Performance evaluation of the AFIAS IGRA-TB (IFN-gamma) test versus QuantiFERON®-TB gold plus (QFT®-Plus) ELISA in the Barrio Obrero hospital network, Asunción—Paraguay, 2025

TL;DR

This study compares two TB diagnostic tests in Paraguay and finds the AFIAS test performs similarly to the WHO-endorsed QFT-Plus test.

Contribution

The study evaluates AFIAS IGRA-TB as a potential alternative to QFT-Plus in low-resource settings.

Findings

AFIAS and QFT-Plus showed 89% agreement with strong concordance in high-risk groups.

AFIAS demonstrated a strong correlation with QFT-Plus and an AUC of 0.890 in ROC analysis.

AFIAS may offer operational advantages for TB testing in resource-limited areas.

Abstract

Tuberculosis infection affects an estimated one-quarter of the global population and represents a key target for TB elimination strategies. While interferon-gamma release assays (IGRAs) such as QuantiFERON-TB Gold Plus (QFT-Plus) are WHO-endorsed, they remain logistically complex in low-resource settings. This study evaluates the performance of the AFIAS IGRA-TB, a qualitative fluorescence immunoassay (FIA), compared to QFT-Plus in Paraguay.

A cross-sectional diagnostic accuracy study was conducted from January to May 2025 among 210 individuals aged 18–59 years within the Barrio Obrero healthcare network in Asunción, Paraguay. Participants were stratified into three TB risk groups: low-risk (no known exposure), high-risk (close contacts and incarcerated individuals), and active TB cases. Blood samples were tested with both AFIAS and QFT-Plus assays. Discordant results were retested after six to eight weeks. Concordance was assessed using Cohen’s Kappa; quantitative correlations and ROC curves were also analysed.

Of 210 participants, 75.2% were male. Overall positivity rates were 38.5% for QFT-Plus and 37.0% for AFIAS, with an agreement of 89.0% (κ = 0.767; p < 0.0001). Strong concordance was observed in high-risk groups. Among 23 discordant cases, retesting confirmed the initial AFIAS result in 5 cases and QFT-Plus in 3; 7 remained discordant. Spearman correlation showed strong, significant association between quantitative values. ROC analysis yielded an AUC of 0.890 for AFIAS.

AFIAS IGRA-TB demonstrates comparable performance to QFT-Plus with operational advantages, suggesting it is a viable diagnostic alternative for TB infection, particularly in decentralized or resource-limited settings.

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