Legionnaires' Disease Outbreak at a Resort in Cozumel, Mexico.

 A Legionnaires' disease (LD) outbreak at a resort on Cozumel Island in Mexico was investigated by a joint Mexico-United States team in 2010. This is the first reported LD outbreak in Mexico, where LD is not a reportable disease.  Reports of LD among travelers were solicited from US health departments and the European Working Group for Infections. Records from the resort and Cozumel Island health facilities were searched for possible LD cases. In April 2010, the resort was searched for possible exposure sources. The temperature and total chlorine of the water at 38 sites in the resort were measured, and samples from those sites were tested for .  Nine travelers became ill with laboratory-confirmed LD within 2 weeks of staying at the resort between May 2008 and April 2010. The resort and its potable water system were the only common exposures. No possible LD cases were identified among resort workers. were found to have extensively colonized the resort's potable water system. matching a case isolate were found in the resort's potable water system.  Medical providers should test for LD when treating community-acquired pneumonia that is severe or affecting patients who traveled in the 2 weeks before the onset of symptoms. When an LD outbreak is detected, the source should be identified and then aggressively remediated. Because LD can occur in tropical and temperate areas, all countries should consider making LD a reportable disease if they have not already done so.