Lower Risk Of Tuberculosis Research Articles

Incidence and mortality of tuberculosis before and after initiation of antiretroviral therapy: an HIV cohort study in India.

IntroductionIndia has the highest burden of tuberculosis (TB) in the world, but the epidemiology of HIV-associated TB is not well known.MethodsWe describe the incidence and the mortality of TB from HIV diagnosis to antiretroviral therapy (ART) initiation (pre-ART group) and after ART initiation (on-ART group) in an HIV cohort study in Anantapur, India. Multivariable analysis of factors associated with TB was performed using competing risk regression and restricted cubic spline methods.ResultsA total of 4590 patients and 3133 person-years (py) of follow-up were included in the pre-ART group, and 3784 patients and 4756 py were included in the on-ART group. In the pre-ART group, the incidence of TB was high during the first month after HIV diagnosis and dropped nearly four times soon after. In the on-ART group, the incidence of TB increased after ART initiation reaching a peak in the third month. The probability of having TB within 30 months was 22.3% (95% confidence interval [CI], 21.1–23.6) in the pre-ART group and 17.8% (95% CI, 16.3–19.3) in the on-ART group. In a multivariable analysis, women had a lower risk of TB in both groups. Poor socio-economical conditions were associated with an increased risk of TB in the pre-ART group, but not in the group on-ART. While the association between low CD4 counts and TB was strong in the pre-ART group, this association was weaker in the on-ART group, and the highest risk of TB was seen in those patients with CD4 counts around 110 cells/mm3. The cumulative incidence of mortality at 12 months in patients with TB was 29.6% (95% CI, 26.9–32.6) in pre-ART TB and 34.9% (95% CI, 31–39.1) in on-ART TB. Half deaths before ART initiation and two thirds of deaths after ART initiation occurred in patients with TB.ConclusionsThe high incidence and mortality of TB seen in this study underscore the urgent need to improve the prevention and diagnosis of HIV-associated TB in India. We found substantial differences between TB before and after ART initiation.

Parasite Infection and Tuberculosis Disease among Children: A Case–Control Study

We conducted a case-control study to examine associations between parasite infection, including protozoa infection, and tuberculosis (TB) in children in Lima, Peru. We enrolled 189 matched-pairs. In multivariable conditional logistic regression analyses, Blastocystis hominis infection (rate ratio = 0.30, 95% confidence interval = 0.14-0.64, P = 0.002) was strongly associated with a lower risk of TB. We observed a statistically significant inverse linear dose-response relationship between Blastocystis hominis infection and TB. These findings should be confirmed in future prospective studies.

Occupational health policies and practices related to tuberculosis in health care workers in KwaZulu-Natal, South Africa.

Three district hospitals in KwaZulu-Natal, South Africa, with specialized drug-resistant tuberculosis (TB) wards. To increase understanding of the implementation of occupational health (OH) and infection control (IC) guidelines for the prevention and control of TB among health care workers (HCWs). An operational cross-sectional study conducted between July and September 2011, consisting of interviews with OH and IC nurses and chart review of OH medical records. Although general national and provincial OH policies are in place, no specific OH policies exist for hospital settings. Two of three hospitals had a full-time OH nurse and all had a full-time IC nurse. All hospitals offered TB symptom screening; however, only 19% of HCWs were screened in 2010. TB incidence among HCWs was 1958 per 100 000 population in 2010. All hospitals offered HIV counseling and testing; however, only 22% of staff were tested across sites. Two hospitals offered isoniazid preventive therapy to HIV-positive staff and reassigned these staff to low TB risk areas. While OH policies and procedures are in place, implementation of these policies and procedures is inconsistent. This potentially places HCWs at risk of acquiring TB. These findings support the need for strengthening OH and IC services to prevent TB.

