Serial interferon-gamma release assays after rifampicin prophylaxis in a tuberculosis outbreak

Respiratory Medicine (2010) 104, 448e453 available at www.sciencedirect.com

journal homepage: www.elsevier.com/locate/rmed

Serial interferon-gamma release assays after rifampicin prophylaxis in a tuberculosis outbreak Seung Heon Lee a, Woo Jin Lew b, Hee Jin Kim b, Hyun-Kyung Lee a, Young Min Lee a, Chong Hee Cho c, Eun Joo Lee c, Dong Yeol Lee c, Sung Weon Ryu b, Soo Yeon Oh b, Sin Ok Kim b, Tae Sun Shim d,* a

Division of Pulmonary and Critical Care Medicine, Department of Internal Medicine, Busan Paik Hospital, Inje University College of Medicine, Busan, South Korea b Korean Institute of Tuberculosis, Seoul, South Korea c Public Healthcare Center, Seoul, South Korea d Division of Pulmonary and Critical Care Medicine, Department of Internal Medicine, University of Ulsan College of Medicine, Asan Medical Center, Seoul 138-736, South Korea Received 22 July 2009; accepted 8 October 2009 Available online 29 October 2009

KEYWORDS Tuberculosis; Interferon-gamma release assay; Rifampicin prophylaxis; Serial testing

Summary Even though some studies have reported the results of serial interferon-gamma release assays (IGRAs) during isoniazid prophylactic treatment, serial results have not been reported after rifampicin prophylaxis. A contact investigation was conducted after a tuberculosis (TB) outbreak in an accommodation facility. The tuberculin skin test (TST) and the QuantiFERON-TB Gold InTube (QFT-GIT) test were performed in 214 contacts with normal chest radiographs. Rifampicin prophylaxis was initiated in TSTþ/QFT-GITþ subjects, and the QFT-GIT test was repeated upon completion of 4 months of rifampicin treatment. Among the 214 contacts, the TST and QFT-GIT test results were positive in 67.7% and 56.7%, respectively, and the agreement between the two tests was fair-to-good (78.3%, kappa Z 0.55, p < 0.001). The QFT-GIT test was positive in 77% (97/126) of contacts with positive TST results. Rifampicin prophylaxis was completed in 81 subjects with good compliance. Among 74 subjects with valid serial QFT-GIT test results, IFNg levels decreased in 97.3% (72/74) of the subjects and QFT-GIT test reversion (positive to negative) was achieved in 31 subjects (41.9%). Subjects without QFT-GIT test reversion had a significantly higher baseline TST induration sizes (18.3  4.8 vs. 14.9  3.4 mm, p < 0.01) and IFN-g levels (18.6  17.9 vs. 3.2  7.5 IU/mL, p < 0.01) than the subjects with QFT-GIT test reversion. Thus, IGRAs may be useful in evaluating the therapeutic response to rifampicin prophylaxis in TB contacts. However, considering that this was not a controlled study, a prospective controlled study is needed to determine whether rifampicin prophylaxis truly affects QFT-GIT reversion. ª 2009 Elsevier Ltd. All rights reserved.

* Corresponding author. Tel.: þ82 2 3010 3892; fax: þ82 2 3010 6968. E-mail address: [email protected] (T.S. Shim). 0954-6111/$ - see front matter ª 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.rmed.2009.10.006

