6.9 Tuberculosis
Overview
Tuberculosis (TB) is a contagious bacterial infection caused by Mycobacterium tuberculosis. It primarily affects the lungs but can also target other parts of the body. TB spreads through the air when an infected person coughs or sneezes, releasing small infectious droplets into the environment. It is a serious public health concern worldwide.[1]
Pathophysiology
TB is caused by an organism called a bacillus that enters the lung. Over the course of 2 to 12 weeks, the bacillus replicates and the immune response becomes activated. The immune response involves macrophages and lymphocytes migrating to the site of inflammation and walling off the bacillus, forming a tubercle. Over time, cheese-like material develops in the center of the tubercle, called caseous necrosis. Individuals with healthy immune systems may heal this initial lesion and develop latent TB before any signs or symptoms of the illness occur. However, the tubercle may calcify and remain dormant for many years, but over time, or in immunocompromised states, spread to other areas of the lung or to other organs.
There are several risk factors for TB. Primary risk factors include close contact with an TB-infected person, HIV infection or otherwise weakened immune system, and substance abuse. TB is a common disease around the world, so individuals who travel or live in regions with high TB prevalence such as Africa, Asia, or parts of Latin America have increased risk. Individuals who immigrate from high-incidence countries or experience homelessness are also at increased risk. Additionally, individuals who live in overcrowded conditions are at increased risk for TB transmission, including individuals who work or live in long-term health care settings or prisons.[2]
In regions of the world with high TB prevalence, a Bacillus Calmette-Guérin (BCG) vaccine is commonly administered. Receiving a BCG vaccine has a substantial effect on tuberculin skin test reactivity, with individuals who received BCG after infancy having tuberculin skin test reactions up to 55 years post-immunization.[3] Nurses must be aware of an individual’s history of receiving a BCG vaccine when interpreting the results of a tuberculin skin test. Anyone who has received the BCG vaccine within the last ten years will have a positive test result for their skin test.
Mycobacterium tuberculosis has developed drug resistance in many areas of the world, causing a significant treatment problem. Multidrug-resistant TB (MDR TB) is caused by an organism that is resistant to at least isoniazid and rifampin, the two most potent TB drugs used to treat all persons with TB disease. Extensively drug-resistant TB (XDR TB) is a rare type of MDR TB that is resistant to isoniazid and rifampin, plus any fluoroquinolone and at least one of the second-line drugs. XDR TB is of special concern for persons with HIV infection or other conditions that weaken the immune system. These persons are more likely to develop TB diseas