Record High in Syphilis Cases Among Pregnant Women in Japan; Three-Fourths Had No Confirmed Symptoms at Time of Diagnosis

Yomiuri Shimbun file photo
The National Institute of Infectious Diseases in Shinjuku Ward, Tokyo

A total of 383 pregnant women were infected with syphilis in 2023, the highest number for Japan since 2019, according to preliminary data compiled by the National Institute of Infectious Diseases (NIID).

The NIID added data on pregnant women infected with syphilis to its statistics in 2019. The institute has called for caution because babies with congenital syphilis — which is transmitted to an unborn child in the womb — may develop hearing loss or intellectual disability.

The total number of syphilis cases confirmed in 2023 reached 14,906, the highest since 1999 when the current survey method was introduced, according to preliminary figures released by the institute.

More pregnant women were also infected with syphilis. The number of confirmed pregnancies at the time syphilis was diagnosed was about 200 per year from 2019 to 2021. The number rose to 267 in 2022 and to 383 in 2023, an increase of about 40%.

The preliminary figures for 2023 also showed that the number of babies with congenital syphilis also reached a record high.

The Yomiuri Shimbun

Syphilis is spread mainly through sexual contact. It causes lumps on the genitals and mouth, and a rash all over the body. Infection is detected by a blood test.

Of the pregnant women with syphilis, 75.2% had no confirmed symptoms at their time of diagnosis in 2023. Syphilis can be treated with antimicrobial agents.

“The syphilis test during pregnancy checkups can detect syphilis even if the patient is asymptomatic, so we want [pregnant women] to make sure they receive the test,” said Prof. Hiroshige Mikamo at Aichi Medical University, a specialist in clinical infectious disease. “If infected, prompt antimicrobial treatment can reduce the risk of mother-to-child transmission.”