Evaluation of a whole-blood interferon-gamma release assay for the detection of Mycobacterium tuberculosis infection in 2 study populations

Toll-Like Receptor-Induced Immune Responses During Early Childhood and Their Associations With Clinical Outcomes Following Acute Illness Among Infants in Sub-Saharan Africa

Severely ill children in low- and middle-income countries (LMICs) experience high rates of mortality from a broad range of infectious diseases, with the risk of infection-related death compounded by co-existing undernutrition. How undernutrition and acute illness impact immune responses in young children in LMICs remains understudied, and it is unclear what aspects of immunity are compromised in this highly vulnerable population. To address this knowledge gap, we profiled longitudinal whole blood cytokine responses to Toll-like receptor (TLR) ligands among severely ill children (n=63; 2-23 months old) with varied nutritional backgrounds, enrolled in the CHAIN Network cohort from Kampala, Uganda, and Kilifi, Kenya, and compared these responses to similar-aged well children in local communities (n=41). Cytokine responses to ligands for TLR-4 and TLR-7/8, as well as Staphylococcus enterotoxin B (SEB), demonstrated transient impairment in T cell function among acutely ill children, whereas innate cytokine responses were exaggerated during both acute illness and following clinical recovery. Nutritional status was associated with the magnitude of cytokine responses in all stimulated conditions. Among children who died following hospital discharge or required hospital re-admission, exaggerated production of interleukin-7 (IL-7) to all stimulation conditions, as well as leukopenia with reduced lymphocyte and monocyte counts, were observed. Overall, our findings demonstrate exaggerated innate immune responses to pathogen-associated molecules among acutely ill young children that persist during recovery. Heightened innate immune responses to TLR ligands may contribute to chronic systemic inflammation and dysregulated responses to subsequent infectious challenges. Further delineating mechanisms of innate immune dysregulation in this population should be prioritized to identify novel interventions that promote immune homeostasis and improve outcomes.

LIODetect®TB-ST: Evaluation of novel blood test for a rapid diagnosis of active pulmonary and extra-pulmonary tuberculosis in IGRA confirmed patients

Because of the current limits of immunological tests in the diagnosis of tuberculosis there is a need to identify new and rapid tests that can be carried out on a large scale in endemic countries and useful in the identification of infected subjects, but also able to discriminate those with latent infection from subjects with active. We have taken into consideration and analysed the LIODetect®TB-ST Tuberculosis Rapid Test, a membrane test for the qualitative detection of specific IgG, IgA, and IgM antibodies against Mycobacterium tuberculosis, performed on serum, plasma, or whole blood.85 samples positive to QuantiFERON TB-GOLD PLUS test were processed using this test and the results obtained were concordant with clinical diagnosis.To our knowledge, the LIODetect®TB-ST Tuberculosis Rapid Test is the only test; that identifies active tuberculosis disease with high sensitivity and specificity and its use might be of help in the diagnosis of tuberculosis, especially in endemic countries.

Microarray-based selection of a serum biomarker panel that can discriminate between latent and active pulmonary TB

Bacterial culture of M. tuberculosis (MTB), the causative agent of tuberculosis (TB), from clinical specimens is the gold standard for laboratory diagnosis of TB, but is slow and culture-negative TB cases are common. Alternative immune-based and molecular approaches have been developed, but cannot discriminate between active TB (ATB) and latent TB (LTBI). Here, to identify biomarkers that can discriminate between ATB and LTBI/healthy individuals (HC), we profiled 116 serum samples (HC, LTBI and ATB) using a protein microarray containing 257 MTB secreted proteins, identifying 23 antibodies against MTB antigens that were present at significantly higher levels in patients with ATB than in those with LTBI and HC (Fold change > 1.2; p < 0.05). A 4-protein biomarker panel (Rv0934, Rv3881c, Rv1860 and Rv1827), optimized using SAM and ROC analysis, had a sensitivity of 67.3% and specificity of 91.2% for distinguishing ATB from LTBI, and 71.2% sensitivity and 96.3% specificity for distinguishing ATB from HC. Validation of the four candidate biomarkers in ELISA assays using 440 serum samples gave consistent results. The promising sensitivity and specificity of this biomarker panel suggest it merits further investigation for its potential as a diagnostic for discriminating between latent and active TB.

Immunological Aspects of Diagnosis and Management of Childhood Tuberculosis

The diagnosis of tuberculosis (TB) in children is difficult because of the low sensitivity and specificity of traditional microbiology techniques in this age group. Whereas in adults the culture of Mycobacterium tuberculosis (M. tuberculosis), the gold standard test, detects 80% of positive cases, it only detects around 30-40% of cases in children. The new methods based on the immune response to M. tuberculosis infection could be affected by many factors. It is necessary to evaluate the medical record, clinical features, presence of drug-resistant M. tuberculosis strains, comorbidities, and BCG vaccination history for the diagnosis in children. There is no ideal biomarker for all TB cases in children. A new strategy based on personalized diagnosis could be used to evaluate specific molecules produced by the host immune response and make therapeutic decisions in each child, thereby changing standard immunological signatures to personalized signatures in TB. In this way, immune diagnosis, prognosis, and the use of potential immunomodulators as adjunct TB treatments will meet personalized treatment.

Comparison of tuberculin skin test and QuantiFERON-TB Gold In-Tube test in Bacillus Calmette-Guerin-vaccinated children

Objectives:

The aim of this study is to determine the concordance between QuantiFERON-TB Gold In-Tube (QFT-GIT) and tuberculin skin test (TST) in children vaccinated with Bacillus Calmette–Guerin (BCG).

Methods:

This cross-sectional study was done at a pediatric tertiary care center in 33 BCG-vaccinated children aged 6 months–15 years suspected of Mycobacterium tuberculosis infection or in contact with a patient with open tuberculosis (TB). All patients were tested for TST with purified protein derivative-S 5 tuberculin units and QFT-GIT assays. Concordance was evaluated between TST and QFT assay by kappa coefficient (k). Agreement between the tests was classified into categories: poor if k < 0.20, fair (k = 0.21–0.40), moderate (k = 0.41–0.60), good (k = 0.61–0.80), and very good (k = 0.81–1.00).

Results:

Both the TST and QFT assay were positive in 13 and negative in eight children, respectively, resulting in an agreement of 63% (κ = 0.31). Eight children were <4 years of age of which only one patient had a positive TST and QFT-GIT, and TST and QFT-GIT were negative in two patients resulting in an agreement of 37.5% (κ = 0.063). Among children 4 years of age and older, 12 patients had a positive TST and QFT-GIT and 6 patients had a negative TST and QFT-GIT resulting in an agreement of 72% (κ = 0.41). Among 12 children who had been in contact with an adult having open TB, both the TST and QFT-GIT were positive in 6 patients and negative in two patients, respectively, resulting in an agreement of 66% (κ = 0.41). TST specificity was only 29.6% with a positive predictive value of 42.4% as compared to QFT-GIT. Among children <4 years of age, TST specificity was only 28.6% with a positive predictive rate of 16.7%, and among children >4 years of age, TST specificity was 50% with a positive predictive value of 66.7%. In patients with contact with a patient having TB, TST specificity was 33.3%. Considering TST of 15 mm and above as positive, TST specificity increased to 63.2% and a positive predictive value was 56.3%.

