Switching from dual to monotherapy for Gonorrhea is associated with a halving of Gonococcal resistance to Azithromycin-A modelling study of MSM in Belgium

Background
Chlamydia trachomatis (CT) and Neisseria gonorrhoeae (NG) are 2 of the most common bacterial sexually transmitted infections. The prevalence of azithromycin resistance in NG (AR-NG) has increased from 1% to 47.9% in the past 10 years among men who have sex with men (MSM) in Belgium. Dual therapy with ceftriaxone and azithromycin was until recently the standard-of-care in Belgium. Our objective was to reproduce the azithromycin-resistance epidemic among MSM in Belgium using dual therapy and to evaluate the counterfactual scenario of using ceftriaxone monotherapy on the emergence of AR-NG.

Methods
We developed a network-based model for CT and NG transmission among MSM in Belgium to estimate the prevalence of CT, NG, and AR-NG in the population. The model simulates transmission of NG among 3 anatomical sites in a population of 10 000 MSM over 10 years. The effect of different treatment strategies was evaluated in terms of CT, NG, and AR-NG prevalence as well as antibiotic consumption.

Results
Our model captured adequately well the observed azithromycin-resistance epidemic over a 10-year period in Belgium, with AR-NG increasing from 0% to 44%. Antibiotic consumption, and prevalences of NG and AR-NG decreased when ceftriaxone monotherapy was used against NG, while CT prevalence increased, compared to dual therapy. In the ceftriaxone monotherapy scenario, the prevalence of AR-NG was approximately half of that in the dual-therapy scenario (23%).

Conclusions
Switching from dual to monotherapy was associated with a halving of the prevalence of AR-NG. These results provide further evidence to favor mono- over dual therapy for the treatment of gonorrhea.