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.
From Chapter 3:
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