The rubella epidemic is spreading quickly, particularly in the Kanto region.

Usually limited to developing countries, the disease, also known as German measles, poses a threat to pregnant women as it can cause disorders in fetuses, including hearing impairments, cardiac disease and cataracts.

Rubella cases spiked to 2,021 from Jan. 1 to March 21, 22 times the same period last year, the National Institute of Infectious Diseases said. Tokyo had the most cases at 899, followed by Kanagawa with 259 and Chiba with 167. Nearly 80 percent of the patients were male.