Detection Of Mycobacterium Tuberculosis Infection Research Articles

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Mycobacterium tuberculosis in Solid Organ Transplant Recipients

Mycobacterium tuberculosis in Solid Organ Transplant Recipients

Detection and diagnosis of Mycobacterium tuberculosis

Tuberculosis continues to be a major health problem worldwide, affecting millions of people each year. Accurate and rapid diagnosis is key to controlling the disease, yet the traditional tests for TB produce results that are either inaccurate or take too long to be definitive. A fast and reliable diagnostic method that would differentiate between active and latent TB infection is also lacking. The current routine diagnostic tests for TB – chest x-ray, tissue culture, tuberculin skin test (TST) and acid-fast staining – all have their limitations. A chest x-ray alone is inconclusive; a tissue culture takes too long to produce a result; the TST lacks specificity and reliability; and acid-fast staining depends on a large number of bacteria in the sputum to give an accurate reading. Serological tests using different TB antigens to detect Mycobacterium tuberculosis infection are fast but lack the desired sensitivity. New methods have been developed, such as nucleic acid amplification technology which, although specific, can yield false-positive results. Immunologic tests (QuantiFERON and T-SPOT.TB), which measure the production of IFN-γ by TB-specific T lymphocytes after encountering M. tuberculosis antigens, have certain advantages over the conventional tests, but they also have their disadvantages and unanswered questions. The need remains for a cost-effective, accurate and rapid method of diagnosing both active and latent TB infection.

POSITIVE QUANTIFERON-TB GOLD TEST IN A PATIENT WITH MYCOBACTERIUM KANSASII INFECTION

INTRODUCTION: QuantiFERON®-TB Gold is a test that is now being widely used in the United States for the detection of Mycobacterium tuberculosis infection. This enzyme-linked immunosorbent assay (ELISA) test detects the release of interferon-gamma (IFN-g) in fresh heparinized whole blood from sensitized persons when it is incubated with mixtures of synthetic peptides simulating two protein that are present in M. tuberculosis ESAT-6 and CFP-10 (1). Non tuberculous mycobacteria have generally been associated with immunosuppression.

High-sensitive and rapid detection of Mycobacterium tuberculosis infection by IFN-γ release assay among HIV-infected individuals in BCG-vaccinated area

BackgroundAn accurate test for Mycobacterium tuberculosis infection is urgently needed in immunosuppressed populations. The aim of this study was to investigate the diagnostic power of enzyme-linked immunospot (ELISPOT)-based IFN-γ release assay in detecting active and latent tuberculosis in HIV-infected population in bacillus Calmette-Guerin (BCG)-vaccinated area. A total of 100 HIV-infected individuals including 32 active tuberculosis patients were recruited. An ELISPOT-based IFN-γ release assay, T-SPOT.TB, was used to evaluate the M. tuberculosis ESAT-6 and CFP-10 specific IFN-γ response. Tuberculin skin test (TST) was performed for all recruited subjects.ResultsThe subjects were divided into group HIV+ATB (HIV-infected individuals with active tuberculosis, n = 32), group HIV+LTB (HIV-infected individuals with positive results of T-SPOT.TB assay, n = 46) and group HIV only (HIV-infected individuals with negative results of T-SPOT.TB assay and without evidence of tuberculosis infection, n = 22). In group HIV+ATB and HIV+LTB, T-SPOT.TB positive rate in subjects with TST <5 mm were 50% (16/32) and 41.3% (19/46), respectively. Individuals in group HIV+ATB and HIV+LTB with CD4+ T cells <500/μl, T-SPOT.TB showed a higher sensitivity than TST (64.5% vs. 22.6% and 62.2% vs. 29.7%, respectively, both P < 0.0001). In addition, the sensitivity of T-SPOT.TB assay in group HIV+ATB increased to >85% in patients with TB treatment for less than 1 month and CD4+ T cells ≥200/μl, while for patients treated for more than 3 months and CD4+ T cells <200/μl, the sensitivity was decreased to only 33.3%. Furthermore, the results could be generated by T-SPOT.TB assay within 24 hours, which was more rapid than TST with 48–72 hours.ConclusionELISPOT-based IFN-γ release assay is more sensitive and rapid for the diagnosis of TB infection in Chinese HIV-infected individuals with history of BCG vaccination, and could be an effective tool for guiding preventive treatment with isoniazid in latently infected people and for TB control in China.