Diagnostic and prognostic value of serum C-reactive protein for screening for HIV-associated tuberculosis

Rapid means of ruling in or ruling out tuberculosis (TB) would permit more efficient management of patients starting antiretroviral treatment (ART). To assess the diagnostic and prognostic utility of C-reactive protein (CRP) among patients being screened for TB before ART in a South African ART clinic. Patients were microbiologically screened for TB regardless of symptoms; serum CRP was measured, and mortality at 3 months was assessed. Among 496 patients (median CD4 count 171 cells/l), culture-positive TB was diagnosed in 81 (16.3%). CRP concentrations were much higher among TB cases (median 57.8 mg/l, IQR 20.0202.7) than in those without TB (6.4 mg/l, IQR 2.121.8, P < 0.001). Very low (<1.5 mg/l) CRP concentrations excluded TB (100% negative predictive value), whereas very high concentrations (>400 mg/l) were strongly predictive of TB (100% positive predictive value). However, these thresholds encompassed only 14.3% and 2.0%, respectively, of all patients screened and identified only 12.3% of TB cases. CRP concentrations ≥50 mg/l were associated with poor prognostic characteristics, higher mycobacterial load, disseminated disease and greater mortality risk. CRP concentrations identified groups of patients with very high or very low TB risk, but only in an unacceptably small minority of patients screened. However, in those with confirmed TB, CRP concentrations had useful prognostic value.

Increasing Tuberculosis Notification Rates Among Young Adults are Not Associated with Migration in Da Nang, Vietnam

Tuberculosis (TB) case notification rates in Vietnam have stabilized since 2000, but in 2007 were increasing among young adults. The emerging HIV epidemic only partly explains this increase. Other factors are probably involved. We aimed to assess whether rural-to-urban migration is such a factor. We conducted a case-control study at district TB units (DTUs) in Da Nang province, Vietnam, recruiting equal numbers (170) of TB patients aged 15-35 years, TB suspects of the same age in whom TB was excluded, and TB patients of 35 years and older. Risk factors for TB were assessed through interviews using pre-structured questionnaires. Among persons seeking care at DTUs, migration was not a significant risk factor for TB. Young male migrants had a lower risk of TB than other young adults (odds ratio (OR) 0.4; 95% confidence interval (95%CI) 0.03-0.64). Instead, TB was associated with male sex and a higher level of education. Compared to older TB patients, younger TB patients were more likely to be female, have a higher education level and a job involving indoor contacts with other people. Migration does not account for the increase in TB case notification rates among young adults in Vietnam. However, migration cannot be excluded as a risk factor for TB in Vietnam, because migrants may not seek diagnosis and treatment for TB at DTUs.

Incidence, Predictive Factors and Prognosis of Tuberculosis among Patients with HIV Infection in Guadeloupe 1988-2009

Objective: To determine the incidence, risk factors and prognosis for incident tuberculosis during the follow-up of HIV-infected patients in Guadeloupe. Methods: We conducted a retrospective cohort study using STATA version IC 10.0 (College Station, Texas, USA). Results: A single failure Cox proportional hazards model showed that patients with B CDC category (HR=4.50; 95%CI=1.50-13.60; P=0.007) and patients with C CDC category (HR=138.30; 95%CI=62.80-304.90; P=0.000) were at an increased risk of tuberculosis, whereas patients with low median CD4 count at enrolment ( HR=0.50; 95%CI=0.30- 0.84; P=0.009) and patients treated by ART ( HR=0.45; 95%CI=0.34-0.62; P=0.000) were associated with a low risk of tuberculosis. Conclusion: Our data showed a high incidence of tuberculosis and no socio-economic factors related to tuberculosis among HIV-infected patients. These findings help to effectively guide public health interventions.

Identification of False-Positive QuantiFERON-TB Gold In-Tube Assays by Repeat Testing in HIV-Infected Patients at Low Risk for Tuberculosis

Identification of False-Positive QuantiFERON-TB Gold In-Tube Assays by Repeat Testing in HIV-Infected Patients at Low Risk for Tuberculosis

Screening for tuberculosis and the use of a borderline zone for the interpretation of the interferon-γ release assay (IGRA) in Portuguese healthcare workers

