TST-positive Individuals Research Articles

The Risk of False-Positive Serological Results for Paratuberculosis in Mycobacterium bovis-Infected Cattle.

Both bovine tuberculosis (BTB) and paratuberculosis (paraTB) continue to cause significant economic losses in cattle breeding; in addition, their etiological agents have zoonotic potential. Although the diagnostics of both diseases are still being improved, problems still remain, such as the potential for cross-reactivity to the antigens used in tests. The aim of the present study was to confirm whether animals known to harbor Mycobacterium bovis antibodies are at increased risk of yielding positive results in paraTB serotesting and, additionally, to verify the accuracy of three commonly used methods for confirming M. bovis infection: ELISA, the tuberculin skin test (TST), and the presence of gross lesions. Material was collected from 98 dairy cattle suspected of BTB due to TST-positive results. During postmortem examination, gross lesions were assessed visually. Blood, lymph nodes, and TB-suspected organs were collected. Serum was obtained from the collected blood and tested serologically for TB and paraTB. The tissues underwent standard microbiological testing for M. tuberculosis complex. Among the 98 TST-positive individuals, tuberculous gross lesions were detected in 57 (58.1%), MTBC were isolated in 83 (84.7%), and the ELISA test was positive for 21 (21.4%). None of the lesions characteristic for paraTB were detected. The chance of obtaining a positive TB result by ELISA was seven times higher using the ELISA-paraTB method; hence, there is a significant risk of obtaining false-positive serological results for paraTB in M. bovis-infected cattle. However, the hypothesis that infection of M. bovis or prior TST performance may have boosted the host immune response and therefore increased the sensitivity of the paraTB-ELISA cannot be excluded.

Expression of USP18 and IL2RA Is Increased in Individuals Receiving Latent Tuberculosis Treatment with Isoniazid.

Background The treatment of latent tuberculosis infection (LTBI) in individuals at risk of reactivation is essential for tuberculosis control. However, blood biomarkers associated with LTBI treatment have not been identified. Methods Blood samples from tuberculin skin test (TST) reactive individuals were collected before and after one and six months of isoniazid (INH) therapy. Peripheral mononuclear cells (PBMC) were isolated, and an in-house interferon-γ release assay (IGRA) was performed. Expression of chemokine ligand 4 (CCL4), chemokine ligand 10 (CXCL10), chemokine ligand 11 (CXCL11), interferon alpha (IFNA), radical S-adenosyl methionine domain-containing 2 (RSAD2), ubiquitin-specific peptidase 18 (USP18), interferon-induced protein 44 (IFI44), interferon-induced protein 44 like (IFI44L), interferon-induced protein tetratricopeptide repeats 1(IFIT1), and interleukin 2 receptor subunit alpha (IL2RA) mRNA levels were assessed by qPCR before, during, and after INH treatment. Results We observed significantly lower relative abundances of USP18, IFI44L, IFNA, and IL2RA transcripts in PBMC from IGRA-positive individuals compared to levels in IGRA-negative individuals before INH therapy. Also, relative abundance of CXCL11 was significantly lower in IGRA-positive than in IGRA-negative individuals before and after one month of INH therapy. However, the relative abundance of CCL4, CXCL10, and CXCL11 mRNA was significantly decreased and that of IL2RA and USP18 significantly increased after INH therapy, regardless of the IGRA result. Our results show that USP18, IFI44L, IFIT1, and IL2RA relative abundances increased significantly, meanwhile the relative abundance of CCL4, CXCL11, and IFNA decreased significantly after six months of INH therapy in TST-positive individuals. Conclusions Changes in the profiles of USP18, IL2RA, IFNA, CCL4, and CXCL11 expressions during INH treatment in TST-positive individuals, regardless of IGRA status, are potential tools for monitoring latent tuberculosis treatment.

