Positive Tuberculin Skin Test Results Research Articles

Effect of immunosuppressive therapy on interferon γ release assay for latent tuberculosis screening in patients with autoimmune diseases: a systematic review and meta-analysis

ObjectiveInterferon γ release assay (IGRA) is commonly used to diagnose latent TB infection (LTBI). Immunosuppressive therapy may affect its performance but data are conflicting. We aimed to determine the effect...

Evaluation of Chest X-ray and Thoracic Computed Tomography in Patients with Suspected Tuberculosis.

To investigate if there is any correlation between positive findings detected by posterior-anterior (PA) chest radiograph and thoracic computerized tomography (CT) in cases with suspected lung tuberculosis (TB) due to positive tuberculin skin test (TST) results. This is a retrospective evaluation of the medical files of patients who visited the Department of Pediatrics, Istanbul University, Istanbul Faculty of Medicine from 2006, through 2011 as outpatients and had positive TST (>15mm) results. A total of 326 patients were included in the study; 45.7% (n=149) were girls, and the mean age was 9.0±4.1 y (range: 1-17 y). In total, 14.4% (n=47) had TB findings, all of which were in the form of hilar lymphadenopathy. Among the 47 cases with TB findings in PA chest X-ray, 45 (95.7%) also had findings in thoracic CT. Only 2 (4.3%) patients had normal thoracic CT results although their PA chest X-ray results were positive. Evaluation for pulmonary TB in children with positive isolated TSTs should be made primarily with PA chest X-ray. A routine thoracic CT scan is not necessary for asymptomatic patients with only hilar lymphadenopathy findings in PA chest radiographs.

Nosocomial exposure to active pulmonary tuberculosis in a neonatal intensive care unit

Nosocomial transmission of tuberculosis (TB) in a neonatal intensive care unit (NICU) is a recognized risk. We investigated TB transmission to neonates and health care workers (HCWs) exposed to a nurse with active TB in a NICU. A NICU nurse in a tertiary referral hospital in Seoul, Korea, developed pulmonary TB. The investigation included 108 infants and 75 HCWs. Tuberculin skin test (TST) and chest radiograph were performed at baseline. Isoniazid prophylaxis was started in neonates. After 3 months of prophylaxis, infants underwent repeat TST and chest radiograph. HCWs underwent a second TST after 3 months. Baseline chest radiographs were negative in infants and HCWs. Four (3.7%) of 108 infants screened had a positive TST, including 2 conversions, and received isoniazid for 6-9 months. Among the 59 HCWs screened, 27 (45.8%) had an initial positive TST result, and 6 (10.2%) had a positive TST result at 3 months. Four of the 6 HCWs with TST conversions received isoniazid treatment for 9 months. In the 2-year period after exposure, none of the exposed infants or HCWs developed active TB. In this investigation, 4 (3.7%) of 108 infants exposed to a nurse with active TB developed latent TB infection. They were given isoniazid therapy without any adverse events and did not progress to TB disease in the 2 years after exposure.

A Pulmonary Tuberculosis Cluster in an Institution in Southern Taiwan, 2012

A mental institution resident in Southern Taiwan was ill and sought medical service in March 2014; later was confirmed as pulmonary tuberculosis (TB). Two contacts were found having abnormal chest radiography at the twelfth month and were notified. In July 2013, there were six reported probable patients with pulmonary tuberculosis from the institution including the index case. Five of them were confirmed, and one was excluded. Restriction fragment length polymorphism (RFLP) molecular study done at the Research and Diagnostic Center of Taiwan CDC revealed that the five isolates belonged to the same subtype, thus, proved this cluster of patients with pulmonary tuberculosis. After two serial meetings with TB specialists, not only chest radiographies of related contacts were followed, but also extended the immunoassay from the previous existing tuberculin skin test (TST) to both interferon-gamma release assay (IGRA; QuantiFERON-TB, QFT) and TST for those identified contacts. After evaluation by physicians, the contacts who had both positive results of TST and IGRA were undergone latent tuberculosis infection (LTBI) treatment. Besides, we suggested the administrator keeping the confirmed TB patients in the isolation room on the first floor until his/her sputum was negative for acid-fast stain or TB culture, and also to isolate those suspected TB patients.Of total 85 contacted people, the positive rate of TST was 77.6% (66/85), the positive rate of QFT was 29.5% (18/61), and the positive rate for both TST and QFT was 21.2% (18/85). Twenty-four people underwent LTBI treatment, of whom 22 people completed the treatment course, and 2 people discontinued due to the adverse effects. There was not any tuberculosis patient found in the institution by October 2014.