IntroductionThe effect of using a borderline zone for the interpretation of the interferon-γ release assay (IGRA) on the prediction of progression to active tuberculosis (TB) in healthcare workers (HCW) is analysed.MethodsData from a published study on TB screening in Portuguese HCW is reanalysed using a borderline zone for the interpretation of the IGRA. Testing was performed with the QuantiFERON-TB Gold In-Tube (QFT). The borderline zone for the QFT was defined as interferon (INF) in QFT ≥0.2 to <0.7 IU/mL. An X-ray was performed when the IGRA was positive (≥0.35 IU/mL) or typical symptoms were present. Sputum analysis was performed according to the X-ray or the presence of typical symptoms.ResultsThe cohort comprised 2,884 HCW with a QFT that could be interpreted. In 1,780 (61.7%) HCW, the QFT was <0.2 IU/mL. A borderline result was found in 341 (11.8%) and a QFT >0.7 IU/mL in 763 (26.3%) HCW. Fifty-seven HCW had a TB in their medical history, eight had a TB at the time of screening and progression to active TB was observed in four HCW. Two out of eight HCW (25%) with active TB at the time of screening had a QFT result falling into the borderline zone. One out of four HCW (25%) who progressed towards active TB after being tested with QFT had QFT results falling into the borderline zone. A second IGRA was performed in 1,199 HCW. In total, 292 (24.4%) HCW had at least one of the two IGRA results pertaining to the borderline zone.ConclusionUsing a borderline zone for the QFT from 0.2 to 0.7 IU/mL should be administered with care, as active TB as well as progression to active TB might be overlooked. Therefore, the borderline zone should be restricted to populations with a low TB risk only.

Comparison of specificities between two interferon-gamma release assays in Japan [Short communication

We compared the specificities of two interferon-gamma release assays (IGRAs), T-SPOT®.TB (T-SPOT) and the QuantiFERON®-TB Gold In-Tube (QFT-GIT) assay, in strictly selected subjects with a low risk of tuberculosis (TB) infection in a Japanese population. Of 111 subjects who were mostly bacille Calmette-Guérin vaccinated, one was positive using both assays and 110 were negative, using international cut-off values. Although several meta-analyses report that QFT-GIT has higher specificity than T-SPOT, our study demonstrates that the specificity of both assays is equally high in a population with a truly low risk of TB infection.

A Strong Tuberculin Reaction in Primary School Children Predicts Tuberculosis in Adolescence

In Hong Kong, neonatal bacillus Calmette-Guerin vaccination coverage has been around 99% since 1970. Children younger than 14 years of age appear to have a relatively low risk of tuberculosis (TB), but the risk of TB increases rapidly after 15 years of age to a secondary peak in young adulthood. We followed prospectively 19,383 students who were 6 to 10 years of age participating in the 1999/2000 bacillus Calmette-Guerin revaccination program by cross-matching with the territory-wide TB registry until December 31, 2010, using the identity card number as a unique identifier. After 214,753 person-years of follow-up, 44 active TB cases (22 culture-confirmed) were detected for an overall incidence of 20.5/100,000 person-years. The incidence differed significantly by baseline tuberculin reaction sizes (13.0, 18.8, 22.5, 280.4 per 100,000 person-years for reaction size of 0-4, 5-9, 10-14, and ≥15 mm, respectively, P < 0.001). Consistent results were observed for culture-confirmed cases and after adjustment for gender and baseline age. For those with tuberculin reaction size ≥15 mm, the incidence of TB was significantly higher beyond the age of 15 years than for those less than 15 years (608.1 vs. 37.5 per 100,000 person-years, P < 0.001). Although older baseline age was associated with larger tuberculin reaction sizes, it did not independently predict subsequent development of disease. Strong tuberculin reactions in primary school children predicted TB in adolescents after an initial quiescent period. Endogenous reactivation, possibly related to changes in host immunity, might account for the upsurge of TB in adolescence.

Does empirical treatment of community-acquired pneumonia with fluoroquinolones delay tuberculosis treatment and result in fluoroquinolone resistance in Mycobacterium tuberculosis? Controversies and solutions

The role of fluoroquinolones (FQs) as empirical therapy for community-acquired pneumonia (CAP) remains controversial in countries with high tuberculosis (TB) endemicity owing to the possibility of delayed TB diagnosis and treatment and the emergence of FQ resistance in Mycobacterium tuberculosis. Although the rates of macrolide-resistant Streptococcus pneumoniae and amoxicillin/clavulanic acid-resistant Haemophilus influenzae have risen to alarming levels, the rates of respiratory FQ (RFQ) resistance amongst these isolates remain relatively low. It is reported that ca. 1–7% of CAP cases are re-diagnosed as pulmonary TB in Asian countries. A longer duration (≥7 days) of symptoms, a history of night sweats, lack of fever (>38°C), infection involving the upper lobe, presence of cavitary infiltrates, opacity in the lower lung without the presence of air, low total white blood cell count and the presence of lymphopenia are predictive of pulmonary TB. Amongst patients with CAP who reside in TB-endemic countries who are suspected of having TB, imaging studies as well as aggressive microbiological investigations need to be performed early on. Previous exposure to a FQ for >10 days in patients with TB is associated with the emergence of FQ-resistant M. tuberculosis isolates. However, rates of M. tuberculosis isolates with FQ resistance are significantly higher amongst multidrug-resistant M. tuberculosis isolates than amongst susceptible isolates. Consequently, in Taiwan and also in other countries with TB endemicity, a short-course (5-day) regimen of a RFQ is still recommended for empirical therapy for CAP patients if the patient is at low risk for TB.