Conclusion:

The concordance of TST and QFT-GIT is low in children with previous BCG vaccination and especially in children <4 years of age. QFT-GIT may help to rule out false-positive TST.

Development and Validation of the Evaluation Platform in COPD (EPIC): A Population-Based Outcomes Model of COPD for Canada

BACKGROUND

We report the development, validation, and implementation of an open-source population-based outcomes model of chronic obstructive pulmonary disease (COPD) for Canada.

METHODS

Evaluation Platform in COPD (EPIC) is a discrete-event simulation model of Canadians 40 years of age or older. Three core features of EPIC are its open-population design (incorporating projections of future population growth, aging, and smoking trends), its incorporation of heterogeneity in lung function decline and burden of exacerbations, and its modeling of the natural history of COPD from inception. Multiple original data analyses, as well as values reported in the literature, were used to populate the model. Extensive face validity and internal and external validity evaluations were performed.

RESULTS

The model was internally validated on demographic projections, mortality rates, lung function trajectories, COPD exacerbations, costs and health state utility values, and stability of COPD prevalence over time within strata of risk factors. In external validation, it moderately overestimated the rate of overall exacerbations in 2 independent trials but generated consistent estimates of rate of severe exacerbations and mortality.

LIMITATIONS

In its current version, EPIC does not consider uncertainty in the evidence. Several components such as additional (e.g., environmental and occupational) risk factors, treatment, symptoms, and comorbidity will have to be added in future iterations. Predictive validity of EPIC needs to be examined prospectively against future empirical studies.

CONCLUSIONS

EPIC is the first multipurpose, open-source, outcome- and policy-focused model of COPD for Canada. Platforms of this type have the capacity to be iteratively updated to incorporate the latest evidence and to project the outcomes of many different scenarios within a consistent framework.

Tuberculous Peritonitis

Tuberculous peritonitis is rare in the United States but continues to be reported to occur in certain high-risk populations, which include patients with AIDS or cirrhosis, patients on continuous ambulatory peritoneal dialysis, recent immigrants from areas of high endemicity, and those who are immunosuppressed. The diagnosis of this disease requires a high clinical index of suspicion and should be considered in the differential of ascites with a lymphocyte predominance and serum-ascitic albumin gradient of <1.1 mg/dl. Microbiological or pathological confirmation remains the gold standard for diagnosis. Ascitic fluid cultures have low yield, but peritoneoscopy with biopsy or cultures frequently confirms the diagnosis. Newer techniques with future application include determination of adenosine deaminase and interferon gamma levels in ascitic fluid. Ultrasound and computed tomography are frequently used to guide fluid aspiration and biopsies. Six months of treatment with antituberculosis therapy is adequate except in cases of drug-resistant tuberculosis. The role of steroids remains controversial. Surgical approaches may be required to deal with complications including bowel perforation, intestinal obstruction from adhesions, fistula formation, or bleeding.

Revisiting annual screening for latent tuberculosis infection in healthcare workers: a cost-effectiveness analysis

BACKGROUND

In North America, tuberculosis incidence is now very low and risk to healthcare workers has fallen. Indeed, recent cohort data question routine annual tuberculosis screening in this context. We compared the cost-effectiveness of three potential strategies for ongoing screening of North American healthcare workers at risk of exposure. The analysis did not evaluate the cost-effectiveness of screening at hiring, and considered only workers with negative baseline tests.

METHODS

A decision analysis model simulated a hypothetical cohort of 1000 workers following negative baseline tests, considering duties, tuberculosis exposure, testing and treatment. Two tests were modelled, the tuberculin skin test (TST) and QuantiFERON®-TB-Gold In-Tube (QFT). Three screening strategies were compared: (1) annual screening, where workers were tested yearly; (2) targeted screening, where workers with high-risk duties (e.g. respiratory therapy) were tested yearly and other workers only after recognised exposure; and (3) post exposure-only screening, where all workers were tested only after recognised exposure. Workers with high-risk duties had 1% annual risk of infection, while workers with standard patient care duties had 0.3%. In an alternate higher-risk scenario, the corresponding annual risks of infection were 3% and 1%, respectively. We projected costs, morbidity, quality-adjusted survival and mortality over 20 years after hiring. The analysis used the healthcare system perspective and a 3% annual discount rate.

RESULTS

Over 20 years, annual screening with TST yielded an expected 2.68 active tuberculosis cases/1000 workers, versus 2.83 for targeted screening and 3.03 for post-exposure screening only. In all cases, annual screening was associated with poorer quality-adjusted survival, i.e. lost quality-adjusted life years, compared to targeted or post-exposure screening only. The annual TST screening strategy yielded an incremental cost estimate of $1,717,539 per additional case prevented versus targeted TST screening, which in turn cost an incremental $426,678 per additional case prevented versus post-exposure TST screening only. With the alternate "higher-risk" scenario, the annual TST strategy cost an estimated $426,678 per additional case prevented versus the targeted TST strategy, which cost an estimated $52,552 per additional case prevented versus post-exposure TST screening only. In all cases, QFT was more expensive than TST, with no or limited added benefit. Sensitivity analysis suggested that, even with limited exposure recognition, annual screening was poorly cost-effective.

CONCLUSIONS

For most North American healthcare workers, annual tuberculosis screening appears poorly cost-effective. Reconsideration of screening practices is warranted.

Orchestration of pulmonary T cell immunity during Mycobacterium tuberculosis infection: immunity interruptus

Despite the introduction almost a century ago of Mycobacterium bovis BCG (BCG), an attenuated form of M. bovis that is used as a vaccine against Mycobacterium tuberculosis, tuberculosis remains a global health threat and kills more than 1.5 million people each year. This is mostly because BCG fails to prevent pulmonary disease--the contagious form of tuberculosis. Although there have been significant advances in understanding how the immune system responds to infection, the qualities that define protective immunity against M. tuberculosis remain poorly characterized. The ability to predict who will maintain control over the infection and who will succumb to clinical disease would revolutionize our approach to surveillance, control, and treatment. Here we review the current understanding of pulmonary T cell responses following M. tuberculosis infection. While infection elicits a strong immune response that contains infection, M. tuberculosis evades eradication. Traditionally, its intracellular lifestyle and alteration of macrophage function are viewed as the dominant mechanisms of evasion. Now we appreciate that chronic inflammation leads to T cell dysfunction. While this may arise as the host balances the goals of bacterial sterilization and avoidance of tissue damage, it is becoming clear that T cell dysfunction impairs host resistance. Defining the mechanisms that lead to T cell dysfunction is crucial as memory T cell responses are likely to be subject to the same subject to the same pressures. Thus, success of T cell based vaccines is predicated on memory T cells avoiding exhaustion while at the same time not promoting overt tissue damage.

