3.6: Pulmonary Tuberculosis I

Tuberculosis, often called TB, is a contagious illness primarily caused by Mycobacterium tuberculosis. It mainly affects the lung parenchyma but can also impact other body parts.

Causative Organism

The primary infectious agent causing tuberculosis is Mycobacterium tuberculosis, a slow-growing, acid-fast, aerobic rod that exhibits sensitivity to heat and ultraviolet light. Instances of Mycobacterium bovis and Mycobacterium avium contributing to the development of TB infection are rare.

Mode of Transmission

Mycobacterium tuberculosis primarily spreads through respiratory droplets generated when infected individuals breathe, talk, sing, sneeze, or cough. As the droplets evaporate, tiny nuclei measuring 1 to 5 µm remain suspended in the air for varying durations, ranging from minutes to hours. Another person can acquire the infection by inhaling these droplet nuclei. It is important to note that TB is not highly contagious, and transmission generally occurs with close, frequent, or prolonged exposure. Brief contact with a few tubercle bacilli rarely leads to infection. It is worth mentioning that TB cannot be transmitted through touch, sharing of food utensils, kissing, or any other form of physical contact.

Various factors increase the transmission probability, such as the number of microorganisms released into the air. The concentration of these microorganisms is higher in small and poorly ventilated spaces, like prisons and homeless shelters. The length of time of exposure also influences transmission. Additionally, the individual's immune system can impact the likelihood of transmission.

While anyone can contract TB, certain risk factors significantly increase the likelihood of transmission, including the following.

• Close contact with an individual with active TB increases the risk of inhaling airborne nuclei. The level of risk depends on the duration of exposure, proximity, and ventilation conditions.

• For instance, Healthcare workers are involved in high-risk activities, such as administering aerosolized medications, bronchoscopy, suctioning, caring for immunocompromised patients, and conducting anesthesia-related procedures like intubation and suctioning.

• Immunocompromised status encompasses individuals with HIV infection, cancer, organ transplant recipients, and those undergoing prolonged high-dose corticosteroid therapy. These conditions render the immune system vulnerable, necessitating special care and attention.

• Individuals who abuse alcohol or use intravenous drugs are at an increased risk of developing substance use disorder, which impairs their immune function and weakens their ability to fight infections, such as tuberculosis. Intravenous drug use, particularly through needle sharing, significantly increases the risk of contracting HIV. When left untreated, HIV causes a substantial reduction in CD4+ T-cells—cells that play a critical role in the immune response. This severe immunosuppression makes individuals far more vulnerable to opportunistic infections, including TB.

• Certain medical conditions or specialized treatments can heighten vulnerability. These include diabetes, chronic kidney disease, malnourishment, specific malignancies, hemodialysis, organ transplantation, gastrectomy, and jejunoileal bypass.

• Additionally, living in overcrowded and substandard housing, institutionalization, immigration from or recent travel to countries with a high prevalence of TB, and limited healthcare access are all factors that contribute to a higher risk of tuberculosis.

Tuberculosis or TB is an infectious disease caused by Mycobacterium tuberculosis primarily affecting the lung parenchyma.

It can also affect other body parts, such as the meninges, kidneys, bones, and lymph nodes.

The disease spreads through airborne droplets released when infected individuals breathe, talk, sing, sneeze, or cough.

These droplets evaporate, leaving tiny nuclei, ranging from 1-5 µm in size, suspended in the air for durations varying from minutes to hours. Inhaling these nuclei spreads the infection to others.

Several factors increase the risk of tuberculosis transmission.

Close contact with someone with active TB heightens the risk of inhaling airborne nuclei, depending on exposure duration, proximity, and ventilation conditions.

Healthcare workers performing high-risk procedures, such as bronchoscopy and suctioning, are particularly vulnerable.

Immunocompromised individuals, such as organ transplant recipients, people undergoing hemodialysis, and people with HIV, substance use disorders, or long-term diabetes, can heighten susceptibility to tuberculosis.

• Pulmonary Tuberculosis - An infectious disease primarily caused by Mycobacterium tuberculosis.
• Mycobacterium tuberculosis - The bacterium causing pulmonary tuberculosis, it can affect other body parts.
• TB Transmission - The TB spreads through respiratory droplets generated by infected individuals.
• Respiratory Droplet Nuclei - These tiny airborne particles carry Mycobacterium tuberculosis, they can be inhaled leading to transmission.
• Risk Factors - Certain conditions or behaviors, increase an individual's susceptibility to contracting tuberculosis.

• Define Pulmonary Tuberculosis – understand it's causes and symptoms (e.g., pulmonary tb).
• Contrast Active infection vs Latent infection – Identify key differences (e.g., symptom severity).
• Explore Transmission modes – Understand how Mycobacterium tuberculosis spreads (e.g., respiratory droplets).
• Explain Risk Factors – understand factors that increase chances of contracting TB.
• Apply in Healthcare Context – Learn about preventive methods and patient treatment.

• What is Pulmonary Tuberculosis and what causes it?
• How does the transmission of Mycobacterium tuberculosis occur?
• What are the risk factors contributing to the transmission of tuberculosis?

• Students - Provides clear understanding of TB causes, transmission, and prevention.
• Healthcare Workers - Offers guidelines for treating TB and preventing its spread.
• Public Health Officials - Aids in planning public health strategies for TB prevention and control.
• General Public - Helps in boosting awareness about TB and its prevention strategy.