Syphilis cases head toward new annual record in Japan

The Japanese government has mandated that all diagnosed cases of syphilis be reported under the Notifiable Disease Surveillance law since 1948. The annual number of reported syphilis cases throughout the country ranged from 500 to 900 between 2000 and 2012. However, the number has indicated a steady and alarming increase since then: 1228 in 2013, 1661 in 2014, 2690 in 2015, 4575 in 2016, 5826 in 2017, and 7002 (5.6 per 100,000; males, 4588; females, 2414) in 2018 and finally hitting 7,983 cases in 2021.

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Last year, the number of reported syphilis patients hit a record high with 13,228 total cases in 2022.

In 2023, the number of cases reported by the National Institute of Infectious Diseases (NIID) through October 8 shows 11,546 cases, and on the way to setting another annual record with nearly three months left in the year.

Tokyo (2823) and Osaka (1558) prefectures have seen the most cases this year, followed by Fukuoka, Aichi and Hokkaido.

In addition to the large numbers of primary and secondary syphilis reported in Japan in recent years, the country has also seen an increase in congenital syphilis, caused by mother-to-child transmission, with about 20 reported annually since 2018.

Syphilis was a major issue in Japan until shortly after the end of World War II, but the total reported cases declined to several hundred annually until about a decade ago, when a rebound began.

According to a paper published in the Journal of the Japan Medical Association (JMA) in 2019, changes of sexual behavior or commercial sex work, insufficient funding for prevention, and poor education during school years are possible causes of the increase in the number of sexually transmitted infections (STIs), but the true reasons for the current syphilis resurgence in Japan still remain unknown.

Some hypothesize about its association with the abrupt increase in the number of foreign visitors to Japan, a 3.43 times increase in 2017 compared to 2012. Alternatively, its been hypothesized that the explosive spread of specific software applications (apps) on smartphones used to locate and connect with members of the opposite sex (also known as mobile dating apps) launched in 2012, and that had gained wide-ranging popularity since 2013, might have contributed to the significant rise in syphilis cases due to their potential to accelerate casual sex among unfamiliar partners.

Syphilis is a sexually-transmitted infection that can cause long-term complications if not treated correctly. Symptoms of syphilis in adults include a painless sore that will go away without treatment followed by a non-itchy body rash. If left untreated syphilis can lead to damage through the body including neurological and cardiovascular complications. 

Congenital syphilis is an infectious disease transmitted by an infected mother to her baby in the womb. Adults transmit syphilis through sexual contact but mothers can transmit the infection to their baby in the womb or through the birthing process. The disease can cause miscarriage, stillbirth, death shortly after birth, prematurity and birth defects. A woman can be treated and cured for syphilis during pregnancy, but it is important for women to be tested in time for treatment to be effective. Babies who test positive for syphilis at birth must be treated immediately to prevent serious health issues.