Impact of diabetes mellitus on indeterminate results of the QuantiFERON TB Gold In-Tube test: A propensity score matching analysis

BACKGROUND

The sensitivity of interferon-gamma release assays (IGRAs) in the detection of Mycobacterium tuberculosis infection could be affected by conditions of immune dysregulation. For this reason, diabetes mellitus (DM) may increase the frequency of indeterminate results of IGRAs. However, there have been inconsistent reports of role of DM on indeterminate IGRA results.

METHODS

We retrospectively reviewed all patients who underwent QuantiFERON-TB Gold In-Tube testing (QFT-GIT) at Chonnam National University Hospital. We collected the clinical and laboratory data of these patients.

RESULTS

Of all 3,391 subjects, 1,265 (37.3%) had a positive QFT-GIT result, 266 (7.8%) had an indeterminate result, and 1,860 (54.9%) had a negative result. The mean age was 54.8 ± 18.1 years and 55.0% of the patients were male. There were 512 (15.1%) patients with DM. Multivariable analysis revealed that systemic corticosteroid use, tuberculosis, lymphocytopenia, low serum albumin, and high serum C-reactive protein (CRP) levels were significantly associated with indeterminate QFT-GIT results. However, DM was not associated with indeterminate QFT-GIT results (adjusted odds ratio, 0.98; 95% confidence interval, 0.69-1.41; P = 0.939). After propensity score matching, DM was not associated with indeterminate results of QFT-GIT.

CONCLUSION

In this large cohort study, DM does not affect the incidence of indeterminate results of QFT-GIT.

The sensitivity of the QuantiFERON®-TB Gold Plus assay in Zambian adults with active tuberculosis

SETTING AND OBJECTIVE

To investigate the sensitivity of the new interferon-gamma release assay (IGRA), QuantiFERON®-TB Gold Plus (QFT-Plus), for active TB (used as a surrogate for latent tuberculous infection) in a Zambian TB clinic.

DESIGN

Consecutive smear or Xpert® MTB/RIF-positive adult (age 18 years) pulmonary TB patients were recruited between June 2015 and March 2016. Venous blood was tested using QFT-Plus. The sensitivity was defined as the number positive divided by the total number tested. Using logistic regression, factors associated with positive QFT-Plus results were explored.

RESULTS

Of 108 patients (median age 32 years, interquartile range 27-38; 73% male; 63% human immunodeficiency virus [HIV] positive), 90 were QFT-Plus-positive, 11 were negative and seven had indeterminate results; sensitivity was 83% (95%CI 75-90). There was no difference in sensitivity by HIV status (HIV-positive 85%, 95%CI 75-93; n = 68 vs. HIV-negative 80%, 95%CI 64-91; n = 40; P = 0.59). In models adjusted for age alone, CD4 cell count <100 cells/μl (OR 0.15, 95%CI 0.02-0.96; P = 0.05) and body mass index <18.5 kg/m2 (OR 0.27, 95%CI 0.08-0.91; P = 0.02) were associated with decreased odds of positive QFT-Plus results.

CONCLUSION

Overall, the sensitivity of QFT-Plus is similar to that of the tuberculin skin test and other IGRAs. While overall sensitivity is not affected by HIV status, QFT-Plus sensitivity was lower among people living with HIV/acquired immune-deficiency syndrome with severe immunosuppression.

Assessment of the QuantiFERON-TB Gold In-Tube test for the detection of Mycobacterium tuberculosis infection in United States Navy recruits

Background

Immunologic tests such as the tuberculin skin test (TST) and QuantiFERON^®-TB Gold In-Tube test (QFT-GIT) are designed to detect Mycobacterium tuberculosis infection, both latent M. tuberculosis infection (LTBI) and infection manifesting as active tuberculosis disease (TB). These tests need high specificity to minimize unnecessary treatment and high sensitivity to allow maximum detection and prevention of TB.

Methods

Estimate QFT-GIT specificity, compare QFT-GIT and TST results, and assess factor associations with test discordance among U.S. Navy recruits.

