Impact of targeted testing for latent tuberculosis infection using commercially available diagnostics

Latent tuberculosis infection prevalence in second generation immigrants from high to low TB burden countries

BACKGROUND

Latent tuberculosis infection (LTBI) diagnosis in a country with a low tuberculosis burden is complicated. Since the prevalence of LTBI in second generation immigrants has not been well recognized, we conducted a cross-sectional study which aimed to explore the differences in LTBI prevalence between offspring of immigrants from high tuberculosis (TB) burden countries and those whose parents were born in countries with a low TB burden.

METHODS

Between May 2014 and April 2018 young native Israelis who were required to perform pre-occupational tuberculin skin tests (TST) (medical and paramedical personnel or teaching assistants of immigrants from high TB burden countries) and who had a TST result of 10mm and above were tested for QuantiFERON-TB In Tube (QFT-GIT). Statistical comparisons were made between second generation immigrants and those with both parents from a low TB burden country.

RESULTS

Of 102 patients, 71 were born to parents both of whom were from low-risk countries, 14 to one parent from a high-risk country and 17 to parents both of whom were from a high-risk country. The odds ratio for LTBI was 4.5 (95% CI, 1.2...17.2; p=0.03) if both parents were born in a high-risk country compared to both parents being from a low-risk country and 4.01 (95% CI, 1.12...14.3; p=0.03) higher compared to persons for whom at least one parent was born in a low-risk country.

CONCLUSION

The risk for latent TB is significantly higher in second generation immigrants if both parents were born in a high-risk country. IGRA should be considered before treatment to patients with a positive TST if at least one parent was born in a low-risk country in order to confirm LTBI.

Infectious Disease Clinical Research Program: Building the Bench

The role of physicians in the U.S. Armed Forces is diverse, encompassing a wide array of skills and responsibilities to provide superior healthcare to their patients and to advance military medicine. In addition to healthcare delivery and medical education, military physicians are engaged in public health, operational medicine, and cutting-edge medical research. Thus, clinical research is a crucial component of Graduate Medical Education (GME) and supports critical thinking (knowledge, skills, and abilities) and the development of leadership skills among U.S. military physicians. The Infectious Disease Clinical Research Program (IDCRP) education mission was established in 2005 with the overall goal of supporting the development and training of the next generation of clinical researchers in infectious diseases and related public health disciplines in the Armed Forces using several strategies, including didactic learning, mentored research, and research engagement. Through involvement in the IDCRP, infectious disease fellows, residents (e.g., surgical, internal medicine, and pediatrics), and Master of Public Health (MPH) students have continued their education and gained valuable skills related to clinical research. Trainees either conduct research with IDCRP mentors or participate in IDCRP-led practicum experiences, with research projects ranging from epidemiologic studies to microbiological assessments. Consistent with the needs of the Military Health System (MHS), and in accordance with Accreditation Council for Graduate Medical Education goals, the IDCRP provides opportunities for medical and graduate students, residents, and infectious disease fellows to conduct mentored research within the MHS, as well as gain important leadership skills in the conduct of clinical research. Overall, IDCRP continues to further infectious disease research through the support and education of the next generation of active-duty infectious disease researchers in the MHS.

Point of Care Tuberculosis Sero-Diagnosis Kit for Wild Animals: Combination of Proteins for Improving the Diagnostic Sensitivity and Specificity

Tuberculosis is a significant problem globally for domestic animals as well as captive and free ranging wild life. Rapid point of care (POC) serology kits are well suited for the diagnosis of TB in wild animals. However, wild animals are invariably exposed to environmental non-pathogenic mycobacterium species with the development of cross reacting antibodies. In the present study, POC TB diagnosis kit was developed using a combination of pathogenic Mycobacteria specific recombinant antigens and purified protein derivatives of pathogenic and non-pathogenic Mycobacteria. To benchmark the TB antibody detection kit, particularly in respect to specificity which could not be determined in wildlife due to the lack of samples from confirmed uninfected animals, we first tested well-characterized sera from 100 M. bovis infected and 100 uninfected cattle. Then we investigated the kit's performance using sera samples from wildlife, namely Sloth Bears (n = 74), Elephants (n = 9), Cervidae (n = 14), Felidae (n = 21), Cape buffalo (n = 2), Wild bear (n = 1) and Wild dog (n = 1).In cattle, a sensitivity of 81% and a specificity of 90% were obtained. The diagnostic sensitivity of the kit was 94% when the kit was tested using known TB positive sloth bear sera samples. 47.4% of the in-contact sloth bears turned seropositive using the rapid POC TB diagnostic kit. Seropositivity in other wild animals was 25% when the sera samples were tested using the kit. A point of care TB sero-diagnostic kit with the combination of proteins was developed and the kit was validated using the sera samples of wild animals.

