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.

BACKGROUND

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.

METHODS

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.

RESULTS

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.

CONCLUSION

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.