Assortative Sexual Mixing by Age, Region of Birth, and Time of Arrival in Male-Female Partnerships in Melbourne, Australia.

Background: Patterns of sexual mixing may be influenced by demographic factors where individuals show a preference for partners with particular traits and may have different levels of risk for HIV and sexually transmitted infection transmission. We aimed to explore age differences and mixing by region of birth among male-female partnerships.

Methods: Male-female partnerships who presented to Melbourne Sexual Health Centre in Australia between 2015 and 2019 were investigated. Age and country of birth of sexual partners were collected. We calculated the age differences between partners and created tables demonstrating partnership mixing by age groups and by international region of birth.

Results: A total of 2112 male-female partnerships (i.e., 4224 individuals) were included. The median age was 27 years (interquartile range, 23-31 years). Between men and women in partnerships, the median age difference was 1 year. Nearly half of all individuals (49.1% [2072 of 4224]) were in a partnership with another individual in the same 5-year interval age group as their own, and a majority of individuals (58.5% [2334 of 3988]) were in a partnership with another individual from the same region of birth when compared with other regions.

Conclusions: There is a strong assortative sexual mixing pattern by age and region of birth among male-female partnerships in Melbourne, Australia. These results may have applications in further research to understand sexually transmitted infection transmission among clients attending sexual health centers, particularly those born overseas.