Abstract
BackgroundThere is little information concerning community-based prevalence of latent tuberculosis infection (LTBI) using T-cell based interferon-γ (IFN-γ) release assays (IGRAs), particularly in TB endemic settings. In this study, the prevalence of LTBI in the Afar pastoral community was assessed using QuantiFERON-TB Gold In-Tube (QFTGIT) and tuberculin skin tests (TST).MethodsA community-based cross-sectional survey of LTBI involving 652 apparently healthy adult pastoralists was undertaken in the pastoral community of Amibara District of the Afar Region between April and June 2010.ResultsThe prevalence of LTBI was estimated as 63.7% (363/570) using QFTGIT at the cut-off point recommended by the manufacturer (≥ 0.35 IU/ml IFN-γ), while it was 74.9% (427/570) using a cut-off point ≥ 0.1 IU/ml IFN-γ. The QFTGIT-based prevalence of LTBI was not significantly associated with the gender or age of the study participants. However, the prevalence of LTBI was 31.2% (183/587) using TST at a cut-off point ≥ 10 mm of skin indurations, and it was higher in males than females (36.8% vs. 23.5%, X2 = 11.76; p < 0.001). There was poor agreement between the results of the tests (k = 0.098, 95% CI, 0.08 - 0.13). However, there was a positive trend between QFTGIT and TST positivity (X2 = 96.76, P < 0.001). Furthermore, individuals with skin indurations ≥ 10 mm were 13.6 times more likely to have positive results using QFTGIT than individuals with skin indurations of 0 mm (adjusted OR = 13.6; 95%CI, 7.5 to 24.7, p < 0.001).ConclusionsThere is currently no agreed gold standard for diagnosis of LTBI. However, the higher prevalence of LTBI detected using QFTGIT rather than TST suggests that QFTGIT could be used for epidemiological studies concerning LTBI at the community level, even in a population unreactive to TST. Further studies of adults and children will be required to assess the effects of factors such as malnutrition, non-tuberculosis mycobacterial infections, HIV and parasitic infections on the performance of QFTGIT.
Highlights
There is little information concerning community-based prevalence of latent tuberculosis infection (LTBI) using T-cell based interferon-g (IFN-g) release assays (IGRAs), in TB endemic settings
T-cell-based IFN-g release assays (IGRAs) have been developed and approved for the diagnosis of LTBI [8], and one study demonstrated that IGRAs have a higher specificity than TST as the results are not affected by the bacille Calmette-Guérin (BCG) status of the subject [9]
Regardless of their limitations, it is believed that IGRAs could improve existing information about the global epidemiology of LTBI [15], but the majority of studies concerning LTBI and IGRAs have been limited to patients with active TB or health care workers and refugees [16,17,18,19,20]
Summary
There is little information concerning community-based prevalence of latent tuberculosis infection (LTBI) using T-cell based interferon-g (IFN-g) release assays (IGRAs), in TB endemic settings. Tuberculosis (TB) is one of the major public health problems in sub-Saharan Africa and Asia [1] It is responsible for approximately two million deaths, and eight million new cases are reported each year; approximately 80% of all new cases occur in the 22 countries with a high burden of TB [2]. T-cell-based IFN-g release assays (IGRAs) have been developed and approved for the diagnosis of LTBI [8], and one study demonstrated that IGRAs have a higher specificity than TST as the results are not affected by the BCG status of the subject [9]. Few studies have assessed community-based prevalence of LTBI using IGRAs [21,22 ]
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