Results

Among 792 subjects with completed TST and QFT-GIT, 42(5.3%) had TST indurations ≥10mm, 23(2.9%) had indurations ≥15mm, 14(1.8%) had positive QFT-GIT results, and 5(0.6%) had indeterminate QFT-GITs. Of 787 subjects with completed TST and determinate QFT-GIT, 510(64.8%) were at low-risk for infection, 277(35.2%) were at increased risk, and none had TB. Among 510 subjects at low-risk (presumed not infected), estimated TST specificity using a 15mm cutoff, 99.0% (95%CI: 98.2–99.9%), and QFT-GIT specificity, 98.8% (95%CI: 97.9–99.8%), were not significantly different (p>0.99). Most discordance was among recruits at increased risk of infection, and most was TST-positive but QFT-GIT-negative discordance. Of 18 recruits with TST ≥15mm but QFT-GIT negative discordance, 14(78%) were at increased risk. TB prevalence in country of birth was the strongest predictor of positive TST results, positive QFT-GIT results, and TST-positive but QFT-GIT-negative discordance. Reactivity to M. avium purified protein derivative (PPD) was associated with positive TST results and with TST-positive but QFT-GIT-negative discordance using a 10 mm cutoff, but not using a 15 mm cutoff or with QFT-GIT results.

Conclusions

M. tuberculosis infection prevalence was low, with the vast majority of infection occurring in recruits with recognizable risks. QFT-GIT and TST specificities were high and not significantly different. Negative QFT-GIT results among subjects with TST induration ≥15 mm who were born in countries with high TB prevalence, raise concerns.

Screening and Treatment Rates for Latent Tuberculosis Among Newly-Arrived Refugees in an Urban Facility in Connecticut

There is a high prevalence of latent tuberculosis infection (LTBI) and risk of reactivation among refugees. This study describes LTBI prevalence, treatment initiation, and completion rates in refugee patients seen at one urban Connecticut hospital. This retrospective chart review includes 248 adult refugee patients screened between January 2009 and April 2012. Demographics, tuberculin skin test (TST) results, treatment initiation and completion rates, and treatment-related variables were collected. Ninety-eight percent of adult refugees received TST screening and 44.0% were diagnosed with LTBI. Of these, 95.5% initiated treatment, and of those, 48.2% completed treatment. Early treatment discontinuation was high, with 29.5% of patients diagnosed with LTBI defaulting after the first clinic visit. Despite near-universal screening within this refugee population, LTBI treatment initiation and completion rates remain low. Greater efforts should be made to ensure LTBI treatment initiation and completion among refugees through early case management and shorter treatment duration.

Tuberculin skin test and/or interferon gamma release assay: is it still time to debate?

Not available.

Tuberculosis Detection in Paratuberculosis Vaccinated Calves: New Alternatives against Interference

Paratuberculosis vaccination in cattle has been restricted due to its possible interference with the official diagnostic methods used in tuberculosis eradication programs. To overcome this drawback, new possibilities to detect Mycobacterium bovis infected cattle in paratuberculosis vaccinated animals were studied under experimental conditions. Three groups of 5 calves each were included in the experiment: one paratuberculosis vaccinated group, one paratuberculosis vaccinated and M. bovis infected group and one M. bovis infected group. The performance of the IFN-gamma release assay (IGRA) and the skin test using conventional avian and bovine tuberculins (A- and B-PPD) but also other more specific antigens (ESAT-6/CFP10 and Rv3615c) was studied under official and new diagnostic criteria. Regarding the IGRA of vaccinated groups, when A- and B-PPD were used the sensitivity reached 100% at the first post-challenge sampling, dropping down to 40–80% in subsequent samplings. The sensitivity for the specific antigens was 80–100% and the specificity was also improved. After adapting the diagnostic criteria for the conventional antigens in the skin test, the ability to differentiate between M. bovis infected and non-infected animals included in paratuberculosis vaccinated groups was enhanced. Taking for positive a relative skin thickness increase of at least 100%, the single intradermal test specificity and sensitivity yielded 100%. The comparative intradermal test was equally accurate considering a B-PPD relative skin increase of at least 100% and greater than or equal to that produced by A-PPD. Using the specific antigens as a proteic cocktail, the specificity and sensitivity reached 100% considering the new relative and absolute cut-offs in all experimental groups (Δ≥30% and Δmm ≥ 2, respectively). Results suggest that the interference caused by paratuberculosis vaccination in cattle could be completely overcome by applying new approaches to the official tuberculosis diagnostic tests.

Comparison of TST and IGRA in Diagnosis of Latent Tuberculosis Infection in a High TB-Burden Setting

Background

There are currently two tests for diagnosing latent tuberculosis infection (LTBI); TST and IGRA. However, it is still unclear that which one of these tests performs better in high TB-burden settings.

