Screening for gonorrhoea and chlamydia: identifying key target populations and intensity-a modelling study of MSM in...

Chlamydia trachomatis (CT) and Neisseria gonorrhoeae (NG) are two of the most common bacterial sexually transmitted infections (STIs) among men who have sex with men (MSM). Screening for CT and NG has been promoted as an intervention to reduce the prevalence of these STIs. We aimed to evaluate the effect of different screening intensities on the prevalence of CT, NG and the emergence of azithromycin-resistant NG (AR-NG) in an MSM population.

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 CT/NG among three anatomical sites in a population of 10 000 MSM, divided into high-activity and low-activity groups, over 10 years. The effect of different screening frequencies and coverage was evaluated in terms of CT, NG and AR-NG prevalence.

Gonorrhoea prevalence ranged between 12% and 16% in scenarios screening 0-80% of the population. Screening among the low-activity MSM (LA-MSM) group had little effect on NG prevalence but increased the risk of AR-NG. Infrequent screening (less than every 180 days) with high coverage (over 40%) resulted in the highest risk for the spread of AR-NG in the population. Screening up to 40% of low-activity (HA-MSM) every 90 days and up to 20% of LA-MSM reduced NG prevalence to 14% without selecting for AMR. Screening coverage and frequency had little impact on CT prevalence in all scenarios.

Our model suggests that NG/CT screening has a modest effect in controlling the prevalence of these infections in the MSM population in Belgium. Screening efforts should move away from LA-MSM. Screening alone would not be sufficient to control the CT/NG epidemic, and future models should incorporate the impact of additional interventions such as vaccination and doxycycline post-exposure prophylaxis.