QFT-GIT after rifampicin prophylaxis

Introduction Tuberculosis (TB) is a significant global health issue. It is the single most significant infectious cause of morbidity and mortality worldwide, with approximately 1.7 million deaths and 9.2 million new cases in 2006.1e3 Rapid diagnosis and treatment of infectious patients are important components of effective and efficient disease control and treatment in developing countries. However, the treatment of latent TB infection (LTBI) to prevent progression to active disease in countries with low or intermediate TB burden is an essential public health strategic point for TB elimination.4,5 Small numbers of viable TB bacilli reside in an individual with LTBI without obvious clinical symptoms. Individuals with LTBI typically have normal chest radiographs (CXR), and the tuberculin skin test (TST) has historically been the only available diagnostic tool. Targeted TSTs for LTBI treatment is a TB control strategy that selects subjects at high risk of developing TB who would benefit from LTBI therapy.6 Interferon-gamma (IFN-g) release assays (IGRAs) are new tools for LTBI diagnosis and surveillance for a new TB infection.7,8 IGRAs are in vitro assays based on IFN-g production in response to early-secreted antigenic target 6-kDa protein (ESAT-6) and culture filtrate protein 10 (CFP-10). These antigens are specific to Mycobacterium tuberculosis and are absent from all BCG vaccine strains and most environmental mycobacteria.9,10 Commercial IGRAs approved by the United States Food and Drug Administration include the QuantiFERON-TB Gold test (QFT-G; Cellestis Ltd., Carnegie, VIC, Australia), the QuantiFERON-TB Gold In-Tube test (QFT-GIT; Cellestis Ltd., Carnegie, VIC, Australia), and the T-SPOT.TB assay (T-SPOT; Oxford Immunotec, Abingdon, UK). The QFT-GIT test contains a third M. tuberculosis-specific antigen (TB7.7) and uses an enzyme-linked immunosorbent assay for detection of IFN-g responses. The Centers for Disease Control and Prevention have recommended use of the QFT-G test as an appropriate substitute for the TST in contact investigations.11 The National Institute for Health and Clinical Excellence (NICE) guidelines recommend that positive TST reactors should be tested by IGRAs as a two-stage strategy, if available.12 Combination testing is likely to reduce TB infection screening costs compared to TST alone.13,14 The interpretation of serial IGRAs is challenging because of non-specific variation, conversions, and reversions. Previous studies have proposed that conversions, reversions, and non-specific variations occur with both serial IGRA testing and TSTs.15e20 In addition, previous TST may boost the subsequent IGRA responses, rendering the interpretation of serial IGRA results more difficult.21 Some guidelines have supported serial IGRA testing in place of TST, while others do not recommend serial IGRA testing.22e25 Until now, in LTBI subjects, most serial IGRA tests were performed in subjects taking isoniazid prophylaxis.26,27 However, to our knowledge, there are no reports evaluating serial IGRA tests after rifampicin prophylaxis, even though one study evaluated serial IGRA changes in subjects who took combined isoniazid and rifampicin prophylaxis.17

449 The incidence of active TB in South Korea is intermediate (88/10,000 per year) and BCG vaccination is mandatory at birth.1 Recently, a TB outbreak occurred in South Korea, and due to the possibility of an isoniazid-resistant index case, rifampicin prophylaxis was administered. We evaluated serial QFT-GIT test results both at baseline and upon completion of rifampicin prophylaxis for this outbreak.

Materials and methods Study design Five residents of a group home for individuals with intellectual disabilities (Seoul, South Korea) were diagnosed with active pulmonary TB in March 2007. The index case was diagnosed with bacteriologicallyconfirmed laryngeal and pulmonary TB. Initially, a National TB Programme (NTP)-driven investigation of the outbreak was initiated with serial CXR screening only. Serial CXR screening was performed in March, April, and May 2007 and active TB was diagnosed in 9, 9, and 1 contact, respectively. The TB patients were evenly distributed in all classes. Acid-fast bacillus (AFB) smears were positive in four patients and AFB cultures were positive in two patients. The culture-positive patients had DNA genotypes with different patterns. A M. tuberculosis isolate was pan-susceptible to antibiotics while another isolate was isoniazid-resistant. Faced with the persistent development of TB, the NTP performed TSTs and QFT-GIT tests for all residents and teachers (n Z 214) in May 2007. For the analysis of the results, individuals were divided into the following four groups based on TSTs and QFT-GIT tests: TSTþ/QFT-GITþ, TSTþ/QFT-GIT, TST/QFT-GITþ, and TST/QFT-GIT. Rifampicin was prescribed for 4 months in individuals with TSTþ/QFT-GITþ results, and most of the individuals took the medication daily under direct observation due to intellectual disabilities. The QFT-GIT test was repeated upon completion of rifampicin prophylaxis. CXRs were repeated every 3 months for 1 year and every 6 months for the following year on all contacts. Written informed consent was obtained from study participants and guardians, and the study was approved by the Institutional Review Board of the Korea Institute of Tuberculosis.