Immunoscreening of the M. tuberculosis F15/LAM4/KZN secretome library against TB patients′ sera identifies unique active- and latent-TB specific biomarkers

Tuberculosis (TB) protein biomarkers are urgently needed for the development of point-of-care diagnostics, new drugs and vaccines. Mycobacterium tuberculosis extracellular and secreted proteins play an important role in host-pathogen interactions. Antibodies produced against M. tuberculosis proteins before the onset of clinical symptoms can be used in proteomic studies to identify their target proteins. In this study, M. tuberculosis F15/LAM4/KZN strain phage secretome library was screened against immobilized polyclonal sera from active TB patients (n = 20), TST positive individuals (n = 15) and M. tuberculosis uninfected individuals (n = 20) to select and identify proteins recognized by patients′ antibodies. DNA sequence analysis from randomly selected latent TB and active TB specific phage clones revealed 118 and 96 ORFs, respectively. Proteins essential for growth, virulence and metabolic pathways were identified using different TB databases. The identified active TB specific biomarkers included five proteins, namely, TrpG, Alr, TreY, BfrA and EspR, with no human homologs, whilst latent TB specific biomarkers included NarG, PonA1, PonA2 and HspR. Future studies will assess potential applications of identified protein biomarkers as TB drug or vaccine candidates/targets and diagnostic markers with the ability to discriminate LTBI from active TB.

CD14-159C/T polymorphism in the development of delayed skin hypersensitivity to tuberculin.

The skin tuberculin test (TST), an example of a delayed-type hypersensitivity (DTH) reaction, is based on measuring the extent of skin induration to mycobacterial tuberculin (PPD). Little is known about the genetic basis of TST reactivity, widely used for diagnosing TB infection. The study investigated the relationship of the single base change polymorphic variants in CD14 gene (CD14(-159C/T)) with the development of DTH to PPD in BCG-vaccinated Polish Caucasian individuals. We found persistent lack of TST reactivity in about 40% of healthy subjects despite receiving more than one dose of BCG. The TST size was negatively correlated with the number of BCG inoculations. The distribution of C/T genotype was significantly more frequent among TST-negative compared with TST-positive individuals. The concentration of serum sCD14 was positively associated with mCD14 expression, but not with the TST status or CD14(-159C/T) polymorphism. A significant increase in mCD14 expression and serum sCD14 levels was found in TB group. We hypothesize that CD14(-159C/T) polymorphic variants might be one of genetic components in the response to attenuated M. bovis BCG bacilli.

Prevalence of latent tuberculosis infection in healthcare workers at a hospital in Naples, Italy, a low-incidence country.

BackgroundHealthcare workers (HCWs) are at higher risk than the general population of contracting tuberculosis (TB). Moreover, although subjects with latent TB infection (LTBI) are asymptomatic and are not infectious, they may eventually develop active disease. Thus, a fundamental tool of TB control programs for HCWs is the screening and treatment of LTBI.MethodsFrom January 2014 to January 2015, hospital personnel at Azienda Ospedaliera Universitaria, Naples, Italy, were screened for TB. To this end, a tuberculin skin test (TST) was administered as an initial examination, unless when contraindicated, in which case the QuantiFERON® TB-Gold (QFT) assay was performed. Moreover, QFT was carried out on all TST-positive cases to confirm the initial result.ResultsOf 628 personnel asked to participate, 28 (4.5%) denied consent, 533 were administered TST as the baseline examination, and 67 were tested only with QFT. In the TST group, 73 (13.2%) individuals were found positive, 418 (78.4%) were negative, and 42 (7.9%) were absent for the reading window; QFT confirmed the result in 39 (53.4%) TST-positive individuals. In the QFT-only group, 44 (65.7%) individuals were found positive. All TST- and/or QFT-positive subjects were referred for chest X-ray and examination by an infectious diseases specialist. None were found to have active TB, and were thus diagnosed with LTBI.ConclusionsAlthough Italy is a low-incidence country regarding TB, our findings suggest that the prevalence of LTBI in HCWs may be relatively high. As a result, active screening for TB and LTBI is needed for these workers.Electronic supplementary materialThe online version of this article (doi:10.1186/s12995-016-0141-6) contains supplementary material, which is available to authorized users.

Relating Tuberculosis (TB) Contact Characteristics to QuantiFERON-TB-Gold and Tuberculin Skin Test Results in the Toronto Pediatric TB Clinic.

