Challenges with QuantiFERON-TB Gold assay for large-scale, routine screening of U.S. healthcare workers

Effect of BCG vaccination against Mycobacterium tuberculosis infection in adult Brazilian health-care workers: a nested clinical trial

BACKGROUND

The effectiveness of BCG vaccine for adult pulmonary tuberculosis remains uncertain. In this study, we aimed to evaluate the effect of vaccination with BCG-Denmark to prevent initial and sustained interferon-γ release assay conversion in Brazilian health-care workers.

METHODS

This substudy is a nested randomised controlled trial embedded within the BRACE trial (NCT04327206). Specifically, this substudy enrolled Brazilian health-care workers (aged ≥18 years) from three sites in Brazil (Manaus, Campo Grande, and Rio de Janeiro) irrespective of previously receiving BCG vaccination. Participants were excluded if they had contraindications to BCG vaccination, more than 1 month of treatment with specific tuberculosis treatment drugs, previous adverse reactions to BCG, recent BCG vaccination, or non-compliance with assigned interventions. Those eligible were randomly assigned (1:1) to either the BCG group (0·1 mL intradermal injection of BCG-Denmark [Danish strain 1331; AJ Vaccines, Copenhagen]) or the placebo group (intradermal injection of 0·9% saline) using a web-based randomisation process in variable-length blocks (2, 4, or 6), and were stratified based on the study site, age (<40, ≥40 to <60, ≥60 years), and comorbidity presence (diabetes, chronic respiratory disease, cardiac condition, hypertension). Sealed syringes were used to prevent inadvertent disclosure of group assignments. The QuantiFERON-TB Gold (QFT) Plus test (Qiagen; Hilden, Germany) was used for baseline and 12-month tuberculosis infection assessments. The primary efficacy outcome was QFT Plus conversion (≥0·35 IU/mL) by 12 months following vaccination in participants who had a negative baseline result (<0·35 IU/mL).

FINDINGS

Between Oct 7, 2020, and April 12, 2021, 1985 (77·3%) of 2568 participants were eligible for QFT Plus assessment at 12 months and were included in this substudy; 996 (50·2%) of 1985 were in the BCG group and 989 (49·8%) were in the placebo group. Overall, 1475 (74·3%) of 1985 participants were women and 510 (25·7%) were men, and the median age was 39 years (IQR 32-47). During the first 12 months, QFT Plus conversion occurred in 66 (3·3%) of 1985 participants, with no significant differences by study site (p=0·897). Specifically, 34 (3·4%) of 996 participants had initial QFT conversion in the BCG group compared with 32 (3·2%) of 989 in the placebo group (risk ratio 1·09 [95% CI 0·67-1·77]; p=0·791).

INTERPRETATION

BCG-Denmark vaccination did not reduce initial QFT Plus conversion risk in Brazilian health-care workers. This finding underscores the need to better understand tuberculosis prevention in populations at high risk.

FUNDING

Bill & Melinda Gates Foundation, the Minderoo Foundation, Sarah and Lachlan Murdoch, the Royal Children's Hospital Foundation, Health Services Union NSW, the Peter Sowerby Foundation, SA Health, the Insurance Advisernet Foundation, the NAB Foundation, the Calvert-Jones Foundation, the Modara Pines Charitable Foundation, the United Health Group Foundation, Epworth Healthcare, and individual donors.

TRANSLATION

For the Portuguese translation of the abstract see Supplementary Materials section.

Serial interferon-gamma release assay in lung cancer patients receiving immune checkpoint inhibitors: a prospective cohort study

Recent advancements in cancer immunotherapy using immune checkpoint inhibitors (ICIs) have received considerable attention. Although advantageous, ICI therapies cause unique immune-related adverse events (irAEs) in some patients. Moreover, infectious diseases, such as tuberculosis, have been recognized as emerging concerns during immunotherapy. We aimed to evaluate the interferon-gamma release assay (IGRA) conversion rate and active tuberculosis incidence during immunotherapy to elucidate the incidence of tuberculosis reactivation after ICI therapy induction.We prospectively assessed IGRA results in lung cancer patients who received ICI monotherapy before ICI treatment and at 6 and 12 months after ICI treatment. We also assessed computed tomography findings to determine the presence of active tuberculosis when positive IGRA results were obtained. The ICIs used were nivolumab, pembrolizumab, atezolizumab, and durvalumab.In all, 178 patients were prospectively recruited between March 2017 and March 2020. Of these, 123 completed serial IGRAs, of whom 18, 101, and 4, respectively, had positive, negative, and indeterminate IGRAs at baseline. Three and four patients, respectively, showed IGRA reversion and conversion during immunotherapy. One patient with a sustained, stable positive IGRA and one with IGRA conversion developed active pulmonary tuberculosis during immunotherapy.We found that 3.3% and 1.6% of the patients developed IGRA conversion and active tuberculosis, respectively. Of the four patients who developed IGRA conversion, one developed active pulmonary tuberculosis during immunotherapy. Another patient with sustained, stable positive IGRA developed active tuberculosis. Physicians should be alert to tuberculosis development during ICI therapy, and IGRA testing is a useful tool to assess the risk of developing active tuberculosis.

Changes in Interferon-Gamma Release Assay Readout after COVID-19 Vaccination: A Prospective Cohort Study

OBJECTIVES

Interferon-gamma release assays (IGRAs) are widely used in public health practice to diagnose latent tuberculosis. During the coronavirus disease (COVID-19) pandemic and rollout of COVID-19 vaccination, it has remained unclear whether COVID-19 vaccines interfere with IGRA readouts.

METHODS

We prospectively recruited healthcare workers during their annual occupational health examinations in 2021. Baseline IGRA readouts were compared with follow-up data after the participants had received two doses of COVID-19 vaccination.

RESULTS

A total of 134 baseline IGRA-negative cases (92 with ChAdOx1 vaccine, 27 with mRNA-1273 vaccine, and 15 with heterologous vaccination) and seven baseline IGRA-positive cases were analysed. Among the baseline IGRA-negative cases, there were decreased interferon-γ concentrations over the Nil (p = 0.005) and increased Mitogen-Nil (p < 0.001) values post-vaccination. For TB2-Nil value, there was a similar trend (p = 0.057) of increase observed. Compared with the 0.35 IU/mL threshold, the baseline and follow-up readout differences were less than |±0.10| IU/mL over the TB1-Nil and TB2-Nil values in >90% baseline IGRA-negative cases. No significant readout difference was observed among baseline IGRA-positive cases.

CONCLUSIONS

COVID-19 vaccination did not change IGRA interpretation in most cases. Cases showing conversion/borderline IGRA readouts should be given special consideration.

