**Core Concept:** The transmission of tuberculosis (TB) is influenced by several factors including the infectiousness of the TB patient, the duration of close contact, and the susceptibility of the exposed person. TB infection is primarily spread through the air when an infected person with active TB disease coughs, sneezes, or speaks, releasing mycobacteria into the air. These mycobacteria can remain airborne for several hours and can be inhaled by others, leading to infection.

**Why the Correct Answer is Right:** The correct answer, **C. 2-3**, represents the approximate number of people an infectious TB patient can infect within a year. This value is based on the concept of infectiousness, which is determined by the extent of lung involvement and the presence of TB symptoms. A higher infectiousness index correlates with more people being infected. In the context of TB, a person with active TB disease is considered more infectious than someone with latent TB infection (LTBI).

**Why Each Wrong Option is Incorrect:** Option **A:** One infected person can infect fewer than 2-3 people if the infection is latent, as LTBI individuals are less infectious. Option **B:** One infected person can infect more than 2-3 people in a year if the TB disease is severe and the person is coughing heavily, increasing the chances of transmission. Option **D:** This option does not accurately represent the number of people an infectious TB patient can infect in a year.

**Clinical Pearl:** Latent TB infection (LTBI) is a condition where an individual has been infected with TB bacteria but is not yet diseased. LTBI individuals can progress to active TB disease later in life if their immune system weakens, such as in immunocompromised individuals or following stress. Early diagnosis and treatment of LTBI can prevent the development of active TB disease and its complications, reducing the risk of transmission.

**Correct Answer:** C. 2-3

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**Question:** A person with active tuberculosis (TB) disease can infect how many people in a year?

**Core Concept:** TB is a communicable airborne infection caused by the bacterium Mycobacterium tuberculosis. Infected individuals with active TB disease can transmit the infection to a small proportion of the contacts. The number of contacts depends on factors such as the severity of the disease, the duration of exposure, and the susceptibility of the contact person.

**Why the Correct Answer is Right:** An infectious TB patient can infect an average of 2-3 people in a year, considering factors such as the extent of lung involvement and the frequency of coughing. The number is not fixed and may vary depending on the severity of the TB disease and the time spent in close contact with the infected person.

**Why Each Wrong Option is Incorrect:**

- Option **A**: One infected person may infect fewer than 2-3 people if the TB disease is mild and the individual does not cough frequently.
- Option **B**: One infected person may infect more than 2-3 people if the disease is severe and the person coughs frequently for a long period. However, this option is still not precise because the actual number of infections depends on various factors mentioned above.
- Option **C**: