Pulmonary Tuberculosis (TB) is a contagious and potentially life-threatening infection that primarily affects the lungs but can also spread to other organs. It remains one of the most common forms of tuberculosis and is the primary way TB is transmitted from person to person. Despite advances in medicine, TB continues to be a global health challenge, especially in areas with high prevalence rates such as Asia, Africa, and Eastern Europe.

Pulmonary TB is caused by the bacterium Mycobacterium tuberculosis, which triggers lung inflammation and damage. After exposure, the bacteria can remain inactive in the body for years in a state known as latent TB infection. While latent TB causes no symptoms and cannot spread to others, it may reactivate when the immune system weakens, leading to active pulmonary TB. Active TB is contagious and can cause permanent lung damage if not properly treated.

This article explores the causes, risk factors, transmission, symptoms, diagnosis, and treatment of pulmonary tuberculosis, as well as prevention strategies and long-term outcomes.

Pulmonary Tuberculosis is the manifestation of tuberculosis bacteria in the lungs. It represents the most common form of the disease and is responsible for the airborne spread of TB. TB bacteria can be inhaled into the lungs through tiny airborne droplets expelled when someone with active TB coughs, sneezes, or even talks. Once inside the body, the bacteria can either remain dormant (latent TB) or progress to active disease.

The distinction between latent TB infection (LTBI) and active pulmonary TB is crucial. People with LTBI do not feel sick and are not contagious, while those with active TB show symptoms and can spread the bacteria to others. Without timely treatment, active pulmonary TB can lead to severe complications and even death.

The primary cause of pulmonary TB is infection with Mycobacterium tuberculosis. However, certain risk factors increase susceptibility to infection or progression from latent TB to active TB disease.

Key risk factors include:

1. Weakened immune system:
   • HIV/AIDS
   • Organ transplant recipients
   • People undergoing chemotherapy
   • Chronic illnesses such as diabetes or kidney disease
   • Severe malnutrition
2. Close contact with infected individuals:
   • Living with or caring for someone with active TB
   • Spending time in crowded or poorly ventilated spaces increases transmission risk
3. Geographic exposure:
   • Living in or traveling to regions where TB is common, including parts of Asia, Africa, and Eastern Europe
4. Substance use:
   • Smoking, alcohol misuse, and recreational drug use weaken immune defenses, making infection more likely
5. Age and overall health:
   • Children, elderly adults, and those with chronic health conditions are at higher risk
6. Poor nutrition:
   • Malnutrition compromises the immune system, increasing vulnerability to both infection and reactivation of latent TB

Pulmonary TB spreads through airborne transmission. When a person with active TB coughs, sneezes, or even talks, they release droplets containing Mycobacterium tuberculosis into the air. These droplets can remain suspended for hours, especially in enclosed or poorly ventilated spaces.

Transmission and development occur in stages:

1. Exposure: A person inhales droplets containing TB bacteria.
2. Infection: The bacteria settle in the lungs and are ingested by immune cells called macrophages.
3. Latent or active disease: In healthy individuals, the immune system suppresses bacterial growth, leading to latent TB infection. In those with weakened immunity, the bacteria multiply and cause active TB disease.

Important facts about TB transmission:

• TB is not spread through shaking hands, sharing food or drink, touching surfaces, or kissing.
• Infection usually requires prolonged or close contact with someone who has active pulmonary TB.

Pulmonary TB remains a major public health problem worldwide. According to the World Health Organization, millions of new cases occur annually, with the highest burden in low- and middle-income countries. Migrants, healthcare workers, and individuals with compromised immune systems are disproportionately affected.

Efforts such as vaccination with the Bacillus Calmette-Guérin (BCG) vaccine, early screening, and improved access to treatment have reduced incidence in some regions, but TB continues to be a leading cause of infectious disease-related death globally.

The symptoms of pulmonary TB depend on whether the infection is latent or active, and they can vary in intensity, progression, and duration. Understanding these differences is critical, because latent TB may remain silent for years, while active TB produces noticeable and often debilitating respiratory and systemic symptoms that can worsen if untreated.

Latent TB infection:

• No symptoms
• Normal chest X-ray
• Negative sputum tests
• Positive TB skin test or blood test
• Not contagious

Active pulmonary TB:

• Persistent cough lasting more than 3 weeks
• Coughing up blood or thick mucus
• Chest pain when breathing or coughing
• Fatigue or weakness
• Unexplained weight loss
• Loss of appetite
• Low-grade fever
• Night sweats
• Shortness of breath (especially in advanced cases)
• Wheezing

Because TB symptoms resemble those of pneumonia, bronchitis, and other lung diseases, accurate testing and diagnosis are critical.

