### Date : 2024-11-07 09:50 ### Topic : Tuberculosis (TB) infection #pulmonology ---- **Tuberculosis (TB) infection** is caused by the bacterium **Mycobacterium tuberculosis** and primarily affects the lungs, although it can spread to other organs. TB infection exists in two forms: **latent TB infection (LTBI)**, where the bacteria remain dormant without causing symptoms, and **active TB disease**, where the bacteria are actively multiplying and causing illness. Without proper treatment, TB can lead to severe respiratory damage and may be fatal. ### Pathophysiology of TB Infection When Mycobacterium tuberculosis bacteria enter the body, they travel to the alveoli (air sacs) in the lungs. Here, the body’s immune response attempts to contain the infection, resulting in either latent or active disease: 1. **Inhalation and Immune Response**: - TB bacteria enter the lungs and are engulfed by immune cells called **macrophages**. However, M. tuberculosis has a thick, waxy cell wall that enables it to survive and replicate within these immune cells. - The immune system forms a structure called a **granuloma** to wall off the infection. This granuloma is a cluster of immune cells that attempt to prevent the spread of bacteria. 2. **Latent TB Infection (LTBI)**: - In most people with a healthy immune system, the infection becomes contained within granulomas, and the bacteria enter a **dormant state**. - Individuals with latent TB are asymptomatic and not contagious, as the bacteria are inactive. However, the bacteria can reactivate if the immune system weakens. 3. **Active TB Disease**: - If the immune system cannot contain the bacteria or if it later weakens (e.g., due to age, malnutrition, or HIV infection), TB bacteria can multiply, breaking out of the granulomas and causing **active TB**. - In active TB, the bacteria spread, leading to inflammation, tissue damage, and symptoms. Active TB is contagious and can be spread through respiratory droplets when the person coughs or sneezes. ### Risk Factors for TB Infection Certain factors increase the risk of TB infection or progression to active TB: - **Immunocompromised States**: Conditions such as HIV/AIDS, diabetes, cancer, or immunosuppressive therapy. - **Close Contact with TB Patients**: Living or working closely with someone who has active TB. - **Age**: Both young children and elderly individuals have higher risk. - **Malnutrition and Poverty**: Poor nutrition weakens the immune system and is common in areas with high TB prevalence. - **Living in High-Risk Environments**: Healthcare workers, prison populations, and people in homeless shelters have higher exposure rates. ### Symptoms of Active TB Active TB typically presents with respiratory and systemic symptoms, particularly in **pulmonary TB** (TB of the lungs). Common symptoms include: - **Chronic cough** (lasting three or more weeks) - **Hemoptysis** (coughing up blood) - **Chest pain** and shortness of breath - **Fever** and night sweats - **Unintended weight loss** and fatigue - **Loss of appetite** In cases of **extrapulmonary TB** (when TB spreads outside the lungs), symptoms depend on the affected area. Extrapulmonary TB can affect the lymph nodes, bones, joints, kidneys, and brain, potentially causing swollen lymph nodes, back pain, or neurological symptoms. ### Diagnosis of TB Infection Diagnosing TB infection involves identifying either latent infection or active disease: 1. **Latent TB Infection (LTBI)**: - **Tuberculin Skin Test (TST)**: Also known as the Mantoux test, it involves injecting a small amount of purified protein derivative (PPD) under the skin. A positive result (raised area at the injection site) indicates TB exposure, but it cannot distinguish between latent and active TB. - **Interferon-Gamma Release Assay (IGRA)**: A blood test that measures the immune response to TB antigens. Common IGRAs include the **QuantiFERON-TB Gold** and **T-SPOT.TB** tests. IGRAs are preferred for individuals who have received the [[BCG vaccine]], as they are more specific. 