Variability of interferon-γ release assays in people at high risk of tuberculosis infection or progression to tuberculosis disease living in the United States

OBJECTIVES

Interferon-γ release assays, including T-SPOT.TB (TSPOT) and QuantiFERON Gold In-Tube (QFT), are important diagnostic tools for tuberculosis infection, but little work has been done to study the performance of these tests in populations prioritized for tuberculosis testing in the United States, especially those other than health care personnel.

METHODS

Participants were enrolled as part of a large, prospective cohort of people at high risk of tuberculosis infection or progression to tuberculosis disease. All participants were administered a tuberculin skin test, TSPOT, and QFT test. A subset of participants had their QFT (n = 919) and TSPOT (n = 885) tests repeated when they returned to get their tuberculin skin test read 2 to 3 days later (repeat study). A total of 531 participants had a TSPOT performed twice on the same sample taken at the same time (split study).

RESULTS

The QFT repeat test interpretations were discordant (one test positive and the other negative) for 6.4% of participants (59 of 919), and the TSPOT tests were discordant for 60 of 885 participants in the repeat study (6.8%) and 41 of 531 participants in the split study (7.7%). There was a high degree of variability in the quantitative test results for both QFT and TSPOT, and discordance was not associated with both test results being near the established cut-offs. Furthermore, the proportion of discordance was similar when comparing participants in both the TSPOT repeat and TSPOT split studies.

DISCUSSION

Both QFT and TSPOT were 6% to 8% discordant. The results should be interpreted with caution, particularly when seeing a conversion or reversion in serial testing.

Surveillance of Employees of Swiss Federal Asylum Centres for Latent Tuberculosis Infection

BACKGROUND

Asylum seekers in Switzerland have to register in federal asylum centres (FACs) before formal permission to enter the country. Some of them may have active tuberculosis (TB), exposing fellow refugees and employees.

OBJECTIVES

The aim of this study was to assess the risk of TB infection among employees of Swiss FACs.

METHODS

Between 2010 and 2018, a free interferon-gamma release assay (IGRA) was offered to all employees of 8 FACs, at employment and at yearly intervals. We defined latent TB infection as IGRA conversion from negative to positive. IGRA-positive employees were referred to a medical centre for further clinical follow-up.

RESULTS

1,427 tests were performed among 737 employees (54.6% male). 403 (55%) persons were tested only once; 330 (44.5%) were tested several times; for 4 (0.5%) persons, the number of IGRA tests is unknown. Twenty employees (2.7%) had a positive IGRA at baseline, 2 (0.6%) converted from negative to positive during follow-up, resulting in an incidence of 22/10,000 person-years. We observed no case of active TB among employees.

CONCLUSIONS

The prevalence of latent TB among employees to Swiss FACs and the risk of acquiring TB infection through work-related exposure are low. Yearly IGRA controls in the absence of documented TB exposure seem unnecessary.

Risk stratification and management of QuantiFERON-positive solid-organ living donors

PURPOSE OF REVIEW

Donor-derived disease with Mycobacterium tuberculosis (MTB) is likely to become more common as donor pools expand due to increasing transplant volume coupled with patterns of migration and global mobility. Our article reviews the current literature and provides a rational approach for clinicians managing the scenario of a living donor who has epidemiologic risk factors for tuberculosis exposure.

RECENT FINDINGS

Tuberculous bacilli, formerly thought to exist latently only in pulmonary granulomas, are now known reside dormant in nonpulmonary organs. Kidney and liver grafts are thus vectors for donor transmitted MTB disease. Donors with elevated risk for latent MTB disease can be identified with tuberculin skin testing or IFN-γ release assay screening in combination with a thorough history to identify risk factors for latent disease.

SUMMARY

Living donors with an elevated risk for prior MTB exposure provide an opportunity to treat latent disease prior to organ procurement and reduce the risk of donor transmitted disease and secondary morbidity. Improved identification of these high-risk donors can reduce both the incidence of posttransplant MTB disease and the risk of allograft compromise associated with treatment of latent and active disease in posttransplant recipients.

Primary Prophylaxis to Prevent Tuberculosis Infection in Prison Inmates: A Randomized, Double-Blind, Placebo-Controlled Trial

In many low- and middle-income countries, tuberculosis (TB) incidence in prisons is high, exposing incarcerated populations to an elevated risk of TB infection. We conducted a randomized, double-blind, placebo-controlled trial among HIV-negative male inmates of a high TB burden prison to determine whether isoniazid given twice weekly (900 mg) for 12 months prevents TB infection. The primary outcome was QuantiFERON-TB Gold in Plus (QFT) conversion to ≥ 0.35 international units per milliliter (IU/mL) at 6 months; secondary outcomes included alternative QFT thresholds (≥ 0.7, ≥ 2.0, and ≥ 4.0 IU/mL). In total, 467 participants were randomly assigned to intervention (N = 258) or control (N = 209). In an interim analysis of participants who had completed 6 months of follow-up (N = 170), QFT conversion occurred in 20.8% (19/91) and 21.5% (17/79) of participants in intervention and control arms (efficacy: 2.9%, P = 0.91), respectively. The trial was then stopped according to the trial protocol, and the remaining participants prematurely discontinued. In an analysis of secondary outcomes, the intervention arm had significantly lower rates of conversion at a cutoff of ≥ 2.0 IU/mL (efficacy: 82.6%, P < 0.01). In conclusion, 900 mg of isoniazid, administered twice a week, did not effectively prevent QFT conversion at a cutoff point ≥ 0.35 IU/mL in a trial of QFT-negative inmates. Higher QFT cutoffs are associated with sustained conversion and greater protection. Future clinical trials that evaluate protection for latent infection should use the highest cutoff than that recommended by the manufacturer.

Tuberculosis and Other Airborne Microbes in Occupational Health and Safety

Airborne pathogens and non-malignant infectious diseases such as tuberculosis are highly contagious and can have severe effects on healthcare workers. The symptoms of these diseases take time to manifest, which can prevent workers from noticing that they have been exposed until symptoms appear. The current paper sought to assess the occupational safety and preventative measures taken in laboratories in Spain, and to compare these measures with those reported by other studies worldwide. A cross-sectional study of workers (35–50 years old) was conducted using a web survey (N = 30), and a bibliometric analysis was carried out in the Scopus database (92 documents were selected). The occupational safety and health measures were inadequate, according to the opinions of the workers. The training (p < 0.01), the amount of work (p < 0.05), and how the workers followed their protocols (p < 0.001) were linked to incidents and exposure to airborne pathogens. The most significant previous publication was a report (848 citations) stating that the previous variables linked to exposure are vital for prevention. Most works focused on countries like the U.S.A. (p = 0.009) were reviews, with a limited number of studies focused on occupational safety.