Latent tuberculosis infection in patients with chronic plaque psoriasis: evidence from the Italian Psocare Registry.

The nationwide prevalence of latent tuberculosis infection (LTBI) in Italian patients with psoriasis has never been investigated. To estimate the nationwide prevalence of LTBI in Italian patients with psoriasis who are candidates for systemic treatment. Data were obtained from the Psocare Registry on those patients (n=4946) with age >18years, systemic treatment at entry specified and tuberculin skin test (TST) performed according to the Mantoux method. LTBI diagnosis was based on a positive TST result in the absence of any clinical, radiological or microbiological evidence of active tuberculosis. Latent tuberculosis infection was diagnosed in 8·3% of patients with psoriasis (409 of 4946). The prevalence of LTBI was lower in patients on biologics than in those on conventional systemic treatments, ranging from 4·3% (19 of 444) of patients on adalimumab to 31% (eight of 26) of those on psoralen-ultraviolet A (P<0·05). Independent factors associated with LTBI were male sex [odds ratio (OR) 1·30, 95% confidence interval (CI) 1·04-1·62; P=0·02], age over 55years (OR 2·93, 95% CI 2·18-3·93; P<0·001) and being entered into a conventional treatment (OR 3·83, 95% CI 3·10-4·74; P<0·001). Positive history of tuberculosis was seen in 1% of patients (n=49). The nationwide prevalence of LTBI in Italian patients with psoriasis candidate to systemic treatment is high, and screening is recommended prior to biological treatment.

Risk for Tuberculosis Disease Among Contacts with Prior Positive Tuberculin Skin Test: A retrospective Cohort Study, New York City.

Patients with prior positive tuberculin skin test (TST) results may benefit from prophylaxis after repeat exposure to infectious tuberculosis (TB). To evaluate factors associated with active TB disease among persons with prior positive TST results named as contacts of persons with infectious TB. Population-based retrospective cohort study. A total of 2,933 contacts with prior positive TST results recently exposed to infectious TB identified in New York City's TB registry during the period from January 1, 1997 through December 31, 2003. Contacts developing active TB disease ≤ 4 years after exposure were identified and compared with those who did not, using Poisson regression analysis. Genotyping was performed on selected Mycobacterium tuberculosis-positive isolates. Among contacts with prior positive TST results, 39 (1.3 %) developed active TB disease ≤ 4 years after exposure (≤ 2 years: 34). Risk factors for contacts that were independently associated with TB were age < 5 years (adjusted prevalence ratio [aPR] = 19.48; 95 % confidence interval [CI] = 7.15-53.09), household exposure (aPR = 2.60;CI = 1.30-5.21), exposure to infectious patients (i.e., cavities on chest radiograph, acid-fast bacilli on sputum smear; aPR = 1.9 3; CI = 1.01-3.71), and exposure to a U.S.-born index patient (aPR = 4.04; CI = 1.95-8.38). Receipt of more than 1 month of treatment for latent TB infection following the current contact investigation was found to be protective (aPR = 0.27; CI = .08-0.93). Genotype results were concordant with the index patients among 14 of 15 contacts who developed active TB disease and had genotyping results available. Concordant genotype results and a high proportion of contacts developing active TB disease within 2 years of exposure indicate that those with prior positive TST results likely developed active TB disease from recent rather than remote infection. Healthcare providers should consider prophylaxis for contacts with prior TB infection, especially young children and close contacts of TB patients (e.g., those with household exposure).

Cost-effectiveness of alternative strategies for interferon-γ release assays and tuberculin skin test in tuberculous uveitis

BackgroundAlthough tuberculous uveitis remains a major cause of ocular morbidity in the developing world, there is no consensus on which diagnostic test or testing strategy is the most cost effective....

Latent tuberculosis infection and occupational protection among health care workers in two types of public hospitals in China.

