Tuberculosis screening on a health science campus: use of QuantiFERON-TB Gold Test for students and employees

Detecting and managing Mycobacterium tuberculosis (TB) infection in a health-science center population is a clinical dilemma. Tuberculin skin tests are still the preferred method for detecting present or past infection of TB. The authors discuss the performance of whole blood interferon gamma release assay test commercially known as QuantiFERON-TB Gold Test (QFT-G) as an additional tool for a TB surveillance program for the students and employees at an academic medical center. QFT-G was successfully implemented as a confirmatory test for screening of TB infection.

PrimaTB STAT-PAK assay, a novel, rapid lateral-flow test for tuberculosis in nonhuman primates

Tuberculosis (TB) is the most important zoonotic bacterial disease in nonhuman primates (NHP). The current diagnostic method, the intradermal palpebral tuberculin test, has serious shortcomings. We characterized antibody responses in NHP against Mycobacterium tuberculosis to identify immunodominant antigens and develop a rapid serodiagnostic test for TB. A total of 422 NHP were evaluated, including 243 rhesus (Macaca mulatta), 46 cynomolgus (Macaca fascicularis), and 133 African green (Cercopithecus aethiops sabaeus) monkeys at five collaborative centers. Of those, 50 monkeys of the three species were experimentally inoculated with M. tuberculosis. Antibody responses were monitored every 2 to 4 weeks for up to 8 months postinfection by MultiAntigen Print ImmunoAssay with a panel of 12 recombinant antigens. All of the infected monkeys produced antibodies at various levels and with different antigen recognition patterns. ESAT-6 and MPB83 were the most frequently recognized proteins during infection. A combination of selected antigens which detected antibodies in all of the infected monkeys was designed to develop the PrimaTB STAT-PAK assay by lateral-flow technology. Serological evaluation demonstrated high diagnostic sensitivity (90%) and specificity (99%). The highest rate of TB detection was achieved when the skin test was combined with the PrimaTB STAT-PAK kit. This novel immunoassay provides a simple, rapid, and accurate test for TB in NHP.

[Treatment of latent tuberculosis infection: update of guidelines, 2006]

The Tuberculosis Working Group of the Portuguese Society of Pulmonology, feeling the need to develop guidelines for the diagnosis and treatment of latent tuberculosis infection, compiled a set of recommendations, in view to standardize procedures on this area. This document was prepared in collaboration with the Portuguese Societies of Internal Medicine, Pediatrics and Infectious Diseases, A review and update of guidelines for tracing and treatment of latent tuberculosis infection was made, concerning immunocompetent children and adults, as well as immunocompromised children and adults due to HIV infection. It is understood that these guidelines are to be used as general recommendations, and they should not replace the individual analysis of each case.

Prevalence of abnormal radiological findings in health care workers with latent tuberculosis infection and correlations with T cell immune response

Background

More than half of all health care workers (HCWs) in high TB-incidence, low and middle income countries are latently infected with tuberculosis (TB). We determined radiological lesions in a cohort of HCWs with latent TB infection (LTBI) in India, and determined their association with demographic, occupational and T-cell immune response variables.

Methodology

We obtained chest radiographs of HCWs who had undergone tuberculin skin test (TST) and QuantiFERON-TB Gold In Tube (QFT), an interferon-γ release assay, in a previous cross-sectional study, and were diagnosed to have LTBI because they were positive by either TST or QFT, but had no evidence of clinical disease. Two observers independently interpreted these radiographs using a standardized data form and any discordance between them resolved by a third observer. The radiological diagnostic categories (normal, suggestive of inactive TB, and suggestive of active TB) were compared with results of TST, QFT assay, demographic, and occupational covariates.

Results

A total of 330 HCWs with positive TST or QFT underwent standard chest radiography. Of these 330, 113 radiographs (34.2%) were finally classified as normal, 206 (62.4%) had lesions suggestive of inactive TB, and 11 (3.4%) had features suggestive of active TB. The mean TST indurations and interferon-γ levels in the HCWs in these three categories were not significantly different. None of the demographic or occupational covariates was associated with prevalence of inactive TB lesions on chest radiography.

