Latent Infection In the nonimmune (susceptible) host, the bacilli initially multiply unopposed by normal host defense mechanisms. The organisms are then taken into alveolar macrophages by phagocytosis and may remain viable, multiplying within the cells for extended periods of time. After 14 to 21 days of replication, the tubercle bacilli spread via the lymphatic system to the hilar lymph nodes and through the bloodstream to other organs.

Active Disease (Tuberculosis) In most patients, active TB disease results from reactivation of a previously controlled latent infection, termed reactivation tuberculosis. Approximately 10% of individuals who acquire TB infection and do not receive therapy for the latent infection will develop active TB disease. The risk of developing active disease is highest in the first 2 years after infection, when half of the cases occur.

Active Disease (Tuberculosis) The annual and lifetime risks for reactivation TB have been shown, however, to be directly related to the size of the induration on tuberculin skin testing. The risks for reactivation TB were greater in patients with larger induration diameters. The ability of the host to respond to M. tuberculosis may also be reduced by certain diseases such as diabetes mellitus, silicosis, chronic renal failure, and diseases or drugs associated with immunosuppression (e.g., HIV infection, antitumor necrosis factor-α agents, organ transplantation, corticosteroids, and other immunosuppressive agents).

Treatment of Active Disease The overall goals for the treatment of TB are to cure the patient and to minimize the transmission of M. tuberculosis to others. The primary goals of antituberculosis chemotherapy are to kill the tubercle bacilli rapidly, prevent the emergence of drug resistance, and eliminate persistent bacilli from the host's tissues to prevent relapse. To accomplish these goals, it is essential that treatment be tailored and supervision be based on each patient's clinical and social circumstances (patient-centered care).

Treatment of Active Disease Effective treatment of TB requires a substantial period (minimum 6 months) of intensive drug therapy with at least two bactericidal drugs that are active against the organism. The initial phase of treatment is crucial for preventing the emergence of resistance and for the ultimate outcome of TB therapy. Four basic regimens are recommended for the treatment of adult patients with TB caused by organisms that are known or presumed to be drug susceptible.