• Abstract

• Pulmonary tuberculosis (TB) is a chronic infectious disease caused by Mycobacterium tuberculosis, primarily affecting the lungs but with the potential to disseminate to other organs via hematogenous or lymphatic routes.

• It remains one of the most persistent and deadly communicable diseases globally, particularly in low- and middle-income countries where healthcare access, socioeconomic conditions, and comorbidities such as HIV contribute to high incidence and mortality rates.

• Despite the development of effective diagnostic tools and curative treatment regimens, TB control efforts are hampered by challenges such as delayed diagnosis, patient non-adherence, stigma, and the emergence of multidrug-resistant (MDR) and extensively drug-resistant (XDR) TB strains.

• This study comprehensively reviews the epidemiology, pathogenesis, risk factors, clinical features, diagnostic modalities (including molecular techniques like GeneXpert), current treatment protocols (including DOTS), and preventive strategies like BCG vaccination.

• Introduction

• Pulmonary Tuberculosis (TB), a form of tuberculosis involving the lung parenchyma, is the most prevalent and highly contagious manifestation of the disease. It is primarily transmitted via airborne droplets expelled by individuals with active TB during coughing, sneezing, talking, or even breathing. Inhalation of these infectious droplets can lead to latent or active infection, depending on the host's immune response.

• Despite the availability of effective treatment, pulmonary TB remains a significant public health challenge, particularly in resource-limited settings. According to the World Health Organization (WHO), approximately 10 million people develop TB each year, with over 1.5 million deaths, making it one of the leading causes of death from a single infectious agent, surpassing even HIV/AIDS.

Major Risk Factors for Pulmonary TB:

• Close contact with TB-infected individuals (especially in household or healthcare settings)

• Immunosuppression, particularly due to HIV/AIDS, cancer therapy, or organ transplantation

• Malnutrition, which weakens the immune system and increases susceptibility

• Chronic conditions like diabetes mellitus, which triple the risk of developing TB

• Substance use, including smoking and excessive alcohol consumption, which impair lung function and immunity

• Living in overcrowded, poorly ventilated, or unsanitary environments, common in refugee camps, prisons, or slums

• Young children and the elderly, due to their relatively weaker immune defenses

Addressing these risk factors through public health policies, vaccination programs, and early intervention strategies is crucial to curbing the spread of TB and improving treatment outcomes.

Methods

A structured literature review was conducted using PubMed, Scopus, Google Scholar, and WHO databases from 2012–2023. Clinical trials, national guidelines, and observational studies were prioritized to ensure evidence-based findings.

Search Terms Used:

“Pulmonary tuberculosis,” “Mycobacterium tuberculosis,” “TB diagnosis,” “GeneXpert,” “drug-resistant TB,” “DOTS,” “anti-TB therapy,” “TB-HIV coinfection,” “BCG vaccine.”

Inclusion Criteria:

• Peer-reviewed clinical studies

• National and WHO TB guidelines

• English-language articles

• Studies related to diagnosis, treatment, and prevention

Exclusion Criteria:

• Non-English publications

• Animal studies and non-human models

• Studies without clinical relevance to pulmonary TB

Diagnostic Techniques and Their Clinical Importance

1. Sputum Microscopy (Ziehl-Neelsen Staining):

   • Quick, cost-effective; detects acid-fast bacilli

   • Limited sensitivity in HIV+ and paucibacillary patients

2. GeneXpert MTB/RIF:

   • Rapid molecular test; detects M. tuberculosis and rifampicin resistance

   • WHO-endorsed for high-priority use

3. Chest X-Ray:

   • Supports diagnosis; identifies lung lesions, cavities, infiltrates

   • Not confirmatory without microbiological evidence

4. Tuberculin Skin Test (TST) & Interferon-Gamma Release Assays (IGRAs):

   • Detect latent TB infections

   • IGRAs preferred in BCG-vaccinated individuals

5. Culture (Löwenstein–Jensen medium or MGIT):

   • Gold standard for TB diagnosis

   • Time-consuming (up to 6 weeks) but allows drug susceptibility testing

Results

1. Epidemiology & Burden

   • TB is one of the top 10 causes of death worldwide

   • India, China, Indonesia, Philippines, and Pakistan have the highest burden

   • HIV co-infection and MDR-TB are major complicating factors

2. Clinical Features

   • Persistent cough (>2 weeks), hemoptysis

   • Fever, night sweats, weight loss, fatigue

   • Chest pain and breathlessness in severe cases

3. Pathogenesis

   • Inhaled bacilli reach alveoli, ingested by macrophages

   • Formation of granulomas to contain infection

   • Reactivation occurs in immunocompromised individuals

4. Treatment & Outcomes

   • Standard Regimen (2HRZE/4HR):

     • Isoniazid, Rifampicin, Pyrazinamide, Ethambutol for 2 months (intensive phase)

     • Followed by Isoniazid and Rifampicin for 4 months (continuation phase)

   • DOTS Strategy (Directly Observed Therapy, Short-course):

     • Ensures adherence, reduces resistance

   • Multidrug-Resistant TB (MDR-TB):

     • Requires second-line drugs like fluoroquinolones, bedaquiline

   • High success rates with adherence; however, MDR-TB treatment is longer and less effective

Discussion

Pulmonary TB continues to pose public health challenges, especially in resource-limited settings. The airborne nature of transmission and asymptomatic latent infections contribute to its widespread nature. Early and accurate diagnosis remains a cornerstone of TB control, with rapid molecular tests such as GeneXpert revolutionizing care in recent years.

The DOTS strategy, endorsed by WHO, has shown effectiveness in improving adherence and reducing transmission, but stigma, poor infrastructure, and socioeconomic barriers continue to hinder TB control efforts.

Emergence of drug-resistant TB, particularly MDR-TB and extensively drug-resistant TB (XDR-TB), calls for new drugs, shorter regimens, and robust surveillance systems.

To reduce the global burden:

• Universal access to rapid diagnostics and quality-assured treatment is essential

• Contact tracing and latent TB treatment can prevent new infections

• BCG vaccination at birth remains important in endemic regions

• Public health education can counter stigma and improve health-seeking behavior

Conclusion

Pulmonary tuberculosis remains a formidable global health challenge, even in the face of significant advancements in diagnostics and curative therapy. Its high transmissibility through airborne particles, the persistence of latent infections in a large proportion of the global population, and the emergence of multidrug-resistant (MDR) and extensively drug-resistant (XDR) TB strains continue to pose serious threats to public health.

Addressing this complex disease requires a multifaceted and aggressive approach. Early and accurate detection, prompt initiation of standardized treatment regimens, and adherence to long-term therapy are crucial for breaking the transmission cycle.

The integration of modern molecular diagnostics, such as GeneXpert and line probe assays, with traditional methods has significantly improved the ability to detect and manage TB, especially drug-resistant cases.

Furthermore, expanding equitable access to TB care, particularly in underserved and high-burden areas, alongside community education and awareness initiatives, plays a key role in reducing stigma and promoting treatment adherence. Strengthening health systems, ensuring uninterrupted drug supplies, and training healthcare personnel are foundational elements for effective TB control.

Ultimately, global cooperation, sustained research and innovation, and strong political commitment are essential to accelerate progress towards the WHO End TB Strategy goals, which aim to reduce TB deaths by 90% and incidence by 80% by 2030. By uniting efforts across countries, disciplines, and sectors, the vision of a TB-free world can become a reality.

Reference

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