Half of Seoul-based patients of waterborne diseases this year contracted their illnesses overseas, the city government said Wednesday as it urged extra caution for travelers. According to the Seoul Metropolitan Government, 20 of 40 waterborne disease patients in the city so far this year were infected outside the country. Among them, seven contracted bacterial dysentery, and six had typhoid. The total number of waterborne disease patients represents a 17.6-percent increase from a year ago, the government said.