Legionellosis is caused by Legionella. The main route of transmission is through cooling water towers, faucets and shower equipment. Hot springs and swimming pools may also become a medium for transmitting the disease. On November 25, 2006, the CDC received a clinical specimen from Chu Shang Show Chwan Hospital. Legionella pneumophila was isolated form the urine specimen of the case, which tested positive for Type 1 serum antibody. L. pneumophila serotype I was later identified in the sputum specimen of the case. Days later, L. pneumophila serotype I was also isolated in the environmental specimens from a swimming pool in an elementary school in the Chu Shang Township. Pulse-field electrophoresis showed that the strain isolated from the case had identical restriction pattern with the strain isolated from the pool, confirming the relationship between the two strains.