The diagnosis of tuberculosis infection is based on a pathological dermal induration (positive Mantoux reaction) after injection of a standard dose of tuberculin (2 U). The positivity criteria of the Mantoux reaction vary according to whether the adolescent was or was not given BCG vaccination in the past. If the intradermal reaction is pathological at the time of the school screening visit, the subject should be referred to his physician, who will perform a second test (control Mantoux). If the pathological reaction is not confirmed, no further investigations will be needed. If the positive Mantoux is confirmed, the practitioner performs a detailed physical examination and a chest X-ray. If there is no abnormality, a natural tuberculosis infection is diagnosed and 6-month preventive monotherapy prescribed. If the chest picture is abnormal, further investigations will be required and, according to the results, preventive treatment or polychemotherapy for tuberculosis disease will be administered.