I-40 Detection of Mycobacterium tuberculosis infection using interferon-gamma release assay in Shenzhen, China

I-40 Detection of Mycobacterium tuberculosis infection using interferon-gamma release assay in Shenzhen, China

QuantiFERON-TB Gold and selected region of difference 1 peptide-based assays for the detection of Mycobacterium tuberculosis infection in a cohort of patients enrolled with suspected tuberculosis

Recently, a simple whole blood test, QuantiFERON-TB Gold (QFT-Gold), has been adopted for immunologic diagnosis of Mycobacterium tuberculosis infection. A total of 369 individuals with suspected tuberculosis (TB) were tested with the QFT-Gold, whereas a subgroup of 62 patients was tested simultaneously with QFT-Gold test and an assay based on selected peptides from early secreted antigenic target 6 and culture filtrate protein 10 proteins. The sensitivity of the QFT-Gold assay for active TB was 72.9%, and the agreement between this test and tuberculin skin test was 75%. Using selected peptides, we found a positive response in the majority of active TB patients, with a sensitivity of 84% and a specificity of 89%. Our study suggests the usefulness of QFT-Gold in routine clinical practice on unselected patients with suspected TB. Moreover, the assay based on selected peptides is a useful tool to discriminate between active and latent TB and shows a high predictive value.

Highly discordant T cell responses in individuals with recent exposure to household tuberculosis

Background:There are limited data comparing interferon-γ release assays (IGRAs) for the detection of Mycobacterium tuberculosis infection in highly endemic settings.Methods:A cross-sectional household contact study was conducted to measure the agreement...

Performance of two commercial blood IFN-γ release assays for the detection of Mycobacterium tuberculosis infection in patient candidates for anti-TNF-α treatment

The reactivation of latent tuberculosis (TB) is a major complication of tumor necrosis factor (TNF)-alpha inhibitors. Screening for TB infection is recommended before anti-TNF therapy is initiated; however, the use of tuberculin skin testing (TST) is controversial, due to the high rate of false-negative results in patients receiving immunosuppressive treatment. To compare the performance of two commercial interferon (IFN)-gamma release assays (IGRA), T-SPOT.TB (TS-TB) and QuantiFERON-TB Gold "In-tube" (QFT-GIT), with TST for the detection of TB infection in patients due to start anti-TNF therapy, 69 human immunodeficiency virus (HIV)-negative Italian patients (mean age: 45.2 +/- 12.6 years; male=39) were enrolled between September 2005 to August 2006. Patients affected by rheumatoid arthritis (n = 18), psoriatic arthritis (n = 26), ulcerous rectocolitis (n = 6), and Crohn's disease (n = 19) were tested simultaneously with TST, TS-TB, and QFT-GIT. Overall, 26% of patients were positive by TST, 30.4% by TS-TB, and 31.8% by QFT-GIT. Agreement with TST was similar (kappa = 0.21, p = 0.0002 and kappa = 0.26, p < 0.001, respectively). In 11 TST-negative cases, IFN-gamma release assays were positive. In addition, in seven Mantoux-positive cases with no TB risk factors, TST result agreement was achieved with at least one blood test. Indeterminate results were detected in 5.8% and 2.8% of cases, respectively, with TS-TB and with QFT-GIT (p = not significant [ns]). In conclusion, our results suggest that IGRAs may be helpful for screening purposes in patient candidates for anti-TNF therapy to confirm positive TST results and in selected cases when false-negative results are suspected. The utility of blood tests in patients with low or no TB risk remains to be assessed.

Performance of QuantiFERON-TB Testing in a Tuberculosis Outbreak at a Primary School

This study compared the effectiveness of the QuantiFERON-TB Gold (QFT) assay with the Mantoux tuberculin skin test to detect Mycobacterium tuberculosis infection in 29 children during a school outbreak of tuberculosis. Of the 21 children with M. tuberculosis infection, 11 had a radiograph suggestive of the infection. The QFT assay was positive in all 21 of the children, and the Mantoux test was negative at first testing in 2 children (1 of whom was the sentinel case). The findings demonstrate that the QFT test is extremely useful in accurately identifying infected and uninfected children, permitting rapid intervention.

