Tuberculosis (TB) is a bacterial infection caused by Mycobacterium tuberculosis, a microorganism that primarily targets the lungs but can also affect other body parts. This contagious disease spreads through the air when an infected individual coughs, sneezes, or speaks, releasing tiny droplets containing the bacteria. Globally, TB remains a significant public health concern, with millions falling ill each year.
Understanding Latent and Active TB
A positive TB test result can indicate one of two main infection states: latent TB infection (LTBI) or active TB disease. With latent TB, the bacteria are present in the body but remain inactive, due to the immune system containing them. Individuals with LTBI do not experience symptoms and cannot transmit the bacteria to others.
In contrast, active TB disease occurs when the bacteria become active and multiply within the body. This state leads to noticeable symptoms, and the infected person can spread the bacteria, particularly if the disease affects the lungs or throat. The distinction between latent and active forms is important, as their manifestations and implications for health differ. While latent TB can persist for years without progression, it carries a risk of becoming active, especially if the immune system weakens.
Diagnostic Indications
Diagnostic tests for TB provide key information. The tuberculin skin test (TST), also known as the Mantoux test, involves injecting a small amount of fluid under the skin, and a positive reaction appears as a raised, hard bump, or induration, which is measured in millimeters. A positive TST indicates only the presence of TB infection, not whether it is latent or active.
Blood tests, specifically Interferon Gamma Release Assays (IGRAs) like QuantiFERON-TB Gold Plus or T-SPOT.TB, identify a positive result by detecting the immune system’s response to TB proteins in a blood sample. Following a positive skin or blood test, a chest X-ray is performed to differentiate between latent and active TB. Findings suggestive of active TB disease on an X-ray can include infiltrates, cavities, nodules, or scarring within the lungs. To confirm active disease, a sputum smear and culture are used to identify the bacteria.
Physical Manifestations of Active TB
Active TB disease manifests through a range of symptoms and signs, distinguishing it from latent infection’s asymptomatic nature. General symptoms common to active TB, regardless of the affected body part, include unexplained weight loss, persistent fever, night sweats, loss of appetite, chills, and fatigue. These systemic signs develop gradually over several weeks.
When TB primarily affects the lungs, known as pulmonary TB, specific symptoms emerge. These commonly include a persistent cough lasting three weeks or longer, chest pain, and coughing up sputum or blood. Extrapulmonary TB occurs when the infection spreads beyond the lungs, and its symptoms vary depending on the affected organ or body system. For instance, TB of the spine can cause back pain, kidney TB may lead to changes in urination, and lymph node TB can result in swollen glands.
Next Steps After a Positive Result
Upon receiving a positive TB test result, further evaluation is necessary to determine if the infection is latent or active. This involves additional tests, such as a chest X-ray and possibly sputum analysis, to determine the infection type and rule out other conditions. Both latent and active TB are treatable with antibiotics, but the duration and specific medication regimens differ considerably. It is important to complete the entire course of prescribed medication to eliminate the bacteria and prevent drug-resistant strains.
For active TB cases, public health measures include contact investigation to identify and test exposed individuals, helping prevent further spread. A positive result requires consultation with a healthcare provider. This guidance ensures diagnosis and an appropriate treatment plan.