Tuberculin skin test A TST was performed using the Mantoux method and 2TU PPD RT23 (Statens Serum Institute, Copenhagen, Denmark). The induration size was measured after 48e72 h by experienced nurses, and a 10 mm induration size was set as the cut-off value.

QuantiFERON-TB Gold In-Tube test All participants were tested with the QFT-GIT test per the manufacturer’s instructions. An IFN-g response to the ESAT-6/CFP-10/TB7.7 mixture 0.35 IU/mL above the nil

450

S.H. Lee et al. Contact screening by chest radiographs (n=246) Active or suspected TB (n=32) Normal chest radiographs TST and QFT-GIT examination (n=214)

Valid TST and QFT-GIT results (n=185)

TST (+)/ QFT-GIT (+) (n=97)

TST (+)/ QFT-GIT (–) (n=29)

Rifampicin prophylaxis (n=86)

QFT-GIT follow-up

QFT-GIT skipped (n=7) TST skipped (n=18) both tests skipped (n=4)

TST (–)/ QFT-GIT (+) (n=11)

TST (–)/ QFT-GIT (–) (n=48)

Exclusion due to TB history (n=4) Refusal of prophylactic treatment (n=7) Drug withdrawal (n=5) Refusal of repeated QFT-GIT test (n=6)

(n=75) Indeterminate result (n=1) QFT-GIT Reversion (n=31)

QFT-GIT Non-reversion (n=43)

Figure 1 Flow diagram of contact investigation of infectious tuberculosis patients (n Z 246). TB: Tuberculosis, TST: tuberculin skin test, QFT-GIT: QuantiFERON-TB Gold In-Tube.

Table 1 Clinical characteristics of 214 contacts with normal chest radiographs. Clinical characteristics

Values (n Z 214)

Mean age, years (range) Gender (Male:Female) BMI, kg/m2, mean  SD History of previous anti-TB treatment (%) Presence of BCG scar (%) TST induration size, mm, mean  SD (range) TST induration size  10 mm (%) Positive QFT-GIT (%) Diabetes mellitus (%) Rifampicin prophylaxis completion (%)

41 (16e70) 140:74 21.8  3.3 6/179 (3.4) 135/201 (67.2) 12.4  7.2 (0e29) 130/192 (67.7) 115/203 (56.7) 4 (1.9) 81 (37.9)

BMI Z body mass index, TB Z tuberculosis, BCG Z bacille Calmette-Gue ´rin, TST Z tuberculin skin test, IGRA Z interferongamma release assay, QFT-GIT Z QuantiFERON-TB Gold In-Tube, SD Z standard deviation.

control value (and 25% of the nil control) was considered a positive result for the QFT-GIT test. If a response to M. tuberculosis-specific antigens (corrected for the nil control) was <0.35 IU/mL and the response to the mitogen-positive control was >0.5 IU/mL, the response was considered negative. Indeterminate results were classified as nil-corrected IFN-g responses <0.35 IU/mL and mitogen-positive control responses <0.5 IU/mL. QFTGIT test reversion was arbitrarily defined as a change from a positive (0.35 IU/mL) to a negative (<0.35 IU/mL) result.

Statistical analysis All analyses were performed using SPSS software, version 12.0 (SPSS Inc., Chicago, IL, USA). Between-group comparisons were made with t-test and ManneWhitney test for variables. Concordance between test results from the TST and QFT-GIT test was assessed using kappa coefficients. All tests for significance were two-sided and statistical significance was established at P values < 0.05.

QFT-GIT after rifampicin prophylaxis Table 2

451

TST and QFT-GIT test results in 185 contacts.

QFT-GIT Positive, n (%) QFT-GIT Negative, n (%) All

TST Positive

TST Negative

97 (77.0) 29 (23.0) 126

11 (18.6) 48 (81.4) 59

TST: tuberculin skin test, QFT-GIT: QuantiFERON-TB Gold In-Tube

Table 4 Baseline predictors of QuantiFERON-TB Gold InTube test reversion.