Prevalence of latent tuberculosis infection in Sudan: a case-control study comparing interferon-γ release assay and tuberculin skin test

BACKGROUND

Most people exposed to M. tuberculosis show no evidence of clinical disease. Five to 10% of individuals with latent infection progress to develop overt disease during their life time. Identification of people with latent TB infection will increase case detection rates and may dictate new treatment policies to control tuberculosis. This study aimed to determine LTBI point prevalence in a population from Sudan using two different diagnostic methods: the tuberculin skin test (TST) and the IFN-γ release assay (IGRA).

METHODS

This was a prospective, community-based and case-controlled study. Following informed consent, household contacts (HHCs; n = 98) of smear-positive index cases and Community controls (CCs; 186), were enrolled. Tuberculin skin test (TST), whole blood stimulation with ESAT-6/CFP-10 ± TB7.7 antigens or purified protein derivative (PPD) and IFN-γ levels determination with ELISA were performed. The levels of IFN-γ and TST induration between the CCs and the HHCs were compared using student t-test, Chi-square and Kappa coefficient. Pearson correlation test was used to compare TST and IFN-γ. P levels of <0.05 were considered significant.

RESULTS

TST induration of ≥ 10 mm gave an LTBI point prevalence of 327 cases/1000 individuals among HHCs compared to 126 cases/1000 individuals among CCs (p = 0.000). PPD-induced IFN-γ release assay gave an LTBI point prevalence of 418 cases/1000 individuals among HHCs compared to 301 cases/1000 individuals among CCs (p =0.06). On the other hand ESAT-6/CFP-10 ± TB7.7-induced IFN-γ gave an LTBI point prevalence of 429 cases/1000 individuals among HHCs compared to 268 cases/1000 individuals among CCs (p = 0.01). IFN-γ productions levels induced by ESAT-6/CPF-10 ± TB7.7 antigens in HHCS and CCs were not significantly different from those induced by PPD (p = 0.7).

CONCLUSION

IFN-γ release assay (IGRA) gave higher LTBI point prevalence compared to TST in HHCs and CCs. PPD gave comparable results to ESAT-6/CFP-10 ± TB7.7 antigens in whole blood IFN-γ release, making it a cheap alternative to the recombinant antigens.

Genetic and shared environmental influences on interferon-γ production in response to Mycobacterium tuberculosis antigens in a Ugandan population

Interferon-γ (IFN-γ) is a key cytokine in the immune response to Mycobacterium tuberculosis (Mtb). Many studies established IFN-γ responses are influenced by host genetics, however differed widely by the study design and heritability estimation method. We estimated heritability of IFN-γ responses to Mtb culture filtrate (CF), ESAT-6, and Antigen 85B (Ag85B) in 1,104 Ugandans from a household contact study. Our method separately evaluates shared environmental and genetic variance, therefore heritability estimates were not upwardly biased, ranging from 11.6% for Ag85B to 22.9% for CF. Subset analyses of individuals with latent Mtb infection or without human immunodeficiency virus infection yielded higher heritability estimates, suggesting 10-30% of variation in IFN-γ is caused by a shared environment. Immunosuppression does not negate the role of genetics on IFN-γ response. These estimates are remarkably close to those reported for components of the innate immune response. These findings have implications for the interpretation of IFN-γ response assays and vaccine studies.

A clinical approach to paediatric tuberculosis in Canada

OBJECTIVE

To review clinical aspects of management of tuberculosis (TB) infection and disease in Canadian children in the context of the global TB epidemic and the rising incidence of drug-resistant TB.

DATA SOURCES

ORIGINAL AND REVIEW ARTICLES PERTINENT TO: epidemiology of TB globally and in Canada; management of latent TB infection and TB disease in children; diagnostic tests for latent TB infection and TB disease; and management of drug-resistant TB disease. Multiple Medline searches were used including combinations of the MeSH terms 'Tuberculosis*' (and its multiple subheadings), 'Child*', 'Drug Resistance', 'Mycobacterium tuberculosis*' and 'Canada/epidemiology*'. Select relevant textbooks were reviewed.

DATA SELECTION AND EXTRACTION

The articles were analyzed from the perspective of clinicians managing children in Canada today, and from our experience of managing children with TB in Southern Ontario.

DATA SYNTHESIS

TB in Canada is largely a disease of the foreign-born and their children, but continues to occur in aboriginal children. Drug resistance is increasing globally and in Canada. Most children with TB disease in Canada are asymptomatic and found through contact tracing. False positive skin tests are frequent where TB prevalence is low.

CONCLUSIONS

Obtain source case drug sensitivities when treating TB contacts and those with latent TB infection. Obtain cultures before treating TB disease and treat disease with at least four antituberculous drugs while awaiting sensitivities. Use Directly Observed Therapy for TB disease. Confine TB skin testing to children at high risk for TB infection or disease, including contacts of infectious patients and recent immigrants. A team approach and infection control measures including environmental controls are important in managing TB disease.

Community-based cross-sectional survey of latent tuberculosis infection in Afar pastoralists, Ethiopia, using QuantiFERON-TB Gold In-Tube and tuberculin skin test

Background

There is little information concerning community-based prevalence of latent tuberculosis infection (LTBI) using T-cell based interferon-γ (IFN-γ) release assays (IGRAs), particularly in TB endemic settings. In this study, the prevalence of LTBI in the Afar pastoral community was assessed using QuantiFERON-TB Gold In-Tube (QFTGIT) and tuberculin skin tests (TST).

Methods

A community-based cross-sectional survey of LTBI involving 652 apparently healthy adult pastoralists was undertaken in the pastoral community of Amibara District of the Afar Region between April and June 2010.

Results

The prevalence of LTBI was estimated as 63.7% (363/570) using QFTGIT at the cut-off point recommended by the manufacturer (≥ 0.35 IU/ml IFN-γ), while it was 74.9% (427/570) using a cut-off point ≥ 0.1 IU/ml IFN-γ. The QFTGIT-based prevalence of LTBI was not significantly associated with the gender or age of the study participants. However, the prevalence of LTBI was 31.2% (183/587) using TST at a cut-off point ≥ 10 mm of skin indurations, and it was higher in males than females (36.8% vs. 23.5%, X² = 11.76; p < 0.001). There was poor agreement between the results of the tests (k = 0.098, 95% CI, 0.08 - 0.13). However, there was a positive trend between QFTGIT and TST positivity (X² = 96.76, P < 0.001). Furthermore, individuals with skin indurations ≥ 10 mm were 13.6 times more likely to have positive results using QFTGIT than individuals with skin indurations of 0 mm (adjusted OR = 13.6; 95%CI, 7.5 to 24.7, p < 0.001).

Conclusions

There is currently no agreed gold standard for diagnosis of LTBI. However, the higher prevalence of LTBI detected using QFTGIT rather than TST suggests that QFTGIT could be used for epidemiological studies concerning LTBI at the community level, even in a population unreactive to TST. Further studies of adults and children will be required to assess the effects of factors such as malnutrition, non-tuberculosis mycobacterial infections, HIV and parasitic infections on the performance of QFTGIT.

Lymphocyte proliferation to mycobacterial antigens is detectable across a spectrum of HIV-associated tuberculosis

Background

Identifying novel TB diagnostics is a major public health priority. We explored the diagnostic characteristics of antimycobacterial lymphocyte proliferation assays (LPA) in HIV-infected subjects with latent or active TB.

