great challenge considering the current increase in multidrug resistance and mortality rate. Considerable efforts are therefore being made to develop new effective vaccines, more effective and rapid diagnostic tools as well as new drugs. Shortening the duration of TB treatment with revised regimens and modes of delivery of existing drugs, as well as development of new antimicrobial agents and optimization of the host response with adjuvant immunotherapy could have a profound impact on TB cure rates. Recent data show that chronic worm infection and deficiencies in micronutrients such as vitamin D and arginine are potential areas of intervention to optimize host immunity. Nutritional supplementation to enhance nitric oxide production and vitamin D-mediated effector functions as well as the treatment of worm infection to reduce immunosuppressive effects of regulatory T (Treg) lymphocytes may be more suitable and accessible strategies for highly endemic areas than adjuvant cytokine therapy. In this review, we focus mainly on immune control of human TB, and discuss how current treatment strategies, including immunotherapy and nutritional supplementation, could be optimized to enhance the host response leading to more effective treatment.

Systemic immune activation and microbial translocation in dual HIV/tuberculosis-infected subjects

BACKGROUND

Systemic immune activation is a strong predictor of progression of human immunodeficiency virus type 1 (HIV-1) disease and a prominent feature of infection with Mycobacterium tuberculosis.

OBJECTIVE

To understand the role of systemic immune activation and microbial translocation in HIV/tuberculosis dually infected patients over the full spectrum of HIV-1 immunodeficiency, we studied circulating sCD14 and lipopolysaccharide (LPS) and their relationship to HIV-1 activity.

METHODS

Two cohorts of HIV/tuberculosis subjects defined by CD4 T-cell count at time of diagnosis of tuberculosis were studied: those with low (<350/μL) and those with high (≥ 350/μL) CD4 T-cell count. Circulating soluble CD14 (sCD14) and LPS were assessed.

RESULTS

Levels of sCD14 were higher in HIV/tuberculosis with high (≥ 350/μL) as compared to low CD4 T-cell count (P < .001). Whereas sCD14 levels remained elevated in HIV/tuberculosis subjects with lower CD4 T-cell counts despite treatment of tuberculosis, in HIV/tuberculosis patients with higher CD4 T-cell count (≥ 350/μL), levels declined regardless of whether highly active antiretroviral therapy (HAART) was included with the anti-tuberculosis regimen. Circulating LPS levels in HIV/tuberculosis patients with CD4 T-cell count ≥ 350/μL were unaffected by treatment of tuberculosis with or without HAART.

CONCLUSION

During HIV/tuberculosis, systemic immune activation is dissociated from microbial translocation. Changes in circulating sCD14 and LPS are dependent on CD4 T-cell count.

A twenty-year retrospective study of pediatric tuberculosis in two tertiary hospitals in Rome

BACKGROUND

Tuberculosis (TB) is among the top 10 causes of child death worldwide. Nevertheless, childhood disease has been neglected by tuberculosis control programs.

METHODS

This was a retrospective study of patients < 16 years of age diagnosed with active TB in 2 tertiary hospitals in Rome (Italy), between 1990 and 2009.

RESULTS

Two hundred fourteen cases of active tuberculosis were identified (132 definite, 82 probable). Pulmonary involvement was the most common form (75.5%), followed by lymphadenopathy (15.4%) and central nervous system TB (11%). Fever (51.86%) and cough (40%) were the most common presenting symptoms. A total of 23.4% of children were asymptomatic on admission. Sensitivities of the tuberculin skin test and the quantiferon test were 93.4% and 97%, respectively. Both tests performed in 52 children agreed in 49 cases (94%). Sensitivities for culture, Ziehl-Neelsen staining and polymerase chain reaction were 58%, 25% and 66.3%, respectively. The adult source case was identified in 28% of cases. History of contact with a patient with active TB was associated with pulmonary TB (P = 0.0014), whereas negative history of contact was associated with lymph node (P = 0.0064) and central nervous system TB (P = 0.05).

CONCLUSIONS

Our study emphasizes the difficulty in managing children with suspected TB, because the absence of constitutional symptoms cannot exclude TB, and bacteriologic confirmation is the exception. Immunologic diagnosis can be a valuable tool to identify TB-infected children because the quantiferon test showed high sensitivity in all age groups. This is of primary importance because early identification of children with latent tuberculous infection and appropriate chemoprophylaxis represent, to date, the most important tool to reduce the burden of TB.