Close contact interferon-gamma response to the new PstS1(285-374):CPF10: a preliminary 1-year follow-up study

Background

The available diagnostic tools for latent tuberculosis (TB) infection (LTBI) via interferon-gamma (IFN-g) release assays (IGRA) are based on ESAT6:CFP10 stimulation. However, the mycobacterial antigen PstS1 is also highly immunogenic and some of its fragments, such as PstS1_(285–374), have shown higher immunoreactivity in LTBI than in active TB. PstS1_(285–374), therefore, could increase the accuracy of the existing IGRA to detect LTBI. Thus, a new chimeric protein has recently been developed (PstS1_(285–374):CFP10) showing potential for LTBI screening of recent close contacts (rCt) exposed to Mycobacterium tuberculosis. The aim of this study was to analyze the PstS1_(285–374):CFP10 longitudinal IFN-g profile in comparison to ESAT6:CFP10 and full PstS1/CFP10 stimulation in a rCt cohort and correlate the responses to these in-house IGRA with any clinical changes/interventions that might occur.

Methods

A free-of-cost, one-year follow up was offered to 120 rCt recruited in Rio de Janeiro, RJ, Brazil. Whole blood short-term (WBA), long-term stimulation (LSA) assays, and the tuberculin skin test (TST) were performed during follow up.

Results

Among the enrolled rCt, 44.2% (53/120) returned for re-evaluation and the control group (TST negative, n = 17) showed low IFN-g reactivity to all antigen stimulations during the entire follow up, except for one participant who had shown radiological evidence of past TB/LTBI. Both incident cases were detected by IGRA-PstS1_(285–374):CFP10 during LTBI and after disease progression. Moreover, subsequent to the prophylactic treatment for LTBI (tLTBI), a significant regression in the LSA response was predominantly observed through stimulation of the new chimeric protein (8/10, 80%) followed by ESAT6:CFP10 (5/10, 50%) and PstS1/CFP10 (4/10, 40%). No clinical or epidemiological characteristics were exclusively shared among IGRA convertors.

Conclusion

It was demonstrated that the TST negative rCt without radiological evidence of LTBI/TB did not develop an IGRA-PstS1_(285–374):CFP10 response during the one-year follow up. Moreover, all incident cases were detected by our new IGRA; and a significant decrement of LSA-PstS1_(285–374):CFP10 reactivity post-prophylactic tLTBI was found. To our knowledge, this is the first study to monitor changes in the immune response profile of IGRA-PstS1_(285–374):CFP10 among rCt during a consecutive one-year period, thus providing additional evidence of its potential in the detection of LTBI.

Electronic supplementary material

The online version of this article (doi:10.1186/s13104-016-2360-4) contains supplementary material, which is available to authorized users.

Official American Thoracic Society/Infectious Diseases Society of America/Centers for Disease Control and Prevention Clinical Practice Guidelines: Diagnosis of Tuberculosis in Adults and Children

BACKGROUND

Individuals infected with Mycobacterium tuberculosis (Mtb) may develop symptoms and signs of disease (tuberculosis disease) or may have no clinical evidence of disease (latent tuberculosis infection [LTBI]). Tuberculosis disease is a leading cause of infectious disease morbidity and mortality worldwide, yet many questions related to its diagnosis remain.

METHODS

A task force supported by the American Thoracic Society, Centers for Disease Control and Prevention, and Infectious Diseases Society of America searched, selected, and synthesized relevant evidence. The evidence was then used as the basis for recommendations about the diagnosis of tuberculosis disease and LTBI in adults and children. The recommendations were formulated, written, and graded using the Grading, Recommendations, Assessment, Development and Evaluation (GRADE) approach.

RESULTS

Twenty-three evidence-based recommendations about diagnostic testing for latent tuberculosis infection, pulmonary tuberculosis, and extrapulmonary tuberculosis are provided. Six of the recommendations are strong, whereas the remaining 17 are conditional.

CONCLUSIONS

These guidelines are not intended to impose a standard of care. They provide the basis for rational decisions in the diagnosis of tuberculosis in the context of the existing evidence. No guidelines can take into account all of the often compelling unique individual clinical circumstances.

A retrospective review of the two-step tuberculin skin test in dialysis patients

BACKGROUND

Reactivation of latent Mycobacterium tuberculosis infection (LTBI) is a health concern for patients on dialysis or receiving a kidney transplant, as these patients are often immunosuppressed. The most frequently used test for LTBI screening in this population is the tuberculin skin test (TST). The diagnostic accuracy (sensitivity and specificity) of the TST in a contemporary North American or Western European dialysis population is unknown.