Methods

HIV-infected subjects with bacille Calmette Guérin (BCG) scars and CD4 counts ≥ 200 cells/mm³ entering a TB booster vaccine trial in Tanzania had baseline in vivo and in vitro immune tests performed: tuberculin skin tests (TST), LPA and five day assays of interferon gamma (IFN-γ) release. Assay antigens were early secreted antigenic target 6 (ESAT-6), antigen 85 (Ag85), and Mycobacterium tuberculosis whole cell lysate (WCL). Subjects were screened for active TB at enrollment by history, exam, sputum smear and culture. We compared antimycobacterial immune responses between subjects with and without latent or active TB at enrollment.

Results

Among 1885 subjects screened, 635 had latent TB and 13 had active TB. Subjects with latent TB were more likely than subjects without TB to have LPA responses to ESAT-6 (13.2% vs. 5.5%, P < 0.0001), Ag85 (18.7% vs. 3.1%, P < 0.0001), and WCL (45.7% vs. 17.1%, P < 0.0001). Subjects with active TB also were more likely than those without active TB to have detectable LPA responses to ESAT-6 (38.5% vs. 8.1%, P = 0.0001), Ag85 (46.2% vs. 8.5%, P < 0.0001), and WCL (61.5% vs. 27.0%, P = 0.0053). In subjects with a positive TST, LPA responses to ESAT-6, Ag85 and WCL were more common during active TB (p < 0.0001 for all tests). In diagnosing active TB, in vivo and in vitro tests of mycobacterial immune responses had sensitivity and specificity as follows: TST 84.6% and 65.5%, ESAT-6 LPA 38.5% and 92.0%, Ag85 LPA 46.2% and 91.5%, and WCL LPA 61.5% and 73.0%. Detectable LPA responses were more common in patients with higher CD4 counts, and higher HIV viral loads.

Conclusion

Lymphoproliferative responses to mycobacteria are detectable during HIV-associated active TB, and are less sensitive but more specific than TST.

Trial registration

ClinicalTrials.gov Identifier NCT00052195.

Comparison of interferon-gamma release assay versus tuberculin skin test for tuberculosis screening in inflammatory bowel disease

OBJECTIVES

Reactivation of latent tuberculosis (TB) in inflammatory bowel disease (IBD) patients treated with antitumor necrosis factor-alpha medication is a serious problem. Currently, TB screening includes chest x-rays and a tuberculin skin test (TST). The interferon-gamma release assay (IGRA) QuantiFERON-TB Gold In-Tube (QFT-G-IT) shows better specificity for diagnosing TB than the skin test. This study evaluates the two test methods among IBD patients.

METHODS

Both TST and IGRA were performed on 212 subjects (114 Crohn's disease, 44 ulcerative colitis, 10 indeterminate colitis, 44 controls).

RESULTS

Eighty-one percent of IBD patients were under immunosuppressive therapy; 71% of all subjects were vaccinated with Bacille Calmette Guérin; 18% of IBD patients and 43% of controls tested positive with the skin test (P < 0.0001). Vaccinated controls tested positive more often with the skin test (52%) than did vaccinated IBD patients (23%) (P = 0.011). Significantly fewer immunosuppressed patients tested positive with the skin test than did patients not receiving therapy (P = 0.007); 8% of patients tested positive with the QFT-G-IT test (14/168) compared to 9% (4/44) of controls. Test agreement was significantly higher in the controls (P = 0.044) compared to the IBD group.

CONCLUSIONS

Agreement between the two test methods is poor in IBD patients. In contrast to the QFT-G-IT test, the TST is negatively influenced by immunosuppressive medication and vaccination status, and should thus be replaced by the IGRA for TB screening in immunosuppressed patients having IBD.

Assessment of three commercially available serologic assays for detection of antibodies to Mycobacterium tuberculosis and identification of active tuberculosis

Tuberculosis (TB) caused by Mycobacterium tuberculosis remains a major world disease, with approximately 9 million new cases each year. Identification and treatment of active disease are essential for TB control. Serology may offer increased detection of active disease in patients with a positive tuberculin skin test (TST) or QuantiFERON-TB (QFT-G). The InBios Active TbDetect immunoglobulin G (IgG) enzyme-linked immunosorbent assay (ELISA), IBL M. tuberculosis IgG ELISA, and Anda Biologics TB ELISAs were evaluated for the ability to detect M. tuberculosis antibodies in patients with active disease. Agreement, sensitivity, and specificity for each ELISA were determined and compared to those for culture or amplified direct detection and M. tuberculosis low-risk control patients. The InBios Active TbDetect ELISA had an agreement of 96.2%, a sensitivity of 83.3%, and a specificity of 98.9%. The IBL M. tuberculosis ELISA had an agreement of 84.0%, a sensitivity of 5.6%, and a specificity of 100.0%. The agreement, sensitivity, and specificity of the Anda Biologics TB ELISA were 74.2%, 83.3%, and 72.0%, respectively. The sensitivity for detecting M. tuberculosis antibodies in human immunodeficiency virus-associated TB was 50% for both the InBios Active TbDetect ELISA and the Anda Biologics TB ELISA and 0% for the IBL M. tuberculosis ELISA. The positivity rates for InBios Active TbDetect ELISA, IBL M. tuberculosis ELISA, and Anda Biologics TB ELISA in latently infected individuals positive by TST and/or QFT-G were 5.1%, 0.0%, and 30.8%, respectively. It can be concluded that the InBios Active TbDetect IgG ELISA is superior to the other ELISAs in accurately detecting active TB.

Measurement of cytokine production using whole blood

Whole blood (WB) ex vivo stimulation assays are useful for measuring cytokine responses due to the easy access of samples from healthy donors and patients and the minimal processing of the sample required. Because the assay mimics the natural environment, WB culture may be the best milieu in which to study cell activation and cytokine production in vitro. Whole blood stimulation has been used to investigate the cellular responsiveness to a variety of stimuli, including bacterial endotoxin (LPS), antigens, allergens, and antibiotics. Various clinical uses of whole blood stimulation assays have been suggested, including the assessment of autoimmune diseases, the monitoring of drug and vaccine efficacy, and immunotoxicity. Thus, whole blood cell culture may be useful in studying the biological effects of potential allergenic and/or antigenic substances or drugs on immune cell activation and cytokine secretion.

Review article: the diagnosis and management of Crohn's disease in populations with high-risk rates for tuberculosis

BACKGROUND

Distinguishing Crohn's disease from intestinal tuberculosis in endemic areas is challenging as both conditions have overlapping clinical, radiological, endoscopic and histological characteristics. Furthermore, high rates of latent tuberculosis confer a considerable risk of reactivation once therapy for established Crohn's disease is started.

AIM

To review current strategies in differentiating these two conditions, and in managing Crohn's disease, in populations with high rates of tuberculosis.

METHODS

Literature review and clinical experience.

