Abstract
BackgroundIt has been presumed that Chlamydia trachomatis is transmitted between men only through anal or oral sex, but no mathematical models have tested this presumption.MethodsTo test this presumption, we created 20 compartmental mathematical models of different sexual practices that included both oral and anal sex and calibrated these models to the observed rates of Chlamydia trachomatis infection at three anatomical sites from 4888 men who have sex with men (MSM) in Melbourne Sexual Health Centre during 2018–2019.ResultsA model that included only oral and anal sex could replicate the observed rates of single-site infection at the oropharynx, urethra and rectum alone, but could not replicate infection at more than one of these sites (multisite). However, if we included transmission from sexual practices that followed one another in the same sexual episode (e.g. saliva contamination of the penis from oral sex transmitting chlamydia to the rectum by anal sex), we significantly improved the calibration of multisite infection rates substantially.ConclusionsOur modelling study suggests that transmission routes other than just oral and anal sex are necessary to explain the high rate of Chlamydia trachomatis infection at more than one site.
Highlights
It has been presumed that Chlamydia trachomatis is transmitted between men only through anal or oral sex, but no mathematical models have tested this presumption
Model assumptions Our chlamydia models included the following assumptions related to multisite infections: (1) multisite infection could develop in a man who is already infected at one site when he has sex with another infected partner; and (2) within the same individual, and the Chlamydia trachomatis infection may be transmitted from one infected site to a different non-infected site through sexual practices during the same sexual episode (‘sequential sexual practices’) with another sex partner during a sequential sexual practice, we assumed that the medium anatomical site would act as a conduit for the transmission of the bacteria but not habour the bacteria at the site
The five validation datasets showed that anorectal infections and anal sex contributed the most to chlamydia incidence. This is the first modelling study to explore the role that different sexual practices play in chlamydia transmission at each anatomical site in men who have sex with men (MSM)
Summary
It has been presumed that Chlamydia trachomatis is transmitted between men only through anal or oral sex, but no mathematical models have tested this presumption. If the rates of condom use are to fall, new Mathematical models are important for investigating the transmission of infections in populations, when the transmission is complex or may be difficult to study epidemiologically [7, 8]. Studying the potential contribution of these sexual practices to transmission using epidemiological studies is difficult because of the great number of questions that would be required for potentially many sexual partners. Such studies would be difficult to analyse because men usually have multiple sexual practices in one sexual episode, making it hard to separate the individual contribution of each sexual practice. The majority of MSM had multiple sexual practices in one sexual episode [25], which were not included in previous chlamydia models
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