Assessing uncertainty in an anatomical site-specific gonococcal infection transmission model of men who have sex with men.

BACKGROUND: Increased gonorrhea detection highlights the need for additional prevention efforts. Gonorrhea may only be acquired when there is contact between infected and uninfected anatomical sites. With three sites of infection this leads to seven plausible routes of MSM transmission: urethra-to-rectum, rectum-to-urethra, urethra-to-oropharynx, rectum-to-oropharynx, oropharynx-to-urethra, oropharynx-to-rectum, and oropharynx-to-oropharynx. We characterize the uncertainty and potential importance of transmission from each anatomical site using a deterministic compartmental mathematical model.

METHODS: We developed a model of site-specific gonococcal infection, where individuals are infected at zero, one, two, or all three sites. Sexual behavior and infection duration parameters were fixed similar to a recent model analysis of Australian MSM. Markov Chain Monte Carlo methods were used to sample the posterior distribution of transmission probabilities that were consistent with site-specific prevalence in American MSM populations under specific scenarios. Scenarios were defined by whether transmission routes may or may not transmit by constraining specific transmission probabilities to zero rather than fitting them.

RESULTS: Transmission contributions from each site have greater uncertainty when more routes may transmit; in the most extreme case, when all routes may transmit, the oropharynx can contribute 0-100% of all transmissions. In contrast, when only anal or oral sex may transmit, transmission from the oropharynx can account for only 0-25% of transmission. Intervention effectiveness against transmission from each site also has greater uncertainty when more routes may transmit.

CONCLUSION: Even under ideal conditions (i.e., when site-specific gonococcal prevalence, relative rates of specific sex acts, and duration of infection at each anatomical site are known and do not vary), the relative importance of different anatomical sites for gonococcal infection transmission cannot be inferred with precision. Additional data informing per act transmissibility are needed to understand site-specific gonococcal infection transmission. This understanding is essential for predicting population-specific intervention effectiveness.