Legionnaires’ disease is a severe infection caused by Legionella species, primarily L. pneumophila. L. pneumophila is responsible for 90 percent of infections. The disease is a common cause of severe pneumonia that requires hospitalization.  Symptoms may include a high fever, chills, cough, muscle aches, headaches, and diarrhea. In the United States, it is estimated that about 8,000 to 18,000 people hospitalized each year due to Legionnaires’ disease, however only about 3,000 cases are reported to the CDC.