RESULTS

While various clinical, radiological, endoscopic and histological parameters may aid in differentiating Crohn's disease from intestinal tuberculosis, these remain imperfect and as treatment options differ misdiagnosis has grave consequences. We propose a diagnostic algorithm, based on currently available evidence and experience, to aid in this dilemma. We also discuss approaches to the management of Crohn's disease, including agents targeting tumour necrosis factor-alpha, in patients at risk of developing tuberculosis.

CONCLUSIONS

A diagnosis of Crohn's disease in individuals at risk for tuberculosis should only be made after careful interpretation of clinical signs, abdominal imaging and systematic endoscopic and histological assessment. Newer techniques for the diagnosis of latent tuberculosis still need to be validated in this environment, and guidelines on the treatment of latent tuberculosis in this setting require clarification.

Longitudinal assessment of an ELISPOT test for Mycobacterium tuberculosis infection

BACKGROUND

Very little longitudinal information is available regarding the performance of T cell-based tests for Mycobacterium tuberculosis infection. To address this deficiency, we conducted a longitudinal assessment of the enzyme-linked immunosorbent spot test (ELISPOT) test in comparison to the standard tuberculin skin test (TST).

METHODS AND FINDINGS

In tuberculosis (TB) contacts we repeated ELISPOT tests 3 mo (n = 341) and 18 mo (n = 210) after recruitment and TSTs at 18 mo (n = 130). We evaluated factors for association with conversion and reversion and investigated suspected cases of TB. Of 207 ELISPOT-negative contacts, 51 (24.6%) had 3-mo ELISPOT conversion, which was associated with a positive recruitment TST (odds ratio [OR] 2.2, 95% confidence interval [CI] 1.0-5.0, p = 0.048) and negatively associated with bacillus Calmette-Guérin (BCG) vaccination (OR 0.5, 95% CI 0.2-1.0, p = 0.06). Of 134 contacts, 54 (40.2%) underwent 3-mo ELISPOT reversion, which was less likely in those with a positive recruitment TST (OR 0.3, 95% CI 0.1-0.8, p = 0.014). Between 3 and 18 mo, 35/132 (26.5%) contacts underwent ELISPOT conversion and 28/78 (35.9%) underwent ELISPOT reversion. Of the 210 contacts with complete results, 73 (34.8%) were ELISPOT negative at all three time points; 36 (17.1%) were positive at all three time points. Between recruitment and 18 mo, 20 (27%) contacts had ELISPOT conversion; 37 (50%) had TST conversion, which was associated with a positive recruitment ELISPOT (OR 7.2, 95% CI 1.4-37.1, p = 0.019); 18 (32.7%) underwent ELISPOT reversion; and five (8.9%) underwent TST reversion. Results in 13 contacts diagnosed as having TB were mixed, but suggested higher TST sensitivity.

CONCLUSIONS

Both ELISPOT conversion and reversion occur after M. tuberculosis exposure. Rapid ELISPOT reversion may reflect M. tuberculosis clearance or transition into dormancy and may contribute to the relatively low reported ELISPOT conversion rate. Therefore, a negative ELISPOT test for M. tuberculosis infection should be interpreted with caution.

Screening for tuberculosis among 2381 household contacts of sputum-smear-positive cases in The Gambia

Contact investigation is a key component of tuberculosis (TB) control in developed, but not developing, countries. We aimed to measure the prevalence of TB among household contacts of sputum-smear-positive TB cases in The Gambia and to assess the sensitivity of an enzyme-linked immunospot (ELISPOT) assay in this regard. Household contacts of adult smear-positive TB patients were assessed by questionnaire, purified protein derivative (PPD) skin test, ELISPOT assay, physical examination, chest X-ray and sputum/gastric aspirate. Thirty-three TB cases were identified from 2174 of 2381 contacts of 317 adult smear-positive pulmonary TB patients, giving a prevalence of 1518/100000. The cases identified tended to have milder disease than those passively detected. The sensitivity of ESAT-6/CFP-10 ELISPOT test as a screening test for TB disease was estimated as 71%. Fifty-six per cent of contacts with a PPD skin test result >or=10mm induration had detectable responses to ESAT-6/CFP-10 by ELISPOT; 11% with a negative PPD skin test (<10mm) had a positive ESAT-6/CFP-10 response. Active screening for TB among contacts of TB patients may have a role in TB control in The Gambia. These individuals are a high-risk group, and the disease identified is less advanced than that found through passive case detection. An ELISPOT assay was relatively insensitive as a screening test for TB.

MHC class II tetramer guided detection of Mycobacterium tuberculosis-specific CD4+ T cells in peripheral blood from patients with pulmonary tuberculosis

Novel diagnostic tools are needed to diagnose latent infection and to provide biologically meaningful surrogate markers to define cellular immune responses against Mycobacterium tuberculosis (MTB). Interferon gamma-based assays have recently been developed in addition to the more than 100-year-old tuberculin skin test (TST) for the immune diagnosis of MTB in blood. The advent of soluble MHC/peptide tetramer molecules allows to objectively enumerate antigen-specific T cells. We identified novel MHC class II-restricted MTB epitopes and used HLA-DR4 tetrameric complexes to visualize ex vivo CD4(+) T cells directed against the antigens Ag85B and the 19-kDa lipoprotein, shared between MTB and other Mycobacterium species, and CD4(+) T cells which recognize the MTB-associated ESAT-6 antigen. MTB-reactive CD4(+) T cells reside predominantly in the CD45RA(+) CD28(+) and CD45(-) CD28(+) T-cell subset and recognize naturally processed and presented MTB epitopes. HLA-DR4-restricted, Ag85B or ESAT-6-specific CD4(+) T cells show similar dynamics over time in peripheral blood mononuclear cells (PBMC) when compared with CD8(+) T cells directed against the corresponding HLA-A2-presented MTB epitopes in patients with pulmonary MTB infection and subsequent successful therapy. This was not found to be true for T-cell responses directed against the 19-kDa lipoprotein. The dissection of the cellular immune response in M. tuberculosis infection will enable novel strategies for monitoring MTB vaccine candidates and to gauge CD4(+) T cells directed against MTB.

Les nouveaux tests immunologiques dans le diagnostic de la tuberculose (TB or not TB)

INTRODUCTION

Targeted testing and treatment of individuals with latent tuberculosis infection (LTBI), at high risk of progression to active tuberculosis (ATB), are key elements in the battle against tuberculosis, both in France and in many parts of the world. Though the finding of tubercle bacilli is the essential examination for the diagnosis of ATB, there is no indisputable test for LTBI.