Frequency of and risk factors for reversion of QuantiFERON test in healthcare workers in an intermediate-tuberculosis-burden country

OBJECTIVES

High-risk healthcare workers (HCWs) are often screened for latent tuberculosis infection (LTBI) using QuantiFERON tests (QFTs), with annual serial tests often showing reversion from positive to negative results. We assessed the frequency of and risk factors for reversion of QFTs in HCWs in an intermediate-tuberculosis burden country.

METHODS

We enrolled high-risk HCWs at a tertiary-care hospital in South Korea, who were assessed by QFTs at least twice between 2017 and 2019.

RESULTS

Of the 1870 HCWs screened, 1542 (82%) had persistent negative results, 229 (12%) had persistent positive results, 53 (3%) showed reversion, and 46 (2%) showed conversion from negative to positive. Multivariate analysis comparing the characteristics of the 229 HCWs with persistent positive results and the 53 who experienced reversion showed that older age (adjusted odds ratio (aOR): 0.96; 95% confidence interval (CI): 0.92-0.99), male sex (aOR: 0.29; 95% CI: 0.11-0.78) and high (≥0.70 IU/mL) baseline QFT results (aOR: 0.15; 95% CI: 0.07-0.31) were inversely associated with reversion. Using an ROC curve-derived cut-off of <0.738 IU/mL, the area under the curve was 0.79. Of 53 HCWs with reversion, 36 (78%) had below 0.738 IU/mL of baseline QFT, while 181 (79%) of 229 HCWs without reversion had above 0.738 IU/mL of baseline QFT.

CONCLUSION

Reversion during serial testing is unlikely in HCWs who are male, older in age, and have higher baseline QFT results. Serial testing without LTBI treatment may be indicated in HCWs who are female, younger and, especially, have lower QFT results.

High prevalence of latent tuberculosis in hematopoietic stem cell transplant recipients: A First Report

TB is an increasing health problem, and patients undergoing HSCT are more prone to develop tuberculosis. The aim of our study was to evaluate prevalence of latent tuberculosis in HSCT recipients. In this study, 84 patients (2 months to 18 years) who were candidates for HSCT at the referral hospital of Tehran Children's Medical Center were enrolled. The TST and the QFT-GIT test were performed in all 84 patients, simultaneously. LTBI was considered when one of the tests was positive. Overall, the prevalence of LTBI in HSCT recipients in our study was 12% (10 cases). TST induration ≥5 mm was seen in only three patients (3.5%). Eight patients (9.5%) had a positive result for IGRA test, and 11 of them (13%) had indeterminate QFT-GIT result. The agreement between the TST results (induration size ≥5 mm) and the QFT-GIT results was poor (kappa = 0.14). In conclusion, there was a high rate of discordance between TST and IGRA results with many more positive QFT-GIT tests. However, more studies are needed in this population to determine whether this discordance reflects true infection.

Serial testing of health care workers for tuberculosis infection: A prospective cohort study

Health Care Workers (HCW) may have an occupational risk of latent tuberculosis infection (LTBI) and TB disease. The objective of this study was to evaluate the performance of the 2-step strategy: tuberculin skin test (TST) followed by confirmation with Interferon (IFN)-γ- release assays (IGRAs) in HCW. A secondary objective was to determine the factors related to conversions and reversions. HCW at risk of occupational exposure who attended the Occupational Department of the Hospital Germans Trias i Pujol were included during the study period (2013-2016). All professionals testing negative for LTBI were included in a cohort study. These workers were followed up with the administration of a TST and an IGRA quantification at least one year after inclusion in the study. Workers with positive TST, regardless of the results of the IGRA tests, were followed-up with an IGRA. 255 workers were enrolled in the study and 108 workers from the same cohort were followed up. During the follow-up period, seven workers presented TST test conversion. One of these conversions was also confirmed by an IGRA test. There were 2 conversions of cases only testing positive with the IGRA. There have been only 2 reversions of cases testing negative with the IGRA. In this study, not all TST conversions were confirmed when using the IGRA test, which highlights the importance of the 2-step strategy. We have detected a low number of conversions and reversions. Our conclusions should be confirmed in studies with a longer follow-up time.

Latent tuberculosis infection among health-care workers using Quantiferon-TB Gold-Plus in a country with a low burden for tuberculosis: prevalence and risk factors

BACKGROUND

Health-care workers (HCW) are susceptible to latent tuberculosis infection (LTBI). The prevalence of LTBI in HCW in Saudi Arabia has not been reported using the fourth-generation interferon gamma release assay QuantiFERON-TB Gold Plus (QFT-Plus).

OBJECTIVE

Determine the prevalence of LTBI in a large heterogeneous HCW population and assess risk factors for LTBI.

DESIGN

Cross-sectional and case-control study.

SETTING

Tertiary academic hospital, Riyadh, Saudi Arabia.

PATIENTS AND METHODS

Medical records of HCWs who had QFT-Plus performed between January to December 2018 were reviewed and included in the cross-sectional study. In a subset analysis, randomly selected positive QFT-Plus cases were compared with controls selected from the same areas of work. Univariate and binary logistic regression analyses were performed to assess the significance of other factors to QFT-PLus positivity.

MAIN OUTCOME MEASURES

Prevalence of LTBI in HCWs and potential risk factors for LTBI.

SAMPLE SIZE

3024 HCWs in the cross-sectional analysis; 294 cases and 294 controls in the case-control analysis.

RESULTS

Twenty-four percent (n=733) of the HCWs had a positive QFT-Plus. The median (interquartile range) age was 34.0 (31.0-37.1) years, 71% were female, and only 24.8% were of Saudi nationals. Nursing represented 57.7% of HCWs, and 24.7% were working in a non-clinical area. Only 20.3% worked in TB-related departments. A higher risk of LTBI was present in HCWs who were older than 50 years (OR=1.95), from either Philippines (OR=4.7) or the Indian subcontinent (OR=4.1), working as a nurse (OR=2.7), allied health profession (OR=2.1), radiology technician (OR=3.1), or in the emergency room (OR=2.4) or intensive care unit (OR=2.1). In the binary logistic regression, independent predictors for positive QFT-Plus were age group older than 50 years (aOR=2.96), known TB exposure (aOR=1.97), and not receiving BCG at birth (aOR=3.08).

LIMITATION

Single-center, retrospective, possible recall bias for BCG vaccination.

CONCLUSION

The high prevalence of LTBI among HCW emphasizes the need to continue pre-employment screening, especially for employed personnel from high endemic areas, with targeted annual screening for the same group and other identified high-risk groups. These findings can aid in the development of national screening guidelines for LTBI in HCW.

CONFLICT OF INTEREST

None.