Conclusion/Significance

In a high TB incidence setting, nearly two-thirds of HCWs with latent TB infection had abnormal radiographic findings, and these findings had no clear correlation with T cell immune responses. Further studies are needed to verify these findings and to identify the causes and prognosis of radiologic abnormalities in health care workers.

Tuberculosis: Diagnostics

While microscopy and culture are still the major backbone for laboratory diagnosis of tuberculosis (TB), new methods including molecular diagnostic tests have evolved over the last two decades. The majority of molecular tests have been focused on: (i) detection of nucleic acids both DNA and RNA, which are specific to Mycobacterium tuberculosis, by amplification techniques such as polymerase chain reaction (PCR); and (ii) detection of mutations in the genes which are associated with resistance to anti-tuberculosis drugs by sequencing or nucleic acid hybridization. In the session of the conference on diagnosis of TB, there were two presentations: one on the development of new diagnostic tools for drug resistant M. tuberculosis, and the other on issues involved in the application of new diagnostic tools for multidrug resistant (MDR)-TB, pediatric TB and HIV-TB.

Follow-up study of tuberculosis-exposed supermarket customers with negative tuberculin skin test results in association with positive gamma interferon release assay results

We report a follow-up study of 29 subjects with negative tuberculin skin test (TST) results in association with positive gamma interferon release assay (IGRA) results, mainly due to responses to CFP-10 in the T-SPOT.TB assay, during a contact investigation. One year later, 12/29 subjects (41%) had converted to positive TST results in association with negative IGRA results.

Comparison of tuberculin reaction sizes at 48 and 72 hours among children in Tiruvallur district, south India

SETTING

A rural population in Tiruvallur district, south India.

OBJECTIVE

To study the variability of skin test reaction sizes between 48 and 72 hours.

METHODS

A tuberculin test survey was conducted among children aged less than 10 years. The reaction sizes were read by the same reader at 48 hours and 72 hours independently. The results of the tuberculin test were compared.

RESULTS

Of 957 children aged below 10 years were included in the study; the male and female ratio was 1: 1.1. There were no significant differences between the readings of reaction size at 48 and 72 hours.

CONCLUSION

The tuberculin test results can be read either at 48 hours or 72 hours without compromising the validity.

Booster phenomenon of QuantiFERON-TB Gold after prior intradermal PPD injection

SETTING

University medical school in Japan.

OBJECTIVE

To clarify the influence of prior intradermal purified protein derivative (PPD) injection on QuantiFERON-TB Gold (QFT-G).

DESIGN

Ninety-seven sixth-year university medical students aged 20-29 years concurrently underwent QFT-G and tuberculin skin test (TST). The first negative QFT-G and the first TST <15 mm were followed by a second QFT-G one month later.

RESULTS

Five of the 97 (5%) subjects tested positive for the first QFT-G. Thirty-three underwent a second QFT-G, five of whom (15%) turned positive, demonstrating the booster phenomenon of QFT-G.

CONCLUSIONS

Prior intradermal PPD injection may boost QFT-G. Further studies of the diagnostic significance and immunological mechanisms of this phenomenon are needed. For clinical application, especially during contact screening, QFT-G should be evaluated while keeping in mind the possible influence of prior PPD intradermal injection.

[Use of QuantiFeron TB-2G test on high-risk groups for tuberculosis infection at our hospital]

PURPOSE

To investigate the infection rate of tuberculosis in high-risk employees at our hospital.

METHODS

We measured interferon gamma levels in 40 employees and evaluated the infection rate in doctors working in the Tuberculosis Ward (D group), nurses in the Tuberculosis Ward (N group), and other high-risk employees (O group).

RESULTS

The overall infection rate including probable infection was 6/40 (15.0%). The infection rate in the N group was 0%, while those in the D and O groups were 27.3% and 20.0% respectively. No new infection of tuberculosis was observed after the introduction of tuberculosis infection measure manual of our hospital.

CONCLUSION

Our hospital's tuberculosis infection measure manual was effective in decreasing the new tuberculosis infection despite a high infection rate in high-risk employees at our hospital.

[Analysis of tuberculosis infection among foreigners using QuantiFeron TB-2G test]

OBJECTIVE

The purpose of this study was to investigate contacts of a tuberculosis patient among foreigners using QuantiFERON TB-2G (QFT-2G) test.

