Evaluation of the T-SPOT(RTM).TB test in the diagnosis of latent tuberculosis infection in HIV-infected children in Uganda

Background. About a third of the world’s population is infected with tuberculosis (TB) with sub-Saharan Africa being the worst hit. Uganda is ranked 16th among the countries with the biggest TB burden. The burden in children however has not been determined. The burden of TB has been worsened by the advent of HIV and TB is the leading cause of mortality in HIV infected individuals. Development of TB disease can be prevented if TB is diagnosed during its latent stage and treated with isoniazid. For over a century, latent TB infection (LTBI) was diagnosed using the Tuberculin Skin Test (TST). New interferon gamma release assays (IGRA) have been approved by FDA for the diagnosis of LTBI and adult studies have shown that IGRAs are superior to the TST but there have been few studies in children especially in areas of high TB and HIV endemicity. ^ Objective. The objective of this study was to examine whether the IGRAs had a role in LTBI diagnosis in HIV infected children in Uganda. ^ Methods. Three hundred and eighty one (381) children were recruited at the Baylor College of Medicine-Bristol Meyers Squibb Children’s Clinical Center of Excellence at Mulago Hospital, Kampala, Uganda between March and August 2010. All the children were subjected to a TST and T-SPOT ®.TB test which was the IGRA chosen for this study. Sputum examination and chest x-rays were also done to rule out active TB. ^ Results. There was no statistically significant difference between the tests. The agreement between the two assays was 95.9% and the kappa statistic was 0.7 (95% CI: 0.55–0.85, p-value<0.05) indicating a substantial or good agreement. The TST was associated with older age and higher weight for age z-scores but the T-SPOT®. TB was not. Both tests were associated with history of taking anti-retroviral therapy (ART). ^ Conclusion. Before promoting use of IGRAs in children living in HIV/TB endemic countries, more research needs to be done. ^

Interferon-gamma release assays for latent tuberculosis infection in child and young adult candidates or recipients of tumor necrosis factor inhibitor therapy

Background. Inhibition of tumor necrosis factor (TNF) is associated with progression of latent tuberculosis infection (LTBI) to active disease. LTBI screening prior to starting TNF inhibitor therapy is recommended. Blood tests, collectively known as interferon-gamma release assays (IGRAs), offer a means other than the tuberculin skin test (TST) of screening for LTBI. However, in the setting of immune compromise, anergy may limit the clinical utility of IGRAs. ^ Methods. A cross-sectional study was conducted in children and young adults ≤ 21 years of age who were cared for at Texas Children's Hospital in Houston, TX, during 2011 and who were candidates for, or were receiving, tumor necrosis factor (TNF)-inhibitor therapy. All subjects answered a risk factor questionnaire and were tested for LTBI by two commercially available IGRAs (QuantiFERON-Gold In-Tube assay and the T-SPOT.TB assay), along with the TST. T-cell phenotypes were evaluated through flow cytometry, both at baseline and after antigen stimulation. ^ Results. Twenty-eight subjects were enrolled. All were TST negative and none were IGRA positive. Results were negative for the 27 subjects who were tested with QuantiFERON-Gold In-Tube. However, 26% of subjects demonstrated anergy in the T-SPOT.T. Patients with T-SPOT. TB anergy had lower quantitative IFN-γ responses to mitogen in the QFT assay—the mean IFN-γ level to mitogen in patients without T-SPOT.TB anergy was 9.84 IU/ml compared to 6.91 IU/ml in patients with T-SPOT.TB anergy (P = 0.046). Age and use of TNF inhibitors, corticosteroids, or methotrexate use were not significantly associated with T-SPOT.TB anergy. Antigen stimulation revealed depressed expression of intracellular IFN-γ in subjects with T-SPOT. TB anergy. ^ Conclusions. The frequency of anergy in this population is higher than would be expected from studies in adults. There appears to be inappropriate IFN-γ responses to antigen in subjects with T-SPOT. TB anergy. This immune defect was detected by the T-SPOT. TB assay but not by the QuantiFERON-Gold In-Tube assay. Further data are needed to clarify the utility of IGRAs in this population.^

Economic evaluation of latent tuberculosis infection screening among health care workers in Houston