BACKGROUND

The help currently given to the diagnosis of LTBI by the degree of positivity of the tuberculin skin test (TST) is limited, both operationally and logistically, in populations vaccinated with BCG or sensitised by atypical mycobacteria, and by its low sensitivity in those immuno-suppressed persons who are at greatest risk of progression. Moreover the TST has other operational limitations linked to return visits, repeat testing causing a boosting effect and subjective interpretation. A new approach follows the availability of two biological tests for the diagnosis of LTBI (QuantiFERON-TB and T-SPOT-TB) that measure the in-vitro production of interferon gamma (IFN-gamma) by the blood mononuclear cells in response to M. tuberculosis specific antigens (ESAT-6 and CFP10). This revue analyses the published studies, undertaken with varying numbers of patients, that evaluate the diagnostic accuracy of these two tests in comparison with TST. However, validation is handicapped by the lack of a "gold standard" for the diagnosis of LTBI. These studies demonstrate similar levels of specificity for the two biological tests. They are statistically higher than those for TST, particularly in populations vaccinated by BCG. On the other hand, their sensitivity was at least equivalent to that of TST and, in certain studies, superior with T-SPOT-TB. Finally, several studies in contacts have been undertaken with the aim of measuring the concordance between these biological tests and TST. The essential finding is of a very good correlation between positivity of the biological tests and the degree of exposure of the contacts. These tests have additional operational advantages over TST: completed in one visit, results available in 24 hours, absence of inter and intra observer divergence, detection of potential immuno-depression and avoidance of boosting by repeat testing.

VIEWPOINT

Currently, however, these biological tests present several operational limits: lower sensitivity in severe disease, incomplete data in immuno-suppressed subjects and in children, lack of predictive value for future development of ATB, lack of distinction between LTBI and ATB. Numerous clinical studies are under way, in France and elsewhere, in order to reduce these limitations and to allow the appropriate incorporation of these tests into protocols for the diagnosis of tuberculosis.

CONCLUSIONS

These two biological tests should, in the near future, replace or complement TST in the diagnosis of recent LTBI, leading to their optimal incorporation into the decision making processes of the national plans for the control of tuberculosis.

Diagnosis of latent tuberculosis infection: The potential role of new technologies

Tuberculosis (TB) is a major cause of morbidity and mortality worldwide. TB control programmes need improvement in the diagnosis of latent TB infection. The tuberculin skin test (TST) is far from a 'gold' standard as it often gives false results. Interferon-gamma assays are newly available tests to detect latent TB infection, but they are currently not routinely used. They are based on immune responses to purified protein derivative (PPD) or to region of difference 1 (RD1) specific antigens. Assays based on RD-1 specific antigens perform better than both PPD based assays and TST. They correlate with TB exposure and are less likely to give false results in non-tuberculous mycobacterial disease, Bacille Calmette-Guerin (BCG) vaccination and immunosuppression. More accurate diagnosis of latent TB infection with RD-1 specific antigen based interferon-gamma assays may allow targeting of chemoprophylaxis to reduce the burden of active TB while decreasing wastage of health care resources due to false results associated with TST. However, further research and development is required to verify that new tests can predict the risk of later development of active TB and to make it feasible to perform these tests in a reproducible fashion at low cost, particularly in developing countries.

Modern approaches to a rapid diagnosis of tuberculosis: promises and challenges ahead

The limitations of the conventional methods for diagnosing tuberculosis have spurred multi-faceted research activities in this field throughout the world. Chromatographic methods appear promising but may not be widely available in the developing countries. Immuno-diagnostic methods using combinations ("cocktails") of antigens have high sensitivity and specificity and can easily be applied in the peripheral laboratories and in the field settings. Though expensive, molecular methods for diagnosis of tuberculosis have advantages of speed, sensitivity, and specificity. Adequate training of the eligible personnels in molecular methods and prevention of laboratory-dependent contamination may help reduce false positive results. Although, there are no clear guidelines, so far on how to make out the best from the gene amplification methods, yet their use may be encouraged with adequate quality controls, because of the inherent ingenuity and promises of these methods. Phage-based molecular methods provide rapid results in susceptibility tests for anti-tubercular drugs. In future, many sophisticated techniques are expected to hit the market for a rapid diagnosis of tuberculosis. In the developing countries, it is necessary to evaluate availability of suitable infrastructure and trained personnels before adopting modern diagnostic methods.

High rate of negative results of tuberculin and QuantiFERON tests among individuals with a history of positive skin test results

OBJECTIVES

To evaluate individuals at high risk for tuberculosis exposure who had a history of a positive tuberculin skin test (TST) result in order to determine the prevalence of unsuspected negative TST results. To confirm these findings with the QuantiFERON-TB test (QFT), an in vitro whole-blood assay that measures tuberculin-induced secretion of interferon-gamma.

METHODS

This survey was conducted from November 2001 through December 2003 at 3 sites where TST screening is regularly done. Detailed histories and reviews of medical records were performed. TSTs were placed and read by 2 experienced healthcare workers, and blood was drawn for QFT. Any subject with a negative result of an initial TST during the study (induration diameter, <10 mm) underwent a second TST and a second QFT. The TST-negative group comprised individuals for whom both TSTs had an induration diameter of <10 mm. The confirmed-negative group comprised individuals for whom both TSTs yielded no detectable induration and results of both QFTs were negative.

RESULTS

A total of 67 immunocompetent subjects with positive results of a previous TST were enrolled in the study. Of 56 subjects who completed the TST protocol, 25 (44.6%; 95% confidence interval [CI], 31.6%-57.6%) were TST negative (P<.001). Of 31 subjects who completed the TST protocol and the QFT protocol, 8 (25.8%; 95% CI, 10.4%-41.2%) were confirmed negative (P<.005).

CONCLUSIONS

A significant proportion of subjects with positive results of a previous TST were TST negative in this study, and a subset of these were confirmed negative. These individuals' TST status may have reverted or may never have been positive. It will be important in future studies to determine whether such individuals lack immunity to tuberculosis and whether they should be considered for reentry into tuberculosis screening programs.

Preliminary evaluation of whole-blood gamma interferon release for clinical assessment of cellular immunity in patients with active coccidioidomycosis

Assessment of the cellular immune response in coccidioidomycosis has epidemiologic and prognostic importance. Measurement of delayed-type hypersensitivity to skin testing has been used in the past to determine cellular immunity in coccidioidomycosis. However, no skin tests are currently available in the United States. Assay of gamma interferon (IFN-gamma) release in whole blood in response to incubation with antigen has been used to assess cellular immunity in tuberculosis. We used a similar assay using the coccidioidal antigen preparation T27K to measure the in vitro cellular immune responses among a cohort of 69 subjects with active coccidioidomycosis. IFN-gamma release was bimodal, with concentrations above and below 5 IU/ml. Using multivariate logistic regression, underlying disease and disseminated or chronic pulmonary coccidioidomycosis was significantly associated with the release of IFN-gamma at a concentration of <5 IU/ml (P = 0.02 or 0.05, respectively). In addition, the release IFN-gamma concentration was <5 IU/ml in all subjects with a clinical severity score of > or =6 (P = 0.02). The release IFN-gamma concentration correlated with expression of CD69 on T lymphocytes in an in vitro assay using T27K as the antigen (Spearman's rho = 0.59; P < 0.01). These results suggest that the IFN-gamma release assay with T27K as the antigen may be a useful clinical test for assessing cellular immunity in patients with active coccidioidomycosis.

