Immunodiagnostic Potential of an In-Vitro Interferon-Gamma Release Assay for Latent Tuberculosis Infection Among Apparently Healthy Individuals in Okada Community, Nigeria

Benson Olu Akinshipe

doi:10.11648/j.iji.20170503.11

Abstract

A major challenge in the global Tuberculosis (TB) control is the diagnosis and treatment of Latent Tuberculosis Infection (LTBI). In the absence of any reference standard test for the diagnosis of LTBI, this study set out to compare the performance of the two current immune-based tests, Tuberculin Skin Test (TST) and Quantiferon–TB Gold In–Tube (QFT-GIT) ELISA in the diagnosis of LTBI. Two sets of diagnostic results for 196 apparently healthy volunteers from a cross-section of Okada Community, Edo State, Nigeria were compared in terms of age, occupation, BCG-vaccination status, prior TST and cigarette smoking history. Overall, 56 (28.6%) and 81 (41.3%) of the subjects were diagnosed with LTBI by the QFT-GIT test and TST respectively. The LTBI prevalence as assessed by the QFT-GIT test was significantly higher among the non-BCG-vaccinated, compared to the BCG-vaccinees (X<sup>2</sup>=18.79, df=1, p=0.0001). The highest concordance (QFT-GIT+ve/TST+ve) was found in the occupation categories (Ʀ=-0.009, p=0.747) and the highest discordance(QFT-GIT –ve/TST +ve) was with respect to the BCG-vaccination status (Ʀ=-0.194, p=0.046).The disparity in the performance of the two tests is attributable to the high false – positive TST results, which is a direct reflection of high (90.8%) BCG vaccination level among the study population. It is advocated that the two-step testing approach, using the QFT-GIT assay as a confirmatory test for LTBI after initial positive screening by the TST, be introduced into the TB control strategy in TB – laden communities with high BCG vaccination coverage.

Highlights

Tuberculosis (TB) continues to be one of the leading infectious causes of morbidity and mortality and remains a major public health problem worldwide, despite progress being made globally to prevent and control the disease
The observed significantly higher overall Latent Tuberculosis Infection (LTBI) prevalence rate of 81(41.3%) as detected by the TST compared to 56(28.6 % ) by Quantiferon-TB Gold In-Tube (QFT-GIT) test in this study indicates that some participants who were diagnosed with LTBI based on TST results were found to be QFT-GIT negative(i.e TST +ve / QFT-GIT –ve)
As most TST results are recorded in individual patient records in developing countries, not in electronic databases, Quantiferon–TB Gold In–Tube (QFTGIT) test results can be stored in laboratory databases for easy analysis and management in such settings. This baseline study revealed that the prevalence of LTBI was high in the Okada community regardless of the immunodiagnostic method used

Summary

Introduction

Tuberculosis (TB) continues to be one of the leading infectious causes of morbidity and mortality and remains a major public health problem worldwide, despite progress being made globally to prevent and control the disease. In the vast majority of the infected individuals, an effective cellmediated immune response shortly after infection results in asymptomatic infection, which may remain undiagnosed and could reactivate later in life to cause active TB disease [4], [5]. While most high income countries have incorporated effective LTBI control strategy into their TB control programme and elimination campaigns, this measure is still limited or virtually non-existent in most resource-limited countries [1].Tuberculosis control programmes in developing countries are greatly haunted by low detection rates and LTBIs that constitute hidden pools that continuously feed new cases. Accurate diagnosis of LTBI and appropriate treatment of probable cases – to- be reduce the risk of progression to overt disease and increase case detection rates [6].The Nigeria TB control programme has found it necessary to couple diagnosis and treatment of active TB disease with new approaches to detect LTBI [3]

Results

Discussion

Conclusion