Since interferon-gamma release assays (IGRAs) were introduced in the 2000's, tuberculin skin testing (TST) and IGRAs have been used in various latent tuberculosis infection (LTBI) screening settings. IGRAs are laboratory-based tests and are considered not to be affected by previous Bacille de Calmette et Guérin (BCG) vaccination; however, they are more costly when compared directly with TST, which does not require specimen processing in a laboratory. This study aimed to examine TST and two types of IGRAs, QuantiFERON-TB Gold in Tube (QFT-GIT) and T-SPOT. TB (TSPOT), from an economic viewpoint. Firstly, a systematic literature review was conducted to identify cost related analyses of LTBI screening. Secondly, specific cost information detailing each test's items and labor was collected from an LTBI screening program of health care workers in Houston, and the cost of each test was computed. Thirdly, using the computed cost estimate of each test, cost-effectiveness analyses were conducted to compare TST and IGRAs.^ A literature search showed that a limited number of studies have been conducted, but the IGRA's economic advantages were common among studies. Cost analyses showed that IGRAs were much more costly than TST. The results were consistent with previous studies. In cost-effectiveness analyses, where test cost and consequential TB-related cost were considered, IGRAs showed variable advantages over TST depending on the targeted population. When only non BCG-vaccinated people were considered, TST was the least costly option among the three tests. On the other hand, when only BCG-vaccinated people were considered, IGRAs were less costly options. These results were mostly consistent even with varying assumption parameters.^ IGRAs can be more costly than TST, but their economic disadvantages are alleviated when the target population was BCG-vaccinated. Based on current knowledge, IGRAs may be recommended in a population where the BCG history is mixed. Additional studies are needed to better understand IGRA's reliability among low-incidence and low-risk populations in which background TB prevalence is low.^

School screening for tuberculosis in high risk areas of Texas

Screening for latent tuberculosis infection (LTBI) is an integral component of an effective tuberculosis control strategy, but one that is often relegated to the lowest priority. In a state with higher than national average rates of tuberculosis, due consideration should be given to LTBI screening. Recent large scale contact investigations in the middle school of Del Rio, Texas, raised questions about the status of school screening for LTBI. An evidence based approach was used to evaluate school screening in high risk areas of Texas. A review of the literature revealed that the current recommendations for LTBI screening in children is based on administration of a risk factor questionnaire that should be based on the four main risk factors for LTBI in children that have been identified. Six representative areas in Texas were identified for evaluation of the occurrence of contact investigations in schools for the period of 2006 to 2009 and any use of school screening programs. Of the five reporting areas that responded, only one utilized a school screening program; this reporting area had the lowest percentage of contact investigations occurring in schools. Contact investigations were most common in middle schools and least common in elementary schools. In metropolitan areas, colleges represented up to 42.9% of contact investigations. The number of contact investigations has increased from 2006 to 2008. This report represents a small sample, and further research into the frequency, distribution and risk for contact investigations in schools and the efficacy of screening programs should be done. ^

Indeterminate QunatiFERON-TB Gold In-Tube assay results in association with procedural specimen collection in children

BACKGROUND. The development of interferon-gamma release assays (IGRA) has introduced powerful tools in diagnosing latent tuberculosis infection (LTBI) and may play a critical role in the future of tuberculosis diagnosis. However, there have been reports of high indeterminate results in young patient populations (0-18 years). This study investigated results of the QunatiFERON-TB Gold In-Tube (QFT-GIT) IGRA in a population of children (0-18 years) at Texas Children's Hospital in association with specimen collection procedures using surrogate variables. ^ METHODS. A retrospective case-control study design was used for this investigation. Cases were defined as having QFT-GIT indeterminate results. Controls were defined as having either positive or negative results (determinates). Patients' admission status, staff performing specimen collection, and specific nurse performing specimen collection were used as surrogates to measure specimen collection procedures. ^ To minimize potential confounding, abstraction of patients' electronic medical records was performed. Abstracted data included patients' medications and evaluation at the time of QFT-GIT specimen collection in addition to their medical history. QFT-GIT related data was also abstracted. Cases and controls were characterized using chi-squared tests or Fisher's exact tests across categorical variables. Continuous variables were analyzed using one-way ANOVA and t-tests for continuous variables. A multivariate model was constructed by backward stepwise removal of statistically significant variables from univariate analysis. ^ RESULTS. Patient data was abstracted from 182 individuals aged 0-18 years from July 2010 to August 2011 at Texas Children's Hospital. 56 cases (indeterminates) and 126 controls (determinates) were enrolled. Cancer was found to be an effect modifier with subsequent stratification resulting in a cancer patient population too small to analyze (n=13). Subsequent analyses excluded these patients. ^ The exclusion of cancer patients resulted in a population of 169 patients with 49 indeterminates (28.99%) and 120 determinates (71.01%), with mean ages of 9.73 (95% CI: 8.03, 11.43) years and 11.66 (95% CI: 10.75, 12.56) years (p = 0.033), respectively. Median age of patients who were indeterminates and determinates were 12.37 and 12.87 years, respectively. Lack of data for our specific nurse surrogate (QFTNurse) resulted in its exclusion from analysis. The final model included only our remaining surrogate variables (QFTStaff and QFTInpatientOutpatient). The staff collecting surrogate (QFTStaff) was found to be modestly associated with indeterminates when nurses collected the specimen (OR = 1.54, 95% CI: 0.51, 4.64, p = 0.439) in the final model. Inpatients were found to have a strong and statistically significant association with indeterminates (OR = 11.65, 95% CI: 3.89, 34.9, p < 0.001) in the final model. ^ CONCLUSION. Inpatient status was used as a surrogate for indication of nurse drawn blood specimens. Nurses have had little to no training regarding shaking of tubes versus phlebotomists regarding QFT-GIT testing procedures. This was also measured by two other surrogates; specifically a medical note stating whether a nurse or phlebotomist collected the specimen (QFTStaff) and the name and title of the specific nurse if collection was performed by a nurse (QFTNurse). Results indicated that inpatient status was a strong and statistically significant factor for indeterminates, however, nurse collected specimens and indeterminate results had no statistically significant association in non-cancer patients. The lack of data denoting the specific nurse performing specimen collection excluded the QFTNurse surrogate in our analysis. ^ Findings suggests training of staff personnel in specimen procedures may have little effect on the number of indeterminates while inpatient status and thus possibly illness severity may be the most important factor for indeterminate results in this population. The lack of congruence between our surrogate measures may imply that our inpatient surrogate gauged illness severity rather than collection procedures as intended. ^ Despite the lack of clear findings, our analysis indicated that more than half of indeterminates were found in specimens drawn by nurses and as such staff training may be explored. Future studies may explore methods in measuring modifiable variables during pre-analytical QFT-GIT procedures that can be discerned and controlled. Identification of such measures may provide insight into ways to lowering indeterminate QFT-GIT rates in children.^