TST induration size (mm) QFT-GIT IFN-g (IU/mL)

Reversion (n Z 31)

Non-reversion (n Z 43)

P value

14.9  3.4

18.3  4.8

<0.01

3.2  7.5

18.6  17.9

<0.01

TST Z tuberculin skin test, QFT-GIT Z QuantiFERON-TB Gold In-Tube.

Results Clinical characteristics A total of 246 subjects were screened with chest radiographs and 214 contacts with normal chest radiographs were included in the study (Fig. 1, Table 1). The mean age was 41 years (range, 16e70 years) and the male-to-female ratio was 65.4%:34.6%. A BCG scar was present in 135 subjects (67.2%). The mean TST induration size was 12.4  7.2 mm (range, 0 e 29 mm). The TST and QFT-GIT tests were positive in 67.7% and 56.7% of the subjects, respectively. Both TST and QFT-GIT test results were available for 185 participants, and the agreement between both tests was fair-to-good (78.3%, kappa Z 0.55, p < 0.001). Among 185 subjects, positive TST results were detected in 126 (68.1%), and positive QFT-GIT results among the subjects with positive TST results were obtained in 77.0% of the subjects (97/126; Table 2). Rifampicin prophylaxis was completed in 81 subjects with good drug compliance (Fig. 1).

Serial QuantiFERON-TB Gold In-Tube assay A second round of QFT-GIT tests were performed in 75 subjects upon completion of 4 months of rifampicin prophylaxis (Fig. 1). Excluding one subject with an indeterminate QFT-GIT test result, the QFT-GIT tests were converted to negativity in 31 subjects (41.9%) and were persistently positive in 43 subjects (58.1%). The baseline clinical characteristics and test results of 74 subjects are presented in Table 3. Follow-up CXRs were normal in all Table 3 Clinical characteristics of 74 contacts with valid serial QFT-GIT test results after rifampicin prophylaxis. Characteristics

n Z 74

Mean age, years (range) Gender (Male:Female) History of previous anti-TB treatment (%) Diabetes mellitus (%) Presence of BCG scar (%) BMI, kg/m2, mean  SD Baseline TST induration size 10mm (%) Baseline QFT-GIT positive (%) Reversion of QFT-GIT (%)

44 (27e70) 59:15 0 2 (2.7) 47 (63.5) 21.9  3.1 74 (100.0) 74 (100.0) 31 (41.9)

BCG Z bacille Calmette-Gue ´rin, BMI Z body mass index, TB Z tuberculosis, TST Z tuberculin skin test, QFT-GIT Z QuantiFERON-TB Gold In-Tube, SD Z standard deviation.

subjects. The IFN-g levels detected by the QFT-GIT test were decreased in 72 subjects (97.3%) upon completion of rifampicin prophylaxis compared with the baseline values, and mean decrement extent of all subjects was 82.0  21.5%. Patients with persistently positive QFT-GIT results had significantly higher baseline TST induration sizes (18.3  4.8 vs. 14.9  3.4 mm, p < 0.01) and baseline IFN-g levels by the QFT-GIT test (18.6  17.9 vs. 3.2  7.5 IU/mL, p < 0.01) than patients with QFT-GIT test reversion (Table 4). IFN-g levels in the non-reversion group decreased in 41 of 43 subjects in paired comparisons (Fig. 2).