Methods

1511 household contacts of pulmonary TB patients were enrolled to compare the performance of TST and IGRA for LTBI. At baseline all participant underwent testing for IGRA [QuantiFERON-TB® Gold In-tube (QFT-GIT) assay] and TST [2 tuberculin unit (TU), purified protein derivative (PPD), RT23, Staten Serum Institute (SSI), Copenhagen, Denmark]. All the household contacts were followed-up for two years for incident TB cases.

Results

Active TB was diagnosed in 76 household contacts at an incidence rate of 2.14 per 1000 person-years. Both, TST [Hazard Ratio (HR): 1.14, 95% confidence interval (CI): 0.72–1.79, p = 0.57], as well as QFT-GIT assay (HR: 1.66, 95% CI: 0.97–2.84, p = 0.06) results at baseline were not significantly associated with subsequent development of active TB among household contacts of pulmonary TB patients.

Conclusion

Neither TST nor IGRA predicted subsequent development of active TB among household contacts of pulmonary TB patients during follow-up. However, keeping in view the cost, and other logistics, TST remains the most preferred method for LTBI diagnosis in resource-limited, high TB-burden settings.

The Direct Comparison of Two Interferon-gamma Release Assays in the Tuberculosis Screening of Japanese Healthcare Workers

Objective Two interferon-gamma release assays (IGRAs), the QuantiFERON-TB Gold In-Tube (QFT-GIT) and T-SPOT.TB (T-SPOT), are commercially available. The agreement between the two IGRAs in the screening of healthcare workers (HCWs) for latent tuberculosis is not well known. Methods The QFT-GIT and T-SPOT tests were performed for the baseline tuberculosis screening of 654 HCWs who worked at Mie University Hospital in Japan. The results of the two tests were directly compared. Results Nineteen (2.9%), 28 (4.3%) and 33 (5.0%) of the 654 HCWs were found to be positive by the QFT-GIT, T-SPOT, and the QFT-GIT and/or T-SPOT methods using cut-off values of 0.35 IU/mL (QFT-GIT) and 6 spots (T-SPOT). After excluding 4 cases with indeterminate results, there were 14 concordant positive (2.2%), 618 concordant negative (95.1%), and 18 discordant (2.8%) results using the cut-off values of 0.35 IU/mL (QFT-GIT) and 6 spots (T-SPOT). The agreement of the two IGRAs was 97.2% (κ=0.595). When cut-off values of 0.35 IU/mL (QFT-GIT) and 8 spots (T-SPOT) were applied, there were 11 concordant positive (1.7%), 626 concordant negative (96.3%), and 13 discordant (2.0%) results, with 98.0% agreement (κ=0.618). When the borderline criteria for the QFT-GIT (0.1 to <0.35 IU/mL) and T-SPOT (5-7 spots) were applied, there were 11 concordant positive (1.7%), 11 concordant borderline (1.7%), 586 concordant negative (90.2%), and 42 discordant (6.5%) results, with 93.5% agreement between the two methods (κ=0.538). Conclusion When standard cut-off values were used, the agreement between the two IGRAs in the tuberculosis screening of Japanese HCWs was moderate to high. Importantly, some HCWs showed discordant results, especially those whose results were in the borderline zones.

Tuberculous pericarditis: a case report

Pericardial effusion is common disease and difficult to diagnose. Tuberculosis accounts for up to 4% of acute pericarditis and 7% of cardiac tamponade cases. Quick treatment can be lifesaving but requires accurate diagnosis. We report a case of a 65-year-old man who presented with a 3-week history of fever with chills, non-productive cough and dyspnea. The case was diagnosed by positivity of acid-fast staining, culture and polymerase chain reaction (PCR) of the aspirated pericardial fluid and treated promptly with antituberculosis drugs. The patient showed complete recovery.

Decreased Time to Treatment Initiation for Multidrug-Resistant Tuberculosis Patients after Use of Xpert MTB/RIF Test, Latvia

This test decreased time to treatment initiation by 66%–84%.

