Your nice cool air is not so nice!

       In 1976 the American Legion gathered in Philadelphia Pennsylvania at the Bellevue Stratford Hotel to prepare for a bicentennial celebration when 221 people were stricken with an unknown respiratory disease. Every known antibiotic was tried, most unsuccessfully, however erythromycin seemed to somewhat help. In the end, 34 people died. Two biologists, McDade and Shepard, with the CDC discovered that the causative agent was a small fastidious gram negative rod. They decided to name the bacteria for the unfortunate victims of the American Legion hence the name Legionella. The outbreak was thought to have been caused by contaminated water in the hotel’s air-conditioning system. Legionella bacteria are naturally occurring aquatic bacteria that grow in warm water, particularly in cooling towers, water heaters, and potable-water plumbing. Legionella species are intracellular pathogens residing inside of macrophages. Because of this, the antibiotics used to treat legionaire’s disease must remain active inside the macrophages. Currently macrolides and quinolones are the first choice of treatment.  Tetracyclines are also likely effective but Beta-lactam antibiotics are not. The outbreak in 1976 was a result of Legionella pneumophilia serogroup 1.  Legionella pneumophilia is the most common isolate accounting for 70-90%. There are 49 different Legionella species, 20 of which have been reported to infect humans. In addition, there are at least 16 different serogroups. Each year, between 8,000 and 18,000 people are hospitalized with Legionnaires' disease in the U.S. The actual number is thought to be higher since many infections are thought to be either not reported or not diagnosed. People most at risk of getting sick from the bacteria are people over 50, as well as people who are current or former smokers, or those who have a chronic lung disease like emphysema. The majority of the people at the American legion convention were over 50 making them at higher risk. People who take immunosuppressives are also at a higher risk. This was the case in a 47 year old man who received a heart transplant at UAB hospital in February 1986. In April 1986 a lung biopsy was performed on a lung lesion that had been identified. From that biopsy a new species of Legionella was identified and named Legionella birminghamensis.  Legionella is an obligate aerobe and best grown on BCYEa agar in about 2-5 days in the lab.  I have also added a short video that goes into more detail on the life cycle of Legionella.