Potential effect of antiseptic mouthwash on the incidence of Neisseria gonorrhoeae among men who have sex with men: a mathematical modelling study.

Objectives The incidence of Neisseria gonorrhoeae and its antimicrobial resistance is increasing in many countries. Antibacterial mouthwash may reduce gonorrhoea transmission without using antibiotics. We modelled the effect that antiseptic mouthwash may have on the incidence of gonorrhoea. Design We developed a mathematical model of the transmission of gonorrhoea between each anatomical site (oropharynx, urethra and anorectum) in men who have sex with men (MSM). We constructed four scenarios: (1) mouthwash had no effect; (2) mouthwash increased the susceptibility of the oropharynx; (3) mouthwash reduced the transmissibility from the oropharynx; (4) the combined effect of mouthwash from scenarios 2 and 3. Setting We used data at three anatomical sites from 4873 MSM attending Melbourne Sexual Health Centre in 2018 and 2019 to calibrate our models and data from the USA, Netherlands and Thailand for sensitivity analyses. Participants Published available data on MSM with multisite infections of gonorrhoea. Primary and secondary outcome measures Incidence of gonorrhoea. Results The overall incidence of gonorrhoea was 44 (95% CI 37 to 50)/100 person-years (PY) in scenario 1. Under scenario 2 (20%–80% mouthwash coverage), the total incidence increased (47–60/100 PY) and at all three anatomical sites by between 7.4% (5.9%–60.8%) and 136.6% (108.1%–177.5%). Under scenario 3, with the same coverage, the total incidence decreased (20–39/100 PY) and at all anatomical sites by between 11.6% (10.2%–13.5%) and 99.8% (99.2%–100%). Under scenario 4, changes in the incidence depended on the efficacy of mouthwash on the susceptibility or transmissibility. The effect on the total incidence varied (22–55/100 PY), and at all anatomical sites, there were increases of nearly 130% and large declines of almost 100%. Conclusions The effect of mouthwash on gonorrhoea incidence is largely predictable depending on whether it increases susceptibility to or reduces the transmissibility of gonorrhoea.