Capturing Recent Mycobacterium tuberculosis Infection by Tuberculin Skin Test vs. Interferon-Gamma Release Assay

Area of Science:

• Immunology
• Infectious Diseases
• Public Health

Background:

• Reducing tuberculosis (TB) incidence necessitates identifying individuals at high risk of active disease, often those with recent Mycobacterium tuberculosis (Mtb) infection.
• Diagnostic tools like the tuberculin skin test (TST) and interferon-gamma release assay (IGRA) are used to detect Mtb infection.

Purpose of the Study:

• To evaluate the added value of TST in characterizing IGRA converters in a household contact (HHC) study.
• To determine if TST conversion provides additional diagnostic information beyond IGRA in identifying recent Mtb infection.

Main Methods:

• Prospective household contact (HHC) study in Kampala, Uganda.
• Diagnosis of new Mtb infection using both TST and IGRA.
• Analysis of TST-only, IGRA-only, and dual converters.

Main Results:

• 13 IGRA-only converters, 39 TST-only converters, and 24 dual converters were identified.
• TST-only converters were older and conversion was associated with older age and crowdedness.
• Dual converters showed higher IGRA quantitative values and a larger change in TST quantitative values compared to single converters.

Conclusions:

• TST conversion alone may overestimate Mtb infection, potentially due to environmental mycobacteria boosting in older individuals.
• Dual IGRA/TST conversion might signify a more robust immune response to Mtb infection.
• Findings have implications for TB risk stratification and vaccine development studies.