Few studies have examined whether the Xpert MTB/RIF test improves time to treatment initiation for persons with multidrug-resistant tuberculosis (MDR TB). We determined the impact of this test in Latvia, where it was introduced in 2010. After descriptive analyses of pulmonary MDR TB patients in Latvia during 2009–2012, time to treatment initiation was calculated, and univariate and multivariable accelerated failure time models were constructed. Univariate results showed strong evidence of an association between having rifampin-resistant TB detected by Xpert MTB/RIF and reduced time to treatment initiation versus the test not being used. A multivariable model stratifying by previous TB showed similar results. Our finding that in Latvia, time to treatment initiation was decreased for MDR TB cases that were rifampin-resistant TB by XpertMTB/RIF has implications for the use of this test in other settings with a high burden of MDR TB in which rifampin resistance is highly predictive of MDR TB.

Cost-effectiveness of interferon-gamma release assays for tuberculosis screening in nursing homes

Tuberculosis (TB) in older people is a significant public health problem in low TB-incidence countries. Older persons have increased TB incidence, higher reactivation and mortality. A delay in diagnosis and initiation of TB treatment in patients with atypical clinical and radiological features is a significant factor of widespread transmission. This study aimed to evaluate the cost-effectiveness of interferon-gamma release assays [IGRAs; QuantiFERON®-TB Gold In-Tube (QFT) and T-SPOT®.TB (T-SPOT)] compared to the tuberculin skin test (TST) and chest X-ray (CXR) examination for TB screening for nursing homes. Decision trees and Markov models were constructed using a societal perspective on a lifetime horizon. Seven strategies: no screening, TST, QFT, T-SPOT, TST followed by QFT, TST followed by T-SPOT, and CXR were considered. QFT [US$ 401·9, 4·36 707 QALY (year 2014 values)] was the most cost-effective at the willingness-to-pay level of US$ 50 000/QALY gained. TST followed by QFT was the most cost-effective in residents with comorbidities. CXR was less cost-effective. Cost-effectiveness was sensitive to latent TB infection (LTBI) rate and bacillus Calmette-Guérin vaccination rate. Effective LTBI screening using IGRA is recommended to prevent TB transmission not only in nursing homes but also in local communities in low-incidence countries.

QuantiFERON conversion following tuberculin administration is common in HIV infection and relates to baseline response

BACKGROUND

HIV-1 infection impairs tuberculosis (TB) specific immune responses affecting the diagnosis of latent TB. We aimed to (1) determine the proportion of HIV-1-infected adults with a negative QuantiFERON®-TB Gold in-tube (QFT-GIT) and Tuberculin skin testing (TST) that convert to QFT-GIT positive following TST, and (2) evaluate the relationship between conversion and baseline QFT-GIT results.

METHODS

HIV-1 infected adults being screened for a TB vaccine study in South Africa underwent QFT-GIT followed by TST. As per protocol, QFT-GIT was repeated if randomization was delayed allowing for evaluation of TST boosting in a proportion of participants.

RESULTS

Of the 22 HIV-1 infected, TST and QFT-GIT negative adults (median CD4 477/mm3 IQR 439-621) who had QFT-GIT repeated after median 62 days (IQR 49-70), 40.9 % (95 % CI 18.6-63.2 %) converted. Converters had a significantly greater increase in the background subtracted TB antigen response (TBAg-Nil - all units IU/mL) following TST, 0.82 (IQR 0.39-1.28) vs 0.03 (IQR -0.05-0.06), p = 0.0001. Those who converted also had a significantly higher baseline TBAg-Nil 0.21(IQR 0.17-0.26) vs 0.02(IQR 0.01-0.07), p = 0.002. Converters did not differ with regard to CD4 count or ART status. ROC analysis showed a baseline cut off of 0.15 correctly classified 86.4 % of converters with 88.9 % sensitivity.

CONCLUSIONS

Our findings support the possibility that there are 2 distinct groups in an HIV-1 infected population with negative QFT-GIT and TST; a true negative group and a group showing evidence of a weak Mtb specific immune response that boosts significantly following TST resulting in conversion of the test result that may represent false negatives. Further evaluation of whether a lower cut off may improve sensitivity of QFT-GIT in this population is warranted.

The mantoux test: should we change the site?

Recent studies have shown that sunlight-induced immunosuppression negatively alters the skin response to mantoux test. This study aimed to compare the response of the skin to mantoux test over the volar forearm surface, the traditional site, which is exposed to sunlight and the inner thigh, an area which is not. In all, 45 children had the mantoux test administered using 0.1 mL of 5TU purified protein derivative. Reactive induration to the mantoux test was recorded in five of these children. The average induration of the volar surface was 8.2 mm, while that at the inner thigh was 11.6 mm. The results have highlighted the potential of an enhanced mantoux test result, if parts of the body that are not exposed to high doses of ultraviolet light are used as the site for mantoux test.