ObjectiveTo determine the impact factors of latent tuberculosis infection (LTBI) and the knowledge of TB prevention and treatment policy among health care workers (HCWs) in different types of hospitals and explore the strategies for improving TB prevention and control in medical institutions in China.MethodsA cross-sectional study was carried out to evaluate the risk of TB infection and personnel occupational protection among HCWs who directly engage in medical duties in one of two public hospitals. Each potential participant completed a structured questionnaire and performed a tuberculin skin test (TST). Factors associated with LTBI were identified by logistic regression analysis.ResultsSeven hundred twelve HCWs completed questionnaires and 74.3% (n = 529) took the TST or had previous positive results. The TST-positive prevalence was 58.0% (n = 127) in the infectious disease hospital and 33.9% (n = 105) in the non-TB hospital. The duration of employment in the healthcare profession (6–10 years vs. ≤5 years [OR = 1.89; 95% CI = 1.10, 3.25] and>10 vs. ≤5[OR = 1.80; 95% CI = 1.20, 2.68]), type of hospital (OR = 2.40; 95% CI = 1.59, 3.62), and ever-employment in a HIV clinic or ward (OR = 1.87; 95% CI = 1.08, 3.26)were significantly associated with LTBI. The main reasons for an unwillingness to accept TST were previous positive TST results (70.2%) and concerns about skin reaction (31.9%).ConclusionA high prevalence of TB infections was observed among HCWs working in high-risk settings and with long professional experiences in Henan Province in China. Comprehensive guidelines should be developed for different types of medical institutions to reduce TB transmission and ensure the health of HCWs.

An epidemiologic investigation of occupational transmission of Mycobacterium tuberculosis infection to dental health care personnel: Infection prevention and control implications

The authors describe an investigation of a dental hygienist who developed active pulmonary tuberculosis (TB), worked for several months while infectious and likely transmitted Mycobacterium tuberculosis in a dental setting in Washington state. Clark County Public Health (CCPH) conducted an epidemiologic investigation of 20 potentially exposed close contacts and 734 direct-care dental patients in 2010. Of 20 close contacts, one family member and two coworkers, all of whom were from countries in which TB is endemic, had latent TB infection (LTBI). One U.S.-born coworker experienced a tuberculin skin test (TST) conversion from 0 to 8 millimeters. Of the 305 of 731 (41.7 percent) potentially exposed patients who received a single TST, 23 (7.5 percent) had a positive TST result of at least 5 mm. Among the subset of 157 patients tested by CCPH staff, 16 (10.2 percent) had a positive TST result. The dental office did not have infection prevention and control policies related to TB identification, prevention or education. The coworker's TST conversion indicated a recent infection, likely owed to occupational transmission. The proportion of dental patients with positive TST results was greater than the 1999-2000 National Health and Nutrition Examination Survey prevalence estimate in the general population, and it may reflect transmission from the hygienist with active TB or a prevalence of LTBI in the community. Practical Implications All dental practices should implement administrative procedures for TB identification and control as described in this article, even if none of their patients are known to have TB.

A missed tuberculosis diagnosis resulting in hospital transmission.

To find the source of tuberculin skin test conversions among 38 hospital employees on 1 floor during routine testing January-February 2010. Record review of patients at a private hospital during September-December 2009 and interviews with hospital employees. Names of patients from the state tuberculosis (TB) registry were cross-referenced with hospital records for admissions. Mycobacterium tuberculosis genotype results in the county and adjacent counties were examined, and contacts were evaluated for TB infection and disease. One of the 38 employees, a nurse, was diagnosed with pulmonary TB with a matching M. tuberculosis genotype and drug resistance pattern (isoniazid monoresistant) to those of a county jail inmate also recently diagnosed with pulmonary TB. The nurse had no known contact with that inmate; however, another inmate in his 20's from the same jail had been hospitalized under that nurse's care in October 2009. That young man died, and a postmortem examination result subsequently confirmed TB, which had not been suspected. Exposure to this man with undiagnosed TB could explain the transmission: 87 (27%) of the 318 hospital-based contacts without previous positive tuberculin skin test results were infected, and 9 contacts had active TB. This investigation demonstrated M. tuberculosis transmission in a hospital due to a missed diagnosis and nonadherence to national TB infection control guidelines. Routine TB screening of employees allowed early detection of this missed TB diagnosis, facilitating prompt evaluation of contacts. Healthcare providers should suspect TB in symptomatic persons and adhere to TB control policies.

