The health authorities said Sunday they have confirmed four more cases of Influenza A, bringing the nation's total to 39.
One American infant and three Korean nationals were confirmed to have been infected with the H1N1 virus, according to the health ministry.
All four -- a 16-year-old Korean teenager, a 38-year-old Korean woman, a 28-year-old Korean college student and an 18-month-old American infant -- came from the United States this week and were quarantined and treated after showing flu-like symptoms, the ministry said.
Korea was considered relatively insulated from the highly contagious virus until last week, with just four confirmed cases reported.
The number, however, is growing sharply after a group of foreign English teachers was found to be infected by a fellow teacher who arrived here from the U.S. recently, raising concerns the virus might be spreading through person-to-person contact.
Thirteen confirmed cases in Korea are Korean nationals and 21 are U.S. citizens, according to the government.