Legionella Update – Summer 2024

Overview:

Each year, thousands of patients are hospitalized throughout the US with infection due to Legionella¹.  Legionellosis is caused by Legionella pneumophila, a bacterium found in soil and water that can thrive in human-made water systems, such as plumbing systems, cooling towers and air conditioning units, sinks and showers, and decorative water features.  Persons can become infected when water reservoirs harboring Legionella bacteria are aerosolized and transmitted to the lungs of a susceptible host².  Because of its association with soil and water reservoirs, Legionella infection is more common in the summer and fall months³.

Risk Factors:

According to the CDC, persons considered to be at greater risk for Legionella infection include those with the following age or medical conditions:

• Age ≥50 years
• Chronic lung disease (such as emphysema or COPD)
• Immune system disorders due to disease, medication, or underlying malignancy
• Smoking (current or historical)
• Underlying illness such as diabetes, renal failure, or hepatic failure

Clinical Features of Legionella infection:

Infection with Legionella bacteria may lead to Legionnaire’s disease or Pontiac Fever.  Legionnaire’s disease is characterized by the presence of clinical and/or radiographic pneumonia.  Pontiac fever is a more mild, self-limited illness that typically occurs without pneumonia.  Hospitalization is common among patients with Legionella infection.

Why This Matters:

Frontline clinicians caring for patients with confirmed or suspected pneumonia should consider Legionellosis in their patients, particularly during the warmer and wetter months of the season.  The preferred diagnostic tests for Legionnaire’s disease are the Legionella urinary antigen and a respiratory culture for Legionella grown on selective media.  Both tests are available at Corewell Health.

Diagnostic Testing for Legionella:

In both the pre-and post-OEE environment, these diagnostic tests can be ordered as standalone tests or by using the preferred “Pneumonia Management” order set.  If a respiratory culture is ordered, a BPA will prompt the provider to consider ordering Legionella diagnostic testing for the patient, as well.

Thank you for providing exceptional care to our patients.  If you have any questions related to Legionella, please feel free to contact your local Infection Prevention and Epidemiology Department.

References:

1. Michigan Department of Health and Human Services. “MDHHS Legionellosis Surveillance and Outbreak Protocol.”  Published July 2021.  Accessed via michgan.gov on June 13, 2024.
2. Centers for Disease Control and Prevention.  “Clinical Features of Legionnaires' Disease and Pontiac Fever.”  Published January 29, 2024.  Accessed via CDC.gov on June 13, 2024.
3. Marston, BJ et al.  Surveillance for Legionnaires' disease. Risk factors for morbidity and mortality. Arch Intern Med. 1994; 154(21): 2417.