A Feasibility Study for Diagnosis of Latent Tuberculosis Infection Using an IGRA Point-of-Care Platform in South Korea

PURPOSE: This study aimed to evaluate ichroma™ IGRA-TB, a novel point-of-care platform for assaying IFN-γ release, and to compare it with QuantiFERON-TB Gold In-Tube (QFT-GIT) for identifying Mycobacterium tuberculosis (M. tb) infection. MATERIALS AND METHODS: We recruited 60 healthy subjects, and blood samples were obtained in QFT-GIT blood collection tubes. The blood collection tubes were incubated at 37℃, and culture supernatant was harvested after 18–24 hours. IFN-γ responses were assessed by the ichroma™ IGRA-TB cartridge and the QFT-GIT IFN-γ enzyme-linked immunosorbent assay. Three active TB patients were recruited as a positive control for M. tb infection. RESULTS: The area under the receiver operating characteristic curve of the ichroma™ IGRA-TB test for differentiating between infected and non-infected individuals was 0.9706 (p < 0.001). Inconsistent positivity between the two tests was found in three participants who showed weak positive IFN-γ responses ( < 1.0 IU/mL) with QFT-GIT. However, the two tests had excellent agreement (95.2%, κ=0.91, p < 0.001), and a very strong positive correlation was observed between the IFN-γ values of both tests (r=0.91, p < 0.001). CONCLUSION: The diagnostic accuracy demonstrated in this study indicates that the ichroma™ IGRA-TB test could be used as a rapid diagnostic method for detecting latent TB infection. It may be particularly beneficial in resource-limited places that require cost-effective laboratory diagnostics.

Serial QuantiFERON-TB Gold In-Tube assay and tuberculin skin test to diagnose latent tuberculosis in household Mexican contacts: conversion and reversion rates and associated factors using conventional and borderline zone definitions

A cohort of 123 adult contacts was followed for 18‐24 months (86 completed the follow-up) to compare conversion and reversion rates based on two serial measures of QuantiFERON (QFT) and tuberculin skin test (TST) (PPD from TUBERSOL, Aventis Pasteur, Canada) for diagnosing latent tuberculosis (TB) in household contacts of TB patients using conventional (C) and borderline zone (BZ) definitions. Questionnaires were used to obtain information regarding TB exposure, TB risk factors and socio-demographic data. QFT (IU/mL) conversion was defined as <0.35 to ≥0.35 (C) or <0.35 to >0.70 (BZ) and reversion was defined as ≥0.35 to <0.35 (C) or ≥0.35 to <0.20 (BZ); TST (mm) conversion was defined as <5 to ≥5 (C) or <5 to >10 (BZ) and reversion was defined as ≥5 to <5 (C). The QFT conversion and reversion rates were 10.5% and 7% with C and 8.1% and 4.7% with the BZ definitions, respectively. The TST rates were higher compared with QFT, especially with the C definitions (conversion 23.3%, reversion 9.3%). The QFT conversion and reversion rates were higher for TST ≥5; for TST, both rates were lower for QFT <0.35. No risk factors were associated with the probability of converting or reverting. The inconsistency and apparent randomness of serial testing is confusing and adds to the limitations of these tests and definitions to follow-up close TB contacts.

Infection Control in Office-based Practices

Infection control in the setting of the office based clinic, involves the early detection of disease; disease prevention through vaccination as in influenza and pneumococcal vaccinations; and through screening for asymptomatic disease as in tuberculosis. Family physicians play an important role in these aspects within the community. Although influenza vaccination is effective, the take up rate of vaccination locally is low. Annual vaccination with the current vaccines are strongly recommended in high risk populations such as the elderly, the immunocompromised and, those with co-morbidities. The inactivated trivalent vaccine is the most commonly used. Latent Tuberculosis (TB) Infection is asymptomatic and often goes undetected. Prevention of progression to overt TB can be achieved by identifying high risk persons and the early detection by either the tuberculin skin test or interferon gamma release assays (IGRAs). Invasive pneumococcal disease can lead to significant morbidity and mortality in the young and elderly. In the preventive control of this disease, there are two types of pneumococcal vaccines currently available – the polysaccharide vaccine and the conjugate vaccine. Recommendations for the two different vaccines are in accordance with different at risk populations.

A retrospective analysis of tuberculosis screening by interferon-gamma release assay at National Skin Centre, Singapore

Objective The T-Spot.TB is an interferon-gamma release assay (IGRA) which is increasingly used in dermatology as a screen for latent TB before initiation of biologics and for confirming diagnosis of tuberculids. This study aims to explore its concordance with tuberculin skin tests (TST) and eventual diagnosis of latent TB. Study design This is a retrospective review of all patients in NSC who had a TB T-spot test done between 2008 and 2010. We looked at the dermatological diagnosis, results of T-Spot.TB and TST, chest radiograph findings, tuberculosis status and treatment of TB. Result 51 TB T spot tests were ordered in National Skin Centre between 1 January 2008 and 9 June 2010. 31 tests were for patients with psoriasis with the intention of initiating biologics; 5 were for patients with suspected tuberculids and tuberculosis verrucosa cutis; 3 were done as part of work-up for possible erythema nodosum; 3 tests were part of screening for latent TB in hospital staff and 9 tests were performed for other reasons. There were a total of 13 patients eventually diagnosed with latent or active TB infection. All of whom had a positive T-Spot.TB result except for 1 patient with an indeterminate result. On the other hand, out of these 13 patients, only 5 showed a positive TST, 2 had negative TST and 4 patients did not have a TST done. There were a total of 14 positive T-Spot.TB results for which 12 eventually received antituberculous therapy. All patients with erythema induratum had a positive test result. Six patients’ T-Spot.TB tests were borderline, indeterminate or could not be interpreted due to insufficient lymphocyte yield. Conclusion Our study shows the utility of T-Spot. TB test in various conditions seen in dermatology clinics in a local setting. We suggest that the T-spot test can supplant the tuberculin skin test in screening latent TB for psoriasis patients for whom biologics are intended and in erythema induratum. The high incidence of borderline and indeterminate results should not be ignored. This should be taken into account when interpreting the IGRA especially if patients are on immunosuppressive therapy.

Tuberculosis among Dislocated North Koreans Entering Republic of Korea since 1999

The collapse of North Korea's public health system has increased the development of tuberculosis (TB) in its populace. This study investigated the prevalence of active and latent TB infection (LTBI) in such people who have settled in the Republic of Korea since 1999. From 1999 to August 2006, 7,722 dislocated North Koreans entered the Republic of Korea and all were screened immediately for active TB. Demographic and clinical characteristics were reviewed from the official records of the Settlement Support Office for Dislocated North Koreans, based in the Ministry of Unification. Of 7,722 participants, 87 (1.13%) were diagnosed with active TB from 1999 to August 2006. Of these, 78 (90%) had pulmonary TB. Checking for the presence of a Bacille Calmette-Guerin (BCG) scar and tuberculin skin test has been performed in all dislocated North Koreans since November 2005. Of 1,112 participants, BCG vaccination scars were found in 67.4%. The tuberculin-positive rate using two tuberculin unit doses of the purified protein derivative RT23 (> or =10 mm in diameter) was 81.5%. The prevalence of active TB and LTBI in dislocated North Koreans was high. Because this group bears a disproportionate burden of TB, we need to initiate a specific control programme and to plan for the impact of this disease in the Republic of Korea.