Performance Evaluation of a New Automated Chemiluminescent Immunoanalyzer-Based Interferon-Gamma Releasing Assay AdvanSure I3 in Comparison With the QuantiFERON-TB Gold In-Tube Assay

BACKGROUND

The interferon-gamma (IFN-γ) releasing assay (IGRA) is widely used for latent tuberculosis infection (LTBI) diagnosis. We evaluated the analytical performance of a new automated chemiluminescent immunoanalyzer-based IGRA (CLIA-IGRA), AdvanSure I3 (LG Life Sciences, Seoul, Korea) and compared it with that of the QuantiFERON-TB Gold In-Tube (QFT-GIT) assay.

METHODS

Repeatability and reproducibility were evaluated at four levels. Detection capability, including limit of blank (LoB), limit of detection (LoD), and limit of quantification (LoQ), was evaluated using IFN-γ standard material (National Institute for Biological Standards and Control code: 87/586). Agreement between the results of two assays was evaluated using 341 blood samples from healthcare workers and patients at a tertiary care hospital. To determine the cut-off value of CLIA-IGRA for diagnosing LTBI, the ROC curve was analyzed.

RESULTS

Repeatability and reproducibility were 4.86-7.00% and 6.36-7.88% CV, respectively. LoB, LoD, and LoQ were 0.022, 0.077, and 0.249 IU/mL, respectively. IFN-γ values between CLIA-IGRA and QFT-GIT showed a strong correlation within the analytical measurable range of both assays, especially when the value was low. Qualitative comparison of the two assays yielded a 99.1% overall agreement (kappa coefficient=0.98). A cut-off value of 0.35 IU/mL was appropriate for diagnosing LTBI.

CONCLUSIONS

CLIA-IGRA is a reliable assay for LTBI diagnosis, with performance similar to that of QFT-GIT.

Effect of HIV-infection on QuantiFERON-plus accuracy in patients with active tuberculosis and latent infection

OBJECTIVE

HIV-infection increases the risk to progress to active-tuberculosis (TB). Detection of latent TB infection (LTBI) is needed to eventually propose preventive-therapy and reduce TB reservoir. QuantiFERON-TB Plus (QFT-Plus)-test identifies LTBI. Currently, only two studies on QFT-Plus accuracy in HIV-infected-population are available in high TB-endemic-countries. Therefore we aimed to evaluate the effect of HIV-infection on QFT-Plus accuracy to detect LTBI in a low TB-endemic-country.

METHODS

We enrolled 465 participants, among the 167 HIV-infected-persons: 32 with active-TB (HIV-TB), 45 remote-LTBI (HIV-LTBI) and 90 at low M. tuberculosis (Mtb)-infection risk. Among the 298 HIV-uninfected-persons: 170 with active-TB, 76 recent-LTBI, 34 remote-LTBI and 18 with low Mtb-infection risk.

RESULTS

QFT-Plus sensitivity was similar in TB regardless of HIV-status. CD4-count did not influence the distribution of IFN-γ values in HIV-TB and HIV-LTBI. Moreover HIV-LTBI and HIV-uninfected remote LTBI had a similar proportion of results in the uncertain range (IFNγ ≥0.2 ≤ 0.7 IU/ml) differently from those LTBI-persons reporting recent-exposure (p = 0.016). Cytometry results demonstrated that CD8-response was similar in HIV-infected- and -uninfected-persons whereas CD4-response was impaired in HIV-infected-persons (p = 0.011).

CONCLUSIONS

HIV-infection does not affect QFT-Plus response in active-TB, whereas the time of exposure influences the proportion of uncertain-results in LTBI.

Reproducibility of the T-SPOT.TB test for screening Mycobacterium tuberculosis infection in Japan

OBJECTIVES

The interferon-gamma release assay (IGRA) is useful for diagnosing Mycobacterium tuberculosis infections, especially in countries where Bacille Calmette-Guérin vaccinations are performed. However, reproducibility of the IGRA is unclear, as recent data suggest high IGRA conversion and reversion rates in serial tests among healthcare workers. This longitudinal study aimed to evaluate reproducibility of T-SPOT.TB for screening M. tuberculosis infections in Japan.

METHODS

Results of T-SPOT.TB tests performed between April 2014 and March 2016 at two hospitals in Yokohama, Japan, where the incidence of tuberculosis was 18.0 per 100,000 population in 2014, were analyzed.

RESULTS

In total, 3890 T-SPOT.TB tests were included. Overall, positive and negative test rates were 8.4% and 87.6%, respectively. Among 373 serial tests within two years, conversion and reversion rates were only 1.1% and 12.5%, respectively. Almost all patients who were initially negative (98.9%) remained so. There was no statistically significant difference between the outcomes observed at the two hospitals.

CONCLUSIONS

The conversion rate of T-SPOT.TB in Japan is as low as that recently reported in other countries where the incidence of tuberculosis is low. These data indicate that T-SPOT.TB is a reproducible tuberculosis screening tool at local hospitals in areas with a moderate incidence of tuberculosis.

Insights and challenges in tuberculosis vaccine development

Tuberculosis kills more people than any other pathogen and the need for a universally effective vaccine has never been greater. An effective vaccine will be a key tool in achieving the targets set by WHO in the End TB Strategy. Tuberculosis vaccine development is difficult and slow. Substantial progress has been made in research and development of tuberculosis vaccines in the past 20 years, and two clinical trial results from 2018 provide reason for optimism. However, many challenges to the successful licensure and deployment of an effective tuberculosis vaccine remain. The development of new tools for vaccine evaluation might facilitate these processes, and continued collaborative working and sustained funding will be essential.

Evaluating Latent Tuberculosis Infection Test Performance Using Latent Class Analysis in a TB and HIV Endemic Setting

BACKGROUND

Given the lack of a gold standard for latent tuberculosis infection (LTBI) and paucity of performance data from endemic settings, we compared test performance of the tuberculin skin test (TST) and two interferon-gamma-release assays (IGRAs) among health-care workers (HCWs) using latent class analysis. The study was conducted in Cape Town, South Africa, a tuberculosis and human immunodeficiency virus (HIV) endemic setting Methods: 505 HCWs were screened for LTBI using TST, QuantiFERON-gold-in-tube (QFT-GIT) and T-SPOT.TB. A latent class model utilizing prior information on test characteristics was used to estimate test performance.

RESULTS

LTBI prevalence (95% credible interval) was 81% (71-88%). TST (10 mm cut-point) had highest sensitivity (93% (90-96%)) but lowest specificity (57%, (43-71%)). QFT-GIT sensitivity was 80% (74-91%) and specificity 96% (94-98%), and for TSPOT.TB, 74% (67-84%) and 96% (89-99%) respectively. Positive predictive values were high for IGRAs (90%) and TST (99%). All tests displayed low negative predictive values (range 47-66%). A composite rule using both TST and QFT-GIT greatly improved negative predictive value to 90% (range 80-97%).

