Diagnosis of latent tuberculosis infection in bacille Calmette-Guérin vaccinated subjects in China by interferon-gamma ELISpot assay.

OBJECTIVE: To evaluate the performance of an in-house interferon-gamma (IFN-γ) enzyme-linked immunospot (ELISpot) assay for the detection of latent tuberculosis infection (LTBI) in bacille Calmette-Guérin (BCG) vaccinated individuals with or without human immunodeficiency virus (HIV) infection.

METHODS: A total of 202 participants (93 HIV-infected and 109 non-infected) who received BCG vaccination at birth underwent tuberculin skin testing (TST) and T cell-based ELISpot assays. The performance of an in-house IFN-γ ELISpot assay (ELISpot) was evaluated by parallel comparison with the commercial IFN-γ release assay (IGRA) kit, T-SPOT®.TB, in 127 subjects. The effect of BCG vaccination on the ELISpot assay was prospectively determined by comparing the responses of IGRAs before and 3 months after BCG vaccination in 27 individuals.

RESULTS: High agreement between ELISpot and T-SPOT.TB was observed in both HIV-infected (92.47%, κ = 0.754) and non-HIV-infected subjects (97.06%, κ = 0.653). CD4(+) T-cell count does not affect Mycobacterium tuberculosis IFN-γ response as measured by both ELISpot and T-SPOT.TB. BCG vaccination resulted in 100% conversion of TST, but did not change responses to IGRAs.

CONCLUSION: The performance of this in-house ELISpot assay is comparable to commercial T-SPOT.TB in diagnosing LTBI. Both assays are useful for diagnosing LTBI in BCG-vaccinated subjects with or without HIV infection in a setting with a high prevalence of tuberculosis.