Limitations of the QuantiFERON®-TB Gold test in detecting Mycobacterium tuberculosis infection in immunocompromised patients

Four cases are presented, immunosuppressed by at least three different mechanisms: one HIV-positive patient with a CD4 count of 0.29 × 10 6/ml, one malnourished patient, and two kidney-transplanted patients. All patients had a negative interferon (IFN)-γ test for suspected tuberculosis (TB), but a positive culture. We conclude that a negative IFN-γ test does not exclude TB disease in immunosuppressed patients.

Detection of Mycobacterium tuberculosis Infection in United States Navy Recruits Using the Tuberculin Skin Test or Whole-Blood Interferon- Release Assays

Military personnel are at risk for acquiring Mycobacterium tuberculosis infection because of activities in close quarters and in regions with a high prevalence of tuberculosis (TB). Accurate tests are needed to avoid unnecessary treatment because of false-positive results and to avoid TB because of false-negative results and failure to diagnose and treat M. tuberculosis infection. We sought to estimate the specificity of the tuberculin skin test (TST) and 2 whole-blood interferon-gamma release assays (QuantiFERON-TB assay [QFT] and QuantiFERON-TB Gold assay [QFT-G]) and to identify factors associated with test discordance. A cross-sectional comparison study was performed in which 856 US Navy recruits were tested for M. tuberculosis infection using the TST, QFT, and QFT-G. Among the study subjects, 5.1% of TSTs resulted in an induration > or = 10 mm, and 2.9% of TSTs resulted in an induration > or = 15 mm. Eleven percent of QFT results and 0.6% of QFT-G results were positive. Assuming recruits at low risk for M. tuberculosis exposure were not infected, estimates of TST specificity were 99.1% (95% confidence interval [CI], 98.3%-99.9%) when a 15-mm cutoff value was used and 98.4% (95% CI, 97.3%-99.4%) when a 10-mm cutoff value was used. The estimated QFT specificity was 92.3% (95% CI, 90.0%-94.5%), and the estimated QFT-G specificity was 99.8% (95% CI, 99.5%-100%). Recruits who were born in countries with a high prevalence of TB were 26-40 times more likely to have discordant results involving a positive TST result and a negative QFT-G result than were recruits born in countries with a low prevalence of TB. Nineteen (50%) of 38 recruits with this type of discordant results had a TST induration > or = 15 mm. The QFT-G and TST are more specific than the QFT. No statistically significant difference in specificity between the QFT-G and TST was found using a 15-mm induration cutoff value. The discordant results observed among recruits with increased risk of M. tuberculosis infection may have been because of lower TST specificity or lower QFT-G sensitivity. Negative QFT-G results for recruits born in countries where TB is highly prevalent and whose TST induration was > or = 15 mm suggest that the QFT-G may be less sensitive than the TST. Additional studies are needed to determine the risk of TB when TST and QFT-G results are discordant.

Prospective Comparison of the Tuberculin Skin Test and 2 Whole-Blood Interferon- Release Assays in Persons with Suspected Tuberculosis

Interferon-gamma release assays (IGRAs) are attractive alternatives to the tuberculin skin test (TST) for detecting Mycobacterium tuberculosis infection. However, the inability to definitively confirm the presence of most M. tuberculosis infections hampers assessment of IGRA accuracy. Although IGRAs are primarily indicated for the detection of latent tuberculosis infection, we sought to determine the sensitivity of the TST and 2 whole-blood IGRAs (QuantiFERON-TB assay [QFT] and QuantiFERON-TB Gold assay [QFT-G]) in situations in which infection is confirmed by recovery of M. tuberculosis by culture. We conducted a prospective, multicenter, cross-sectional comparison study in which 148 persons suspected to have tuberculosis were tested simultaneously with the TST, QFT, and QFT-G. M. tuberculosis was cultured from samples from 69 (47%) of 148 persons suspected to have tuberculosis; the TST induration was > or = 5 mm for 51 (73.9%) of the 69 subjects (95% confidence interval [CI], 62.5%-82.8%). The QFT indicated tuberculosis infection for 48 (69.6%) of the 69 subjects (95% CI, 57.9%-79.2%) and was indeterminate for 7 (10.1%). The QFT-G yielded positive results for 46 (66.7%) of the 69 subjects (95% CI, 54.9%-76.7%) and indeterminate results for 9 subjects (13.0%). If subjects with indeterminate QFT-G results were excluded, 46 (76.7%) of 60 subjects (95% CI, 64.6%-85.6%) had positive TST results, and the same number of subjects had positive QFT-G results. HIV infection was associated with false-negative TST results but not with false-negative QFT-G results. The TST, QFT, and QFT-G have similar sensitivity in persons with culture-confirmed infection. As with the TST, negative QFT and QFT-G results should not be used to exclude the diagnosis of tuberculosis in persons with suggestive signs or symptoms.