CONCLUSION

In an endemic setting a positive TST or IGRA was highly predictive of LTBI, while a combination of TST and IGRA had high rule-out value. These data inform the utility of LTBI-related immunodiagnostic tests in TB and HIV endemic settings.

Paediatric tuberculosis transmission outside the household: challenging historical paradigms to inform future public health strategies

Tuberculosis is a major cause of death and disability among children globally, yet children have been neglected in global tuberculosis control efforts. Historically, tuberculosis in children has been thought of as a family disease, and because of this, household contact tracing of children after identification of an adult tuberculosis case has been emphasised as the principal public health intervention. However, the population-level effect of household contact tracing is predicated on the assumption that most paediatric tuberculosis infections are acquired within the household. In this Personal View, we focus on accumulating scientific evidence indicating that the majority of Mycobacterium tuberculosis transmission to children in high-burden settings occurs in the community, outside of households in which a person has tuberculosis. We estimate the population-attributable fraction of M tuberculosis transmission to children due to household exposures to be between 10% and 30%. M tuberculosis transmission from the household was low (<30%) even in children younger than age 5 years. We propose that an effective public health response to childhood tuberculosis requires comprehensive, community-based interventions, such as active surveillance in select settings, rather than contact tracing alone. Importantly, the historical paradigm that most paediatric transmission occurs in households should be reconsidered on the basis of the scientific knowledge presented.

Risk of tuberculosis infection among health care workers and nursing students in Japan

It is important to evaluate the risk of tuberculosis (TB) infection among health care workers (HCWs) and nursing students in Japan to propose the optimal countermeasure against new TB infection for them. To estimate the annual incidence of TB infection in HCWs at a Japanese university hospital without TB wards and in nursing students at a Japanese university using interferon-gamma release assay (IGRA). Serial IGRAs were prospectively conducted on the HCWs between August 2010 and December 2015. For nursing students, two IGRA tests were conducted before commencement of clinical training and at employment as nurses between April 2007 and December 2015. A total of 328 HCWs and 298 nursing students were followed for 670.15 and 1212.80 person-years, respectively. Assuming IGRA-positive conversions were all attributable to true infection, the incidence of TB infection in HCWs and nursing students was 0.149/100 and 0.0825/100 person-years, respectively. At a Japanese university hospital without TB wards and a Japanese university, the annual incidence of TB infection among HCWs and nursing students estimated from serial IGRA results was low, but continued vigilance for the prevention of TB infection is essential.

Borderline QuantiFERON results and the distinction between specific responses and test variability

BACKGROUND

QuantiFERON (QFT) results near the cut-off are subject to debate. We aimed to investigate which borderline QFT results were due to Mycobacterium tuberculosis (Mtb)-specific responses or to test variability.

METHODS

In a contact investigation, tuberculin skin test (TST), QFT and T-SPOT.TB (T-SPOT) were performed in 785 BCG-unvaccinated contacts. Contacts with a low-negative (<0.15), borderline (0.15-0.35), low-positive (0.35-0.70) or high-positive QFT (≥0.70 IU/mL) were compared with respect to exposure, TST and T-SPOT results. Development of active tuberculosis was assessed.

RESULTS

Borderline QFT results occurred in threefold excess over test variability (p = 0.0027). In contacts with low-negative, borderline or positive QFT results, a positive TST occurred in 24.9%, 62.1% and 91.4% (p < 0.0001) and a positive T-SPOT result in 6.3%, 41.3% and 86.4%, respectively (p < 0.0001). Two-third (20/29) of contacts with a borderline and 14/16 (88%) with a low-positive QFT had a positive TST and/or T-SPOT, indicating probable Mtb-infection. During 12 years of follow-up, seven patients were diagnosed with active tuberculosis, two of whom after a low-positive QFT.

CONCLUSIONS

In this study, most borderline and low-positive QFT results were Mtb-specific, showing the biological significance of a borderline QFT. The clinical relevance, however, will be most distinct in patients who are or will be immunocompromised.

Reversion of QuantiFERON-TB Gold In-Tube test in individuals with and without prophylactic treatment for latent tuberculosis infection: A systematic review and meta-analysis

OBJECTIVES

Reversion of tuberculosis (TB) infection testing has been suggested to be associated with prophylactic treatment efficacy. However, evidences based on randomized controlled study were sparse.

METHODS

Studies on serial QuantiFERON-TB Gold In-Tube (QFT) test, among individuals with and without prophylactic treatment were identified in the databases of PubMed, MEDLINE and EMBASE up to 28 February 2018. The reversion rates were quantitatively summarized by means of meta-analysis using the random-effect model.

RESULTS

A total of 52 eligible studies were included in the meta-analysis on QFT test reversion rate among participants with (20 studies) and without (32 studies) prophylactic treatment. Summarized reversion rate was found to be 24.9% (95% confidence interval [CI]: 18.4-32.9%) and 25.3% (95% CI: 19.6-32.0%) for those completed or without treatment, respectively. When the analysis was restricted to the participants completed treatment, higher summarized rate of QFT reversion was found among those with longer course therapy (9INH vs. the other regimens), studies from Asia (vs. Europe and America), and individuals with immunosuppression disorders (vs. general populations).

CONCLUSIONS

Our results suggested that QFT reversion was frequently observed regardless of with or without prophylactic treatment. Serial QFT testing might be inappropriate for evaluating preventive treatment efficacy.

IGRA-Based Screening for Latent Tuberculosis Infection in Persons Newly Incarcerated in New York City Jails

In the United States, latent tuberculosis infection (LTBI) detection in correctional settings is a public health priority. Interferon gamma release assay (IGRA)-based LTBI screening was introduced in New York City jails in 2011 to 2012, replacing historically used tuberculin skin testing (TST), which was associated with substantial incomplete screening rates. This retrospective, cross-sectional study evaluated LTBI screening outcomes and correlates of positivity in 40,986 persons newly incarcerated in 2011 to 2013. Of 35,090 eligible patients tested (96.4%), final results were 6.3% positive, 93.4% negative, and 0.2% indeterminate. In multivariable regression modeling, sex, age, race/ethnicity, nativity, marital status, prior jail incarceration, and HIV status were correlated with positivity. IGRA-based screening yielded high screening and low indeterminate test rates and may be recommended in correctional and other settings where TST is currently used.