Risk stratification of latent tuberculosis defined by combined interferon gamma release assays

BACKGROUND

Most individuals infected with Mycobacterium tuberculosis develop latent tuberculosis infection (LTBI). Some may progress to active disease and would benefit from preventive treatment yet no means currently exists to predict who will reactivate. Here, we provide an approach to stratify LTBI based on IFN-γ responses to two antigens, the recombinant Early-Secreted Antigen Target-6 (rESAT-6) and the latency antigen Heparin-Binding Haemagglutinin (HBHA).

METHODS

We retrospectively analyzed results from in-house IFN-γ-release assays with HBHA (HBHA-IGRA) and rESAT-6 (rESAT-6-IGRA) performed during a 12-year period on serial blood samples (3 to 9) collected from 23 LTBI subjects in a low-TB incidence country. Both the kinetics of the absolute IFN-γ concentrations secreted in response to each antigen and the dynamics of HBHA/rESAT-6-induced IFN-γ concentrations ratios were examined.

RESULTS

This analysis allowed the identification among the LTBI subjects of three major groups. Group A featured stable HBHA and rESAT-6-IGRA profiles with an HBHA/rESAT-6 ratio persistently higher than 1, and with high HBHA- and usually negative rESAT-6-IGRA responses throughout the study. Group B had changing HBHA/rESAT-6 ratios fluctuating from 0.0001 to 10,000, with both HBHA and rESAT-6 responses varying over time at least once during the follow-up. Group C was characterized by a progressive disappearance of all responses.

CONCLUSIONS

By combining the measures of IFN-γ concentrations secreted in response to an early and a latency antigens, LTBI subjects can be stratified into different risk groups. We propose that disappearing responses indicate cure, that persistent responses to HBHA with HBHA/rESAT-6 ratios ≥ 1 represent stable LTBI subjects, whereas subjects with ratios varying from >1 to <1 should be closely monitored as they may represent the highest-risk group, as illustrated by a case report, and should therefore be prioritized for preventive treatment.

The role of biomedical research in global tuberculosis control: gaps and challenges: A perspective from the US National Institute of Allergy and Infectious Diseases, National Institutes of Health

Tuberculosis (TB) has been a persistent public health concern for hundreds of years. Despite advances in medicine and science, eliminating this disease has been beyond our reach. Several organizations, including the National Institute of Allergy and Infectious Diseases (NIAID), part of the National Institutes of Health (NIH), have expressed their commitment to advancing biomedical research in TB in order to increase our understanding of the causative pathogen and the disease. This basic knowledge is a critical first step in the development and implementation of new therapeutics, vaccines and diagnostics. Collaboration between researchers is a key component to accomplishing this goal; product development can no longer be limited to separate programs. Rather, the interconnectedness and possible combination of interventions must be investigated. This review will discuss ongoing TB research including NIAID's role, as well as future research that is needed to improve TB control. Emphasizing the importance of coordination among researchers, funders and advocacy groups, we aim to illustrate the fact that biomedical research, and particularly basic research, is a vital part of a complementary approach to eliminating TB across the globe.

Impact of antiretroviral therapy on tuberculosis incidence among HIV-positive patients in high-income countries

BACKGROUND

The lower tuberculosis incidence reported in human immunodeficiency virus (HIV)-positive individuals receiving combined antiretroviral therapy (cART) is difficult to interpret causally. Furthermore, the role of unmasking immune reconstitution inflammatory syndrome (IRIS) is unclear. We aim to estimate the effect of cART on tuberculosis incidence in HIV-positive individuals in high-income countries.

METHODS

The HIV-CAUSAL Collaboration consisted of 12 cohorts from the United States and Europe of HIV-positive, ART-naive, AIDS-free individuals aged ≥18 years with baseline CD4 cell count and HIV RNA levels followed up from 1996 through 2007. We estimated hazard ratios (HRs) for cART versus no cART, adjusted for time-varying CD4 cell count and HIV RNA level via inverse probability weighting.

