Most TB infections are initiated by the respiratory route of exposure.

Clinical manifestations of pulmonary TB infection typically include cough, night sweats and weight loss. Extrapulmonary lesions can appear in some individuals. Infection may be divided into stages which include primary TB, latent infection and reactivation.

Infection can remain latent in a proportion of cases. Latent tuberculosis infection carriers are asymptomatic and not infectious, however, about 10% will go on to develop active TB. Reactivation of infection is more common in immunocompromised patients.