The number of syphilis patients is rising rapidly, especially among young women, according to new statistics issued by the National Institute of Infectious Diseases.

Syphilis, a bacterial infection mainly spread by sexual contact and whose cases surged to epidemic proportions worldwide in the 1960s, has been making a quiet comeback in Japan in the last 10 years or so.

The number of patients reported between Jan. 1 and Oct. 28 was 2,037, already surpassing 1,617, the number logged for 2014, the NIID said.

Of the 2,037 cases, men accounted for 1,463 and women for 574.

By age, females aged 15 to 35 made up more than 75 percent of the cases involving women, or 437. In particular, women from 20 to 24 were found to be the most vulnerable with 177 cases, 2.7 times last year's level.

Ten cases out of the total for men and women were congenital, meaning the patients were infected before or at birth through their mothers.

The number of women contracting syphilis through heterosexual contact stood at 405, 2.1 times last year's level.

"Education needs to be stepped up, especially among high-risk groups," the NIID said in its report on syphilis issued earlier this month.

"Sexual contact with unspecified individuals is a risk, and so is sex without appropriate use of condoms. Education should focus on the fact that syphilis can also be spread by oral sex or anal sex, and that the syphilis bacteria can stay dormant in the body and become active again."

The disease starts as a painless sore — typically on genitals, rectum or mouth. Syphilis spreads via skin or mucous membrane contact with these sores.

If detected early, syphilis can be cured with penicillin. Without treatment, syphilis can severely damage the heart, brain or other organs, and can be life-threatening.