Levels of Interferon-Gamma Increase after Treatment for Latent Tuberculosis Infection in a High-Transmission Setting

Objectives . We investigated IFN- γ levels before and after a six month course of isoniazid among individuals with latent tuberculosis infection (LTBI) in a high-transmission setting. Design . A total of 26 household contacts of pulmonary tuberculosis patients who were positive for LTBI by tuberculin skin test completed six months of treatment and submitted a blood sample for a follow-up examination. The IFN- γ response to Mycobacterium tuberculosis -specific antigens was measured, and the results before and after the completion of LTBI treatment were compared. Results . Of the 26 study participants, 25 (96%) showed an IFN- γ level higher than their baseline level before treatment ( P ≤ 0.001). Only one individual had a decreased IFN- γ level after treatment but remained positive for LTBI. Conclusion . In a high-transmission setting, the IFN- γ level has increased after LTBI treatment. Further studies must be undertaken to understand if this elevation is transient.