Association of HIV-syphilis coinfection with optimal antiretroviral adherence: a nation-wide claims study.

Condomless sex is not totally discouraged after achieving undetectable human immunodeficiency virus (HIV) load, but the prevalence of sexually transmitted diseases (STDs) in the group is unknown. This study was retrospective in nature, using the claims database of the National Health Insurance system from 2008 to 2016. The clinical characteristics of people living with HIV with or without syphilis coinfection were analyzed. People with HIV and syphilis coinfection were divided into two groups according to antiretroviral therapy adherence, as optimal and suboptimal adherence groups by a medication possession ratio of 95%. Of the 9393 people living with HIV, 4536 (48.3%) were diagnosed with syphilis coinfection. Optimal adherence was associated with syphilis coinfection (odds ratio [OR] 1.18; 95% confidence interval [95CI] 1.08-1.30; p = .001). This suggests that unsafe sex occurs regardless of medication adherence. Being male, bacterial/protozoa STDs, and genital herpes virus infection were also risk factors for HIV-syphilis coinfection. Although HIV is unlikely to be transmittable when viral load is controlled, consistent use of condoms is necessary to prevent infection with syphilis.