Biological Causes
Pulmonary tuberculosis is caused by a bacterium called Mycobacterium tuberculosis. When a person inhales these bacteria, they travel down the windpipe into the lungs. In many people, the body's immune system successfully contains the bacteria, preventing sickness; this is called latent tuberculosis. However, if the immune system cannot stop the bacteria from growing, they multiply and destroy lung tissue, resulting in active pulmonary tuberculosis disease.

Transmission
The bacteria spread through the air when a person with active pulmonary tuberculosis coughs, sneezes, speaks, or sings. People nearby may breathe in these microscopic droplets and become infected. It is not spread by shaking hands, sharing food or drink, touching bed linens, or sharing toilet seats. Prolonged or frequent contact is usually required for transmission.

Risk Factors
Certain factors increase the likelihood of becoming infected or developing active disease after infection. A weakened immune system is the most significant risk factor, as the body cannot fight the bacteria effectively. Common risk factors include:

• Having HIV/AIDS or other conditions that suppress the immune system
• Taking medications that weaken immunity, such as chemotherapy or biologic drugs for autoimmune diseases
• Diabetes mellitus or severe kidney disease
• Malnutrition or low body weight
• Tobacco use and excessive alcohol consumption
• Living or working in crowded conditions like nursing homes, shelters, or correctional facilities
• Traveling to or living in regions with high tuberculosis rates

Prevention
Prevention strategies focus on stopping transmission and preventing latent infection from becoming active. Primary prevention involves infection control measures like good ventilation and isolating infectious individuals. A vaccine called BCG is used in many countries for infants to prevent severe forms of the disease, though its use is less common in the United States. For those already exposed, preventive therapy with antibiotics can kill the dormant bacteria before they cause active disease. Maintaining a healthy immune system through proper nutrition and avoiding smoking also supports the body's natural defenses.

Signs and Symptoms
The symptoms of active pulmonary tuberculosis often develop gradually over weeks or months. Because the onset is slow, some people may not realize they are ill until the disease has progressed. The hallmark symptom is a bad cough that lasts three weeks or longer. Other common clinical signs include:

• Coughing up blood or mucus (sputum)
• Chest pain or pain with breathing and coughing
• Unexplained weight loss and loss of appetite
• Night sweats and fever
• Chills and profound fatigue

Diagnostic Tests
Clinicians use several tools to identify tuberculosis. A skin test (Mantoux tuberculin skin test) or a specific blood test (IGRA) checks for immune system exposure to the bacteria. If these are positive, further testing is needed to distinguish between latent infection and active disease. A chest X-ray is standard to look for lung changes, such as white spots or cavities. To confirm the diagnosis, a sample of sputum (phlegm) is collected and analyzed in a lab to detect the bacteria. Drug susceptibility testing is also performed to determine which antibiotics will work best.

Differential Diagnosis
Because symptoms like cough, fever, and weight loss are non-specific, pulmonary tuberculosis can be confused with other respiratory conditions. Doctors may consider pneumonia, lung cancer, chronic obstructive pulmonary disease (COPD), or fungal lung infections during the diagnostic process. A definitive diagnosis relies on identifying the specific bacteria in lab samples.

Medications and Treatment Protocols
The cornerstone of treating active pulmonary tuberculosis is a course of antibiotics. Treatment is extensive and typically lasts for six to nine months. It usually involves a combination of four different antibiotics for the first two months, followed by two antibiotics for the remaining period. This combination approach is vital to kill all bacteria and prevent them from becoming resistant to the drugs. Patients typically feel better within a few weeks of starting treatment, but the bacteria are still present in the body.

Adherence to Treatment
Strict adherence to the medication schedule is the most critical part of management. Stopping medication too soon or skipping doses can allow the bacteria to mutate and become drug-resistant, which is much harder and more toxic to treat. To ensure success, healthcare providers often use "Directly Observed Therapy" (DOT), where a health worker watches the patient swallow their medication every day or several times a week. This support helps patients complete the full course safely.