SUBJECTS AND METHODS

Three index cases in this study were all foreigners. Contacts, who were mostly foreigners and some Japanese, were investigated by a chest X-ray examination, tuberculin skin test (TST) and QFT-2G, and all data were compared.

RESULTS

Among 48 subjects (30 Vietnamese and 18 Japanese) in case 1, 8 Vietnamese and 2 Japanese were QFT-2G positive. One contacts among 3 most close contacts who lived in the same room with the index case was QFT-2G positive. In case 2, three Chinese among 22 contacts were QFT-2G positive, and a very close contact who lived in the next door to the index case was QFT-2G negative. Seven QFT-2G positive Chinese were identified among 24 contacts in case 3. However, four very close contacts among them were QFT-2G negative.

CONCLUSION

Although it was unclear whether QFT-2G positives in cases 1 and 2 were infected with M. tuberculosis through the index cases, it is possible to speculate that these QFT-2G positives were already infected with M. tuberculosis while they live in their own country based on the prevalence of TB in their countries and the fact that many very close contacts were QFT-2G negative. Also, it was suggested that QFT-2G positives in case 3 may not be infected through the index case, but infected in their country, since all close contacts were QFT-2G negative. The results of this study suggested that using the QFT-2G test for foreigners prior to or soon after their entry to Japan and recommending chemoprophylaxis for those who are QFT-2G positive would be a very efficient control measures against immigrant foreigners with TB infection.

Quantitative scoring of an interferon-gamma assay for differentiating active from latent tuberculosis

The aim of this study was to assess the contribution of an interferon-gamma release assay (T-SPOT.TB) to the differentiation of active tuberculosis (TB) from latent TB infection by quantifying spot-forming units (sfu). The investigation was a prospective study of contacts exposed to a case of contagious TB and cases of HIV-negative culture-proven TB referred over a 16-month period. Tuberculin skin tests (TSTs) and T-SPOT.TB were performed in 310 contacts 8-12 weeks after exposure. In subjects with culture-proven TB, T-SPOT.TB was performed within 2 weeks of initiation of treatment. The analysis included all contacts with a positive T-SPOT.TB result and all subjects with TB. TB contacts (n = 127) and cases (n = 58) were included. Mean+/-sd T-SPOT.TB results were 107+/-56 (range 1-207) sfu for TB, 54+/-60 (7-239) sfu for contacts with positive T-SPOT.TB results and a TST induration diameter of >5 mm, and 19+/-27 (7-143) sfu for contacts with positive T-SPOT.TB results and a TST induration diameter of < or =5 mm. By receiver operating characteristic curve analysis, a threshold value of 49.5 sfu showed a sensitivity of 83% and specificity of 74% for distinguishing latent TB infection from TB. Although T-SPOT.TB results were significantly related to disease activity, the test cannot be recommended for the diagnosis of tuberculosis.

Two-Step Tuberculin Skin Testing in Drug Users

To assess the utility of booster testing and to identify factors associated with a positive booster test, two-step tuberculin testing was performed in drug users recruited from methadone treatment. Participants also received a standardized interview on demographics and testing for HIV and CD4+ lymphocyte count. Of 619 enrollees completing the protocol, 174 (28%) had a positive PPD and 24 of the remaining 445 (5%) had a positive booster test. On multivariate analysis, boosting was associated with older age (adjusted odds ratio [ORadj] 2.38/decade, 95% confidence interval [CI] 1.34-4.22), history of using crack cocaine (ORadj 2.61, 95% CI 1.10-6.18) and a history of working as a home health aide (ORadj 4.23, 95% CI 1.39-12.86). Two-step tuberculin skin testing increased the proportion of participants with latent tuberculosis infection from 22% to 25%. Given the effectiveness of chemoprophylaxis, booster testing should be considered when drug users are screened for tuberculosis infection.

