Population rates of HIV, gonorrhoea and syphilis diagnoses by sexual orientation in New Zealand

Abstract

Introduction: Globally, gay and bisexual men (GBM) are overrepresented in HIV, syphilis and gonorrhoea cases. However, surveillance systems rarely provide meaningful measures of inequity, such as population-specific rates, due to a lack of sexual orientation denominators. HIV, gonorrhoea and syphilis are legally notifiable diseases in New Zealand (NZ); we calculate rates by sexual orientation for the first time.

Methods: We analysed 2019 national surveillance data on HIV, syphilis and gonorrhoea notifications disaggregated by sexual orientation. Unique health records identified duplicate notifications and re-infections. Missing data were imputed from known cases. We used the NZ Health Survey 2014/15 to estimate population sizes by sexual orientation, measured in two ways (current sexual identity, sexual contact in the previous 12 months with men, women or both). We calculated notification rates per 100,000 for each sexual orientation subgroup and rate ratios.

Results: In 2019, GBM accounted for 76.3%, 65.7% and 39.4% of HIV, syphilis and gonorrhoea notifications respectively. Population rates per 100,000 for HIV were 158.3 (gay/bisexual men), 0.5 (heterosexuals); for syphilis were 1231.1 (gay/bisexual men), 5.0 (lesbian/bisexual women), 7.6 (heterosexuals); for gonorrhoea (imputed) were 6843.2 (gay/bisexual men), 225.1 (lesbian/bisexual women), 120.9 (heterosexuals). The rate ratios for GBM compared to heterosexuals were: 348.3 (HIV); 162.7 (syphilis); 56.6 (gonorrhoea). Inequities remained in sensitivity analysis (substituting sexual identity with sexual behaviour in the previous 12 months).

Conclusion: GBM in NZ experience profound inequities in HIV, syphilis and gonorrhoea. Rate ratios by sexual orientation provide useful “at-a-glance” measures of inequity in disease incidence.