When to Seek Medical Care
Early medical intervention is essential to prevent the spread of infection and damage to the lungs. Individuals should see a doctor if they experience:

• A cough lasting more than three weeks
• Coughing up blood, even in small amounts
• Unexplained weight loss or drenching night sweats
• Persistent fever or chills

Emergency Care
Immediate medical attention is necessary if a person experiences severe difficulty breathing, significant chest pain, or coughs up a large amount of blood. Routine follow-up during treatment is required to monitor side effects and ensure the infection is clearing.

Severity and Disease Course
Pulmonary tuberculosis ranges from mild, latent infections (where the person is not sick) to severe, active disease that destroys lung tissue. Without treatment, the condition is serious and progressive. The bacteria can create cavities in the lungs and may spread to other parts of the body. The severity is often higher in people with compromised immune systems, such as those with HIV, where the disease progresses more rapidly.

Prognosis and Recovery
With modern medical treatment, pulmonary tuberculosis is almost always curable. The vast majority of patients who complete their antibiotic regimen fully recover without relapse. Recovery depends heavily on early diagnosis and adherence to the medication plan. Once a patient has completed therapy and tests show no bacteria, they are considered cured. However, significant lung damage that occurred before treatment may cause lasting breathing issues.

Complications
If left untreated or if treatment is interrupted, serious complications can arise. The most concerning is the development of Multi-Drug Resistant Tuberculosis (MDR-TB), which requires longer treatment with more side effects. Physical complications can include:

• Permanent lung damage or reduced lung function
• Spinal pain or joint damage if the infection spreads
• Inflammation of the membranes around the brain (meningitis)
• Liver or kidney problems, sometimes associated with medication side effects

Daily Activities and Isolation
During the first few weeks of treatment, patients with active pulmonary tuberculosis are often contagious. They may need to stay home from work, school, and social gatherings to avoid infecting others. Once a doctor confirms they are no longer infectious (usually after a few weeks of medication), they can return to normal activities. During the recovery phase, fatigue is common, so resting and gradually increasing activity levels is important.

Mental and Emotional Health
The long duration of treatment and the need for isolation can be isolating and stressful. Patients may feel stigma or anxiety about their diagnosis. Maintaining social connections through phone or video calls during the isolation period can help. Support groups or counseling can provide a space to discuss the challenges of sticking to a long medication schedule.

Questions to Ask Your Healthcare Provider
Being informed helps patients manage their condition effectively. Useful questions include:

• How long will I be contagious, and when can I return to work or school?
• What are the specific side effects of my medications, and which ones should I report immediately?
• How will we know if the treatment is working?
• Do my family members or housemates need to be tested?
• Are there foods or other medications I should avoid while taking these antibiotics?

Q: Is pulmonary tuberculosis contagious?
A: Yes, active pulmonary tuberculosis is contagious. It spreads through the air when an infected person coughs, sneezes, or speaks. However, it is not as easily spread as the flu or a cold; usually, you need to spend a lot of time with an infected person to catch it.

Q: What is the difference between latent TB and active TB disease?
A: In latent TB, the bacteria are in your body but are inactive; you do not feel sick, do not have symptoms, and cannot spread the disease to others. In active TB disease, the bacteria are multiplying, making you sick, and you can spread the infection.

Q: Can pulmonary tuberculosis be cured?
A: Yes, it is curable. Taking the prescribed antibiotics for the full duration (usually 6 to 9 months) kills the bacteria. Stopping treatment early can cause the disease to return and become resistant to drugs.

Q: Is there a vaccine for tuberculosis?
A: Yes, the BCG vaccine exists and is given to infants in many countries with high tuberculosis rates. It is not routinely used in the United States or other low-risk countries because it is not always effective in adults and can interfere with skin test results.

Q: Can I get tuberculosis more than once?
A: Yes, having had tuberculosis in the past does not guarantee immunity. You can be reinfected if you are exposed to the bacteria again, or a previous latent infection could become active if your immune system weakens.