Tuberculosis (TB) is a contagious disease caused by the bacterium Mycobacterium tuberculosis. While it primarily affects the lungs, it can also impact other organs like the brain, spine, and kidneys. The bacteria spread through the air, and the infection can exist in a dormant state or become an active disease. Although TB is treatable and curable with medication, it remains a notable global health concern.
How Tuberculosis Spreads and Develops
Tuberculosis is an airborne disease transmitted when a person with active TB in their lungs or throat coughs, speaks, or sneezes, releasing microscopic droplets into the air. People nearby can inhale these germs and become infected, with the risk increasing in enclosed spaces with poor air circulation. It is not spread by shaking hands, sharing food, or touching surfaces like bed linens or toilet seats.
Once the bacteria enter the body, the infection can manifest in two states. The first is Latent TB Infection (LTBI), where the immune system contains the germs and prevents them from multiplying. In this state, the person does not feel sick, has no symptoms, and cannot spread the disease, though the bacteria can become active later.
The second state is Active TB Disease, which develops when the immune system can no longer control the bacteria. This can happen soon after infection or years later, particularly if the immune system weakens. An individual with active TB disease feels sick, has symptoms, and can transmit the bacteria to others.
Signs and Symptoms of Active TB
When TB becomes active, the signs and symptoms often develop gradually. The most common indicator of active pulmonary TB is a persistent cough that lasts for three weeks or longer. This cough may be accompanied by the production of sputum (mucus from the lungs) and, in some cases, blood.
Beyond the cough, individuals with active TB frequently experience chest pain, which can be noticeable when breathing or coughing. Other common symptoms include unexplained weight loss, a diminished appetite, and a feeling of fatigue or weakness. Many people with active TB also report experiencing fever, chills, and drenching night sweats.
Diagnosis and Medical Evaluation
Diagnosing tuberculosis begins with screening tests to detect the presence of Mycobacterium tuberculosis. One common method is the tuberculin skin test (TST), or Mantoux test, which involves injecting a substance into the skin of the forearm and observing the reaction. Another option is a TB blood test, or Interferon-Gamma Release Assay (IGRA), which measures the immune system’s reaction to TB bacteria.
A positive result on either the skin or blood test indicates that the person has been infected with TB bacteria, but it does not distinguish between latent infection and active disease. If one of these initial tests is positive, further diagnostic steps are required to confirm if the disease is active.
To confirm a diagnosis of active pulmonary TB, a chest X-ray is performed. The X-ray can reveal abnormalities in the lungs that are characteristic of the disease. In addition to imaging, analyzing sputum samples is a key diagnostic tool, as it can directly identify the presence of the TB bacteria.
Standard Treatment Regimens
Treatment for both latent and active tuberculosis involves a course of specific antibiotics. For active TB, a combination of drugs is used to kill all the bacteria and prevent antibiotic resistance. The most common first-line medications include:
- Isoniazid
- Rifampin
- Pyrazinamide
- Ethambutol
The duration of treatment for active TB is lengthy, lasting for six months or sometimes longer. It is important that patients complete the entire course of medication without interruption, even if they start to feel better. Stopping treatment prematurely can lead to a relapse and allows surviving bacteria to develop resistance.
Failure to complete the full treatment course is a primary driver of Multidrug-Resistant TB (MDR-TB). This is a form of the disease caused by bacteria resistant to at least isoniazid and rifampin, the two most potent TB drugs. Treating MDR-TB is much more complicated, requiring second-line drugs that are often less effective, more toxic, and must be taken for up to two years.
Risk Factors and Prevention
A weakened immune system is the most significant risk factor for developing active TB disease after being infected. This can be due to medical conditions like HIV/AIDS, diabetes, or certain cancers. Treatments that suppress the immune system, such as chemotherapy or medications used after an organ transplant, also elevate this risk.
Other risk factors include malnutrition, low body weight, alcohol misuse, and smoking. Close and prolonged contact with a person who has active TB disease also increases the likelihood of becoming infected. Living in or traveling to parts of the world where tuberculosis is more common presents a higher risk of exposure.
Preventive measures for TB are available. For individuals with latent TB infection, especially those with weakened immune systems, taking a course of antibiotics can prevent the infection from becoming active. The Bacille Calmette-Guérin (BCG) vaccine is used in many countries with high TB prevalence to prevent severe forms of the disease in young children, though its effectiveness in adults is variable.