Discussion This is the first Korean study to compare the TST and QFTGIT results in a contact investigation of TB outbreak and the first to serially check QFT-GIT tests in LTBI contacts who took rifampicin prophylaxis. After rifampicin prophylaxis, QFT-GIT test reversion occurred in 41.9% (31/74) of the subjects and IFN-g levels decreased in almost all subjects, suggesting that rifampicin prophylaxis may be effective in the treatment of LTBI and the QFT-GIT test may be useful in the evaluation of therapeutic responses in LTBI subjects. In this study, TSTs and QFT-GIT tests were used for the diagnosis of LTBI and the selection of candidates for LTBI treatment. Twenty-three percent (29/126) of the subjects with a positive TST and a negative QFT-GIT test result avoided unnecessary prophylactic LTBI treatment by additional QFT-GIT test to the TST. The NICE guidelines recommend prophylactic treatment for IGRA-positive individuals tested from a TST-positive population. In this study, nearly 80% of TST-positive subjects demonstrated positive QFT-GIT test results, whereas in other studies the proportion of IGRA-positive subjects among the TST-positive population was about 7.6%e50%.28e31 The high positive QFT-GIT test results among TST-positive subjects in this study may be due to prolonged close contact with infectious TB patients. Among the 11 contacts with baseline TST-/QFT-GITþ results, nobody was progressed to active TB during the mean time of 23.9 months for follow-up. There is not a generally approved definition of QFT-GIT test reversion.16,32 The reported IGRA reversion (positive to negative) rates in active TB after treatment are quite variable (from 5.5% to 81%).7,33,34 Regarding LTBI, the IGRA reversion rate was 10% (1/10) after 4 months of isoniazid treatment.35 After completion of 6 months of isonizid treatment, IGRA reversion rates were 7.9% (3/38), 10.7% (3/28), and 25.0% (7/28).15,27,36 However, Pai et al.32

452

S.H. Lee et al.

Figure 2 Paired changes of interferon-gamma levels in QuantiFERON-TB Gold In-Tube tests after rifampicin prophylaxis in the reversion group (A) and in the non-reversion group (B). The horizontal bold lines at pre- and post-treatment values represent the mean interferon-gamma values (A: 3.16  7.49 and 0.11  0.08, B: 18.62  17.85 and 3.75  4.74).

described persistently elevated IFN-g responses 4 and 10 months after completion of 6 months of isoniazid treatment among rural Indian health care workers. Compared with the previous studies, LTBI was treated with rifampicin in our study; the reversion rate was relatively high (41.9%) and follow-up IFN-g levels decreased in almost all subjects with a mean decrement of 82.0  21.5%, suggesting that rifampicin may be more effective in treating LTBI. Theoretically, rifampicin is more effective than isoniazid in mycobacterial subpopulations with short bursts of metabolic activity.37 In a murine model, the prophylactic efficacy of 2e3 months of rifampicin therapy was superior to 6 months of isoniazid therapy in reducing the burden of M. tuberculosis in splenic cultures.38 Wilkinson et al.17 also reported that the mean number of IFN-g spot-forming cells decreased after 82 days of treatment with isoniazid and rifampicin in 16 LTBI subjects, suggesting that the rifampicin-containing regimen may be superior to isoniazid alone in inducing the reduction of IFN-g levels during and after treatment. However, the interpretation of serial IGRA test results should be viewed with caution because there are huge within-subject variabilities, especially in serial testing, and boosting of T cell IFN-g responses following a TST.21 In this study, we could not identify the reasons why subjects without QFT-GIT test reversion had a significantly higher baseline TST induration size and IFN-g level than the subjects with QFT-GIT test reversion. The subjects with higher baseline TST induration size and IFN-g level may require long interval to get the IFN-g under the cut-off level. In order to confirm this, serial repeated QFT-GIT tests are mandatory. Or, the subjects with higher baseline values may need longer LTBI treatment for QFT-GIT reversion, otherwise some of the higher reversion rate in the subjects with lower baseline values may be caused by the nonspecific variations around the cut-off value in this group. This study had some limitations. The number of participants was small and serial IFN-g responses were measured

only in rifampicin-treated contacts without control subjects (no treatment or isoniazid treatment). In conclusion, 77% of contacts with positive TST results were QFT-GIT-positive, and QFT-GIT test reversions were achieved in 41.9% of the subjects (31/74) after 4 months of rifampicin treatment. The serial test results suggest the possibility that the QFT-GIT test may be useful to monitor the response to rifampicin prophylaxis. Further controlled studies with more participants and long-term follow-up are required to clarify these issues.

