. A 60-year-old man is diagnosed to be suffering from Legionnaires’ disease after attending a conference. How did he acquire it?
**Core Concept**
Legionnaires' disease is a type of pneumonia caused by the bacterium *Legionella pneumophila*, which is typically acquired through inhalation of aerosolized water droplets contaminated with the bacteria. This occurs when the bacteria multiply in water systems, such as air conditioning units, cooling towers, or fountains, and are then dispersed into the air as water droplets.
**Why the Correct Answer is Right**
The correct answer is that the patient acquired the disease through inhalation of contaminated aerosolized water droplets. This occurs when the bacteria *Legionella pneumophila* multiply in water systems and are then dispersed into the air as water droplets, which the patient inhales. The bacteria can also be inhaled from contaminated water sources, such as hot tubs, whirlpools, or showerheads. The patient's attendance at a conference, where he may have been exposed to contaminated water systems, increases his risk of acquiring the disease.
**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because Legionnaires' disease is not typically acquired through direct contact with contaminated water. While direct contact can occur, inhalation of aerosolized water droplets is the primary mode of transmission.
* **Option B:** This option is incorrect because Legionnaires' disease is not typically acquired through ingestion of contaminated food or water. While ingestion can occur, inhalation of aerosolized water droplets is the primary mode of transmission.
* **Option C:** This option is incorrect because Legionnaires' disease is not typically acquired through vector-borne transmission, such as through mosquitoes or ticks. Inhalation of aerosolized water droplets is the primary mode of transmission.
**Clinical Pearl / High-Yield Fact**
Legionnaires' disease is often associated with outbreaks in hotels, hospitals, and other settings where water systems are shared among many people. This is because the bacteria can multiply in water systems and be dispersed into the air as water droplets, increasing the risk of transmission to others.
**Correct Answer: D. Inhalation of aerosolized water droplets contaminated with Legionella pneumophila.**