Tuberculosis natural history, complications, and prognosis


 * Assistant Editor-in-Chief: Somal Khan

Overview
Tuberculosis, or TB is a bacterial infection that kills 3 million people worldwide, more people than any other infection in the world. Approximately one-third of the world is infected, and 15 million people in the US. Active tuberculosis kills 60% of the time if not treated, but treatment cures 90% of patients. Most people are infected with TB have latent TB. This means that the bacteria is controlled by the body's immune system. People with latent TB do not have symptoms and cannot transmit TB to other people. However, later if the infected person has a weakened immune system (AIDS, young children, elderly, sick with other diseases, etc.), the bacteria can break out leading to active TB, or TB disease. The results of a Mantoux tuberculin skin test must be interpreted carefully. The person's medical risk factors determine at which increment (5 mm, 10 mm, or 15 mm) of induration the result is considered positive. A positive result indicates TB exposure.


 * 5 mm or more is positive in
 * HIV-positive person
 * Recent contacts of TB case
 * Persons with nodular or fibrotic changes on chest x-ray consistent with old healed TB
 * Patients with organ transplants and other immunosuppressed patients


 * 10 mm or more is positive in
 * Recent arrivals (less than 5 years) from high-prevalence countries
 * Injection drug users
 * Residents and employees of high-risk congregate settings (e.g., prisons, nursing homes, hospitals, homeless shelters, etc.)
 * Mycobacteriology lab personnel
 * Persons with clinical conditions that place them at high risk (e.g., diabetes, prolonged corticosteroid therapy, leukemia, end-stage renal disease, chronic malabsorption syndromes, low body weight, etc)
 * Children less than 4 years of age, or children and adolescents exposed to adults in high-risk categories


 * 15 mm or more is positive in
 * Persons with no known risk factors for TB
 * (Note: Targeted skin testing programs should only be conducted among high-risk groups)

A few important notes about Mantoux tuberculin skin tests:
 * A tuberculin test conversion is defined as an increase of 10 mm or more within a 2-year period, regardless of age.
 * Mycobacterium avium intracellulare (MAI) or other mycobacterium cause 5 mm induration, but TB is what causes ≥10mm.
 * Decision to test is decision to treat.
 * If a patient is treated fully, then re-exposed, they should only be retreated if they are HIV positive (immunocompromised) or the risk of reinfection is high.