Latent Tuberculosis

Latent tuberculosis (LTB), also called latent tuberculosis infection (LTBI) is where a patient is infected with Mycobacterium tuberculosis, but does not have active tuberculosis disease. Patients with latent tuberculosis are not infectious—it is not possible to get TB from someone with latent tuberculosis. The main risk is that approximately 10% of these patients (5% in the first two years after infection and 0.1% per year thereafter but higher risk if immunosuppressed) will go on to develop active tuberculosis at a later stage of their life. This is particularly true under any of the following circumstances:

• if there is onset of a disease affecting the immune system (such as AIDS) or a disease whose treatment affects the immune system (such as chemotherapy in cancer or systemic steroids in asthma or Enbrel, Humira or Orencia in rheumatoid arthritis);
• malnutrition (which may be the result of illness or injury affecting the digestive system, or of a prolonged period of not eating, or disturbance in food availability such as famine, residence in refugee camp or concentration camp, or civil war;
• degradation of the immune system due to aging. The identification and treatment of people with latent TB is an important part of controlling this disease.