Cytokine response to antigen stimulation of whole blood from patients with Mycobacterium ulcerans disease compared to that from patients with tuberculosis

Mycobacterium ulcerans disease (Buruli ulcer) is a skin-ulcerating infection common in some parts of the tropics. We have investigated cytokine secretion after stimulation of whole blood from Buruli ulcer (BU) patients in a region of endemicity in Ghana with M. ulcerans sonicate or culture filtrate antigens to investigate the development of the response over time and its specificity by comparison with the response to Mycobacterium tuberculosis sonicate in human immunodeficiency virus-negative tuberculosis patients. Significant gamma interferon (IFN-gamma) production in response to whole-blood stimulation with M. ulcerans sonicate was detected in patients with ulcers, which was higher than that in patients with nodules but similar to subjects with healed BU. The mean IFN-gamma response in household contacts of BU patients was not significantly different from that in healthy control subjects from an area of nonendemicity. Results in patients with untreated, smear-positive pulmonary tuberculosis and tuberculosis patients on treatment for more than 2 weeks showed that BU patients responded better to M. ulcerans antigens than tuberculosis patients. In contrast, interleukin-10 results were higher in patients with active M. ulcerans disease than in those with healed lesions, but the pattern of response was similar to that seen in tuberculosis. A similar pattern of cytokine secretion was found using M. tuberculosis sonicate as an antigen. Neither of the two culture filtrate antigens of M. ulcerans appeared to be more specific than M. ulcerans sonicate. In the early stages of M. ulcerans disease there was a mixed Th1 and Th2 cytokine response, but the Th1 response emerged as the dominant type.

The diagnosis of tuberculosis

Diagnostic testing for tuberculosis has remained unchanged for nearly a century, but newer technologies hold the promise of a true revolution in tuberculosis diagnostics. New tests may well supplant the tuberculin skin test in diagnosing latent tuberculosis infection in much of the world. Tests such as the nucleic acid amplification assays allow more rapid and accurate diagnosing of pulmonary and extrapulmonary tuberculosis. The appropriate and affordable use of any of these tests depends on the setting in which they are employed.

Evaluation of an in vitro assay for gamma interferon production in response to Mycobacterium tuberculosis infections

The tuberculin skin test (TST) is the "gold standard" for detecting infection with Mycobacterium tuberculosis. We compared the TST using purified protein derivative to the QuantiFERON-TB test (QFT). Two groups were examined. Group 1 individuals (n = 66) (low risk) were at low risk for exposure to M. tuberculosis and were not Mycobacterium bovis BCG vaccinated. Group 2 (n = 29) include individuals who were likely to have been exposed to a high prevalence of M. tuberculosis infections and were BCG vaccinated. Group 1 individuals were given a TST. Group 2 individuals were not given a TST because of possible adverse reactions. A 10- to 15-mm indurated area 48 h after TST was considered positive. A positive QFT result was defined as a significant gamma interferon response to M. tuberculosis antigen, Mycobacterium avium antigen, and a nonspecific mitogen stimulus and no response in the negative control. In group 1, 60 of 66 individuals (90.9%) were negative by both methods, and 1 person was positive by both methods. There was one QFT-negative, TST-positive case, one QFT-positive, TST-negative case, and three conditional QFT-positive, TST-negative cases. In group 2, 12 of 29 (41.4%) were positive by QFT and considered likely to be TST positive because of prior BCG vaccination. QFT testing in our low-risk group resulted in an agreement of 96.8%, a sensitivity of 50%, and a specificity of 98.4% compared with TST results. QFT testing with TST in low-risk groups can aid in the detection of latent M. tuberculosis infections.

High risk of Mycobacterium tuberculosis infection during the Hajj pilgrimage

INTRODUCTION

Annually more than 2 million pilgrims from all over the world attend the Hajj in Saudi Arabia. Overcrowding during this pilgrimage leads to a high risk of transmission of airborne infectious diseases. Tuberculosis (TB) is common among hospitalized pilgrims, but the overall risk of acquiring Mycobacterium tuberculosis infection during this pilgrimage is not known. We conducted a prospective study to assess the risk of M. tuberculosis infection among Hajj pilgrims.

METHODS

We measured the immune response to TB antigens using a whole-blood assay (QuantiFERON TB assay) prior to departure and 3 months after return from the Hajj pilgrimage.

RESULTS

Of 357 paired assays, 149 pilgrims were negative prior to the Hajj and 15 (10%) of these had a significant rise in immune response to TB antigens.

CONCLUSIONS

Pilgrims may be at high risk of acquiring M. tuberculosis infection during the Hajj. This has significant public health implications for TB control in countries with large Muslim populations.

Improved protection by recombinant BCG

Mycobacterium bovis bacille Calmette Guérin (BCG) is one of the most widely used live vaccines. Technologic advancement in genome manipulation enables the construction of recombinant BCG (rBCG) strains, which can be employed as highly immunogenic vaccines against tuberculosis with improved safety profile.

Comparing Interferon- Release Assay with Tuberculin Skin Test Readings at 48-72 Hours and 144-168 Hours with Use of 2 Commercial Reagents

BACKGROUND

Despite widespread use, the tuberculin skin test (TST) has many limitations, including a requirement for a second visit between 48 and 72 hours. The goal of this study was to determine the reliability of a TST reading between 144 and 168 hours.

METHODS

Tuberculin antigen was applied into both forearms (Aplisol in one arm and Tubersol in the other, from single lots of each product) by the Mantoux method. Blood samples were obtained for interferon- gamma release assay. Subjects were seen at 48-72 hours for the initial (day 2) TST reading and returned at 144-168 hours for a second (day 7) reading.

RESULTS

A total of 116 subjects at increased risk for tuberculosis were studied; 25 (22%) had positive results at day 2 with Tubersol and 27 (23%) had positive results at day 2 with Aplisol. Overall agreement between Tubersol and Aplisol at day 2 was 93% (kappa = 0.80) and at day 7 was 94% (kappa = 0.76). Overall agreement between day 2 and day 7 was 89% for Tubersol and 86% for Aplisol. Discordant results between day 2 and day 7 occurred mostly in persons with a history of bacille Calmette-Guerin vaccination.

CONCLUSIONS

Subjects who fail to present at 48-72 hours for TST reading may still have a reliable TST reading at up to 168 hours. Aplisol and Tubersol reagents produce comparable results when compared with the interferon- gamma release assay.

Interferon-γ assays in the immunodiagnosis of tuberculosis: a systematic review

A major challenge in tuberculosis control is the diagnosis and treatment of latent tuberculosis infection. Until recently, there were no alternatives to the tuberculin skin test (TST) for diagnosing latent tuberculosis. However, an alternative has now emerged in the form of a new in-vitro test: the interferon-gamma assay. We did a systematic review to assess the performance of interferon-gamma assays in the immunodiagnosis of tuberculosis. By searching databases, contacting experts and test manufacturers, we identified 75 relevant studies. The results suggest that interferon-gamma assays that use Mycobacterium tuberculosis-specific region of difference 1 (RD1) antigens (such as early secretory antigenic target 6 and culture filtrate protein 10) may have advantages over the TST, in terms of higher specificity, better correlation with exposure to M tuberculosis, and less cross-reactivity due to BCG vaccination and non-tuberculous mycobacterial infection. However, interferon-gamma assays that use RD1 antigens in isolation may maximise specificity at the cost of sensitivity. Assays that use cocktails of RD1 antigens seem to overcome this problem, and such assays have the highest accuracy. RD1-based interferon-gamma assays can potentially identify those with latent tuberculosis who are at high risk for developing active disease, but this requires confirmation. There is inadequate evidence on the value of interferon-gamma assays in the management of immunocompromised individuals, children, patients with extrapulmonary or non-tuberculous mycobacterial disease, and populations in countries where tuberculosis is endemic. Current evidence suggests that interferon-gamma assays based on cocktails of RD1 antigens have the potential to become useful diagnostic tools. Whether this potential can be realised in practice remains to be confirmed in well designed, long-term studies.

