New blood tests have become available to detect either latent or active tuberculosis. These tests - which according to the CDC can replace the tuberculin skin test - measure the production of gamma-interferon (a cytokine) by peripheral lymphocytes (white cells) when exposed to antigens which are highly specific of mycobacterium tuberculosis (the bacteria responsible for tuberculosis). Our hypothesis was that the production of gamma-interferon would be much higher at the beginning of treatment than at the end, and that decline in gamma-interferon secretion could be an indicator of clinical response to treatment.

Patients either treated for active culture proven tuberculosis (TB) or having completed treatment during the preceding 6 months were recruited. Exclusion criteria were : HIV infection and previous TB. Interferon gamma release assay (T-SPOT.TB, Oxford Immunotec) was sampled during the 2 first weeks of treatment, at the end of treatment and 6 months later.

T-SPOT.TB was analysed qualitatively (pos/neg) and quantitatively (Spot forming units: SFU) to determine if there was a higher rate of negative tests at the end of treatment and 6 months after treatment than initially. Paired samples were analysed to compare SFU counts between beginning of treatment and end of treatment, and SFU counts between end of treatment and 6 months later.

Clinical response to treatment was recorded, as well as treatment failures and relapses.

Inclusion Criteria:

• culture proven tuberculosis

Exclusion Criteria:

• age < 18
• prior tuberculosis
• HIV infection

Patients either at diagnosis of tuberculosis, under treatment for tuberculosis, or within 6 months after treatment completion