Daniel D. Rhoads, MD, FCAP, chair of the CAP Microbiology Committee, shares insights on common questions about Legionnaires' disease.
What is Legionnaires' disease?
Legionnaires' disease is a serious type of pneumonia caused by Legionella species bacteria, most commonly, L. pneumophila. These bacteria commonly live in freshwater environments but can become a health concern when they grow in human-made water systems such as cooling towers, hot tubs, decorative fountains, and large plumbing systems.
What are the symptoms of Legionnaires' disease?
Common symptoms include fever, chills, cough, muscle aches, headache, fatigue, and shortness of breath. Some people may also experience confusion, diarrhea, or loss of appetite. Because the disease is a form of pneumonia, symptoms can become severe and require hospitalization, especially in high-risk individuals.
How is Legionnaires' disease diagnosed?
Legionnaires' disease can be diagnosed using laboratory testing. Most commonly, urine is tested to detect an antigen from the bacterium, and if the antigen is detected, then it indicates the bacterium is in the body. Only the most common cause of Legionnaires’ disease can be detected using urine. A second type of test that can be used to detect the Legionella species is a culture of sputum or other respiratory specimens using a special nutrient medium designed especially for Legionella species, which is called buffered charcoal yeast extract (BCYE) medium. Legionella species do not grow using the typical lab methods that can detect other causes of bacterial pneumonia. It is important to use BCYE medium. Third, molecular methods such as polymerase chain reaction (PCR) can be used to detect the DNA of the bacteria. Pathologists and laboratory professionals perform and interpret these specialized tests to help to confirm Legionnaires’ disease.
Why can Legionnaires' disease be difficult to diagnose?
The symptoms often resemble other forms of pneumonia, influenza, or respiratory infections; and Legionella species can only be detected using specialized testing that specifically looks for Legionella species (described above). Without specific testing, Legionnaires' disease may be overlooked, making laboratory confirmation essential for an accurate diagnosis.
Can Legionella be detected on routine laboratory testing?
No. Detecting Legionella requires targeted testing, such as a urinary antigen test, culture specifically for Legionella species, or PCR assays specifically designed to identify the cause of Legionnaires’ disease.
When should someone be tested for Legionnaires' disease?
Testing should be considered for patients with pneumonia, particularly those with severe illness, recent exposure to potential sources of Legionella, or risk factors such as older age, smoking history, chronic medical conditions, or a weakened immune system. Certain clinical and radiographic findings help a physician to know whether or not Legionnaires’ disease might be the cause of pneumonia, so they can request appropriate laboratory testing.
What role do pathologists play in diagnosing Legionnaires' disease?
Pathologists and laboratory professionals play a critical role in identifying Legionella infections. Pathologists oversee laboratory testing, ensure diagnostic accuracy, help differentiate Legionnaires' disease from other causes of pneumonia, and provide results that guide treatment decisions and public health investigations.
How does Legionella spread?
People become infected by breathing in tiny water droplets or mist containing Legionella bacteria. Less commonly, infection can occur when contaminated water is accidentally aspirated into the lungs. Common sources of exposure include cooling towers, hot tubs, decorative fountains, showerheads, and complex building water systems.
Is Legionnaires' disease contagious?
No, Legionnaires' disease is not spread from person to person. Infections occur after exposure to contaminated water sources.
Where is Legionella commonly found?
Legionella bacteria are naturally present in lakes, rivers, and other freshwater environments. Human infections typically occur when the bacteria grow in building water systems where conditions such as warm temperatures, stagnant water, inadequate disinfectant levels, or biofilm facilitate the cells’ replication.
Who is most at risk for Legionnaires' disease?
Adults aged 50 years and older, current or former smokers, people with chronic lung disease, diabetes, kidney or liver disease, cancer, and individuals with weakened immune systems are at increased risk of developing severe illness.
How is Legionnaires' disease treated?
Legionnaires' disease is treated with antibiotics, commonly azithromycin. Early diagnosis and prompt treatment improve outcomes and reduce the risk of serious complications. Most patients recover with appropriate medical care.
Can you get Legionnaires' disease from drinking water?
Legionnaires' disease is not acquired by drinking water, but in some cases, contaminated water may cause infection if it is accidentally aspirated into the lungs while drinking. Infection occurs when the bacteria are inhaled, typically via contaminated water droplets.
Can you get Legionnaires' disease from air conditioning?
Home and automobile air-conditioning systems are not considered sources of Legionella because they do not use water to cool the air. However, large cooling towers associated with some building air-cooling systems can support bacterial growth and may spread contaminated mist if not properly maintained.
How can Legionnaires' disease be prevented?
The most effective prevention strategy is proper maintenance and management of building water systems. Monitoring water quality, maintaining appropriate disinfectant levels, controlling water temperature, and preventing stagnation can reduce the likelihood of Legionella growth.