Legionellosis is a clinical syndrome caused by Legionella bacteria. 1976 was named after the outbreak of the veterans conference in Philadelphia, USA. Pathogens mainly come from soil and sewage, spread by air and invade from respiratory tract. According to the guidelines of the World Health Organization (WHO) in 2007, Legionellosis can be divided into three subtypes: ① Legionella pneumonia (LD) with pneumonia as the main clinical manifestation, also known as Legionella pneumonia; ② Extrapulmonary syndrome, that is, infection spreads from the lung to other systems outside the lung; ③ Pontiac fever is mainly characterized by acute fever, and the course of disease is self-limited. The main pathogen of Legionellosis is Legionella pneumophila serum 1 type. There are more men than women. The elderly, smokers, alcoholics and immunocompromised people are prone to this disease.