The Sensitivity of Gross Necropsy, Caudal Fold and Comparative Cervical Tests for the Diagnosis of Bovine Tuberculosis

Bovine tuberculosis (bTb) was diagnosed in 22 cattle herds in the northeast corner of Michigan's lower peninsula. Of these 22 herds, 494 animals in 7 herds were examined by gross necropsy, histopathologic exam, mycobacterial culture, and polymerase chain reaction (PCR) assay performed only on samples that were histologically compatible for bTb. Results of culture and PCR assay interpreted in parallel were used as the reference test for calculation of the sensitivity of 1) the caudal fold test (CFT), 2) the caudal fold and comparative cervical skin tests used in series (CFTCCTSER), and 3) gross necropsy. Mycobacterium bovis was isolated from 43 animals. Using all 7 herds, the sensitivities of the CFT, the CFTCCTSER, and gross necropsy were 93.02%, 88.37%, and 86.05%, respectively. When the data were stratified by low- and moderate-prevalence herds, the sensitivities were 83.33%, 75.0%, and 83.33% in low-prevalence herds and 96.77%, 93.55%, and 87.10% in moderate-prevalence herds. The sensitivities of the 2 skin tests were slightly higher when 2 or more gross lesions were present, and the sensitivity of gross necropsy was significantly higher ( P = 0.049). The sensitivity of the CFT was found to be notably higher than most estimates in other studies; however, a direct comparison was not possible because the amount of purified protein derivative and the reference methods were different in this study compared with other published studies. Although the sensitivities are high, 2 of the 7 herds (29%) would have had 1 or more positive animals left in the herd if a test-and-removal program had been used. This suggests that when positive herds are identified, selective culling of skin test reactors is a less acceptable disease control strategy than is complete depopulation.

[Risk of tuberculosis in healthcare workers: risk assessment and medical surveillance]

Tuberculosis screening is recommended for all health care workers. We evaluated the prevalence of latent tuberculosis infection among 939 hospital workers of Tor Vergata University teaching hospital in Rome, Italy, in the period 2007-2013, by using the QuantiFERON Gold In-Tube (QFT) test. The mean age of subjects tested was 31 years. The prevalence of positive subjects (cut-off 0.35 UI/ml) was 5.5% (46/939) and the mean age of those who tested positive was 39 years. The low rate of positivity may be partly related to the higher reliability of QFT in comparison to tuberculin skin testing.

[USE OF QuantiFERON® TB-GOLD IN-TUBE IN A CONTACT INVESTIGATION TO DETERMINE THE ONSET OF TUBERCULOSIS WITH OR WITHOUT LATENT TUBERCULOSIS INFECTION TREATMENT]

PURPOSE

QuantiFERON® TB-Gold In-Tube (3G) testing was performed on tuberculosis-positive index cases and their contacts. The purpose of this study was to evaluate the relationship between 3G test results and the subsequent development of tuberculosis, and to identify effective strategies to prevent the onset of tuberculosis.

METHODS

Index cases and their contacts were subjected to 3G testing in a contact investigation in Osaka City in 2011-2012. For index cases, sputum smears were tested, and the infecting organism was identified. For the contacts, the following information was collected: age, results of 3G testing, presence or absence of latent tuberculosis infection (LTBI) treatment, and onset of tuberculosis disease within 2 years of follow-up from the last contact with the index cases.

RESULTS

(1) There were 830 index cases, including 774 subjects with pulmonary tuberculosis (93.3%) and 3 with laryngeal tuberculosis (0.4%). From sputum smear tests, 726 patients (87.5%) were determined to be 3G positive, and 83 (10.0%) were determined to be 3G negative. (2) In total, 2,644 contacts were subjected to 3G testing. Of these, 2,072 patients (78.4%) tested negative, 196 (7.4%) showed an equivocal result, and 375 (14.2%) tested positive. Their mean ages were 33.7, 38.0, and 38.8 years, respectively, showing significant differences in tuberculosis status according to age (P < 0.001). (3) Among the 2,072 3G-negative contacts, tuberculosis developed in 2 (0.1%) of 2063. None of these contacts was treated for LTBI. Among the 375 3G-positive contacts, tuberculosis developed in 36 (36.0%) of 100 subjects that were not LTBI treated, while tuberculosis developed in 3 (1.1 %) of 275 subjects that were LTBI treated. A significant difference in the incidence of tuberculosis between treated and untreated 3G-positive contacts was observed (P < 0.001).