Performance of QuantiFERON TB in a student population at low risk of tuberculosis

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Identification of False-Positive QuantiFERON-TB Gold In-Tube Assays by Repeat Testing in HIV-Infected Patients at Low Risk for Tuberculosis

The QuantiFERON-TB Gold In-Tube assay (QFT) is increasingly being used for latent tuberculosis screening in patients infected with human immunodeficiency virus (HIV) in the United States. This is a retrospective analysis of repeating positive QFT assays as a strategy to identify false-positive results in HIV-infected patients at low risk for tuberculosis.

Reducing the Burden of Tuberculosis Presenting during the Initial Months of Antiretroviral Therapy in Resource‐Limited Settings

SIR-The high burden of tuberculosis (TB) within antiretroviral treatment (ART) programs in resource-limited settings is challenging [1,2]. We read with interest the article by Koenig and colleagues from Haiti in which they reported a very high mortality rate (27% at one year) among patients with TB diagnosed during the first 3 months of ART [3]. This observation is important and entirely consistent with other data from sub-Saharan Africa [1, 2]. It was also reported, however, that in both adjusted and unadjusted analyses, the mortality in this patient group was substantially greater than that of patients with either prevalent TB diagnosed pre-ART or incident TB diagnosed at some time beyond 3 months of ART [3]. Data from the latter two groups were pooled to form a combined comparator group with low overall TB risk. The much higher mortality risk of patients with TB presenting in early ART compared to that of patients with TB at baseline differs from the findings of previous studies [1,2] and we are concerned that this observation could be misinterpreted as showing a deleterious impact of ART on survival. We wonder whether this may be the result of patient selection. The mortality rate of patients with advanced immunodeficiency just prior to starting ART in resource limited settings is extremely high and TB in this period is difficult and time-consuming to diagnose [4–7]. Thus, many deaths occur in this period among patients with either diagnosed TB or unrecognised TB. Only selected patients in whom TB diagnosis was possible and who survived long enough to start ART could form the pre-ART group. Such patient selection may have substantially diminished the observed mortality risk of the pre-ART group. This would be consistent with the Kaplan Meier plot, which shows an unusually low frequency of deaths in the first 6 weeks of TB treatment in the comparator arm containing this patient group. Notwithstanding this potential limitation, we agree that TB is very likely to be an important contributor to early mortality in ART services [4]. The key question is how to tackle this problem. Koenig and colleagues suggested that many patients with incident TB during early ART are likely to have active TB that was present at baseline but remained undiagnosed. In agreement with this, we recently estimated that in our South African ART cohort, approximately 40% of the TB cases presenting in this period is due to ‘unmasking’ of asymptomatic or minimally symptomatic disease present at baseline [8]. Moreover, in a more recent study, all patients entering our program without a pre-existing TB diagnosis were (regardless of symptoms) systematically screened by culturing induced sputum samples. The yield of culture-confirmed TB diagnoses in these patients at baseline was extremely high (25%) [9] and was more that 2-fold higher than had been diagnosed during routine program screening in preceding years [1]. Of note, during the period of this study, the proportion of patients who presented with TB in the first 3 months of ART was correspondingly more than two-fold lower than previously observed. Thus, following the observation by Koenig and colleagues of the very high mortality rate among patients presenting with TB in the first 3 months of ART, we have found that effective baseline screening substantially reduces incident TB during this period. This suggests a need for routine pre-ART TB screening using high sensitivity tests, such automated liquid culture of sputum, and highlights an urgent need for much more rapid and sensitive diagnostics for use in this clinical setting. It remains to be demonstrated, however, whether this strategy would reduce mortality risk.