Cost-effectiveness of interferon-gamma release assay testing for the treatment of latent tuberculosis

The aim of the present study was to assess the cost-effectiveness of the new T-SPOT.TB assay versus the tuberculin skin test (TST) for screening contacts for latent tuberculosis (TB) infection in Switzerland. Health and economic outcomes of isoniazid treatment of 20- and 40-yr-old close contacts were compared in a Markov model over a 20-yr period following screening with TST only (at three cut-off values) and T-SPOT.TB alone or in combination with the TST. T-SPOT.TB-based treatment was cost-effective at (Euro)11,621 and (Euro)23,692 per life-year-gained (LYG) in the younger and older age group, respectively. No TST-based programmes were cost-effective, except at a 15-mm cut-off in the younger group only, where the cost-effectiveness ((Euro)26,451.LYG(-1)) fell just below the willingness-to-pay threshold. Combination of the TST with T-SPOT.TB slightly reduced the total cost compared with the T-SPOT.TB alone by 4.4 and 5.0% in the younger and older groups respectively. The number of contacts treated to avoid one case of TB decreased from 50 (95% confidence interval 32-106) with the TST (10-mm cut-off) to 18 (95%CI 11-43) if T-SPOT.TB was used. Using T-SPOT.TB alone or in combination with the tuberculin skin test for screening of close contacts before latent tuberculosis infection treatment is highly cost-effective in reducing the disease burden of tuberculosis.

Cost-effectiveness of Interferon-γ Release Assay Screening for Latent Tuberculosis Infection Treatment in Germany

OBJECTIVES

To assess the cost-effectiveness of the new QuantiFERON-TB Gold In-Tube (QFT-G) [Cellestis; Carnegie, VIC, Australia] assay for screening and treating of persons who have had close contact with tuberculosis (TB) patients and are suspected of having latent tuberculosis infection (LTBI) [hereafter called close-contacts] in Germany.

METHODS

The health and economic outcomes of isoniazid treatment of 20-year-old close-contacts were compared in a Markov model over a period of 20 years, using two different cutoff values for the tuberculin skin test (TST), the QFT-G assay alone, or the QFT-G assay as a confirmatory test for the TST results.

RESULTS

QFT-G assay-based treatment led to cost savings of $542.9 and 3.8 life-days gained per LTBI case. TST-based treatment at a 10-mm induration size cutoff gained $177.4 and 2.0 life-days gained per test-positive contact. When the cutoff induration size for the TST was reduced to 5 mm, the incremental cost-effectiveness ratio fell below the willingness-to-pay threshold ($30,170 per life-years gained) but resulted in unnecessary treatment of 77% of contacts owing to false-positive TST results. Combination with the 5-mm induration size TST cutoff value compared to the results of the QFT-G assay alone reduced the total costs per 1,000 contacts by 1.8% to $222,869. The number treated to prevent 1 TB case was 22 for the two QFT-G assay-based procedures, 40 for the TST at a cutoff induration size of 10 mm, and 96 for the TST at a cutoff induration size of 5 mm. When the sensitivity rates of the TST and the QFT-G assay were compounded, the QFT-G assay strategy alone was slightly less costly (0.6%) than the two-step approach.

CONCLUSIONS

Using the QFT-G assay, but especially combining the QFT-G assay following the TST screening of close-contacts at a cutoff induration size of 5 mm before LTBI treatment is highly cost-effective in reducing the disease burden of TB.

Enhanced anti-mycobacterial immunity in children with erythema nodosum and a positive tuberculin skin test

Erythema nodosum (EN) may follow a variety of infections, but in regions with a high prevalence of tuberculosis, is frequently associated with a positive tuberculin skin test (TST) and tuberculosis infection. We aimed to investigate the immunological differences between patients with EN as a manifestation of primary tuberculosis, and those with progressive pulmonary tuberculosis (PTB) or asymptomatic infection. We studied the inflammatory response to both mycobacterial and non-mycobacterial antigens in 11 children with EN associated with a positive TST, 22 children with culture-confirmed tuberculosis, and 53 healthy skin test-positive children. In addition, we evaluated functional anti-mycobacterial immunity using an ex vivo assay of mycobacterial growth restriction in five children with EN and 15 with PTB. Patients with EN were distinguished by enhanced mycobacterial growth restriction on the functional assay, which was associated with a markedly increased production of IFNgamma in response to stimulation with purified protein derivative of Mycobacterium tuberculosis. Children presenting with EN and a positive TST show evidence of responses associated with enhanced anti-mycobacterial immunity.

