Legionella pneumonia, an infectious disease with high fatality, produces symptoms after inhalation of an aerosol contaminated by Legionella species. Legionella bacteria are Gram-negative, glucose-nonfermentative, and proliferative in human macrophages and monocytes. Over 40 types of Legionella species are pathogenic in human beings. Of these,L. pneumophilahas the strongest pathogenicity. Hot springs and bathtubs with circulating systems are considered sources of infection and sometimes cause cases of hospital-acquired infection. The urinary antigen detection test is a new diagnostic technique, and proved to be effective for rapid and correct diagnosis ofL. pneumophilaserogroup-1 infection.