Boosted tuberculin skin testing in hemodialysis patients

Tuberculosis remains a significant health problem for patients receiving long-term hemodialysis (HD). The tuberculin skin test (TST) is an important method of detecting Mycobacterium tuberculosis infection. Cutaneous anergy decreases the accuracy of the test in these patients. Higher and repeating doses have been mentioned in the immunosuppressed patients. This study examined the significance and frequency of the booster phenomenon in 2-step tuberculin testing of these patients. A total of 106 outpatients in a hospital-based HD center in Turkey were screened with 5 and 10 tuberculin units (TU) and Candida antigen. To determine the frequency of booster phenomenon, patients with <10 mm indurations to the initial TST with 5 TU were given a second test with 10 TU, 7 days later. Forty (37.7%) of 106 patients had a significant tuberculin reaction (>or=10 mm) on the initial TST with 5 TU. The booster effect was detected in 16 (24.3%) of 66 patients who had a negative reaction (<or=10 mm) to the initial test. Overall, 56 (52.8%) patients showed a significant reaction on both tests. Anergy was found in 39 (36.8%) of 106 patients. Even with the high rate of anergy, TST seems to be useful for these patients; also, it is inexpensive and easy to perform. We suggest repeating the test with higher doses in patients with a high risk for tuberculosis. Anergy testing with Candida antigen may be helpful in determining the value of TST.

Comparison of two commercial interferon- assays for diagnosing Mycobacterium tuberculosis infection

The clinical usefulness of ex vivo interferon-gamma assays may largely depend on the assay format and epidemiological status of tuberculosis (TB) in the region studied. From July 2004 to June 2005 a prospective comparison study was undertaken at a tertiary referral hospital in South Korea. The results of tuberculin skin tests (TST) and the commercially available QuantiFERON-TB Gold (QFT-G) and T SPOT-TB (SPOT) assays were compared in an intermediate TB-burden country. Of the 224 participants studied, results from all three tests (TST, QFT-G, and SPOT) were available in 218; 87 with active TB and 131 at a low risk for TB. Using 10 mm as a cut-off for TST, SPOT sensitivity (96.6%) was significantly higher than that seen for TST (66.7%) and QFT-G (70.1%). QFT-G showed superior specificity over TST (91.6 versus 78.6%). Although the specificity of QFT-G was higher than that of SPOT (91.6 versus 84.7%), the difference was not statistically significant. Whilst some differences were found in the performance of the two commercialised interferon-gamma assays, they seemed to be superior in their detection of Mycobacterium tuberculosis infection compared with tuberculin skin tests. The most appropriate choice of interferon-gamma assay to use may depend on the clinical setting.

Avoiding the effect of BCG vaccination in detecting Mycobacterium tuberculosis infection with a blood test

Bacille Calmette-Guérin (BCG) vaccination can confound tuberculin skin test (TST) reactions in the diagnosis of latent tuberculosis infection (LTBI). The TST was compared with a Mycobacterium tuberculosis (MTB)-specific enzyme-linked immunospot (ELISPOT) assay during an outbreak of MTB infection at a police academy in Germany. Participants were grouped according to their risk of LTBI in close (n = 36) or occasional (n = 333) contacts to the index case. For the TST, the positive response rate was 53% (19 out of 36) among close and 16% (52 out of 333) among occasional contacts. In total, 56 TST-positive contacts (56 out of 71 = 78.9%) and 27 TST-negative controls (27 out of 298 = 9.1%) underwent ELISPOT testing. The odds ratio (OR) of a positive test result across the two groups was 29.2 (95% confidence interval (CI) 3.5-245.0) for the ELISPOT and 19.7 (95% CI 2.0-190.2) for the TST with a 5 mm cut-off. Of 369 contacts, 158 (42.8%) had previously received BCG vaccination. The overall agreement between the TST and the ELISPOT was low, and positive TST reactions were confounded by BCG vaccination (OR 4.8 (95% CI 1.3-18.0)). In contrast, use of a 10-mm induration cut-off for the TST among occasional contacts showed strong agreement between TST and ELISPOT in nonvaccinated persons. In bacille Calmette-Guérin-vaccinated individuals, the Mycobacterium tuberculosis-specific enzyme-linked immunospot assay is a better indicator for the risk of latent tuberculosis infection than the tuberculin skin test.

