Trends in the incidence of syphilis in the middle‐aged and older adults in Japan: A nationwide observational study, 2009–2019

Aim Sexually transmitted infections remain a neglected area of research in geriatrics. However, in the global aging societies, sexual health among the middle‐aged and older adults is an emerging public concern. High‐income countries are facing a resurgence of syphilis cases among young generations, but little is known about its prevalence in older populations. We aimed to investigate the national trend of syphilis cases in Japan. Methods This nationwide observational study used the publicly‐available database (2009–2019) to calculate crude and age‐adjusted incidence rates of syphilis per 100 000 population by age, sex and clinical stage. We collected data from patients aged ≥50 years and performed joinpoint regression analysis to estimate long‐term trends and average annual percentage changes (AAPCs). Results The total number of patients with syphilis increased about 8‐fold from 165 in 2009 to 1280 in 2019. AAPCs of crude incidence rates significantly increased in every age category; 33.2% in 50–59 years, 23.8% in 60–69 years and 20.9% in ≥70 years. Age‐adjusted incidence rates have surged at AAPCs of 28.7% in men and 23.1% in women, reaching 4.09 in men and 0.71 in women in 2019. By clinical stage, marked increases were observed in primary (AAPCs, 42.3% in men and 41.6% in women) and secondary syphilis (AAPCs, 24.9% in men and 24.2% in women). Conclusions An up‐toward trend of syphilis among people aged ≥50 years was observed. The importance of sexual health among older people should be highlighted in this aging Japanese society. Geriatr Gerontol Int 2022; 22: 1019–1024. In Japan, an up‐toward trend of syphilis among people aged 50 years or older was observed. The importance of sexual health among older people should be highlighted in this aging Japanese society.