Abstract
BackgroundThe tuberculin skin test (TST) and interferon-gamma-release-assays (IGRAs) are utilized in screening programmes for presumed latent tuberculosis infection (LTBI) in health care workers (HCWs). However, inter-test comparison yields high rates of discordance, which is poorly understood. The aim of the study was therefore to identify factors associated with discordance amongst HCWs in a TB and HIV endemic setting.Methods505 HCWs were screened for LTBI in South Africa using the TST and two IGRA assays (QuantiFERON-TB-Gold-In-Tube (QFT-GIT) and TSPOT.TB). Factors associated with discordance were analyzed using a multinomial logistic regression model.ResultsTST-IGRA discordance was negatively associated with longer duration of employment for both TSPOT.TB (OR = 0.92; 95% confidence interval (CI) 0.85–0.99) and QFT-GIT (OR = 0.90; 95% CI 0.84–0.96). Marked test discordance occurred in HIV-infected individuals who were more likely to have TSPOT.TB + ve / TST-ve discordance (OR 4.44; 95% CI 1.14–17.27) or TSPOT.TB + ve / QFT-GIT-ve test discordance (OR 5.72; 95% CI 1.95–16.78). Those engaged in home care were less likely to have QFT-GIT + ve/TSPOT.TB -ve / discordance (OR 0.32; 95% CI 0.10–0.95).ConclusionThe marked TST-IGRA and IGRA-IGRA discordance in HIV-infected individuals suggest greater sensitivity of TSPOT.TB in immunocompromised persons or potential greater reactivity of TSPOT.TB in this population.
Highlights
The tuberculin skin test (TST) and interferon-gamma-release-assays (IGRAs) are utilized in screening programmes for presumed latent tuberculosis infection (LTBI) in health care workers (HCWs)
There was only fair agreement between TST and the IGRAs, with κ = 0.28 [95% confidence interval (CI) 0.20–0.36] and κ = 0.25 for QuantiFERON-TB Gold-In-Tube (QFT-GIT) and TSPOT.TB respectively
The lack of a gold standard to confirm LTBI diagnosis makes it difficult to compare test performance and arrive at conclusive answers in this regard. In this population BCG vaccination is associated with discordance suggesting an enduring effect for BCG given at birth and likely impact on TST test specificity
Summary
The tuberculin skin test (TST) and interferon-gamma-release-assays (IGRAs) are utilized in screening programmes for presumed latent tuberculosis infection (LTBI) in health care workers (HCWs). The World Health Organization (WHO) currently recommends that testing and treatment for LTBI be performed on all HIV positive individuals This recommendation is extended to populations deemed at increased risk of TB such as health care workers (HCWs) in low TB incidence settings only [2]. In South Africa, a high tuberculosis (TB) incidence country, the prevalence of LTBI in HCWs as measured by a positive tuberculin skin test (TST) ranges from 48 to 84% while HIV prevalence is > 10% [4] Despite their high risk for active TB and increased exposure to TB in the workplace, screening for LTBI among HCWs is very limited in practice [5]
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