Effect of Isoniazid Therapy for Latent TB Infection on QuantiFERON-TB Gold In-Tube Responses in Adults With Positive Tuberculin Skin Test Results in a High TB Incidence Area

T-cell interferon-γ release assays (IGRAs) are used in the diagnosis of Mycobacterium tuberculosis infection and could be useful biomarkers of response to treatment of latent TB infection for clinical trials, infection control units, and TB programs. This investigation was a prospective, controlled substudy of IGRA responses in 82 healthy South African adults with HIV seronegative and positive tuberculin skin test results randomly assigned to treatment with 6 months of daily isoniazid preventive therapy (IPT) or observation before Bacillus Calmette-Guérin revaccination in a clinical trial. QuantiFERON-TB Gold In-Tube (QFT-GIT) assay was used to measure interferon-γ (IFN-γ) response to mycobacterial antigens at baseline and after IPT or observation. IFN-γ levels declined between baseline and the end of IPT (signed rank test P ≤ .0001) and between baseline and a similar period of observation without IPT (signed rank test P = .03). The rate of decrease in IFN-γ responses over time did not differ between the groups (Mann-Whitney-Wilcoxon test P = .31). QFT-GIT test results in two subjects (5%) in the IPT group and two subjects (5%) in the observation group reverted from positive to negative during follow-up. No significant difference was found between the groups with respect to baseline positivity or the proportion of patients whose tests reverted to negative. IPT had no effect on changes in QFT-GIT readouts during short-term follow-up of adults with positive tuberculin skin tests in a high TB incidence setting. QFT-GIT is unlikely to be a useful biomarker of response to treatment of latent TB infection. ClinicalTrials.gov; No.: NCT01119521; URL: www.clinicaltrials.gov.

T-Cell Profiling and the Immunodiagnosis of Latent Tuberculosis Infection in Patients with Inflammatory Bowel Disease

Factors associated with performance of interferon-γ release assays (IGRA) and the tuberculin skin test (TST) in screening for latent tuberculosis infection in patients with inflammatory bowel diseases (IBD) are still poorly understood. The influence of peripheral T-cell subset counts on the results also remain unclear. Prospective single-center study in 205 patients with IBD. Latent tuberculosis infection screening included a chest radiograph, TST (retest if negative), and 2 IGRAs: QuantiFERON-TB Gold In-Tube (QFT-GIT) and TSPOT-TB (TSPOT). T-cell subpopulations were determined by flow cytometry. Twenty-one (10.2%) patients had an abnormal chest radiograph, 55 (26.8%) had a positive TST, 16 (7.8%) had a positive QFT-GIT, and 25 (12.6%) had a positive TSPOT. TST positivity was lower in patients on ≥2 immunosuppressants compared with the controls (5-aminosalicylic acid treatment) (10.4% versus 38.2%, respectively) (P = 0.0057). No other drugs influenced TST or IGRA positivity. In patients on corticosteroid treatment, anti-TNF treatment, or ≥2 immunosuppressants, IGRAs detected 10 cases of latent tuberculosis infection not identified by TST. TSPOT and QFT-GIT increased yield by 56% and 22%, respectively. No significant differences in T-cell subpopulations were found between patients with positive or negative TST or TSPOT results. However, patients with positive QFT-GIT findings had more CD8 T cells (mean, 883 ± 576 versus 484 ± 385 cells per microliter in patients with negative results) (P = 0.022). IGRAs can improve TST-based screening in patients with IBD on immunosuppressive therapy. A low CD8 count can affect QFT-GIT results. We suggest combining TSPOT and TST screening in patients with IBD on immunosuppressants.

Tuberculin skin test and interferon-γ release assay in the detection of latent tuberculosis infection among Polish health care workers

For many years, Poland has had a mandatory vaccination program against tuberculosis, which recommended repeated vaccinations from birth to adulthood. Therefore, the clinical value of the tuberculin skin test (TST) in diagnosing latent tuberculosis infection (LTBI) in Poland remains unclear. We conducted a study on the usefulness of the TST and QuantiFERON®-TB test (QFT) for the evaluation of the prevalence and risk factors of L TBI among Polish health care workers. The study group consisted of the Polish health care workers. TST and QFT were performed in each participant. The usefulness of TST and QFT was tested in relation to occupational risk factors. A total of 305 participants were included. A positive TST result was observed in 149 cases (48.9%) and a positive QFT result was observed only in 27 cases (8.9%). In the subgroup that declared contact with tuberculosis (n = 44), positive QFT and TST results were found in 20.5% and 63.3% cases, respectively. Past contact with tuberculosis was the only significant variable associated with a positive TST result. Independent variables associated with positive QFT results were older age, lower education level, longer period of work in health care, and previous contactwith tuberculosis. The QFT has a higher diagnostic value than the TST in the assessment of LTBI in Polish health care workers.

