O10.3 - Gini coefficients for measuring the disparity in the distribution of HIV and sexually transmitted infections in both heterosexual and homosexual populations in Australia

Background:
The risk of HIV and sexually transmitted infections (STIs) varies substantially across diverse population groups in Australia. This study aims to measure the disparity in the distribution of HIV/STIs among attendees in a clinical setting using the Gini coefficient, a measure of inequality to describe the distribution of HIV/STIs.

Methods:
We used demographic and sexual behaviour data from attendees of Melbourne Sexual Health Centre, between 2015-2018. We applied a machine learning-based risk assessment tool, MySTIRisk, to determine the risk scores. Based on individuals’ risk scores and HIV/STIs diagnoses, we calculated the Gini coefficients for HIV, syphilis, gonorrhoea, and chlamydia infections for different subgroups.

Results:
Among all clinic attendees, the Gini coefficients were highest for syphilis (0.60, (95% CIs, 0.57-0.64)) followed by HIV (0.57, 0.52-0.62), gonorrhoea (0.38, 0.36-0.42) and chlamydia (0.31, 0.28-0.35). Men who had sex with men (MSM) had lower Gini coefficients compared to heterosexual men or women; HIV (0.54 vs. 0.94 vs. 0.96), syphilis (0.50 vs. 0.86 vs. 0.93), gonorrhoea (0.24 vs. 0.57 vs. 0.57) and chlamydia (0.23 vs. 0.42 vs. 0.40), respectively. The Gini coefficient was lower among 25-34-year-olds than in other age groups for HIV (0.66 vs. 0.83-0.90), gonorrhoea (0.38 vs. 0.43-0.47) and for some age groups for chlamydia (0.31 vs. 0.39-0.47). For syphilis, the oldest age group (≥45 years) had a lower Gini coefficient than 18-24-year-olds (0.61 vs. 0.70).

Conclusions:
Our study finds that HIV/STIs are more evenly distributed in MSM populations suggesting interventions can be widely disseminated in MSM communities. In contrast, interventions in heterosexual men and women need to be more targeted at higher-risk individuals.