Legionellosis and Legionnaires' Disease Comprehensive Study Guide

What media do we use for Legionellosis culture?

Buffered charcoal yeast extract (BCYE) agar is the primary medium used for isolation.

How does Legionella survive in macrophages?

Legionella enters macrophages via phagocytosis, evades lysosomal fusion, and establishes a specialized Legionella-containing vacuole (LCV) using the Dot/Icm Type IV Secretion System.

Name the most common species causing human infection.

The most common species causing human infection is Legionella pneumophila.

What is the mode of transmission of Legionella?

Legionella is transmitted through inhalation of contaminated aerosols from water sources.

EX : Ice a chain, Spa, AC, Shower, ថ្លុកទឹក …..

What is Pontiac fever?

Pontiac fever is a mild illness resembling the flu and typically resolves without medical treatment. Incubation 24h-48H

What is the drug of choice for treatment of Legionella?

The drug of choice for treatment of Legionella is respiratory fluoroquinolones like Levofloxacin or Moxifloxacin.

What are the treatment options for Legionella, including the specifics for fluoroquinolones, macrolides, and tetracyclines?

Treatment options for Legionella include:

1. Fluoroquinolones: Respiratory fluoroquinolones like Levofloxacin or Moxifloxacin (IV or oral) for $7$ to $14$ days; severely immunocompromised patients may require up to $3$ weeks.

2. Macrolides: Azithromycin is preferred (effective within $5$ to $10$ days); Clarithromycin and Erythromycin may be used but are less effective and limited to mild pneumonia.

3. Tetracyclines: Doxycycline is an alternative for mild pneumonia.

What are the treatment options for Legionella?

Treatment options for Legionella include:

1. Fluoroquinolones: Respiratory fluoroquinolones like Levofloxacin or Moxifloxacin (IV or oral) for $7$ to $14$ days; severely immunocompromised patients may require up to $3$ weeks.

2. Macrolides: Azithromycin is preferred (effective within $5$ to $10$ days); Clarithromycin and Erythromycin may be used but are less effective and limited to mild pneumonia.

3. Tetracyclines: Doxycycline is an alternative for mild pneumonia.

What is the pathophysiology of Legionella infection?

• Legionella enters the lungs via inhalation of contaminated aerosols.

• Once in the lung, it is engulfed by alveolar macrophages but evades destruction by blocking the fusion of phagosomes with lysosomes,

• utilizing the Dot/Icm Type IV Secretion System to inject effector proteins into macrophages.

• This leads to the establishment of a specialized Legionella-Containing Vacuole (LCV) for survival and replication.

• As nutrients deplete, Legionella triggers apoptosis in the host cell and exits to infect new cells, prompting an inflammatory response characterized by an influx of immune cells and potentially causing pneumonia and Acute Lung Injury (ALI).

• Extra pulmonary Legionellosis can occur in immunocompromised patients.