Gamma interferon-based immunodiagnosis of tuberculosis: comparison between whole-blood and enzyme-linked immunospot methods

The gamma interferon secretion levels of 52 adults whose T cells had been stimulated with the Mycobacterium tuberculosis antigens CFP-10 and ESAT-6 were measured by enzyme-linked immunospot methods and a whole-blood-based assay. The test results correlated well (r = 0.689, P < 0.0001). Its simple format and use of only small volumes of blood make the whole-blood assay suitable for pediatric practice and field trials.

Specific detection of tuberculosis infection: an interferon-gamma-based assay using new antigens

The tuberculin skin test for immunologic diagnosis of Mycobacterium tuberculosis infection has many limitations, including being confounded by bacillus Calmette-Guérin (BCG) vaccination or exposure to nontuberculous mycobacteria. M. tuberculosis-specific antigens that are absent from BCG and most nontuberculous mycobacteria have been identified. We examined the use of two of these antigens, CFP-10 and ESAT-6, in a whole blood IFN-gamma assay as a diagnostic test for tuberculosis in BCG-vaccinated individuals. Because of the lack of an accurate standard with which to compare new tests for M. tuberculosis infection, specificity of the whole blood IFN-gamma assay was estimated on the basis of data from people with no identified risk for M. tuberculosis exposure (216 BCG-vaccinated Japanese adults) and sensitivity was estimated on the basis of data from 118 patients with culture-confirmed M. tuberculosis infection who had received less than 1 week of treatment. Using a combination of CFP-10 and ESAT-6 responses, the specificity of the test for the low-risk group was 98.1% and the sensitivity for patients with M. tuberculosis infection was 89.0%. The results demonstrate that the whole blood IFN-gamma assay using CFP-10 and ESAT-6 was highly specific and sensitive for M. tuberculosis infection and was unaffected by BCG vaccination status.

Comparison of a whole-blood interferon-γ assay and tuberculin skin testing in patients with active tuberculosis and individuals at high or low risk of Mycobacterium tuberculosis infection

BACKGROUND

QuantiFeron-TB (QIFN) is a whole-blood interferon-;gamma assay for the recognition of cell-mediated immune response to Mycobacterium tuberculosis infection.

OBJECTIVES

To compare the QIFN assay with the tuberculin skin test (TST) in patients with newly diagnosed culture-proven tuberculosis (TB) and healthy volunteers with high or low risk of latent M tuberculosis infection and to identify factors associated with discordance between tests.

METHOD

Two-hundred fifty-eight subjects underwent both assays. All participants completed a detailed questionnaire, and data from TB patients' medical records were collected.

RESULTS

In the entire study population, agreement between tests was moderate and the correlation between the magnitude of QIFN response and the TST induration diameter was significant. In volunteers with no known risk of exposure to M tuberculosis, the specificity of the assays was comparable. However, in subjects with active TB or those vaccinated with bacille Calmette-Guérin, the QIFN assay detected more reactors than did the TST. In these individuals, agreement between assays was poor and no correlation or only a weak correlation was found between the diameter of TST induration and the magnitude of the interferon-gamma responses.

CONCLUSIONS

The sensitivity of the QIFN assay is greater than that of the TST in patients with active TB before the initiation of anti-TB chemotherapy, but its specificity is influenced more by bacille Calmette-Guérin vaccination. The QIFN assay may provide an improvement over the current practice of the use of the TST to support diagnosis of active M tuberculosis infection in the clinic; however, QIFN cannot be considered an adequate replacement for the TST in the screening for latent infection.

Tuberculosis

Among communicable diseases, tuberculosis is the second leading cause of death worldwide, killing nearly 2 million people each year. Most cases are in less-developed countries; over the past decade, tuberculosis incidence has increased in Africa, mainly as a result of the burden of HIV infection, and in the former Soviet Union, owing to socioeconomic change and decline of the health-care system. Definitive diagnosis of tuberculosis remains based on culture for Mycobacterium tuberculosis, but rapid diagnosis of infectious tuberculosis by simple sputum smear for acid-fast bacilli remains an important tool, and more rapid molecular techniques hold promise. Treatment with several drugs for 6 months or more can cure more than 95% of patients; direct observation of treatment, a component of the recommended five-element DOTS strategy, is judged to be the standard of care by most authorities, but currently only a third of cases worldwide are treated under this approach. Systematic monitoring of case detection and treatment outcomes is essential to effective service delivery. The proportion of patients diagnosed and treated effectively has increased greatly over the past decade but is still far short of global targets. Efforts to develop more effective tuberculosis vaccines are under way, but even if one is identified, more effective treatment systems are likely to be required for decades. Other modes of tuberculosis control, such as treatment of latent infection, have a potentially important role in some contexts. Until tuberculosis is controlled worldwide, it will continue to be a major killer in less-developed countries and a constant threat in most of the more-developed countries.

Diagnosis of tuberculosis: available technologies, limitations, and possibilities

Rapid diagnosis and treatment are important for preventing transmission of Mycobacterium tuberculosis. However, the diagnosis of tuberculosis continues to pose serious problems, mainly because of difficulties in differentiating between patients with active tuberculosis and those with healed lesions, normal mycobacterium boris BCG (Bacillus Calmette Guerin) vaccinated individuals, and unvaccinated Manteux positives. Physicians still rely on conventional methods such as Ziehl-Neelsen (ZN) staining, fluorochrome staining, sputum culture, gastric lavage, and other non-traditional methods. Although the tuberculin test has aided in the diagnosis of tuberculosis for more than 85 years, its interpretation is difficult because sensitization with nontuberculous mycobacteria leads to false-positive tests. There have been numerous unsuccessful attempts to develop clinically useful serodiagnostic kits for tuberculosis. A number of proteinaceous and nonprotein antigens (such as acyltrehaloses and phenolglycolipids) have been explored from time to time for the development of such assays but they have not proved to be clinically useful. It has been difficult to develop an ELISA utilizing a suitable antigen because M. tuberculosis shares a large number of antigenic proteins with other microorganisms that may or may not be pathogenic. With the advent of molecular biology techniques, there have been significant advances in nucleic acid-based amplification and hybridization, which are helping to rectify existing flaws in the diagnosis of tuberculosis. The detection of mycobacterial DNA in clinical samples by polymerase chain reaction (PCR) is a promising approach for the rapid diagnosis of tuberculous infection. However, the PCR results must be corrected for the presence of inhibitors as well as for DNA contamination. In the modern era of genetics, marked by proteomics and genomics, the day is not far off when DNA chip-based hybridization assays will instantly reveal mycobacterial infections.