Few data relate interferon-γ-release-assay results in children to source case sputum status, the best predictor of infectiousness of tuberculosis (TB) patients. We evaluated the QuantiFERON-Gold-in-tube assay (QFT) and tuberculin skin test (TST) in children with different types of TB exposure. The TST and QFT were performed in referred TB-exposed children and adolescents who had not undergone prior TST screening (tested in parallel), and the QFT was performed in referred TST-positive individuals. Source case characteristics were obtained from referring public health units. We excluded children with known immunocompromising conditions and those known to have TB disease at the time of evaluation. For 103 patients tested in parallel, overall test agreement was very good in the Bacillus Calmette-Guerein (BCG) unimmunized contacts (κ = 0.83) and contacts of household smear-positive (HS+) cases (κ = 0.67), but test agreement was poor in those with lower-risk contact (κ = 0.34). Only 3 of 59 HS+ patients were QFT-positive and TST-negative. On multivariate analysis, a positive QFT was strongly associated with HS+ exposure (odds ratio [OR], 6.6; 95% confidence interval [CI], 2.2-20]) but not BCG; and a positive TST was associated with BCG alone. For 92 referred TST-positive individuals, the QFT was negative in 21% of HS+ contacts, 65% of lower-risk contacts (OR, 6.8; 95% CI, 1.9-25), and 82% of the patients with unknown contact history (OR, 15.5; 95% CI, 5-54). Application of the Canadian 2010 guidelines would exclude from treatment 43 (72%) of the 73 TST+, QFT- patients. For close contacts of HS+ individuals, the QFT added little sensitivity to the TST for detection of TB infection. The QFT correlated much better with exposure than the TST, especially in BCG-immunized children, and it has the greatest potential benefit for evaluation of those at lower risk of latent TB infection.

Eliminating tuberculosis one neighborhood at a time.

We evaluated a strategy for preventing tuberculosis (TB) in communities most affected by it. In 1996, we mapped reported TB cases (1985-1995) and positive tuberculin skin test (TST) reactors (1993-1995) in Smith County, Texas. We delineated the 2 largest, densest clusters, identifying 2 highest-incidence neighborhoods (180 square blocks, 3153 residents). After extensive community preparation, trained health care workers went door-to-door offering TST to all residents unless contraindicated. TST-positive individuals were escorted to a mobile clinic for radiography, clinical evaluation, and isoniazid preventive treatment (IPT) as indicated. To assess long-term impact, we mapped all TB cases in Smith County during the equivalent time period after the project. Of 2258 eligible individuals, 1291 (57.1%) were tested, 229 (17.7%) were TST positive, and 147 were treated. From 1996 to 2006, there were no TB cases in either project neighborhood, in contrast with the preintervention decade and the continued occurrence of TB in the rest of Smith County. Targeting high-incidence neighborhoods for active, community-based screening and IPT may hasten TB elimination in the United States.

Eliminating Tuberculosis One Neighborhood at a Time

We evaluated a strategy for preventing tuberculosis (TB) in communities most affected by it. In 1996, we mapped reported TB cases (1985-1995) and positive tuberculin skin test (TST) reactors (1993-1995) in Smith County, Texas. We delineated the 2 largest, densest clusters, identifying 2 highest-incidence neighborhoods (180 square blocks, 3153 residents). After extensive community preparation, trained health care workers went door-to-door offering TST to all residents unless contraindicated. TST-positive individuals were escorted to a mobile clinic for radiography, clinical evaluation, and isoniazid preventive treatment (IPT) as indicated. To assess long-term impact, we mapped all TB cases in Smith County during the equivalent time period after the project. Of 2258 eligible individuals, 1291 (57.1%) were tested, 229 (17.7%) were TST positive, and 147 were treated. From 1996 to 2006, there were no TB cases in either project neighborhood, in contrast with the preintervention decade and the continued occurrence of TB in the rest of Smith County. Targeting high-incidence neighborhoods for active, community-based screening and IPT may hasten TB elimination in the United States.