Conflict of interest All authors have no financial or other potential conflicts of interest to disclose.

References 1. WHO report 2008. global tuberculosis control, surveillance, planning, financing. Geneva, Switzerland: World Health Organization; 2008. 2. Corbett EL, Watt CJ, Walker N, et al. The growing burden of tuberculosis: global trends and interactions with the HIV epidemic. Arch Intern Med 2003;163:1009e21. 3. Dye C, Scheele S, Dolin P, Pathania V, Raviglione MC. Consensus statement. Global burden of tuberculosis: estimated incidence, prevalence, and mortality by country. WHO global surveillance and monitoring project. JAMA 1999;282:677e86. 4. Broekmans JF, Migliori GB, Rieder HL, et al. European framework for tuberculosis control and elimination in countries with a low incidence. Recommendations of the World Health Organization (WHO), International Union Against Tuberculosis and Lung Disease (IUATLD) and Royal Netherlands Tuberculosis Association (KNCV) Working Group. Eur Respir J 2002;19:765e75. 5. Jasmer RM, Nahid P, Hopewell PC. Clinical practice. Latent tuberculosis infection. N Engl J Med 2002;347:1860e6. 6. American Thoracic Society/Centers for Disease Control and Prevention. Targeted tuberculin testing and treatment of

QFT-GIT after rifampicin prophylaxis

7.

8.

9. 10.

11.

12.

13.

14.

15.

16.

17.

18.

19.

20.

21.

22.

23.

latent tuberculosis infection. Am J Respir Crit Care Med 2000; 161:S221e47. Menzies D, Pai M, Comstock G. Meta-analysis: new tests for the diagnosis of latent tuberculosis infection: areas of uncertainty and recommendations for research. Ann Intern Med 2007;146:340e54. Pai M, Zwerling A, Menzies D. Systematic review: T-cell-based assays for the diagnosis of latent tuberculosis infection: an update. Ann Intern Med 2008;149:177e84. Andersen P, Munk ME, Pollock JM, Doherty TM. Specific immunebased diagnosis of tuberculosis. Lancet 2000;356:1099e104. Dheda K, Udwadia ZF, Huggett JF, Johnson MA, Rook GA. Utility of the antigen-specific interferon-gamma assay for the management of tuberculosis. Curr Opin Pulm Med 2005;11:195e202. Mazurek GH, Jereb J, Lobue P, Iademarco MF, Metchock B, Vernon A. Guidelines for using the QuantiFERON-TB Gold test for detecting Mycobacterium tuberculosis infection, United States. MMWR Recomm Rep 2005;54:49e55. National Institute for Health and Clinical Excellence. Clinical guideline 33. Tuberculosis. Clinical diagnosis and management of tuberculosis, and measures for its prevention and control, ; 2006. Diel R, Nienhaus A, Lange C, Schaberg T. Cost-optimisation of screening for latent tuberculosis in close contacts. Eur Respir J 2006;28:35e44. Wrighton-Smith P, Zellweger JP. Direct costs of three models for the screening of latent tuberculosis infection. Eur Respir J 2006;28:45e50. Ewer K, Millington KA, Deeks JJ, Alvarez L, Bryant G, Lalvani A. Dynamic antigen-specific T-cell responses after point-source exposure to Mycobacterium tuberculosis. Am J Respir Crit Care Med 2006;174:831e9. Pai M, Joshi R, Dogra S, et al. Serial testing of health care workers for tuberculosis using interferon-gamma assay. Am J Respir Crit Care Med 2006;174:349e55. Wilkinson KA, Kon OM, Newton SM, et al. Effect of treatment of latent tuberculosis infection on the T cell response to Mycobacterium tuberculosis antigens. J Infect Dis 2006;193:354e9. Hill PC, Brookes RH, Fox A, et al. Longitudinal assessment of an ELISPOT test for Mycobacterium tuberculosis infection. PLoS Med 2007;4:e192. Franken WP, Arend SM, Thijsen SF, et al. Interferon-gamma release assays during follow-up of tuberculin skin test-positive contacts. Int J Tuberc Lung Dis 2008;12:1286e94. Hill PC, Jeffries DJ, Brookes RH, et al. Using ELISPOT to expose false positive skin test conversion in tuberculosis contacts. PLoS ONE 2007;2:e183. van Zyl-Smit RN, Pai M, Peprah K, et al. Within-subject variability and boosting of T-cell interferon-gamma responses after tuberculin skin testing. Am J Respir Crit Care Med 2009;180: 49e58. Updated recommendations on interferon gamma release assays for latent tuberculosis infection. An Advisory Committee Statement (ACS). Can Commun Dis Rep 2008;34:1e13. National Tuberculosis Advisory Committe. Position statement on interferon-gamma release immunoassays in the detection of

