Interferon Gamma Release Assays for Latent Mycobacterium tuberculosis Detection in Elderly Hispanics

SUMMARYBackgroundAging is a tuberculosis co-morbidity. Interferon Gamma Release Assays (IGRAs) are used to detect latent Mycobacterium tuberculosis (M.tb) infection (LTBI) in adults, but their performance in the elderly is not well-established. We aim to evaluate the performance of IGRAs for LTBI detection in healthy elderly Hispanics with recent, remote or no history of M.tb exposure.Study Design and MethodsCross-sectional study in Hispanic elderly (60+y) and adult (18-50y) recent TB contacts (ReC) or community controls (CoC). LTBI was based on a positive T-SPOT.TB and/or QuantiFERON-Gold in-tube or –Plus assay.ResultsWe enrolled 193 CoC (119 adults/74 elderly) and 459 ReC (361 adults/98 elderly). LTBI positivity increased with age in CoC (range 19-59%; trend p vs. 0.688 in adults) and more inconclusive results (indeterminate/borderline; 11.6% vs. 5.8% in adults; p=0.012). Exclusion of inconclusive results improved concordance between assays, notably in elderly ReC, who have the highest TB risk (from kappa 0.532 to 0.800). When both IGRAs were done simultaneously, inconclusive results were resolved in all cases as positive or negative with the other IGRA. The magnitude of the response to M.tb peptides used in the assays was similar between age groups, but responsiveness to mitogens was lower in the elderly.ConclusionsIGRAs are suitable for LTBI detection in the elderly. Discordant and inconclusive findings are more prevalent in the elderly, but results were resolved when performing different IGRAs simultaneously in the same participant.