QuantiFERON-TB gold in-tube implementation for latent tuberculosis diagnosis in a public health clinic: a cost-effectiveness analysis

BackgroundThe tuberculin skin test (TST) has limitations for latent tuberculosis infection (LTBI) diagnosis in low-prevalence settings. Previously, all TST-positive individuals referred from the community to Baltimore City Health Department (BCHD) were offered LTBI treatment, after active TB was excluded. In 2010, BCHD introduced adjunctive QuantiFERON-TB Gold In-Tube (QFT-GIT) testing for TST-positive referrals. We evaluated costs and cost-effectiveness of this new diagnostic algorithm.MethodsA decision-analysis model compared the strategy of treating all TST-positive referrals versus only those with positive results on adjunctive QFT-GIT testing. Costs were collected at BCHD, and Incremental Cost-Effectiveness Ratios (ICERs) were utilized to report on cost-effectiveness.ResultsQFT-GIT testing at BCHD cost $43.51 per test. Implementation of QFT-GIT testing was associated with an ICER of $1,202 per quality-adjusted life-year gained and was considered highly cost-effective. In sensitivity analysis, the QFT-GIT strategy became cost-saving if QFT-GIT sensitivity increased above 92% or if less than 3.5% of individuals with LTBI progress to active TB disease.ConclusionsLTBI screening with TST in low-prevalence settings may lead to overtreatment and increased expenditures. In this public health clinic, additional QFT-GIT testing of individuals referred for a positive TST was cost-effective.

Short-course untargeted isoniazid preventive therapy in South Africa: time to rethink policy? [Editorial

South Africa has the worst HIV-associated tuberculosis (TB) epidemic in the world with 300,000 cases each year. Previous national TB control policies have failed, confirming the fact that we cannot treat our way out of this epidemic using TB case management alone. Implementation of preventive interventions is therefore imperative and these include antiretroviral therapy (ART) and isoniazid preventive therapy (IPT). Whereas ART has been scaled up rapidly in much of sub-Saharan Africa, implementation of IPT has in contrast been very poor. Recognising that the process of tuberculin skin testing (TST) was a stumbling block to implementation of IPT, the World Health Organization (WHO) in 2011 revised the IPT guidelines and made a strong explicit recommendation that “TST is not a requirement for initiating IPT in people living with HIV” although it “can be used where feasible”.1Eliminating the need for assessment of TST status may be an important factor underlying recent gains in implementation. In line with WHO policy, South Africa revised national IPT policy in 2010 2 and in this issue of the journal, Bristow and colleagues report on the impressive gains in numbers of HIV-infected patients being started on IPT in South Africa over the subsequent year.3 In a country where service delivery often falls well short of desired levels, this is highly commendable. However, as the authors clearly point out, their analysis simply presents numbers of patients started on IPT but not the numbers completing treatment or the benefit derived. Two key features of the current South African policy may greatly limit the impact of scale-up, namely the lack of targeting of IPT and the use of courses of relatively short duration. While IPT benefits those who are TST-positive, there is strong evidence from a meta-analysis of controlled trials that included 2,490 patients with negative or anergic TST reactions that these patients derive no significant benefit from IPT.4 While eliminating the need for TST assessment simplifies implementation of IPT, the downside is that the intervention no longer targets the minority of patients who stand to gain benefit. Thus, large numbers of patients are treated needlessly, undermining cost-effectiveness. Moreover, a small proportion of those unlikely to benefit might actually be harmed. In neighbouring Botswana, just 24.4% of 1,891 HIV-infected patients assessed for IPT were TST-positive and 5 and untargeted therapy would therefore potentially benefit just 1 in every 4 patients treated. The South African guidelines recommend that IPT should be given for 6 months either continuously or over a 9 month period.2 However, increasing data from carefully conducted trials show that the duration of benefit is largely limited to the actual period of treatment.5,6,7 Once treatment has stopped, TB risk rapidly increases again. The likely explanation for this is that the prevailing force of Mycobacterium tuberculosis infection in South Africa and neighbouring countries is extremely high. Even when administered as mass treatment to whole working communities associated with the South African mines, short-course IPT had no impact on TB incidence or prevalence.8 As Nardell and Churchyard rightly stated, unless the force of transmission can be reduced, durable benefits from prevention strategies are likely to be elusive.9 Life expectancy of people living with HIV-infection may now be extended for many decades by ART and so a 6-month course of IPT is likely to have minimal impact on lifetime TB risk. Growing evidence therefore suggests that if IPT is used, to do so on a long-term basis would be a more rational approach.5 This option is included in the WHO guidelines.1 A shift in policy towards long-term or even life-long therapy, however, would provide an even stronger rationale for targeting IPT according to TST status. Indeed, targeted provision of IPT for 36 months to TST-positive individuals in Botswana has been found to be more cost-effective than providing IPT without TST assessment or providing IPT for 6 months only.10 In conclusion, the current rapid scale-up of IPT in South Africa under national guidelines reported by Bristow and colleagues is not being targeted in patients who will benefit and is being given for too short a duration that will not provide durable prevention. This policy is inefficient use of scarce health-care resources. Current scientific evidence suggests that if this intervention is to be appropriately tailored to the local epidemiological situation, it should be given to patients who are confirmed to be TST positive and on a long-term basis.