Epstein-Barr virus infection of Langerhans cell precursors as a mechanism of oral epithelial entry, persistence, and reactivation.

Epstein-Barr virus (EBV) is a ubiquitous human herpesvirus associated with many malignant and nonmalignant human diseases. Life-long latent EBV persistence occurs in blood-borne B lymphocytes, while EBV intermittently productively replicates in mucosal epithelia. Although several models have previously been proposed, the mechanism of EBV transition between these two reservoirs of infection has not been determined. In this study, we present the first evidence demonstrating that EBV latently infects a unique subset of blood-borne mononuclear cells that are direct precursors to Langerhans cells and that EBV both latently and productively infects oral epithelium-resident cells that are likely Langerhans cells. These data form the basis of a proposed new model of EBV transition from blood to oral epithelium in which EBV-infected Langerhans cell precursors serve to transport EBV to the oral epithelium as they migrate and differentiate into oral Langerhans cells. This new model contributes fresh insight into the natural history of EBV infection and the pathogenesis of EBV-associated epithelial disease.

Exploring the role of viral infection in type 2 diabetes

Viral infection is known to play a role in type I diabetes, but there is a paucity of information on the role of viruses in type 2 diabetes. This research examined the seroprevalence of selected viruses in a group of predominantly Mexican-American patients with End Stage Renal Disease (ESRD). Using a case control design, patients with type 2 diabetes were compared with a group of non-diabetic controls. ^ One hundred and thirteen patients, 83 with type 2 diabetes and 30 controls without diabetes, underwent hemodialysis at the same chronic dialysis facility in San Antonio, Texas. AD subjects were tested for IgG, IgM, and neutralizing antibodies against Coxsackie B viruses (CBV), and IgG and IgM antibodies against cytomegalovirus (CMV) and parvovirus B19 (PVB19). Hepatitis B virus antigen (HBVAg), Hepatitis B virus antibody (HBVAb), Hepatitis C virus antibody (HCVAb), and Rubella (IgG) were also measured. A subset of 91 patients, 66 with diabetes and 25 controls, were tested bimonthly for six months. There was a significant difference (P = 0.04) in the seroprevalence of IgG antibodies to CMV between patients with type 2 diabetes (98%) and non-diabetic controls (87%) in the initial sample (OR = 6.2, 95% CI:1.1–36.0). A greater seroprevalence of CMV IgG antibodies was observed over the six month period among patients with type 2 diabetes (M) compared to controls (84%). This difference was also statistically (P < 0.03), with a greater odds ratio (OR = 12.4, 95% CI: 1.3–116.9), but with larger confidence interval related to the small number of subjects. However, when adjusted for age by logistic regression analysis there was no difference between the groups (OR = 1). ^ After one sample, there was a greater seroprevalence of HCVAb in the group without diabetes (28%), compared to those with type 2 diabetes (10%) (P = 0.04). This difference was no longer significant when adjusted for patient age. The prevalence of antibodies to PVB19, HBSAg, HBV, and Rubella was not significantly different in patients with type 2 diabetes and controls. There were significantly more vascular complications (P < 0.02) among patients with diabetes. ^ These results indicate that the significant associations observed in this population between viral infection with CMV, HCV, and type 2 diabetes are confounded by age. Accelerated atherosclerosis has been associated with age, diabetes, as well as CMV. Latent infection may be a factor that links these processes. ^