DISCUSSION

Tuberculosis developed in a high proportion of 3G-positive contacts that were not LTBI treated, suggesting the need for preventive management of 3G-positive contacts.

[IGRA methods in the routine operation - QuantiFERON®-TB Gold or T-SPOT.TB?]

For indirect diagnosis of tuberculosis, two commercial IGRA (Interferon Gamma Release Assay) assays are available - primal QuantiFERON®-TB Gold test, new version QuantiFERON®-TB Gold Plus test (four tube, differentiation in activity CD4+ a CD8+) and T-SPOT®.TB test. Both methods are based on the same principle, but their workflows are different. In this article, both assays are compared on the collection of 284 patients. Inter-rate agreement measure showed 81.3% consistency and Cohens kappa index was calculated as 0.72. In case of discrepancy between IGRA and other methods (clinical aspects, X-ray diagnostic, etc.), results should be confirmed by second IGRA assay for correct interpretation.

Tuberculine reaction measured by infrared thermography

SETTING

The infection with Mycobacterium tuberculosis gives a delayed immune response, measured by the tuberculine skin test. We present a new technique for evaluation based on automatic detection and measurement of skin temperature due to infrared emission.

DESIGN

34 subjects (46.8±16.9 years) (12/22, M/F) with suspected tuberculosis disease were examined with an IR thermal camera, 48 h after tuberculin skin injection.

RESULTS

In 20 subjects, IR analysis was positive for tuberculine test. Mean temperature of injection area was higher, around 1°C, for the positive group (36.2±1.1°C positive group; 35.1±1.6°C negative group, p<0.02 T test for unpaired groups).

CONCLUSION

IR image analysis achieves similar estimation of tuberculin reaction as the visual evaluation, based on higher temperature due to increased heat radiation from the skin lesion.

A Tuberculin Skin Test Survey and the Annual Risk of Mycobacterium tuberculosis Infection in Gambian School Children

Background

A Tuberculin skin test (TST) survey was conducted to assess the prevalence of latent TB Infection (LTBI) and to estimate the annual risk of M. tuberculosis infection (ARTI) in Gambian school children. The results are expected to contribute to understanding of Tuberculosis epidemiology in The Gambia.

Methods

This was a nationwide, multi-cluster survey in children aged 6–11 years. Districts, 20 of 37, were selected by probability proportional to size and schools by simple random sampling. All TST were performed using the Mantoux method. Height and weight measurements were obtained for all participants. We calculated prevalence of LTBI using cut-off points of 10mm, the mirror and mixture modelling methods.

Results

TST readings were completed 13,386 children with median age of 9 years (interquartile range [IQR] 8–10 years). Mixture analysis yielded a cut-off point of 12 mm, and LTBI prevalence of 6.9% [95%CI 6.47–7.37] and the ARTI was 0.75% [95%CI 0.60–0.91]. LTBI was associated gender and urban residence (p <0.01). Nutritional status was not associated with non-reactive TST or sizes of TST indurations. ARTI did not differ significantly by age, gender, BCG vaccination or residence.

Conclusions

This estimates for LTBI prevalence and ARTI were low but this survey provides updated data. Malnutrition did not affect estimates of LTBI and ARTI. Given the low ARTI in this survey and the overlapping distribution of indurations with mixture modelling, further surveys may require complementary tests such as interferon gamma release assays or novel diagnostic tools.

[New methods of diagnosis in tuberculosis]

Bacteriological diagnosis of tuberculosis has benefited in recent years from many technological advances to improve rapidity and sensitivity of the techniques. Thus, new LED fluorescence microscopes are in the process of replacing the optical microscopes and the Ziehl-Neelsen technique, making the examination more precise, faster and easier. The manual and automatic liquid culture has improved Lowenstein-Jensen culture and helped shorten antibiotic sensitivity test, allowing appropriate management of patients. The development and standardization of molecular biology methods led to the rapid detection and identification of mycobacterium directly in clinical samples but also of resistance genes for early diagnosis of MDR-TB and dealing with them quickly. However, the performance of these techniques does not sufficiently cover the diagnosis of smear-negative tuberculosis, extrapulmonary forms, children- and immune-compromised tuberculosis where sensitivity is limited. The diagnosis of latent tuberculosis is reinforced by the in vitro release testing of gamma interferon overcoming the lack of specificity of the tuberculin skin test. Despite considerable progress, more amelioration is still needed to improve these techniques in order to extend them to the paucibacillary tuberculosis and to facilitate their access to low-resource countries.