Predictive value of interferon-γ release assays for incident active tuberculosis: a systematic review and meta-analysis.

We aimed to assess whether interferon-γ release assays (IGRAs) can predict the development of active tuberculosis and whether the predictive ability of these tests is better than that of the tuberculin skin test (TST). Longitudinal studies of the predictive value for active tuberculosis of in-house or commercial IGRAs were identified through searches of PubMed, Embase, Biosis, and Web of Science and complementary manual searches up to June 30, 2011. Eligible studies included adults or children, with or without HIV, who were free of active tuberculosis at study baseline. We summarised incidence rates in forest plots and pooled data with random-effects models when appropriate. We calculated incidence rate ratios (IRR) for rates of disease progression in IGRA-positive versus IGRA-negative individuals. 15 studies had a combined sample size of 26 680 participants. Incidence of tuberculosis during a median follow-up of 4 years (IQR 2-6), even in IGRA-positive individuals, was 4-48 cases per 1000 person-years. Seven studies with no possibility of incorporation bias and reporting baseline stratification on the basis of IGRA results showed a moderate association between positive results and subsequent tuberculosis (pooled unadjusted IRR 2·10, 95% CI 1·42-3·08). Compared with test-negative results, IGRA-positive and TST-positive results were much the same with regard to the risk of tuberculosis (pooled IRR in the five studies that used both was 2·11 [95% CI 1·29-3·46] for IGRA vs 1·60 [0·94-2·72] for TST at the 10 mm cutoff). However, the proportion of IGRA-positive individuals in seven of 11 studies that assessed both IGRAs and TST was generally lower than TST-positive individuals. Neither IGRAs nor the TST have high accuracy for the prediction of active tuberculosis, although use of IGRAs in some populations might reduce the number of people considered for preventive treatment. Until more predictive biomarkers are identified, existing tests for latent tuberculosis infection should be chosen on the basis of relative specificity in different populations, logistics, cost, and patients' preferences rather than on predictive ability alone. Special Programme for Research and Training in Tropical Diseases (WHO), Wellcome Trust, Canadian Institutes of Health Research, UK Medical Research Council, and the European and Developing Countries Clinical Trials Partnership.

Regulatory T Cells Modulate Th17 Responses in Patients with Positive Tuberculin Skin Test Results

The factors governing latency in tuberculosis are not well understood but appear to involve both the pathogen and the host. We have used tuberculin skin test (TST) positivity as a tool to study cytokine responses in latent tuberculosis. To identify the host factors that are important in the maintenance of TST positivity, we examined mycobacteria-specific immune responses of TST-positive (latent tuberculosis) or TST-negative individuals in South India, where TST positivity can define tuberculosis latency. Although purified protein derivative-specific and Mycobacterium tuberculosis culture filtrate antigen-specific Th1 and Th2 cytokines were not statistically significantly different between the 2 groups, the Th17 cytokines (interleukin 17 and interleukin 23) were statistically significantly decreased in TST-positive individuals, compared with those in TST-negative individuals. This Th17 cytokine modulation was associated with statistically significantly increased expression of cytotoxic T lymphocyte antigen 4 (CTLA-4) and Foxp3. Although CTLA-4 blockade failed to restore full production of interleukin 17 and interleukin 23 in TST-positive individuals, depletion of regulatory T cells significantly increased production of these cytokines. TST positivity is characterized by increased activity of regulatory T cells and a coincident down-regulation of the Th17 response.