Sensitivity of human gamma interferon assay and tuberculin skin testing for detecting infection with Mycobacterium tuberculosis in patients with culture positive tuberculosis

Nine university-affiliated chest clinics in Australia. To evaluate the sensitivity of a whole blood human gamma-interferon assay (HGIA, QuantiFERON-TB) for specific T lymphocyte responses and Tuberculin skin testing (TST) for the detection of Mycobacterium tuberculosis infection in subjects with culture-proven M. tuberculosis disease (TBCP). Prospective testing of 129 patients with recent TBCP and 100 patients with non-tuberculosis lung disease (NTBLD). Using a defined level of specific IFN-gamma production and TST 10mm as positive cut-offs, the sensitivity of HGIA was 81% compared to 89% for TST (p=0.06). When positive responses in both TST and HGIA were combined, 96% of TB patients were detected. For the NTBLD group, 43% of whom were born overseas, 73% were negative for both the HGIA and TST. Prior immunization with M. bovis (bacille Calmette-Guerin) (BCG) or the type of TB had no effect on the sensitivities of the assays. For those treated for <2 months, the sensitivities for both assays were 84%, but for those treated for >2 months the sensitivity of TST (90%) tended to be higher than for HGIA (81%) (p=0.07). The distribution of TST results in TB patients showed a broad peak between 10 and 25 mm, while the results in the HGIA were bimodal in both TB and NTBLD patients. HGIA may prove an alternative to skin testing for detecting M. tuberculosis infection in certain settings.

Selected pool of peptides from ESAT-6 and CFP-10 proteins for detection of Mycobacterium tuberculosis infection.

We have validated a new test for detecting Mycobacterium tuberculosis infection. A pool of synthetic peptides derived from ESAT-6 and CFP-10 proteins was used to detect the number of specific gamma interferon-producing T cells by means of an enzyme-linked immunospot assay. Sixty-eight individuals positive for M. tuberculosis infection, either human immunodeficiency virus-seropositive or -seronegative, were studied. The test results were highly specific (87.5%) and sensitive (93.1%), more so than a classical lymphoproliferative assay (specificity and sensitivity of 77.27%), opening new possibilities for diagnosis and screening of tuberculosis. Moreover, the test allowed us to distinguish individuals infected with M. tuberculosis from those vaccinated with BCG.

The booster phenomenon in 2-step tuberculin skin testing of patients receiving long-term hemodialysis

Background Tuberculosis remains a significant health problem for patients receiving long-term hemodialysis (HD). The tuberculin skin test (TST) is an important method for detecting Mycobacterium tuberculosis infection. This study examined the significance and frequency of the booster phenomenon in serial TST of HD patients. Method Fifty-three outpatients in a hospital-based HD center in Turkey were screened for tuberculosis with the TST between August and October 1999. To determine the frequency of booster phenomenon, patients with less than 10 mm indurations to the initial TST were given a second test 7 days later. Results Nineteen (35.8%) of 53 patients had a significant tuberculin reaction (≥ 10 mm) on the initial TST. The booster effect was detected in 10 (29.4%) of 34 patients who had a negative reaction (< 10 mm) to the initial test. Overall, 29 (54.7%) patients showed a significant reaction on both tests. Conclusions These results showed significant rates of TST positivity and the booster effect in this HD center.

The ligase chain reaction as a primary screening tool for the detection of culture positive tuberculosis

BACKGROUNDThe ligase chain reaction Mycobacterium tuberculosis assay uses ligase chain reaction technology to detect tuberculous DNA sequences in clinical specimens. A study was undertaken to determine its sensitivity and specificity...