Use of Interferon-Gamma Release Assay for Latent Tuberculosis Infection Screening in Older Adults Exposed to Tuberculosis in a Nursing Home

OBJECTIVES: To assess the additive value of a newly marketed interferon-gamma release assay, QuantiFERON-TB Gold In-Tube (QFT-GIT), to a single tuberculin skin test (TST) for the detection of latent tuberculosis infection (LTBI) in older adults who have been exposed to TB in a nursing home. DESIGN: Contact tracing included clinical examination, chest radiography, TST, and QFT-GIT in TST-negative people (TST<5 mm). SETTING: A private nursing home. PARTICIPANTS: Seventy-seven individuals (63 elderly residents, 14 young employees) who had been exposed to an active TB case in a private nursing home. MEASUREMENTS: Comparison of TST and QFT-GIT in older adults who have been exposed to TB. RESULTS: For the TST, the positive response rate was 31.7% (n=20) of elderly residents and 43% (n=6) of staff. Positive QFT-GIT results were obtained in seven (16.3%) elderly residents with negative TST, six of whom were aged 80 and older. QFT-GIT increased the percentage of possible LTBI in this group from 31.7% to 42.9%. CONCLUSION: QFT-GIT has a significant additive value to single TST for detecting LTBI in institutionalized older adults, identifying infected subjects anergic to the TST.