Use of QuantiFERON-TB Gold to investigate tuberculosis contacts in a high school

BACKGROUND AND OBJECTIVE

QuantiFERON-TB Gold (QFT-G) was employed in a contact investigation in a high school to evaluate its performance in adolescents.

METHODS

Students of the same school grade as the index case were screened with tuberculin skin test (TST) and CXR examination as an initial contact investigation. QFT-G was performed for students demonstrating a positive TST (erythema larger than 30 mm).

RESULTS

Of 349 students whose TST was completed, 95 had positive TST responses, although the distribution of TST responses was similar for both high and low exposure groups. In contrast, only four of the 88 TST-positive students tested with QFT-G were positive by this test, and three of these were from the high exposure group. Chemoprophylaxis was provided to only those four QFT-G-positive students. Follow up of the 91 students who were TST-positive, but QFT-G-negative (or not tested), for more than 3.5 years revealed that none have developed active tuberculosis.

CONCLUSIONS

QFT-G appears more specific than TST as contacts with positive TST and negative QFT-G responses were not offered prophylaxis and none developed tuberculosis during 3.5 years of follow up. The replacement of TST with QFT-G, or perhaps combined use of TST and QFT-G, may be more useful in diagnosing true infection and thus reducing the number of subjects indicated for chemoprophylaxis.

Falsch-positiver Interferon-γ-Test?

M. tuberculosis specific interferon-gamma tests have been established lately as an important additional instrument in the diagnosis of the latent tuberculosis infection (LTBI). In several studies these tests had a higher specificity compared to the tuberculin skin test (TST). In this report we describe the case of a woman without increased risk for LTBI and with discordant results for the interferon-gamma tests QuantiFERON-TB Gold In-Tube and T-SPOT.TB and for the TST. The findings suggest repeated false-positive results of the QuantiFERON-TB Gold In-Tube test.

Effect of tuberculin skin testing on a Mycobacterium tuberculosis-specific interferon- assay

Recently, interferon-gamma release assays (IGRA) for specific diagnosis of Mycobacterium tuberculosis infection have become available. In recent UK tuberculosis (TB) guidelines, it has been advised to screen for latent M. tuberculosis infection using the tuberculin skin test (TST), followed by IGRA if the TST is positive. Since TST can boost immune responses to tuberculin, the present authors evaluated whether TST administration affects the result of QuantiFERON-TB Gold in-tube (QFT-GIT), a whole blood-based IGRA. QFT-GIT was performed on the day of TST administration and the day of reading in 15 TST-negative subjects, 46 TST-positive subjects with recent or remote exposure to M. tuberculosis and five cured TB patients. No systematic boosting of QFT-GIT responses from negative to positive was observed. Only in a few TST-positive persons did TST enhance pre-existing QFT-GIT responses. Screening for latent Mycobacterium tuberculosis infection using tuberculin skin testing followed by interferon-gamma release assays on the day of reading is a reliable approach, as the specificity of QuantiFERON-TB Gold in-tube is not affected by prior tuberculin skin test administration.

Individual Animals of a Cattle Herd Infected with the Same Mycobacterium bovis Genotype Shows Important Variations in Bacteriological, Histopathological and Immune Response Parameters

Cattle are the host and main reservoir of the etiologic agent of bovine tuberculosis, Mycobacterium bovis; although other mammalian species, including humans, are susceptible. The tuberculin test and/or slaughterhouse surveillance is the diagnostic method used by control programs all around the world to control and eradicate the disease. In order to compare different tuberculosis diagnostic tests and to reach disease confirmation, a study was performed in a group of 14 steers of Friesian breed, reacting positively to tuberculin test. Three ante-mortem assays were performed according to the type of sample: the gamma interferon (IFN-gamma) test (which quantifies the release of this cytokine by sensitized lymphocytes in whole blood in response to purified protein derivative (PPD) and recombinant ESAT-6 and CFP10 proteins); PCR and bacteriologic culture from nasal swab and intradermal tuberculin test. These assays were taken at different times to assess the evolution of clinical parameters. Post-mortem examination showed macroscopic and microscopic tuberculosis lesions with acid-fast bacillus and positive cultures. By spoligotyping, we observed that all the isolates showed the same pattern. The positive results based on comparison to lesions observed ranged from 58% to 75% for the IFN-gamma assays, to 72% for cultures, and ranged from 50% to 90% for PCR in nasal swabs. In conclusion, in a herd infected by the same strain, ante-mortem direct and immune-diagnostic parameters change, suggesting that several tests are needed for a faster control of infection at herd level.

