The number of syphilis cases reported in Japan this year has exceeded 10,000. This is the fastest rate of increase seen since comparable data became available in 1999.

Japan's National Institute of Infectious Diseases said 10,110 cases had been reported as of September 3. That is about 1.24 times the number reported during the same period last year, which was a record high.

If the current pace of increase continues, the number of cases may reach a record high for the third year in a row.

Many cases were reported in urban areas. By prefecture, Tokyo recorded 2,490 cases, and Osaka had 1,365 cases. The number of infections also spiked in the prefectures of Saga, Nagasaki and Ishikawa.

Syphilis is a bacterial infection transmitted mainly through sexual contact. It is curable, but if the infection is not treated, it can cause serious problems in the brain or heart. If pregnant women are infected, their babies could be born with abnormalities.

An expert on sexually transmitted diseases says people who believe they may be infected should get tested, even if they do not have any symptoms.