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; ••: ••–••.