A systematic review of rapid diagnostic tests for the detection of tuberculosis infection

OBJECTIVES

To evaluate the effectiveness of available rapid diagnostic tests to identify tuberculosis (TB) infection.

DATA SOURCES

Electronic databases were searched from 1975 to August 2003 for tests for active TB and to March 2004 for tests for latent tuberculosis infection (LTBI).

REVIEW METHODS

Studies were selected and evaluated that (1) tested for LTBI, (2) compared tuberculin skin test (TST) and interferon-gamma assays based on ESAT-6 and CFP-10 antigens and (3) provided information on TB exposure or bacille Calmette-Guerin (BCG) vaccination or HIV status. For each test comparison, the sensitivity, specificity and 95% confidence intervals (CIs) were calculated. Sources of heterogeneity were investigated by adding covariates to the standard regression model. The authors examined whether interferon-gamma assays were more strongly associated with high versus low TB exposure than TST. Odds ratios (ORs) were calculated for the association between test results and exposures from each study along with their 95% CIs. Within each study, the OR value for one test was divided by that for another to produce a ratio of OR (ROR).

RESULTS

A total of 212 studies were included, providing 368 data sets. A further 19 studies assessing fully automated liquid culture were included. Overall, nucleic acid amplification test (NAAT) accuracy was far superior when applied to respiratory samples as opposed to other body fluids. The better quality in-house studies, were, for pulmonary TB, much better at ruling out TB than the commercial tests (higher sensitivity), but were less good at ruling it in (lower specificity), but it is not possible to recommend any one over another owing to a lack of direct test comparisons. The specificity of NAAT tests was high when applied to body fluids, for example for TB meningitis and pleural TB, but sensitivity was poor, indicating that these tests cannot be used reliably to rule out TB. High specificity estimates suggest that NAAT tests should be the first-line test for ruling in TB meningitis, but that they need to be combined with the result of other tests in order to rule out disease. Evidence for NAAT tests in other forms of TB and for phage-based tests is significantly less prolific than for those above and further research is needed to establish accuracy. There is no evidence to support the use of adenosine deaminase (ADA) tests for diagnosis of pulmonary TB; however, there is considerable evidence to support their use for diagnosis of pleural TB and to a slightly lesser extent for TB meningitis. Anti-TB antibody test performance was universally poor, regardless of type of TB. Fully automated liquid culture methods were superior to culture on solid media, in terms of their speed and their precision. In total, 13 studies were included. Assays based on RD1 specific antigens, ESAT-6 or CFP-10, correlate better with intensity of exposure, and therefore are more likely than TST/purified protein derivative (PPD)-based assays to detect LTBI accurately. An additional advantage is that they are more likely to be independent of BCG vaccination status and HIV status.

CONCLUSIONS

The NAAT tests provide a reliable way of increasing the specificity of diagnosis (ruling in disease) but sensitivity is too poor to rule out disease, especially in smear-negative (paucibacillary) disease where clinical diagnosis is equivocal and where the clinical need is greatest. For extra-pulmonary TB, clinical judgement has both poor sensitivity and specificity. For pleural TB and TB meningitis, adenosine deaminase tests have high sensitivity but limited specificity. NAATs have high specificity and could be used alongside ADA (or interferon-gamma) to increase sensitivity for ruling out disease and NAAT for high specificity to rule it in. All studies from low-prevalence countries strongly suggest that the RD1 antigen-based assays are more accurate than TST- and PPD-based assays for diagnosis of LTBI. If their superior diagnostic capability is found to hold up in routine clinical practice, they could confer several advantages on TB control programmes. Further research for active TB needs to establish diagnostic accuracy in a wide spectrum of patients, against an appropriate reference test, and avoiding the major sources of bias. For LTBI, research needs to address different epidemiological and clinical settings, to evaluate the performance of the main existing commercial assays in head-to-head comparison in both developed and developing countries, and to assess the role of adding more TB-specific antigens to try to improve diagnostic sensitivity.