RESULTS

Of 65 121 individuals, 712 developed tuberculosis over 28 months of median follow-up (incidence, 3.0 cases per 1000 person-years). The HR for tuberculosis for cART versus no cART was 0.56 (95% confidence interval [CI], 0.44-0.72) overall, 1.04 (95% CI, 0.64-1.68) for individuals aged >50 years, and 1.46 (95% CI, 0.70-3.04) for people with a CD4 cell count of <50 cells/μL. Compared with people who had not started cART, HRs differed by time since cART initiation: 1.36 (95% CI, 0.98-1.89) for initiation <3 months ago and 0.44 (95% CI, 0.34-0.58) for initiation ≥3 months ago. Compared with people who had not initiated cART, HRs <3 months after cART initiation were 0.67 (95% CI, 0.38-1.18), 1.51 (95% CI, 0.98-2.31), and 3.20 (95% CI, 1.34-7.60) for people <35, 35-50, and >50 years old, respectively, and 2.30 (95% CI, 1.03-5.14) for people with a CD4 cell count of <50 cells/μL.

CONCLUSIONS

Tuberculosis incidence decreased after cART initiation but not among people >50 years old or with CD4 cell counts of <50 cells/μL. Despite an overall decrease in tuberculosis incidence, the increased rate during 3 months of ART suggests unmasking IRIS.

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.

Incipient and subclinical tuberculosis: defining early disease states in the context of host immune response

Latent Mycobacterium tuberculosis infection (LTBI) and active tuberculosis (TB) are 2 ends of a spectrum of states ranging from asymptomatic infection to overt disease. While progressing from LTBI to TB, patients often undergo asymptomatic states with detectable manifestations indicative of disease. Such asymptomatic disease states frequently remain undiagnosed, and their manifestations and duration are mostly dependent on host immune response. Various terms referring to such states are used in the literature, often interchangeably and without explicit definitions. Defining these intermediate states in concrete terms is important for pragmatic reasons, as they might impact upon the diagnostic performance of TB biomarkers and could also present targets for therapeutic interventions. We here propose definitions for 2 commonly used terms, "incipient" and "subclinical" TB, to describe asymptomatic disease states occurring at opposite ends of the host response spectrum. We propose using the term "incipient TB" when referring to early, contained disease in asymptomatic, relatively immunocompetent persons. In contrast, we propose using the term "subclinical TB" to refer to disease in asymptomatic, immunocompromised individuals in whom it is largely associated with loss of effective containment. The rationale for this article is to facilitate the discussion of such early disease states, especially in relation to their impact on TB biomarker discovery and assessment of new diagnostics, and with regard to treatment decisions and ultimately outcome.

Tuberculosis in antiretroviral treatment services in resource-limited settings: addressing the challenges of screening and diagnosis

The high burden of tuberculosis (TB) among patients accessing antiretroviral treatment (ART) services in resource-limited settings is a major cause of morbidity and mortality and is associated with nosocomial transmission risk. These risks are greatly compounded by multidrug-resistant disease. Screening and diagnosis of TB in this clinical setting is difficult. However, progress has been made in defining a high-sensitivity, standardized symptom screening tool that assesses a combination of symptoms, rather than relying on report of cough alone. Moreover, newly emerging diagnostic tools show great promise in providing more rapid diagnosis of TB, which is predominantly sputum smear–negative. These include culture-based systems, simplified versions of nucleic acid amplification tests (such as the Xpert MTB/RIF assay), and detection of lipoarabinomannan antigen in urine. In addition, new molecular diagnostics now permit rapid detection of drug resistance. Further development and implementation of these tools is vital to permit rapid and effective screening for TB in ART services, which is an essential component of patient care.

Higher frequency of T-cell response to M. tuberculosis latency antigen Rv2628 at the site of active tuberculosis disease than in peripheral blood

Rationale

Due to the invasive nature of the procedures involved, most studies of Mycobacterium tuberculosis (Mtb)-specific immunity in humans have focused on the periphery rather than the site of active infection, the lung. Recently, antigens associated with Mtb-latency and -dormancy have been described using peripheral blood (PB) cells; however their response in the lung is unknown. The objective of this report was to evaluate, in patients prospectively enrolled with suspected active tuberculosis (TB), whether the latency antigen Rv2628 induces local-specific immune response in bronchoalveolar lavage (BAL) cells compared to PB cells.

Material/Methods

Among the 41 subjects enrolled, 20 resulted with active TB. Among the 21 without active disease, 9 were defined as subjects with latent TB-infection (LTBI) [Quantiferon TB Gold In-tube positive]. Cytokine responses to Rv2628 were evaluated by enzyme linked immunospot (ELISPOT) assay and flow cytometric (FACS) analysis. RD1-secreted antigen stimulation was used as control.