Interferon Gamma Response to Combinations 38 kDa/CFP‐10, 38 kDa/MPT‐64, ESAT‐6/MPT‐64 and ESAT‐6/CFP‐10, Each Related to a Single Recombinant Protein of Mycobacterium tuberculosis in Individuals from Tuberculosis Endemic Areas

Several antigens of Mycobacterium tuberculosis have been identified and specificity to one or multiple antigens could determine the distinction between protective and pathogenic host reaction. Therefore T cell immune response to combinations 38 kDa/CFP-10, 38 kDa/MPT-64, ESAT-6/MPT-64 and ESAT-6/CFP-10 (each related to a single protein of Mycobacterium tuberculosis) in individuals from tuberculosis endemic areas have been examined. ELISA was used to detect IFN-gamma production in PBMC priming with single proteins and combinations in a panel of 105 individuals: 38 tuberculosis patients (6 untreated and 32 treated) and 67 healthy controls with tuberculin skin test positive or negative (TST). Brazilian TB patients highly recognized ESAT-6 (66%), but combinations improved response in the following order: ESAT-6/MPT-64 (89%) > ESAT-6/CFP-10 (73%) > 38 kDa/CFP-10 (70%), the last combination showing the highest specificity (TST(/) = 42% and TST(-) = 83%). Average IFN-gamma production in TB patients was signifi-cantly higher for 38 kDa/CFP-10 (P = 0.012) and 38 kDa/MPT-64 (P <0.035), when compared to single antigens. None of the combinations was able to discriminate TB patients from TST(+) controls; however, 38 kDa/CFP-10 displayed a borderline significance (P = 0.053). Similar to the ESAT-6/CFP-10 combination, IFN-gamma response to 38 kDa/CFP-10 showed an increased tendency in treated patients, although not signifi-cant (P = 0.16). We demonstrated for the first time that 38 kDa/CFP-10 had prediction sensitivity for TB patients similar to the ESAT-6/CFP-10 combination and also significant response improvement related to the single proteins with more selective reactivity among TST-positive individuals, which could be of potential interest for diagnostic evaluation for tuberculosis infection.

Tuberculosis active case-finding in a mother-to-child HIV transmission prevention programme in Soweto, South Africa.

HIV markedly increases the risk of tuberculosis. We implemented active tuberculosis case-finding in a prevention of mother-to-child transmission programme in South Africa. Of 438 tuberculin-tested HIV-infected patients, 49% had a reaction ≥ 5 mm induration, 120 underwent further evaluation for active disease. The prevalence of active tuberculosis was 11%, a high rate of tuberculosis in this population, and underscores the need for tuberculosis active case-finding to prevent mortality and transmission, and preventive therapy for latent tuberculosis infection.

LOW PREVALENCE AND INCREASED HOUSEHOLD CLUSTERING OF MYCOBACTERIUM TUBERCULOSIS INFECTION IN HIGH ALTITUDE VILLAGES IN PERU

Anecdotal historical evidence suggests that tuberculosis was uncommon at high altitude, but whether transmission is affected by high altitude is not known. To test whether high altitude lowers infection by Mycobacterium tuberculosis, the prevalence of tuberculin skin test (TST) positivity was compared between two high altitude villages (3,340 meters [10,960 feet] and 3,500 meters [11,480 feet]) and three sea-level sites in Peru. High altitude villages had lower TST-positive prevalence rates (5.7% and 6.8%) than sea level areas (25-33%), and the difference remained significant (odds ratio = 4.5-6.0) after adjusting for age, education, bacille Calmette-Guerin vaccination, and contact with tuberculosis patients. The TST-positive individuals clustered within highland families more than within sea level families. These data suggest that prevention and control efforts targeted to families may be more effective at high altitude. The mechanism by which TST-positivity prevalence is decreased at high altitude is unknown, but may reflect relative hypoxia, low humidity, or an increased ultraviolet effect.