The potential impact of a gel-based point-of-sex intervention in reducing gonorrhoea incidence among gay and bisexual men: a modelling study.

BACKGROUND Increases in sexually transmitted infections (STIs) among gay and bisexual men (GBM) over the past decade have coincided with declines in condom use and rapid uptake of HIV pre-exposure prophylaxis (PrEP). We explored the impact of an antimicrobial gel-based point-of-sex intervention (gel-PSI) with a lower efficacy for reducing gonorrhoea transmission risk than condoms on population-level gonorrhoea incidence among GBM in Victoria, Australia. METHODS A deterministic compartmental model of HIV and gonorrhoea transmission was used to project annual gonorrhoea incidence from 2020 to 2025. Individuals were classified as HIV-negative (PrEP or non-PrEP-users) or HIV-positive, and further stratified gonorrhoea risk (high/low). All possible scenarios where between 0-100% of GBM using condoms transitioned to gel-PSI (considered a downgrade in protection) and 0-100% of GBM not using condoms transitioned to gel-PSI (considered an upgrade in protection), with gel-PSI efficacy ranging from 20-50% were run. RESULTS The baseline scenario of no gel-PSI uptake (status quo) projected 94,367 gonorrhoea infections between 2020-2025, with an exponentially increasing trend in annual infections. For a gel-PSI efficacy of 30%, a net reduction in cumulative gonorrhoea incidence was projected, relative to the status quo, for any ratio of proportion of condom-users 'downgrading' to proportion of non-condom-users 'upgrading' to gel-PSI use of less than 2.6. Under the supposition of equal proportions of condom-users and non-condom-users switching to gel-PSI, a relative reduction was projected for any gel-PSI efficacy greater than 16%. CONCLUSIONS Our model suggests that the introduction of a gel-PSI could have benefits for controlling gonorrhoea transmission among GBM, even in scenarios where the gel-PSI is considerably less efficacious than condoms and when gel-PSI uptake leads to consequent reductions in consistent condom use.