Legionella Pneumonia: Etiology and Treatment

Etiology

Legionella pneumonia is caused by Legionella species, most commonly Legionella pneumophila, which are gram-negative bacteria found in natural and man-made aquatic environments, according to the MMWR Recommendations and Reports 1

Water distribution systems are the primary reservoir, including heated potable water systems, cooling towers, evaporative condensers, showers, faucet aerators, and hot-water tanks, as reported by the MMWR Recommendations and Reports 1, 2, 3, 4
Optimal growth conditions include water temperatures of 25-42°C (77-108°F), water stagnation, presence of scale and sediment, and free-living aquatic amoebae that support intracellular bacterial growth, according to the MMWR Recommendations and Reports 1

Severely immunosuppressed patients, including hematopoietic stem cell transplant (HSCT) recipients, solid organ transplant recipients, and patients with hematologic malignancies, are at markedly increased risk, as stated by the MMWR Recommendations and Reports 1
Patients with chronic conditions, including end-stage renal disease, diabetes mellitus, underlying lung disease, and functional asplenia, have elevated risk, according to the American Journal of Respiratory and Critical Care Medicine and the MMWR Recommendations and Reports 1, 5

Maintain water temperatures >51°C (>124°F) or <20°C (<68°F) at outlets, especially in facilities housing transplant recipients, as recommended by the MMWR Recommendations and Reports 2, 3, 4
Remove faucet aerators in areas for severely immunocompromised patients if Legionella is detected, according to the MMWR Recommendations and Reports 2, 3, 4
Restrict showers for severely immunocompromised patients and provide sterile water for drinking, tooth brushing, and sponge baths if water contamination is detected, as recommended by the MMWR Recommendations and Reports 2, 3, 4
Maintain cooling towers with drift eliminators, regular biocide use, and proper maintenance records, according to the MMWR Recommendations and Reports 2, 3, 4

Patients with hematologic malignancies or end-stage renal disease are at risk of developing Legionella lung abscesses, according to the American Thoracic Society 6

The clinical presentation of Legionella lung abscess may include symptoms indistinguishable from other causes of pneumonia, as stated by the Infectious Diseases Society of America 6, 7
Diagnosing Legionella lung abscess can be challenging because Legionnaires' disease cannot be distinguished clinically or radiographically from pneumonia caused by other agents, as noted by the Centers for Disease Control and Prevention 8
Culture of respiratory secretions or tissues on selective media is the most specific test for diagnosing Legionella lung abscess, recommended by the Infectious Diseases Society of America 7, 9
Urinary antigen testing for L. pneumophila serogroup 1 is a rapid diagnostic approach, but it only detects serogroup 1, as stated by the Infectious Diseases Society of America 7, 10

Azithromycin or a fluoroquinolone (moxifloxacin, gatifloxacin, levofloxacin) are preferred antibiotics for hospitalized patients with Legionella lung abscess, recommended by the Infectious Diseases Society of America 7

Maintaining proper water temperatures, preventing water stagnation, and regular cleaning can help prevent Legionella infections in healthcare settings, as recommended by the Centers for Disease Control and Prevention 8
Following CDC/HICPAC guidelines for preventing healthcare-associated pneumonia can also help prevent Legionella infections, as stated by the American Thoracic Society 11