Legionella pneumophila is a bacteria that causes Legionnaires’ disease, a form of severe pneumonia which was first identified in 1976 during an American Legion convention in Philadelphia, Pennsylvania. The genus of Legionella contains more than 50 species, of which at least 24 have been associated with human infections. The best-characterized member of the genus, L. pneumophila, is the major causative agent of Legionnaires' disease, and comprises approximately 80 percent of reported human Legionella infections. L. pneumophila is a gram-negative, obligate aerobic bacteria that replicates within alveolar macrophages and epithelial cells. Each year, 8,000–18,000 people in the United States are hospitalized with Legionnaires’ disease. Smokers, the elderly, and individuals that are immunocompromised or have preexisting chronic lung disease are at higher risk of serious L. pneumophila infections that often are life-threatening.
There is currently no vaccine to prevent L. pneumophila infection or Legionnaires’ disease. Proactive ways to prevent the growth and spread of the bacteria include:
- Maintaining water temperatures below 20°C (below 77°F), or above 45°C (above 104°F)
- Avoiding water stagnation
- Keeping warm water sources clean
Laboratory diagnosis of Legionnaires’ disease is typically performed by detecting Legionella species in urine or sputum samples. Serological confirmation of infection can be performed by detecting a rise in the levels of antibodies to Legionella from two separate blood samples taken three to six weeks apart.
Legionella infections are susceptible to the usage of antibiotics, however the mortality rates of confirmed Legionnaires’ disease can be quite high, ranging between 5 and 30 percent. The signs and symptoms of Legionella infections are commonly similar to the signs and symptoms of “influenza-like” conditions, which is also referred to as Pontiac fever. Therefore, prompt and accurate diagnosis of the disease is critical to help prevent exposure of other individuals, particularly those who may have been exposed to contaminated water sources in areas such as the home, workplace, community water areas or even the hospital.
