The main cause of the onset of Legionnaires’ disease is bacterial infection of the genus Legionella. Legionella bacteria are widely present in the natural environment of freshwater waters, such as lakes, ponds, etc., the source of infection is the water source and air conditioning system, through airborne usually in the form of aerosols with the human respiratory movement from the respiratory tract into the human body to become infected, common infections of the human body legionella bacteria, including Legionella pneumophila, Legionella longbeach, Legionella mikeddale, and so on. It often manifests as myalgia, fever, headache or cough, high fever, and diarrhea. The disease caused by Legionella infection is called Legionnaires’ disease, so it can be said that the main cause of Legionnaires’ disease is Legionella bacterial infection, which is contagious and can be transmitted from person to person. There are two types of Legionnaires’ disease: non-pneumonic Legionnaires’ disease and pneumonic Legionnaires’ disease, and the latter is more serious, which can be cured with active treatment and has a good prognosis. When you find Legionnaires’ disease, you need to consult a regular hospital in time and standardize the treatment, do not delay, which will affect the prognosis of the disease and cause other people to be infected.