Testing of tuberculosis infection among Chinese adolescents born after terminating the Bacillus Calmette-Guérin booster vaccination: subgroup analysis of a population-based cross-sectional study

The prevalence of tuberculosis infection among adolescents born after terminating the Bacillus Calmette-Guérin (BCG) booster vaccination in China was estimated using tuberculin skin testing (TST) and QuantiFERON-TB Gold assay (QFT) to investigate the influence of neonatal BCG vaccination on the performance of TST. Data analysis was conducted for 2831 eligible participants aged 5-15 years from the baseline survey of a population-based multi-center prospective study. The prevalence rates of TST (induration = 10 mm) and QFT positivity were 9.3% (264/2827) and 2.5% (71/2831), respectively. The rate of QFT indeterminate result was 2.2% (62/2831). The overall agreement between TST and QFT was low (concordance = 88.0%; ? coefficient = 0.125). Only TST was positively associated with BCG vaccination with an adjusted odds ratio of 1.71 [95% confidence interval, 1.26-2.31]. A history of close contact with patients of active TB was significantly associated with positivity for TST and QFT. Our results suggested that BCG neonatal vaccination still affects TST performance, and a twostep approach might be considered for TB infection testing among adolescents in China.

Latent Mycobacterium tuberculosis Infection and Interferon-Gamma Release Assays

The identification of individuals with latent tuberculosis infection (LTBI) is useful for both fundamental understanding of the pathogenesis of disease and for clinical and public health interventions (i.e., to prevent progression to disease). Basic research suggests there is a pathogenetic continuum from exposure to infection to disease, and individuals may advance or reverse positions within the spectrum, depending on changes in the host immunity. Unfortunately, there is no diagnostic test that resolves the various stages within the spectrum of Mycobacterium tuberculosis infection. Two main immune-based approaches are currently used for identification of LTBI: the tuberculin skin test (TST) and the interferon-gamma release assay (IGRA). TST can use either the conventional purified protein derivative or more specific antigens. Extensive research suggests that both TST and IGRA represent indirect markers of M. tuberculosis exposure and indicates a cellular immune response to M. tuberculosis. The imperfect concordance between these two tests suggests that neither test is perfect, presumably due to both technical and biological reasons. Neither test can accurately differentiate between LTBI and active TB. Both IGRA and TST have low sensitivity in a variety of immunocompromised populations. Cohort studies have shown that both TST and IGRA have low predictive value for progression from infection to active TB. For fundamental applications, basic research is necessary to identify those at highest risk of disease with a positive TST and/or IGRA. For clinical applications, the identification of such biomarkers can help prioritize efforts to interrupt progression to disease through preventive therapy.

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.

Evaluation of QuantiFERON-TB Gold-Plus in Health Care Workers in a Low-Incidence Setting

Although launched in 2015, little is known about the accuracy of QuantiFERON-TB Gold-Plus (QFT-Plus) for diagnosis of latent M. tuberculosis infection (LTBI). Unlike its predecessor, QFT-Plus utilizes two antigen tubes to elicit an immune response from CD4⁺ and CD8⁺ T lymphocytes. We conducted a cross-sectional study in low-risk health care workers (HCWs) at a single U.S. center to compare QFT-Plus to QuantiFERON-TB Gold in-tube (QFT). A total of 989 HCWs were tested with both QFT and QFT-Plus. Risk factors for LTBI were obtained from a questionnaire. QFT-Plus was considered positive if either antigen tube 1 (TB1) or TB2 tested positive, per the manufacturer's recommendations, or if both TB1 and TB2 tested positive, using a conservative definition. Results were compared using Cohen's kappa and linear regression, respectively. Agreement of QFT with QFT-Plus was high, at 95.6% (95% confidence interval [CI], 94.3 to 96.9; kappa, 0.57). The majority of discordant results between QFT and QFT-Plus TB1 (84.8%) and QFT and QFT-Plus TB2 (88.6%) fell within the range of 0.2 to 0.7 IU/ml. The positivity rate in 626 HCWs with no identifiable risk factors and no self-reported history of positive LTBI tests was 2.1% (CI, 1.0 to 3.2) and 3.0% (CI, 1.7 to 4.3) with QFT and QFT-Plus, respectively. A conservative definition of a QFT-Plus-positive result yielded a positivity rate of 1.0% (CI, 0.2 to 1.7; P value of 0.0002 versus QFT-Plus and 0.07 versus QFT). On follow-up testing, of 11 HCWs with discordant QFT-Plus results, 90.9% (10/11) had a negative QFT result. The QFT-Plus assay showed a high degree of agreement with QFT in U.S. HCWs. A conservative interpretation of QFT-Plus eliminated nearly all nonreproducible positive results in low-risk HCWs. Larger studies are needed to validate the latter finding and to more clearly define conditions under which a conservative interpretation can be used to minimize nonreproducible positive results in low-risk populations.

Poor predictability of QuantiFERON-TB assay in recipients and donors for tuberculosis development after kidney transplantation in an intermediate-TB-burden country

BACKGROUND

Tuberculosis (TB) is a common opportunistic infection after kidney transplantation (KT). The QuantiFERON-TB-Gold In-Tube test (QFT) is widely used for assessing latent TB; however, it is currently unclear whether the pre-KT QFT of the recipient and donor can predict post-KT TB.

METHODS

We retrospectively reviewed patients who received KT between January 2009 and December 2015 at Seoul National University Hospital. The QFT was performed in 458 KT recipients and 239 paired living donors, and 138 KT recipients underwent both the QFT and tuberculin skin test (TST). After excluding 12 patients diagnosed as having clinically latent TB, we evaluated whether the QFT of the recipient and donor was predictive for new-onset active TB after KT.

RESULTS

The QFT was positive in 101 (22.1%) recipients and associated with clinically latent TB before KT (P < 0.05). However, agreement between the TST and QFT was poor (κ = 0.327). Post-KT TB occurred in 1 of 95 recipients with a positive QFT, and 2 cases of TB occurred among 351 patients with a negative or indeterminate QFT. The incidence of TB was 242 cases/100,000 person-years among 446 KT recipients with a median follow-up of 30.2 months. The QFT of recipients could not predict post-KT TB in Poisson regression analysis (relative risk [RR], 1.847; 95% confidence interval [CI], 0.168-20.373; P = 0.616). Of 234 living donor-recipient pairs, the QFT of the recipient (RR, 5.012; 95% CI, 0.301-83.430; P = 0.261) and QFT of the donor (RR, 1.758; 95% CI, 0.106-29.274; P = 0.694) could not predict post-KT TB.

CONCLUSION

The QFT of recipients or living donors pre-KT cannot predict the short-term development of post-KT TB in an intermediate TB-burden country.

Serial QuantiFERON testing and tuberculosis disease risk among young children: an observational cohort study

BACKGROUND

The value of quantitative interferon-γ release assay results for predicting progression from Mycobacterium tuberculosis infection to active disease is unknown. We aimed to investigate the relation between QuantiFERON-TB Gold In-Tube (QFT) conversion interferon-γ values and risk of subsequent active tuberculosis disease and of QFT reversion.

