Epidemiology of gonorrhoea, chlamydia and HIV in men who have sex with men, and evaluation of new prevention strategies.

This thesis consists of a literature review and twelve original research studies in sexual health epidemiology that focus on the transmission of gonorrhoea among MSM, in order to provide a more nuanced understanding of its transmission dynamics, with the aim of informing evidence-based gonorrhoea prevention strategies. These are:

1. A review of the medical literature that pertains to recent trends in gonorrhoea epidemiology among MSM, particularly focussing on the effect of PrEP on gonorrhoea diagnoses. This is followed by a discussion of a new paradigm of gonorrhoea transmission, in which it is postulated that oropharyngeal rather than urethral gonorrhoea plays a central role in it’s increasing transmission.

2. An analysis of seasonal trends in STI diagnoses in Melbourne, which showed that MSM have more sexual partners in spring through to early summer, and are more likely to be diagnosed with gonorrhoea during those seasons.

3. A quantitative analysis of the importance of “regular casual” partnerships among MSM, in terms of the HIV/STI risk conferred by this often-overlooked partnership type. This found that MSM with “regular casual” partners were at twice the risk of anorectal chlamydia compared to other MSM, even after adjusting for total partner numbers.

4. As part of our inquiries into the likelihood of tongue kissing to transmit oropharyngeal gonorrhoea, we examined whether MSM had a different propensity to kiss their casual partners depending on how they met these partners. This found that MSM who met their casual partners through smartphone dating applications were more likely to kiss their casual partners than other MSM. This indicates that these smartphone applications may serve as useful platforms for health promotion messages that aim to address gonorrhoea transmission through tongue kissing.

5. A study that assessed the within-couple concordance of gonorrhoea diagnosed by culture in same sex male couples, to investigate which anatomic site (urethra, oropharynx, anorectum) is most likely to transmit gonorrhoea to a sexual partner. As a result of being culture-based, which proved to be a relatively insensitive test, this study lacked power to assess whether the oropharynx-to-oropharynx route is a significant driver of gonorrhoea transmission.

6. A study that compared the sensitivity of culture and nucleic acid amplification testing (NAAT) to detect Neisseria gonorrhoeae at the anorectum and oropharynx, which found that NAAT detected five times more diagnoses at the oropharynx and twice as many diagnoses at the anorectum compared to culture.

7. A repeat of the couple study of chapter 5 but using NAAT rather than culture. This analysis found high oropharynx-to-oropharynx gonorrhoea concordance and high oropharynx-to-anorectum gonorrhoea concordance within same sex male couples, even after excluding couples with urethral gonorrhoea. This supports the new paradigm of gonorrhoea transmission, in which oropharyngeal gonorrhoea contributes to onward transmission to the urethra, oropharynx and anorectum of sexual partners.

8. A highly-detailed description of a sexual network of males and females, in which most participants acquired isolated oropharyngeal gonorrhoea. This network provides a compelling illustration of the potential for oropharyngeal gonorrhoea to transmit through tongue kissing.

9. A case-control study of risk factors for oropharyngeal gonorrhoea. Due to the concurrency of different sexual practices, this study was not able to delineate which specific sexual practices (tongue kissing vs oro-anal sex vs oro-penile sex) conferred the greatest risk of oropharyngeal gonorrhoea.

10. A prospective study of the use of mouthwash by MSM, which showed that the use of antiseptic mouthwash is highly acceptable and that MSM will adhere to a regimen of daily mouthwash use if it reduces their risk of oropharyngeal gonorrhoea. This study was conducted in preparation for our “Omega” randomised placebo-controlled controlled trial of the effectiveness of antiseptic mouthwash to prevent oropharyngeal gonorrhoea.

11. A study that assessed within-couple concordance of chlamydia in same sex male couples, to assess transmission dynamics and to compare this to those of gonorrhoea in MSM couples and to those of chlamydia in heterosexual couples.

12. A cross sectional study of anorectal chlamydia in MSM, which assessed associations with oro-anal sex or saliva use as a lubricant for anal sex. This analysis found that the use of a partner’s saliva during receptive anal sex practices was a weak risk factor for anorectal chlamydia. This contrasts to our earlier study (not a chapter of this thesis), which found that saliva use during receptive anal sex practices is a strong risk factor for anorectal gonorrhoea.

13. An analysis of the ability of PrEP eligibility criteria to accurately predict HIV risk, using data from the Victorian PrEPX study and using diagnoses of syphilis, anorectal chlamydia and anorectal gonorrhoea as surrogate biological markers of HIV risk. This study found that those participants who were enrolled under the “high risk” eligibility criteria were indeed at high risk of HIV, thereby validating the use of PrEP eligibility criteria. However, the analysis also found that those participants who did not meet any eligibility criteria when they were enrolled into the PrEPX study nonetheless had significant risk of HIV.