Clinical Prediction Rules in the Isolation of Patients With Suspected Pulmonary Tuberculosis

In this issue of Infectious Diseases in Clinical Practice, Aguilar et al describe their derivation of a clinical prediction rule for isolation of suspected cases of pulmonary tuberculosis (TB). The isolation of patients at high risk for pulmonary TB is an important measure that has shown effectiveness in decreasing nosocomial transmission and is especially important with the emergence of multidrug-resistant strains.1 The decision to isolate patients suspected of TB must balance the risk of nosocomial transmission with the low prevalence of the infection and high associated costs. Clinical prediction rules using readily available clinical indicators are useful in this situation as a means of identifying patients at low risk of active pulmonary TB. At least 4 previous prediction models have been reported in the literature with similar sensitivity as reported in the current study.2 Previously published clinical prediction rules have found the presence of TB risk factors or chronic symptoms, self-reported positive tuberculin skin test, fever, and upper lobe abnormalities on chest radiograph to be predictors of pulmonary TB. Positive tuberculin skin test and upper lobe infiltrates on chest radiograph have shown the strongest association in derivation studies, and this appears to be consistent with the current study. Factors that have been less useful in the derivation of other prediction models have included hemoptysis and white blood cell counts.2 Guidelines for evaluating the quality of clinical prediction rule studies have been proposed and applied to models regarding TB isolation.2,3 The current study appears to demonstrate many characteristics associated with a high-quality study including sufficient description of predictor variables, a detailed reference standard, succinct reporting of important patient characteristics, and a clear account of statistical methods. It is not reported, however, if predictors were ascertained with the knowledge of culture results, potentially biasing the identification of these details during the data collection process. The findings reported in this study represent the derivation of a clinical prediction rule and thus require a validation evaluation to merit clinical applicability.4 Previously reported clinical prediction rules have demonstrated diminished precision when used in different validation populations.5 The negative prediction value of human immunodeficiency virus seropositivity is an important aspect of the model reported in this study that should be validated on a population with a higher prevalence of human immunodeficiency virus infection. This study is the first to include computer-aided tomography (CT) scanning as a predictor variable. Computer-aided tomography scanning has greater discriminatory power than plain radiography in the diagnosis of TB and can at times identify active disease.6 Therefore, it is not surprising that its inclusion appears to improve the sensitivity of the clinical prediction model. It is unlikely, however, that CT scanning improves the prediction model to an extent that justifies its cost. In addition, in many institutions, CT scans or their interpretation may not be available at the time of isolation, further limiting use in clinical prediction models. Clinical prediction rules can serve as a useful tool for the identification of patients who are at a low risk for pulmonary TB and do not require respiratory precautions. Future research should be directed toward evaluating the impact of these clinical tools on physician behavior and evaluating the cost-effectiveness of implementing these rules into institutional practice.

T-cell-based diagnosis of tuberculosis infection in children in Lithuania: a country of high incidence despite a high coverage with bacille Calmette-Guerin vaccination

BackgroundLithuania is a country with a high incidence of tuberculosis (TB), despite a high coverage with bacille Calmette-Guerin (BCG) vaccination. Until now the only method used to detect latent TB infection was the tuberculin skin test (TST). However, TST may have a cross reactivity to the BCG vaccine and to environmental mycobacteria. The aim of this study was to conduct assessments of the diagnostic accuracy of the T-cell based test (T SPOT TB) for TB in children who had previously been BCG vaccinated and compare these with the results of the TST.MethodsBetween January 2005 and February 2007, children with bacteriologically confirmed TB, children having contacts with a case of infectious pulmonary TB and children without any known risk for TB were tested with both the TST and T SPOT TB.ResultsThe TST and T SPOT TB tests were positive for all patients in the „culture-confirmed TB“ group. Whereas, in the „high risk for TB“ group, the TST was positive for 60%, but the T SPOT TB test, only for 17.8%. Meanwhile the results for the „low risk for TB“ group were 65.4% and 9.6%, respectively. A correlation between the TST and T SPOT TB was obtained in the "culture-confirmed TB" group where the TST ≥15 mm (r = 0.35, p < 0.001).ConclusionThe T-cell based method is more objective than the TST for identifying latent TB infection in children who had been previously BCG vaccinated. This method could be useful in countries like Lithuania where there is a high incidence of TB despite a high coverage with BCG vaccination. It may also help to avoid unnecessary chemoprophylaxis when TST reactions are false-positive.

