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.