Diagnosing pulmonary TB requires a combination of clinical evaluation, imaging, and laboratory testing. Because TB symptoms can mimic many other respiratory conditions, physicians often rely on a stepwise process that begins with taking a thorough medical history and performing a physical examination, followed by specific diagnostic tests. This approach ensures not only that TB is confirmed accurately but also that other possible lung conditions are ruled out. The diagnostic process may involve multiple visits, repeat testing, and the integration of different forms of evidence to build a clear picture of whether the patient has latent or active TB infection.

Diagnostic methods include:

1. Medical history and physical exam: Review of symptoms, exposure risk, travel history, and physical signs such as weight loss or abnormal breath sounds.
2. Tuberculin skin test (Mantoux test): Injection of purified protein derivative (PPD) under the skin, with results assessed 48–72 hours later. Can yield false positives in those vaccinated with BCG.
3. Interferon-gamma release assays (IGRAs): Blood tests such as QuantiFERON-TB Gold measure immune response to TB antigens and help confirm latent infection.
4. Chest X-ray: Identifies lung abnormalities such as cavities, nodules, infiltrates, or fibrosis.
5. Sputum tests:
   • Sputum smear microscopy to detect acid-fast bacilli
   • Sputum culture for definitive diagnosis, though results may take weeks
   • GeneXpert MTB/RIF test, a rapid molecular test that identifies TB DNA and rifampicin resistance
6. CT scan or bronchoscopy: Advanced imaging or sampling for patients unable to provide sputum or with unclear results

Differential diagnosis for Pulmonary Tuberculosis

Because TB symptoms overlap with other pulmonary diseases, differential diagnosis is essential. Conditions to rule out include:

• Pneumonia
• Lung cancer
• Bronchitis
• Sarcoidosis
• Fungal infections
• Chronic obstructive pulmonary disease (COPD)

Pulmonary TB is treatable, but requires strict adherence to a lengthy antibiotic regimen. Treatment strategies depend on whether the TB strain is drug-sensitive or drug-resistant.

1. First-line treatment for drug-sensitive TB:

• Antibiotics used: Isoniazid (INH), Rifampicin (RIF), Pyrazinamide (PZA), and Ethambutol (EMB)
• Phases:
  • Intensive phase (2 months): All four drugs taken daily to reduce bacterial load.
  • Continuation phase (4 months): Typically Isoniazid and Rifampicin to eradicate remaining bacteria and prevent relapse.
• Completing the full course is vital to prevent recurrence and drug resistance.

2. Directly observed therapy (DOT):

• Healthcare providers or trained workers directly observe patients taking their medication.
• Improves adherence, ensures correct dosing, and reduces drug resistance.

3. Drug-resistant TB:

• MDR-TB (multidrug-resistant TB): Resistant to at least Isoniazid and Rifampicin.
• XDR-TB (extensively drug-resistant TB): Resistant to Isoniazid, Rifampicin, fluoroquinolones, and one or more second-line injectable drugs.
• Treatment is more complex, lasting 18–24 months or longer, using second-line drugs with more side effects.
• Requires close medical supervision and regular follow-up.

If untreated or inadequately treated, pulmonary TB can lead to serious complications, including:

• Permanent lung damage and scarring
• Chronic respiratory failure
• Spread of TB to other organs (extrapulmonary TB)
• Development of drug-resistant TB
• Increased mortality

The prognosis depends on timely diagnosis and adherence to treatment. With proper therapy, most patients with drug-sensitive TB can expect full recovery. However, delayed treatment, poor adherence, or drug-resistant TB can result in prolonged illness, complications, or death.

Preventing pulmonary TB requires a combination of medical and public health strategies:

• BCG vaccination: Provides partial protection, especially in children.
• Early detection and treatment: Reduces transmission and prevents complications.
• Infection control measures: Wearing masks, ensuring good ventilation, and isolating active TB cases.
• Healthy lifestyle: Good nutrition, quitting smoking, and managing chronic illnesses strengthen immunity.
• Adherence to treatment: Completing prescribed regimens to prevent drug resistance.

Living with TB can be challenging, but with the right support, recovery is achievable. Patients undergoing treatment should:

• Follow medication schedules precisely
• Attend all medical appointments
• Maintain good nutrition and rest
• Avoid smoking and alcohol use
• Practice infection control to protect others
• Seek emotional and social support, including counseling and patient support groups

Pulmonary Tuberculosis caused by Mycobacterium tuberculosis is a serious but preventable and treatable disease. While latent TB causes no symptoms and is not contagious, active TB can spread rapidly and cause severe lung damage. Early diagnosis, adherence to treatment, and preventive measures are critical for controlling TB both at individual and community levels. With global awareness and commitment, TB can be effectively managed and its impact reduced.

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