OBJECTIVES

Our objective was to determine the diagnostic accuracy and clinical utility of the two-step TST in patients receiving dialysis.

DESIGN

This is a retrospective cohort study.

SETTING

This study is set at four tertiary dialysis units across Winnipeg, Manitoba.

PATIENTS

There are 483 chronic hemodialysis and peritoneal dialysis patients in the study.

MEASUREMENTS

The measurements are sensitivity and specificity of the TST with respect to abnormal chest X-ray.

METHODS

All patients received a two-step TST and assessment of risk factors for prior tuberculosis (TB) infection between February 2008 and December 2008. This cohort was retrospectively linked to our tuberculosis registry to ascertain if prophylaxis was received for LTBI.

RESULTS

At an induration cutoff of 5 mm, 62 (13 %) patients had a positive two-step TST. Patients with a known Bacillus Calmette-Guérin (BCG) vaccination were more likely to test positive (50 % of those with a positive TST had a BCG versus 34 % with a negative TST, p = 0.05). Using a diagnostic gold standard of an abnormal chest X-ray as a proxy for LTBI, the sensitivity of the TST was only 14 % and the specificity was 88 %. Only 8 of 62 patients with a positive TST (13 %) received prophylaxis for LTBI. None of the patients who tested negative were treated.

LIMITATIONS

There is a lack of a truly accurate gold standard for LTBI.

CONCLUSIONS

The TST has limited diagnostic and clinical utility for LTBI screening in patients on dialysis. Further research into the diagnostic accuracy of interferon-gamma release assays and a revision of LTBI screening guidelines in patients on dialysis should be considered.

Challenges in Obtaining Estimates of the Risk of Tuberculosis Infection During Overseas Deployment

Estimates of the risk of tuberculosis (TB) infection resulting from overseas deployment among U.S. military service members have varied widely, and have been plagued by methodological problems. The purpose of this study was to estimate the incidence of TB infection in the U.S. military resulting from deployment. Three populations were examined: 1) a unit of 2,228 soldiers redeploying from Iraq in 2008, 2) a cohort of 1,978 soldiers followed up over 5 years after basic training at Fort Jackson in 2009, and 3) 6,062 participants in the 2011-2012 National Health and Nutrition Examination Survey (NHANES). The risk of TB infection in the deployed population was low-0.6% (95% confidence interval [CI]: 0.1-2.3%)-and was similar to the non-deployed population. The prevalence of latent TB infection (LTBI) in the U.S. population was not significantly different among deployed and non-deployed veterans and those with no military service. The limitations of these retrospective studies highlight the challenge in obtaining valid estimates of risk using retrospective data and the need for a more definitive study. Similar to civilian long-term travelers, risks for TB infection during deployment are focal in nature, and testing should be targeted to only those at increased risk.

Discordance among commercially available diagnostics for latent tuberculosis infection

RATIONALE

There is uncertainty regarding how to interpret discordance between tests for latent tuberculosis infection.

OBJECTIVES

The objective of this study was to assess discordance between commercially available tests for latent tuberculosis in a low-prevalence population, including the impact of nontuberculous mycobacteria.

METHODS

This was a cross-sectional comparison study among 2,017 military recruits at Fort Jackson, South Carolina, from April to June 2009. Several tests were performed simultaneously with a risk factor questionnaire, including (1) QuantiFERON-TB Gold In-Tube test, (2) T-SPOT.TB test, (3) tuberculin skin test, and (4) Battey skin test using purified protein derivative from the Battey bacillus.

MEASUREMENTS AND MAIN RESULTS

In this low-prevalence population, the specificities of the three commercially available diagnostic tests were not significantly different. Of the 88 subjects with a positive test, only 10 (11.4%) were positive to all three tests; 20 (22.7%) were positive to at least two tests. Bacille Calmette-Guérin vaccination, tuberculosis prevalence in country of birth, and Battey skin test reaction size were associated with tuberculin skin test-positive, IFN-γ release assay-negative test discordance. Increasing agreement between the three tests was associated with epidemiologic criteria indicating risk of infection and with quantitative test results.

CONCLUSIONS

For most positive results the three tests identified different people, suggesting that in low-prevalence populations most discordant results are caused by false-positives. False-positive tuberculin skin test reactions associated with reactivity to nontuberculous mycobacteria and bacille Calmette-Guérin vaccination may account for a proportion of test discordance observed.