Hypothesis: a combined strategy of tuberculin skin test (TST) followed by QuantiFERON-TB Gold In-Tube (QFT-IT) to confirm positivity (tuberculosis infection,in contact-tracing study will allow avoiding unnecessary preventive treatment without increasing rates of tuberculosis cases among contacts screened.

Aim of the study: to compare a combined strategy of the TST and the QFT-IT with TST alone for the diagnosis of tuberculosis infection and for therapeutic decision in contact tracing study.

Design and setting: Prospective, multicentre, comparative study in 12 hospitals in Spain.

Study population: 870 subjects, household contacts of patients with culture positive pulmonary and/or laryngeal tuberculosis will be randomized to one of two strategies: Arm A (standard practice), in which treatment decisions will be based on the TST result, and Arm B (experimental), in which treatment decisions will be based on the QFT result.

Interventions: participants in arm A will undergo TST; participants in arm B will undergo TST, and, in case of a positive result, QFT-IT as well. Participants with positive TST (arm A) and positive QFT-IT (arm B) will be diagnosed with tuberculosis infection and will be treated with isoniazid for 6 months. All participants will be followed for two years.

End-points of evaluation: development of tuberculosis and proportion of subjects for whom treatment is prescribed in each arm.

Inclusion Criteria:

• Age ≥18 years.
• Close contact of a pulmonary and/or laryngeal tuberculosis case.
• Written informed consent.

Exclusion Criteria:

• HIV infection.
• Immunosuppression other than HIV, such as decompensated liver disease, chronic renal failure, corticosteroids treatment, malignancy under chemotherapy therapy.
• Prior tuberculosis or positive TST.
• Strain resistant to Isoniazid (index case).