Results

There was a significantly higher frequency of Rv2628- and RD1-specific CD4⁺ T-cells in the BAL of active TB patients than in PB. However the trend of the response to Rv2628 in subjects with LTBI was higher than in active TB in both PB and BAL, although this difference was not significant. In active TB, Rv2628 and RD1 induced a cytokine-response profile mainly consisting of interferon (IFN)-γ-single-positive over double-IFN-γ/interleukin (IL)-2 T-cells in both PB and BAL. Finally, BAL-specific CD4⁺ T-cells were mostly effector memory (EM), while peripheral T-cell phenotypes were distributed among naïve, central memory and terminally differentiated effector memory T-cells.

Conclusions

In this observational study, we show that there is a high frequency of specific T-cells for Mtb-latency and RD1-secreted antigens (mostly IFN-γ-single-positive specific T-cells with an EM phenotype) in the BAL of active TB patients. These data may be important for better understanding the pathogenesis of TB in the lung.

Latent tuberculosis: what the host "sees"?

Mycobacterium tuberculosis (MTB), the causative agent of tuberculosis (TB), is the most successful pathogen of mankind and remains a major threat to global health as the leading cause of death due to a bacterial pathogen. Yet 90-95% of those who are infected with MTB remain otherwise healthy. These people are classified as "latently infected," but remain a reservoir from which active TB cases will continue to develop ("reactivation tuberculosis"). Latent infection is defined by the absence of clinical symptoms of TB in addition to a delayed hypersensitivity reaction to the purified protein derivative of MTB used in tuberculin skin test or a T-cell response to MTB-specific antigens. In the absence of reliable control measures for tuberculosis, understanding latent MTB infection and subsequent reactivation is a research priority. This review aims to summarize the recent findings in human and non-human primate models of tuberculosis that have led to new concepts of latent tuberculosis.

Reciprocal seasonal variation in vitamin D status and tuberculosis notifications in Cape Town, South Africa

Vitamin D deficiency is associated with susceptibility to tuberculosis (TB) in HIV-uninfected people in Europe, but it is not known whether such an association exists among HIV-infected people in subtropical Africa. We conducted a cross-sectional study to determine whether vitamin D deficiency was associated with susceptibility to active TB in HIV-uninfected (n = 196) and HIV-infected (n = 174) black Africans in Cape Town, South Africa. We also investigated whether there was evidence of seasonal variation in vitamin D status and TB notifications in this setting over an 8-y period. Vitamin D deficiency (serum 25-hydroxyvitamin D [25(OH)D] <50 nmol/L) was present in 232 (62.7%) of 370 participants and was associated with active TB in both HIV-uninfected (odds ratio = 5.2, 95% confidence interval: 2.8-9.7; P < 0.001) and HIV-infected (odds ratio = 5.6, 95% confidence interval: 2.7-11.6; P < 0.001) people. Vitamin D status varied according to season: The mean serum 25(OH)D concentration was highest in January through March and lowest in July through September (56.8 vs. 30.7 nmol/L, respectively; P < 0.001). Reciprocal seasonal variation in TB notifications was observed: The mean number of TB notifications per quarter for Cape Town in 2003 to 2010 was lowest in April through June and highest in October through December (4,222 vs. 5,080; P < 0.001). Vitamin D deficiency is highly prevalent among black Africans in Cape Town and is associated with susceptibility to active TB both in the presence and absence of HIV infection. Reciprocal seasonal variation in serum 25(OH)D concentration and TB notifications suggests that seasonal variations in vitamin D status and TB incidence in this setting are causally related.

Novel biomarkers distinguishing active tuberculosis from latent infection identified by gene expression profile of peripheral blood mononuclear cells

Background

Humans infected with Mycobacterium tuberculosis (MTB) can delete the pathogen or otherwise become latent infection or active disease. However, the factors influencing the pathogen clearance and disease progression from latent infection are poorly understood. This study attempted to use a genome-wide transcriptome approach to identify immune factors associated with MTB infection and novel biomarkers that can distinguish active disease from latent infection.