Lower Risk of Tuberculosis in Obesity

Obesity is increasingly prevalent in both developed and developing areas. Although undernutrition is well associated with tuberculosis, few studies have systematically examined the association with obesity. Method A cohort of 42 116 individuals 65 years or older enrolled at 18 health centers for elderly patients in Hong Kong, China (which has a tuberculosis incidence of approximately 90 per 100,000 population), in 2000 were followed up prospectively through the territory-wide tuberculosis registry for the development of active tuberculosis from 3 months after enrollment until December 31, 2005, using the identity card number as the unique identifier. The association with body mass index (BMI; calculated as weight in kilograms divided by the square of height in meters), as categorized by the Asian standards, was assessed with the control of other baseline characteristics. Obese (BMI>or=30) and overweight (BMI, 25 to <30) individuals were at significantly lower risks of developing active tuberculosis than normal-weight individuals (BMI, 18.5 to <25), with hazard ratios (95% confidence intervals) of 0.36 (0.20-0.66) and 0.55 (0.44-0.70), respectively, after adjustment for baseline demographic, social, and clinical variables. An inverse linear association was observed predominantly for pulmonary but not extrapulmonary tuberculosis. This association persisted after controlling for potential confounders or excluding individuals with known tuberculosis risk factors. Obesity is associated with a lower risk of active pulmonary tuberculosis in the older population of Hong Kong. The presence of such a strong but selective association across the whole spectrum of BMI could have major biological, clinical, and/or epidemiological implications. Further studies are indicated to explore the underlying mechanisms, potential clinical utilities, and possible epidemiological consequences.

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.

Evaluation of an In Vitro Assay for Interferon γ Production in Response to theMycobacterium tuberculosis–Synthesized Peptide Antigens ESAT-6 and CFP-10 and the PPD Skin Test

We compared the tuberculin skin test (TST) to QuantiFERON-TB (QFT) and QuantiFERON-TB Gold (QFT-G) for the detection of latent tuberculosis. The QFT-G uses synthesized early secretory antigenic target 6 and culture filtrate protein 10 peptide antigens instead of purified protein derivative (PPD) antigens. The study included 137 adults in 3 groups: 1 (n = 81), at low risk for Mycobacterium tuberculosis (TB) and not vaccinated for Mycobacterium bovis bacillus Calmette-Guérin (BCG); 2 (n = 30), probably had TB exposure and were BCG vaccinated; and 3 (n = 26), at low risk for TB, not BCG vaccinated, but previously had a positive TST result. Positive results were as follows: group 1: TST 3 (3.7%); QFT 9 (11.1%); and QFT-G, 0 (0.0%); group 2: TST 26 (86.7%); QFT, 15 (50.0%); and QFT-G, 5 (16. 7%); and group 3: TST, 26 (100.0%); QFT, 13 (50.0%); and QFT-G, 9 (34.6%). The QFT-G demonstrated less cross-reactivity with BCG antigen and was more specific than QFT and TST in low-risk individuals.

Evaluation of an In Vitro Assay for Interferon Production in Response to the Mycobacterium tuberculosis- Synthesized Peptide Antigens ESAT-6 and CFP-10 and the PPD Skin Test

We compared the tuberculin skin test (TST) to QuantiFERON-TB (QFT) and QuantiFERON-TB Gold (QFT-G) for the detection of latent tuberculosis. The QFT-G uses synthesized early secretory antigenic target 6 and culture filtrate protein 10 peptide antigens instead of purified protein derivative (PPD) antigens. The study included 137 adults in 3 groups: 1 (n = 81), at low risk for Mycobacterium tuberculosis (TB) and not vaccinated for Mycobacterium bovis bacillus Calmette-Guérin (BCG); 2 (n = 30), probably had TB exposure and were BCG vaccinated; and 3 (n = 26), at low risk for TB, not BCG vaccinated, but previously had a positive TST result. Positive results were as follows: group 1: TST, 3 (3.7%); QFT, 9 (11.1%); and QFT-G, 0 (0.0%); group 2: TST, 26 (86.7%); QFT, 15 (50.0%); and QFT-G, 5 (16.7%); and group 3: TST, 26 (100.0%); QFT, 13 (50.0%); and QFT-G, 9 (34.6%). The QFT-G demonstrated less cross-reactivity with BCG antigen and was more specific than QFT and TST in low-risk individuals.