502Modelling Chlamydia trachomatis and Mycoplasma genitalium transmission in men who have sex with men.

Background Chlamydia trachomatis (CT) and Mycoplasma genitalium (MG) are two common sexually transmitted infections in men who have sex with men that are assumed to be transmitted only by oral and anal sex. However, this assumption has not been tested in mathematical models before. Methods To test a variety of potential transmission routes against the known proportion of infections at the oropharynx, mouth and anus, we established 20 compartmental models involving different sexual practices. We tested transmission by a) only anal sex and oral sex; b) adding rimming and kissing to anal and oral sex, and c) adding sequential sexual practices (e.g. oral sex followed by oral-anal sex (rimming) or vice versa. Results We could not replicate the proportion of anatomical sites infected with CT using anal or oral sex alone or by adding riming and kissing. However, if we included sequential sexual practices, then we were able to replicate the prevalence of CT at each site including infection at more than one site. In contrast, we were able to replicate infection for MG at the three sites using transmission routes that involved only anal sex and oral sex without the need for adding any other routes of transmission. Conclusions Our model indicates that more complicated transmission routes are required to explain the observed prevalence of infection with CT, but that for MG transmission involving only anal and oral sex is sufficient. Key messages Unlike CT, MG transmission does not require more complicated transmission routes. [ABSTRACT FROM AUTHOR]