METHODS

We analysed data from a reported vaccine efficacy trial of the tuberculosis vaccine MVA85A in South Africa. QFT negative, HIV uninfected young children aged 18-24 weeks were enrolled. We stratified participants by quantitative QFT result (interferon-γ <0·35 IU/mL, 0·35-4·00 IU/mL, and >4·00 IU/mL) at the intermediate study visit (day 336) and determined risk of progression to active tuberculosis disease over the subsequent 6-24 months. No QFT differences were observed between placebo and MVA85A groups at day 336 or end of study; therefore, both groups were included in analyses. Study clinicians were not masked to QFT values, but strict case definitions were used that excluded QFT results. We used generalised additive models to evaluate the quantitative relation between day 336 QFT value and subsequent disease risk, and we compared disease rates between QFT strata using a two-sample Poisson test.

FINDINGS

Among 2512 young children with QFT tests done at day 336, 172 (7%) were positive; 87 (7%) of 1267 in placebo group and 85 (7%) of 1245 in the MVA85A group (p=1·00). Compared with QFT non-converters (tuberculosis disease incidence 0·7 per 100 person-years [95% CI 0·4-1·1]), children with QFT conversion at interferon-γ values between 0·35-4·00 IU/mL did not have significantly increased risk of disease (2·5 per 100 person-years [95% CI 0·4-9·4]; incidence rate ratio (IRR) 3·7 (95% CI 0·4-15·8; p=0·23). However, QFT conversion at interferon-γ values higher than 4·00 IU/mL was associated with substantially increased disease incidence (28·0 per 100 person-years [95% CI 14·9-45·7]) compared with non-converters (IRR 42·5 [95% CI 17·2-99·7]; p<0·0001), and compared with children with interferon-γ values between 0·35-4·00 IU/mL (IRR 11·4 [95% CI 2·4-107·2]; p=0·00047). Among 91 QFT converters who were given a repeat test, 53 (58%) reverted from positive to negative. QFT reversion risk was inversely associated with interferon-γ value at QFT conversion and was highest with interferon-γ values less than 4·00 IU/mL (47 [77%] of 61).

INTERPRETATION

In young children, tuberculosis disease risk was not significantly increased, and QFT reversion was common, following QFT conversion at interferon-γ values up to 10 times the recommended test threshold (0·35 IU/mL). By contrast, QFT conversion at very high interferon-γ values (>4·00 IU/mL) warrants intensified diagnostic and preventive intervention because of the extremely high risk of tuberculosis disease in these young children.

FUNDING

Aeras, Wellcome Trust, and Oxford-Emergent Tuberculosis Consortium (OETC) were the funders of the MVA85A 020 Trial. National Institute of Allergy and Infectious Diseases supported this analysis.

Preventing the Transmission of Tuberculosis in Health Care Settings: Administrative Control

It is well established that health care workers (HCWs) have a considerably higher risk of occupationally acquired tuberculosis (TB). To reduce the transmission of TB to HCWs and patients, TB infection control programs should be implemented in health care settings. The first and most important level of all protection and control programs is administrative control. Its goals are to prevent HCWs, other staff, and patients from being exposed to TB, and to reduce the transmission of infection by ensuring rapid diagnosis and treatment of affected individuals. Administrative control measures recommended by the United States Centers for Disease Control and Prevention and the World Health Organization include prompt identification of people with TB symptoms, isolation of infectious patients, control of the spread of the pathogen, and minimization of time spent in health care facilities. Another key component of measures undertaken is the baseline and serial screening for latent TB infection in HCWs who are at risk of exposure to TB. Although the interferon-gamma release assay has some advantages over the tuberculin skin test, the former has serious limitations, mostly due to its high conversion rate.

Biologic Agents and Tuberculosis

Treatment with biologic agents, in particular tumor necrosis factor alpha (TNF-α) inhibitors, is associated with an increased risk of tuberculosis (TB), and screening and treatment for latent TB infection (LTBI) in patients undergoing such treatment is therefore indicated. The risk of TB associated with different biologics varies significantly, with the highest relative risks, 29.3 and 18.6, associated with adalimumab and infliximab, respectively. The risk of TB with newer TNF-α inhibitors and other biologics appears to be lower. Performance of LTBI screening tests is affected by immune-mediated inflammatory diseases and immunosuppressive therapy in patients due to commence TNF-α inhibitor treatment. Interferon gamma release assays (IGRAs) have a higher specificity than the tuberculin skin test (TST) in patients with Bacillus Calmette–Guérin (BCG) vaccination and have probably a better sensitivity than TST in immunosuppressed patients. LTBI screening programs prior to commencement of anti-TNF-α treatment significantly reduce the incidence of TB, but the optimal screening algorithm, in particular the question of whether a combination of IGRA and TST or a single test only should be used, is a matter of ongoing debate. Use of TST in combination with IGRA is justified to increase sensitivity. Repeat testing for LTBI should be limited to patients at increased risk of TB. If TB develops during anti-TNF-α treatment, it is more likely to be disseminated and extrapulmonary than are other TB cases. Discontinuation of anti-TNF-α treatment in patients diagnosed with TB is associated with an increased risk of immune reconstitution inflammatory syndrome, which is probably best managed by reintroduction of anti-TNF-α treatment.

Diagnosis and management of latent tuberculosis

PURPOSE OF REVIEW

Latent tuberculosis infection (LTBI) may affect over two billion individuals and serves as a potential reservoir for future active tuberculosis. The identification and treatment of LTBI in those at highest risk for progression is an essential part of tuberculosis control.

RECENT FINDINGS

Interferon-γ release assays are increasingly used for targeted testing and diagnosis of latent disease. The performance of these immunodiagnostic tests has been studied in various groups and may be better than the tuberculin skin test in certain populations. Ongoing research is focused on new biomarkers that may diagnose LTBI or predict progression to active tuberculosis. Isoniazid preventive treatment is effective at reducing risk of active disease, but length of treatment and potential side-effects limit patient acceptance and compliance. Rifamycin-based regimens are increasingly studied as a shorter and perhaps less toxic alternative for preventive therapy.

SUMMARY

Identification of those with LTBI is important as it allows treatment of those at highest risk of progression to active disease and thus decreases the overall burden of tuberculosis. The development of new immunodiagnostics may further improve identification of those at risk and alternative medication regimens may increase compliance with and efficacy of preventive therapy.