Methodology/Principal Findings

Using microarray analysis, we comprehensively determined the transcriptional difference in purified protein derivative (PPD) stimulated peripheral blood mononuclear cells (PBMCs) in 12 individuals divided into three groups: TB patients (TB), latent TB infection individuals (LTBI) and healthy controls (HC) (n = 4 per group). A transcriptional profiling of 506 differentially expressed genes could correctly group study individuals into three clusters. Moreover, 55- and 229-transcript signatures for tuberculosis infection (TB&LTBI) and active disease (TB) were identified, respectively. The validation study by quantitative real-time PCR (qPCR) performed in 83 individuals confirmed the expression patterns of 81% of the microarray identified genes. Decision tree analysis indicated that three genes of CXCL10, ATP10A and TLR6 could differentiate TB from LTBI subjects. Additional validation was performed to assess the diagnostic ability of the three biomarkers within 36 subjects, which yielded a sensitivity of 71% and specificity of 89%.

Conclusions/Significance

The transcription profiles of PBMCs induced by PPD identified distinctive gene expression patterns associated with different infectious status and provided new insights into human immune responses to MTB. Furthermore, this study indicated that a combination of CXCL10, ATP10A and TLR6 could be used as novel biomarkers for the discrimination of TB from LTBI.

Modelling the performance of isoniazid preventive therapy for reducing tuberculosis in HIV endemic settings: the effects of network structure

Individuals living with HIV experience a much higher risk of progression from latent M. tuberculosis infection to active tuberculosis (TB) disease relative to individuals with intact immune systems. A several-month daily course of a single drug during latent infection (i.e. isoniazid preventive therapy (IPT)) has proved in clinical trials to substantially reduce an HIV-infected individual's risk of TB disease. As a result of these findings and ongoing studies, the World Health Organization has produced strong guidelines for implementing IPT on a community-wide scale for individuals with HIV at risk of TB disease. To date, there has been limited use of IPT at a community-wide level. In this paper, we present a new co-network model for HIV and TB co-epidemics to address questions about how the population-level impact of community-wide IPT may differ from the individual-level impact of IPT offered to selected individuals. In particular, we examine how the effect of clustering of contacts within high-TB incidence communities may affect the rates of re-infection with TB and how this clustering modifies the expected population-level effects of IPT. We find that populations with clustering of respiratory contacts experience aggregation of TB cases and high numbers of re-infection events. While, encouragingly, the overall population-level effects of community-wide IPT appear to be sustained regardless of network structure, we find that in populations where these contacts are highly clustered, there is dramatic heterogeneity in the impact of IPT: in some sub-regions of these populations, TB is nearly eliminated, while in others, repeated re-infection almost completely undermines the effect of IPT. Our findings imply that as IPT programmes are brought to scale, we should expect local heterogeneity of effectiveness as a result of the complex patterns of disease transmission within communities.

Methylated HBHA produced in M. smegmatis discriminates between active and non-active tuberculosis disease among RD1-responders

Background

A challenge in tuberculosis (TB) research is to develop a new immunological test that can help distinguish, among subjects responsive to QuantiFERON TB Gold In tube (QFT-IT), those who are able to control Mtb replication (remote LTBI, recent infection and past TB) from those who cannot (active TB disease). IFN-γ response to the Heparin-binding-hemagglutinin (HBHA) of Mtb has been associated with LTBI, but the cumbersome procedures of purifying the methylated and immunological active form of the protein from Mtb or M. bovis Bacillus Calmette et Guerin (BCG) have prevented its implementation in a diagnostic test. Therefore, the aim of the present study was to evaluate the IFN-γ response to methylated HBHA of Mtb produced in M. smegmatis (rHBHAms) in individuals at different stages of TB who scored positive to QFT-IT.

Methodology/Principal Findings

87 individuals at different stages of TB who scored positive to QFT-IT were selected. IFN-γ response to in vitro whole blood stimulation with rHBHAms was evaluated by short-term and long-term tests and detected by ELISA or flow cytometry. We demonstrated that the IFN-γ response to rHBHAms is mediated by CD4⁺ T-cells with an effector-memory phenotype. This response, evaluated by short-term-tests, is significantly lower in active TB than in remote LTBI (p = 0.0010) and past TB (p = 0.0152). These results were confirmed by long-term tests. The qualitative data confirmed that IFN-γ responses higher than the cut-off point identified by ROC analysis are associated with the status of non-active disease.

Conclusions

In this study we show that the T-cell response to a recombinant and methylated HBHA of Mtb produced in M. smegmatis is useful to discriminate between active and non-active TB disease among those responsive to QFT-IT in a whole blood system. Further studies are needed to improve the accuracy of the assay.