Effect of delay in diagnosis on the rate of tuberculosis among close contacts of tuberculosis patients

Few studies have explored diagnosis delay by tuberculosis (TB) patients and its effects on the rate of infection among their close contacts. A cross-sectional study of the close contacts of 505 newly diagnosed TB patients was conducted in a TB referral centre in Sana'a, Yemen from 2008 to 2010. Only the close contacts of 89 new TB patients agreed to participate and completed the tuberculin skin test (TST). Of the 239 close contacts investigated, 133 (55.6%) had a positive TST result. Index patients were classified as long or short diagnosis delay (above or below the median). There was no significant difference in the number of infected close contacts between long and short delay index patients (Mann-Whitney U-test). A larger sample size, with more incentives for patients to participate and the use of other investigative tools could provide a better picture of the pattern of TB transmission among all contacts.

Comparison of QuantiFERON-TB Gold With Tuberculin Skin Test for Detection of Latent Tuberculosis Infection Before Kidney Transplantation

IntroductionScreening for latent tuberculosis infection (LTBI) before kidney transplantation (KT) is an indispensable process, purposes of this study were to compare the QuantiFERON-TB Gold In-Tube test (QFT-GIT) with the tuberculin skin test (TST) for screening of LTBI in kidney transplant recipients (KTRs). MethodsWe compared prospectively the results of QFT-GIT with TST in 97 KTRs screened for LTBI between July 2008 and July 2012. Isoniazid (INH) prophylaxis was applied to KTRs with a positive TST or positive QFT-GIT or clinical risk factors for LTBI. Post-transplant tuberculosis (TB) was diagnosed by clinical evidence. ResultsThe mean patients follow-up was 24.6 ± 14.4 months. Positive results on QFT-GIT and TST was obtained among 19 (20.4%) and 12 (12.9%) subjects, respectively, an overall agreement of 79.3% (κ = 0.27, 95% confidence interval [CI] −0.03–0.50; P < .014). The incidence of TB was 0.52 per 100 person-years (95% CI 0.02–3.68). None of the patients in the INH prophylaxis group developed TB, whereas 1 in the no prophylaxis group developed disease at 14 months after KT. Sensitivity of the 2 tests could not be compared because patients who showed positive results on QFT-GIT or TST did not develop TB. The difference of specificity between QFT-GIT (79.3%) and TST (86.9%) was not significant (P = .l67). Abnormal chest radiographs (odds ratio [OR] 27.94, 95% CI 1.22–636.61, P = .037) and positive TST (OR 7.65, 95% CI 1.75–33.30, P = .007) showed significant associations with positive QFT-GIT results. Only positive QFT-GIT (OR 6.03, 95% CI 1.51–24.01, P = .011) showed an association with positive TST results. ConclusionsQFT-GIT and TST for diagnosis of LTBI in KTRs showed reasonable concordance but no superiority of either test.

Acceptability of interferon-gamma release assays among healthcare workers who receive routine employee tuberculosis testing

Healthcare workers (HCWs) undergo annual testing for latent tuberculosis infection (LTBI). Compare acceptability of tuberculin skin test (TST) and interferon-gamma release assay (IGRA) among HCWs. HCWs at four medical centers in the US were administered an acceptability questionnaire including a brief objective description of both tests and eliciting attitudes regarding TST and IGRAs, confidence in results, and likelihood of taking LTBI treatment. Of 406 participants, 75% had never heard of IGRAs. IGRAs were preferred to TST. Belief in accuracy of hypothetical positive results of TST or IGRA and willingness to accept LTBI treatment were similar across tests. When presented with hypothetical discordant results, HCWs expressed more confidence in IGRAs. Perceived accuracy of results was the most important factor in test preferences. Although HCWs preferred and indicated more confidence in IGRAs, the likelihood that HCWs would believe LTBI diagnosis and initiate treatment based on positive results was similar for TST and IGRAs.

Strategy to Better Select HIV-Infected Individuals for Latent TB Treatment in BCG-Vaccinated Population

ObjectiveTo evaluate the T-SPOT.TB interferon-γ releasing assay and the tuberculin skin test (TST), for the diagnosis of latent tuberculosis infection(LTBI) and the development of subsequent active tuberculosis, in BCG-vaccinated HIV-infected individuals.MethodsHIV-infected individuals without clinical suspicion of active TB or a past history of TB were enrolled from 1 January 2008 to 30 November 2010. Both T-SPOT.TB test and TST were offered to the participants whom were followed up prospectively until April 30, 2012 for development of TB.ResultsAmong the 909 participants, 25% had positive TST reactions with cut-off point of 5 mm and 15% had positive T-SPOT.TB results. After a median follow-up of 2.97 years, there were 5 cases developed culture-confirmed active TB (all had dual positive TST and T-SPOT.TB results), and the incidence was 0.17 per 100 person-years. The relative risks (RRs) for subsequent active TB in HIV-infected individuals with positive TST results, positive T-SPOT.TB results and dual positive results compared with the risk for individuals with negative results were 40.6 (95% CI 2.1–767.9), 73.9 (95% CI 3.9–1397.7) and 226.5 (95% CI 12.0–4284), respectively. The number needed to treat to prevent one subsequent TB case among patients with a positive TST, a positive T-SPOT.TB and dual positive results was 35, 22 and 8 respectively.ConclusionsAdopting positive results of the TST and T-SPOT.TB to screen LTBI among BCG-vaccinated HIV-infected individuals might be feasible. Number needed to treat for isoniazid preventive therapy could be reduced significantly by using dual positive strategy.