Serial testing for latent tuberculosis using QuantiFERON-TB Gold In-Tube: A Markov model

Healthcare workers (HCWs) in low-incidence settings are often serially tested for latent TB infection (LTBI) with the QuantiFERON-TB Gold In-Tube (QFT) assay, which exhibits frequent conversions and reversions. The clinical impact of such variability on serial testing remains unknown. We used a microsimulation Markov model that accounts for major sources of variability to project diagnostic outcomes in a simulated North American HCW cohort. Serial testing using a single QFT with the recommended conversion cutoff (IFN-g > 0.35 IU/mL) resulted in 24.6% (95% uncertainty range, UR: 23.8–25.5) of the entire population testing false-positive over ten years. Raising the cutoff to >1.0 IU/mL or confirming initial positive results with a (presumed independent) second test reduced this false-positive percentage to 2.3% (95%UR: 2.0–2.6%) or 4.1% (95%UR: 3.7–4.5%), but also reduced the proportion of true incident infections detected within the first year of infection from 76.5% (95%UR: 66.3–84.6%) to 54.8% (95%UR: 44.6–64.5%) or 61.5% (95%UR: 51.6–70.9%), respectively. Serial QFT testing of HCWs in North America may result in tremendous over-diagnosis and over-treatment of LTBI, with nearly thirty false-positives for every true infection diagnosed. Using higher cutoffs for conversion or confirmatory tests (for initial positives) can mitigate these effects, but will also diagnose fewer true infections.

Using IFN-gamma release assay to confirm tuberculin skin test improves the screening of latent tuberculosis infection in Italian healthcare workers

Background

Healthcare workers (HCWs) represent a tuberculosis (TB) risk group for a wide range of tasks in healthcare, even in countries with low TB incidence, like Italy. Latent Tuberculosis Infection (LTBI) screening programs are an important tool for TB prevention in these setting.

Methods

A retrospective study under a LTBI screening program among HCWs at the Siena University Hospital (Italy), was conducted between September 2011 and July 2015. Tuberculin Skin Test (TST) was used as a first level examination; all TST-positive cases were tested with QuantiFERON-TB Gold In-Tube (QFT-GIT) test, together with a group of TST-negative subjects.

Results

Among the 2136 HCWs screened, 144 (6.7 %) were TST-positive and therefore tested with QFT-GIT, confirming a positive result in 36 cases (25 %). Agreement between two tests was poor (k = 0.092; 95 %, Confidence Interval [CI]- 0.048–0.136, p = 0.002). Among TST-positive cases, discordant results occurred more frequently in BCG vaccinated than unvaccinated HCWs (86.3 %, p < 0.001). The probability of a QFT-GIT-positive result increased according to the TST diameter (p = 0.001). No putative risk factor was associated with LTBI occurrence.

Conclusions

The use of QFT-GIT test as a second step in TST-positive cases offers an appropriate tool for LTBI detection, especially among BCG-vaccinated HCWs.

Annual risk of tuberculosis infection in rural China: a population-based prospective study

Prospective population data on the incidence of tuberculosis (TB) infection has been sparsely reported in the global literature.A population-based prospective study was conducted in rural China to investigate the annual risk of TB infection, and its persistence using serial tuberculin skin tests (TSTs) and an interferon-γ release assay. In total, 13 580 eligible participants from four rural sites, identified as TST negative (<10 mm) or QuantiFERON-TB Gold In-Tube (QFT) (an interferon-γ release assay) negative from a baseline survey, were included in the first year's follow-up examination.The annual conversion rate of QFT among the study sites ranged between 2.1% and 4.9% (average 3.1%), and the incidence of TST conversion ranged between 6.0% and 31.1% (average 14.5%). During the second year's follow-up, infection persistence was investigated using 390 subjects with QFT conversions. Among them, 49.7% (164 out of 330) were found to be consistently QFT positive. Both the conversion and the persistence of QFT positivity were found to be significantly increased with increasing age.In conclusion, the annual TB infection rate was suggested to be ∼1.5% based on persistent positive results after QFT conversion in rural China. Therefore, infection control among those high-risk populations, including the elderly, should be prioritised for TB control in China.

Reactivation tuberculosis: role of surveillance

The incidence and death rates from tuberculosis (TB) have declined through concerted efforts in the diagnosis and treatment of active disease. Despite this, 9.6 million new cases and 1.1 million deaths in 2014 are unacceptably high. To decrease the rates of TB further, the huge number of persons with latent TB infection (LTBI) from whom new cases will arise has to be addressed with a sense of priority. Identifying the highest risk groups and providing effective treatment has been shown to decrease active TB. Further research to refine the predictors of reactivation and shorter effective treatments are urgently needed. Implementing intensified case finding, testing and treatment for LTBI will require continued investment in health care capacity at multiple levels.

Getting to Zero: Tuberculosis Elimination in California

This review of tuberculosis epidemiology is intended to provide a historical perspective on the public health approach to tuberculosis (TB) control in California. This historical context offers a lens through which to view current epidemiologic trends and insight into how new therapeutic tools can be applied. Since 1993, the year detailed case reporting was instituted, California has had a decrease in recent TB transmission as evidenced by a reduction in pediatric cases and an increased percentage of cases attributable to progression of latent infection to TB disease in the foreign-born population. Overall, there has been a dramatic decline in the annual TB case count, but the speed of the decline has slowed over the last several years. At the current pace and case count of 2137 in 2015, California will not achieve TB elimination (<1 TB case per one million population) for at least 100 years. There are an estimated 2.1 million persons in California with latent TB infection. Modeling suggests that LTBI detection and treatment are important in reaching TB elimination. For this reason, a coalition of stakeholders in California is exploring novel approaches to accelerate the case decline in order to prevent unnecessary disease and death.

Clinical Application of Interferon-γ Release Assays for the Prevention of Tuberculosis in Countries with Low Incidence

Despite global efforts to control tuberculosis (TB) the estimated number of people who developed TB worldwide increased to an all-time record of more than 10 million in 2015. The goal of the World Health Organization (WHO) to reduce the global incidence of TB to less than 100 cases per million by 2035, cannot be reached unless TB prevention is markedly improved. There is a need for an improved vaccine that better protects individuals who are exposed to Mycobacterium tuberculosis from infection and active disease compared to the current M. bovis Bacille Calmette Guérin (BCG) vaccine. In the absence of such a vaccine, prevention relies on infection control measures and preventive chemotherapy for people with latent infection with M. tuberculosis (LTBI), who have the highest risk of progression to active TB. During the past decade, interferon-γ release assays (IGRAs) have increasingly replaced the tuberculin skin test as screening tools for the diagnosis of LTBI in countries with a low incidence of TB. Despite recent WHO guidelines on the management of LTBI, the definition of groups at risk for TB remains controversial, and the role of IGRAs for TB prevention in low-incidence countries remains uncertain. We reviewed the scientific literature and provide recommendations for the use of IGRAs for LTBI diagnosis in low-incidence countries. These recommendations are based on the number of patients needing treatment in order to prevent one case of TB. As the positive predictive value of IGRAs for the development of TB is sub-optimal, research must focus on the identification of alternative biomarkers that offer better predictive ability in order to substantially reduce the number needing treatment while improving the prevention of TB and improving the effectiveness of targeted preventive chemotherapy.