Interferon-gamma-release assays detect recent tuberculosis re-infection in elderly contacts

Ferrara, G., Losi, M., D'Amico, R., Cagarelli, R., Pezzi, A.M., Meacci, M., Meccugni, B., Marchetti Dori, I., Rumpianesi, F., Roversi, P., Casali, L., Fabbri, L.M. and Richeldi, L. (2009) Interferon-gamma-release assays detect recent tuberculosis re-infection in elderly contacts. International Journal of Immunopathology and Pharmacology, 22 (3), 669-677. (PMID:19822083)

Abstract

The tuberculin skin test (TST) does not discriminate between recent and remote latent tuberculosis infection (LTBI). This study was carried out to test two interferon-gamma-based blood assays in recent contacts with high prevalence of remote LTBI. We performed a contact tracing investigation in a nursing home for the elderly, where elderly patients were exposed to a case of pulmonary tuberculosis. TST, QuantiFERON-TB Gold (QFT-G) and T-SPOT.TB (TS.TB) were performed 8 weeks after the end of potential exposure. IFN-gamma measurements were recorded and correlation with exposure was evaluated. Twenty-seven (37.5%), 32 (44.4%) and 16 (22.2%) subjects were TST, TS.TB and QFT-G positive, respectively; agreement between TS.TB and QFT-G was good among exposed subjects only (K=0.915, 0.218 in unexposed, p<0.001). When amounts of IFN-gamma were corrected for the number of producing T cells, specific IFN-gamma production was significantly different between exposed and unexposed individuals (16.75+/-5.40 vs 2.33+/-0.71 IFN-gamma IU/1000 SFC, p=0.0001). QFT-G and TS.TB provided discordant results among elderly contacts. Unlike TST, the specific IFN-gamma response might discriminate between recent and long-lasting tuberculosis infection.

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