Temporal Trends in Population Level Impacts of Risk Factors for Sexually Transmitted Infections Among Men Who Have Sex with Men, Heterosexual Men, and Women: Disparities by Sexual Identity (1998-2013)

Sexually transmitted infections (STIs) remain a significant public health problem worldwide. We aimed to describe the temporal trends and relative contributions of established risk factors to STIs among sexual health center attendees. This retrospective study included more than 90,000 individuals who attended a sexual health center in Sydney, Australia, during the period 1998-2013. Multivariable logistic regression models were used to identify the correlates of STI diagnoses for three groups: men who have sex with men (MSM), heterosexual men, and women separately. Trends in population attributable risk percentages (PAR%) were estimated to assess the relative contributions of the risk factors on STI diagnosis. STI diagnosis rates among sexual health clinic attendees increased by 75% from 16 to 28% among MSM and more than doubled among heterosexual men and women (7-15 and 5-12%, respectively). Inconsistent condom use, three or more sex partners, sex overseas, past STI diagnosis, and contact with an STI case collectively contributed 61, 74 and 55% of the STI diagnoses among MSM, heterosexual men and women, respectively. Increase in STI diagnosis associated with temporal trends in combined risk factors including condomless sex, multiple sex partners, past STI diagnosis, and contact with an STI case. Although the majority of the factors considered in this study have been significantly associated with STI positivity in all three groups, their overall population level contributions to the epidemic have changed substantially. Our results indicated significant disparities between the MSM and heterosexual men and women as well as sex-specific differences in terms of sexual behaviors.