Erythema Induratum: Case Series Illustrating the Utility of the Interferon-γ Release Assay in Determining the Association with Tuberculosis

The interferon-γ release assay (IGRA) is a novel method for detecting previous sensitization to tuberculosis (TB). Despite having several advantages over the tuberculin skin test (TST), including higher specificity and no influence from past bacille Calmette-Guérin (BCG) exposure, there are a limited number of reports describing its application in patients with erythema induratum (EI)/nodular vasculitis (NV), which is usually but not always related to TB. The aim of our case series was to evaluate the usefulness of the IGRA for determining a TB association in patients with EI/NV. Retrospective chart reviews were conducted on four patients diagnosed with EI/NV at our institution in whom an IGRA had been performed. All four subjects had positive TST results. The IGRA was also positive and therefore supported a link with TB in two cases. One patient responded completely to anti-TB therapy, whereas the second was lost to follow-up. Both cases unrelated to TB, by virtue of negative IGRAs, demonstrated complete response to immunosuppressive therapy (methotrexate), with one individual having failed anti-TB therapy first. Our case series highlights the utility of the IGRA for establishing a TB association in patients with EI/NV. Although limited by a small sample size, we propose adjunctive use of this test at the time of EI/NV diagnosis, especially in the setting of previous BCG exposure, so that management can be tailored according to whether an underlying relationship with TB exists.

Tuberculin Skin Test and Boosted Reactions among Newly Employed Healthcare Workers: An Observational Study

ObjectiveTo evaluate the prevalence of and factors associated with latent tuberculosis infection (LTBI) based on the tuberculin skin test (TST) and to estimate the boosted reaction rate among newly employed healthcare workers (HCWs).DesignNewly employed HCWs between January 2010 and July 2012 at Severance Hospital in South Korea were enrolled in this study. A one-step TST was conducted before October 2011, and a two-step TST after October 2011.ResultsOf 2132 participants, 778 (36.5%) had positive TST results. Being older (odds ratio [OR] 1.10, 95% confidence interval [CI] 1.06–1.13, P<0.001), male (OR 1.78, 95% CI 1.21–2.62, P = 0.003), rejoining the hospital workforce (OR 1.58, 95% CI 1.04–2.40, P = 0.032), and having a previous history of tuberculosis (TB) (OR 18.21, 95% CI 2.15–154.10, P = 0.008) during the one-step period, and being older (OR 1.15, 95% CI 1.10–1.21, P<0.001) during the two-step period were significantly associated with a positive TST. A two-step TST was performed in 556 HCWs, and a boosted reaction was observed in 79 (14.2%). The induration size on the first TST (5–9-mm group) was the only factor associated with a boosted reaction on the second TST.ConclusionsThe prevalence of LTBI based on the TST among newly employed HCWs was high. The boosted reaction rate on two-step TST was not low; therefore, the use of two-step TST may be necessary for regular monitoring in countries with an intermediate TB burden and a high rate of Bacillus Calmette-Guérin vaccination.

Basic and clinical immunology- 3019. Gamma interferon release assay for diagnosis of latent tuberculosis – comparison with TB skin test

Background The presence of latent tuberculosis is routinely assessed by tuberculin skin test (TST), which detects a cell mediated immune response to the injected tuberculin purified protein derivative (PPD). Although TST has been in use for over a century, its limitations include poor specificity (i.e. numerous false positive results), the need to examine the site 48-72 hours after injection and the subjective interpretation of results (i.e. estimation of the diameter of induration). Recently, an in vitro assay has been investigated as an alternative to overcome limitations posed by TST. This assay, also known as gamma interferon release assay (GIRA) detects the release of gamma interferon from sensitized lymphocytes upon exposure to mycobacterium TB antigen coated tubes.