Interferon-gamma-release assay prevents unnecessary tuberculosis therapy

BACKGROUND

The mass influx of immigrants from tuberculosis-endemic countries into Israel was followed by a considerable increase in the incidence of tuberculosis (TB). All contacts of active TB patients are obliged to be screened by tuberculin skin tests (TST) and, if found positive, prophylactic treatment is considered.

OBJECTIVES

To assess the utility of interferon-gamma (IFNγ)-release assay with a prolonged follow-up in preventing unnecessary anti-TB therapy in individuals with suspected false positive results.

METHODS

Between 2008 and 2012 the QuantiFERON TB gold-in-tube test (QFT-G) was performed in 278 sequential individuals who were mostly TST-positive and/or were in contact with an active TB patient. In all, whole blood was examined by the IFNγ-release assay. We correlated the TST diameter with the QFT-G assay and followed those patients with a negative assay.

RESULTS

The QFT-G test was positive in only 72 (42%) of all 171 TST-positive individuals. There was no correlation between the diameter of TST and QFT-G positivity. Follow-up over 5 years was available in 128 (62%) of all QFT-G-negative individuals. All remained well and none developed active TB.

CONCLUSIONS

A negative QFT-G test may obviate the need for anti-TB therapy in more than half of those with a positive TST.

[Tuberculosis prevention]

Tuberculosis prevention is classically based on early detection of potential contagious cases and their effective treatment. But due to new parameters such as migration flows around the world, the emergence of Mycobacterium tuberculosis resistant strains and the increase of the population at risk, screening should be more active and target those who are more vulnerable to developing the disease. Traditional screening methods such as chest X-ray and tuberculin skin test, due to their high sensitivity and low cost, remain valid especially in populations with a high prevalence of the disease. The interferon-gamma release assays (IGRAs) seem to be very useful in immunodeficient patients with prior BCG vaccination. The treatment of subjects at high risk of developing active tuberculosis with a daily isoniazid self-administrated dosage for a period of 9 months is a prevention measure not only at the individual level but also at the collective one. All prevention interventions should be part of a national program concordant with the guidelines of the WHO Stop TB program that recommend a universal access to quality diagnosis and treatment focused on the patient.

OUTLOOK

New methods of detection based on gene amplification would better suit to detect tuberculosis in immunodeficient patients and identify treatment-resistant strains. The development of the third part of the Stop TB project would reduce the morbidity and mortality of this disease by 2025.

CONCLUSION

The prevention of tuberculosis has been a major epidemiological challenge around the world and is continuously improving to adapt to the evolving disease.

[Childhood tuberculosis]

Childhood TB is an indication of failing TB control in the community. It allows disease persistence in the population. Mortality and morbidity due to TB is high in children. Moreover, HIV co-infection and multidrug-resistant diseases are as frequent in children as in adults. Infection is more frequent in younger children. Disease risk after primary infection is greatest in infants younger than 2 years. In case of exposure, evidence of infection can be obtained using the tuberculin skin test (TST) or an interferon-gamma assay (IGRA). There is no evidence to support the use of IGRA over TST in young children. TB suspicion should be confirmed whenever possible, using new available tools, particularly in case of pulmonary and lymph node TB. Induced sputum, nasopharyngeal aspiration and fine needle aspiration biopsy provide a rapid and definitive diagnosis of mycobacterial infection in a large proportion of patients. Analysis of paediatric samples revealed higher sensitivity and specificity values of molecular techniques in comparison with the ones originated from adults. Children require higher drugs dosages than adults. Short courses of steroids are associated with TB treatment in case of respiratory distress, bronchoscopic desobstruction is proposed for severe airways involvement and antiretroviral therapy is mandatory in case of HIV infection. Post-exposure prophylaxis in children is a highly effective strategy to reduce the risk of TB disease. The optimal therapy for treatment of latent infection with a presumably multidrug-resistant Mycobacterium tuberculosis strain is currently not known.