453

24.

25.

26.

27.

28.

29.

30.

31.

32.

33.

34.

35.

36.

37.

38.

latent tuberculosis infection, October 2007. Commun Dis Intell 2007;31:404e5. Guidelines for the investigation of contacts of persons with infectious tuberculosis. Recommendations from the National Tuberculosis Controllers Association and CDC. MMWR Recomm Rep 2005;54:1e47. Diel R, Forssbohm M, Loytved G, et al. [Recommendations for background studies in tuberculosis]. Pneumologie 2007;61: 440e55. Chee CB, KhinMar KW, Gan SH, Barkham TM, Pushparani M, Wang YT. Latent tuberculosis infection treatment and T-cell responses to Mycobacterium tuberculosis-specific antigens. Am J Respir Crit Care Med 2007;175:282e7. Higuchi K, Harada N, Mori T. Interferon-gamma responses after isoniazid chemotherapy for latent tuberculosis. Respirology 2008;13:468e72. Lew WJ, Jung YJ, Song JW, et al. Combined use of QuantiFERON((R))-TB Gold assay and chest computed tomography in a tuberculosis outbreak. Int J Tuberc Lung Dis 2009;13:633e9. Diel R, Nienhaus A, Lange C, Meywald-Walter K, Forssbohm M, Schaberg T. Tuberculosis contact investigation with a new, specific blood test in a low-incidence population containing a high proportion of BCG-vaccinated persons. Respir Res 2006; 7:77. Zellweger JP, Zellweger A, Ansermet S, de Senarclens B, Wrighton-Smith P. Contact tracing using a new T-cell-based test: better correlation with tuberculosis exposure than the tuberculin skin test. Int J Tuberc Lung Dis 2005;9:1242e7. Arend SM, Thijsen SF, Leyten EM, et al. Comparison of two interferon-gamma assays and tuberculin skin test for tracing tuberculosis contacts. Am J Respir Crit Care Med 2007;175: 618e27. Pai M, Joshi R, Dogra S, et al. T-cell assay conversions and reversions among household contacts of tuberculosis patients in rural India. Int J Tuberc Lung Dis 2009;13:84e92. Bosshard V, Roux-Lombard P, Perneger T, et al. Do results of the T-SPOT.TB interferon-gamma release assay change after treatment of tuberculosis? Respir Med 2009;103:30e4. Dheda K, Pooran A, Pai M, et al. Interpretation of Mycobacterium tuberculosis antigen-specific IFN-gamma release assays (T-SPOT.TB) and factors that may modulate test results. J Infect 2007;55:169e73. Pai M, Joshi R, Dogra S, et al. Persistently elevated T cell interferon-gamma responses after treatment for latent tuberculosis infection among health care workers in India: a preliminary report. J Occup Med Toxicol 2006;1:7. Higuchi K, Okada K, Harada N, Mori T. [Effects of prophylaxis on QuantiFERON TB-2G responses among children]. Kekkaku 2008;83:603e9. Reichman LB, Lardizabal A, Hayden CH. Considering the role of four months of rifampin in the treatment of latent tuberculosis infection. Am J Respir Crit Care Med 2004;170:832e5. Lecoeur HF, Truffot-Pernot C, Grosset JH. Experimental shortcourse preventive therapy of tuberculosis with rifampin and pyrazinamide. Am Rev Respir Dis 1989;140:1189e93.