2. **Active TB Disease**: - **Chest X-ray**: Used to detect abnormalities in the lungs, such as cavitation or infiltrates, characteristic of active pulmonary TB. - **Sputum Smear Microscopy**: A sample of sputum is examined for acid-fast bacilli (AFB), which can indicate TB infection. - **Sputum Culture**: Culturing sputum can confirm TB and provide information on drug sensitivity, but it takes several weeks. - **Nucleic Acid Amplification Test (NAAT)**: Rapid test for detecting TB DNA in sputum samples, providing quicker results than culture. 3. **Drug Susceptibility Testing**: - Important for identifying drug-resistant TB strains and guiding effective treatment, particularly in patients with prior TB treatment or those from areas with high drug resistance rates. ### Treatment of TB Infection TB treatment varies depending on whether it is latent or active: 1. **Latent TB Infection (LTBI)**: - **Isoniazid** for 6-9 months or **Rifampin** for 4 months. - **Isoniazid and Rifapentine** once weekly for 3 months is another regimen, often used for patients at high risk of progressing to active TB (e.g., people with HIV). - Treatment of latent TB reduces the risk of progression to active disease, particularly in high-risk individuals. 2. **Active TB Disease**: - **Initial Phase**: Usually involves **four first-line drugs** for 2 months: **Isoniazid (INH)**, **Rifampin (RIF)**, **Pyrazinamide (PZA)**, and **Ethambutol (EMB)**. This regimen is often referred to as the "RIPE" regimen. - **Continuation Phase**: For the remaining 4-7 months, isoniazid and rifampin are continued. - Total treatment duration is typically **6-9 months**, but may be extended if there are complications, such as drug resistance or extrapulmonary TB. 3. **Multidrug-Resistant TB (MDR-TB)**: - MDR-TB, resistant to at least isoniazid and rifampin, requires longer and more complex treatment with second-line drugs, often lasting **18-24 months**. - Newer drugs like **bedaquiline** and **delamanid** are available for MDR-TB and XDR-TB (extensively drug-resistant TB) in cases where conventional treatments fail. ### Complications of TB If untreated or improperly managed, TB can lead to complications such as: - **Chronic Lung Damage**: Persistent inflammation and fibrosis, leading to respiratory impairment. - **[[Miliary TB]]**: A form of disseminated TB where bacteria spread throughout the body, causing small lesions in multiple organs. - **TB Meningitis**: TB infection of the central nervous system, leading to inflammation of the meninges surrounding the brain and spinal cord. - **Pott’s Disease**: TB infection of the spine, causing vertebral destruction and spinal deformity. ### Prevention of TB Infection Preventive measures for TB include: 1. **BCG Vaccine**: - The Bacillus Calmette-Guerin (BCG) vaccine is commonly given in countries with high TB prevalence. It provides limited protection, especially in children, but does not fully prevent TB in adults. 2. **Screening and Treatment of Latent TB**: - Screening for latent TB in high-risk populations (e.g., healthcare workers, people with HIV) and treating LTBI reduces the risk of progression to active disease. 3. **Infection Control**: - Isolation of patients with active TB, especially in healthcare settings. - Use of masks and proper ventilation to reduce the spread of TB bacteria. 4. **Public Health Measures**: - Public awareness, early diagnosis, contact tracing, and treatment compliance are essential for controlling TB transmission. ### Summary - **Tuberculosis (TB)** is caused by Mycobacterium tuberculosis, primarily affecting the lungs but potentially impacting other organs. - **Latent TB Infection (LTBI)** is asymptomatic and non-contagious, while **active TB** is symptomatic and contagious. - **Symptoms** of active TB include chronic cough, hemoptysis, night sweats, and weight loss. - **Diagnosis** involves skin tests, IGRAs, chest X-rays, sputum analysis, and culture. - **Treatment** consists of a 6-9 month regimen of antibiotics for active TB, with longer courses required for drug-resistant TB. Effective TB management involves early detection, prompt treatment, and compliance with public health measures to reduce transmission and prevent progression to severe disease. ### Reference: - ### Connected Documents: -