Increased cervical Chlamydia trachomatis and syphilis infections in Japanese females of reproductive age in the late 2010s: Possible cause

Abstract

From 2000 to 2019, Japan's reproductive-age population gradually declined by 24%. In comparison, the Chlamydia trachomatis infection rate increased from 2016, with the syphilis infection rate increasing more sharply from 2014. Since 2013, the numbers of foreign tourists to Japan have also increased. From 2011 to 2018, the rate of increase in tourists was 5.02 times, while the rate of increase in syphilis patients was higher at 22.4 times. The lack of a one-to-one relationship between foreign tourists and syphilis cases suggests that cases of syphilis were transmitted to others. Although the prevalence of syphilis in the tourists' home countries (Korea in 2014 and China in 2013) was 20–30 times higher than that in Japan, the Japanese sex industry did not discriminate against foreign tourists, leading to increased STI infections in Japanese female sex workers. Indeed, from 2017 to 2018, a history of working in the sex industry for six months was identified as a risk factor for syphilis. The rise in Chlamydia trachomatis infections has lagged behind that of syphilis by two years, with the rate of increase lower. We suspect the difference in increasing rates of syphilis and chlamydial infections is due to the different methods of infection: syphilis can be transmitted by light physical contact, such as a kiss, whereas chlamydia requires close sexual contact, such as oral sex or sexual intercourse. Regardless, examinations and infection control are necessary to prevent the spread of STIs in Japan due to inbound tourists.