Spatial mixing, geographic distance, and connectivity of sexual partnerships in Melbourne, Australia: a cross-sectional study

Background The geographic mixing of sexual partners remains poorly understood, particularly across different sexual orientation and gender identity groups. We examined how people in Victoria, Australia, met their romantic and casual partners and quantified the geographic distance between partners’ residential suburbs. Methods An anonymous cross-sectional online survey recruited individuals aged 16 years and older residing in Victoria through social media, clinical, and community settings between October 2021 and October 2022. Data were collected using a computer-assisted self-interview and included demographics, sexual practices, partner meeting locations, and recent sexual health history. Participants were categorised as heterosexual cisgender men, heterosexual cisgender women, gay/bisexual cisgender men, lesbian/bisexual cisgender women, and trans and gender-diverse individuals. Descriptive statistics were used to summarise the data. Results A total of 2327 participants were included. Mobile dating apps were the most common method for meeting casual partners across all sexual orientation and gender identity groups (ranging from 41.5% among heterosexual cisgender men to 67.3% among gay/bisexual cisgender men). Mean distances between participants and romantic partners (9.5, s.d. = 30.7 km) and casual partners (9.8, s.d. = 25.2 km) were similar (P = 0.805). Geographic patterns varied by population group, with trans and gender-diverse participants reporting the longest average partner distances (14.1, s.d. = 31.0 km) when compared with other populations. Romantic relationships were largely suburb-based, whereas casual partnerships were far more geographically dispersed, with multiple long-distance connections. Conclusions Distinct partner-seeking and geographic mixing patterns were observed in sexual orientation and gender identity groups. Mobile dating apps play a major role in facilitating casual partners in all populations. Understanding community networks and spatial patterns is important for evaluating the transmission dynamics of sexually transmitted infections and informing targeted prevention strategies.