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Population health research and evaluation
The Kirby Institute case study
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The Kirby Institute case study
Content 1
Modelling the epidemiology of STIs in the gay and bisexual population of NSW in the era of PrEP
Rates of sexually transmitted infections (STI) among Gay and Bisexual Men (GBM) have been rising steadily in recent years.
1,2
This is thought to be due, at least in part, to increases in condom-less sex in this population. This decline in consistent condom use is unsurprising given the reduced threat of HIV due to antiretroviral therapy and the increasing uptake of Pre-Exposure Prophylaxis (PrEP).
3
This last factor is particularly pertinent with the recent addition of PrEP to the Australian Pharmaceutical Benefits Scheme. Conversely, regular testing for STIs has become more common in recent years.
4
This is important because infections are frequently asymptomatic, allowing sexually active individuals to infect multiple partners without being aware of their own infection status. The aim of this PRSP-funded work is to explore the impact that expanding uptake of PrEP is likely to have on STI incidence and prevalence among gay and bisexual men in NSW.
The dynamics of STI epidemiology are complex, multi-factorial, and are often best studied by computer simulations calibrated to real-world data. We have built an agent-based model to simulate STI epidemiology in Sydney’s GBM population. Such models are well-suited to incorporate the large variation in relevant parameters at the individual level. Currently our model only considers the transmission of gonorrhoea and accounts for sexual behaviour, HIV status, PrEP use, and STI testing frequency. The model has been constructed, however, to facilitate the inclusion of other STIs (e.g. chlamydia, syphilis and Mycoplasma genitalium) in due course. The model is also anatomical site-specific, meaning that the infection status of individuals also includes the relevant anatomical sites of infection (rectum, pharynx, urethra). This is important because the various modes of transmission (anal sex, oral sex, etc.) have different transmission probabilities and their involvement in sexual contacts occur with differing frequencies. Furthermore, the use of condoms is only applicable to sexual contacts in which the penis is involved. The current gonorrhoea model is calibrated to trends in gonorrhoea notifications both prior to and following the introduction of PrEP, and makes use of data on testing rates, gonorrhoea diagnoses and sexual behaviour in the PrEP era from the EPIC-NSW PrEP trial
5
that was funded by the NSW government. The model will be used to predict the trajectory of gonorrhoea incidence (and later, other STIs) with the expanding uptake of PrEP, and will evaluate a range of scenarios around testing and changing sexual practices.
A working group has been formed including stakeholders from GBM advocacy groups such as the Australian Federation of AIDS Organisations, as well as representatives from the NSW Ministry of Health and experts from within the Kirby Institute. Our model has the capacity to examine counterfactual scenarios and test hypotheses for which clinical trials are not suitable. Hence questions of relevance to government policy, such as the frequency with which GBM should be tested for STIs, may be addressed and guidelines proposed. It has also been agreed that capability development in modelling, including the interpretation and use of models, will be provided to staff at NSW Health through annual workshops.
Translation into policy and practice will be through the submission of reports to relevant stakeholders, the publication of academic papers, as well as presentations at seminars and conferences. To further enable translation into action, our model is open-source with code readily available for download from a public repository (GitHub
6
), in accordance with emerging publication standards. The work has already leveraged additional research funding from the SPHERE (Sydney Partnership for Health, Education, Research and Enterprise) seed grant scheme
7
for a project in which modelling is being used to evaluate the utility of a range of surveillance and contact tracing strategies in mitigating the emergence and spread of extensively drug resistant gonorrhoea in NSW.
References
Callander D, Guy R, Fairley CK, McManus H, Prestage G, Chow EPF, et al. Gonorrhoea gone wild: rising incidence of gonorrhoea and associated risk factors among gay and bisexual men attending Australian sexual health clinics.
Sex Health
2018; in press.
Kirby Institute. HIV, viral hepatitis and sexually transmissible infections in Australia: Annual surveillance report 2018
Holt M, Murphy DA. Individual versus community-level risk compensation following pre-exposure prophylaxis of HIV.
Am J Public Health
2017; 107(10): 1568-71.
Gay Community Periodic Surveys
EPIC-NSW Study
Individual-based, site-specific simulator of STI transmission
The Sydney Partnership for Health, Education, Research and Enterprise (SPHERE)
Content 2
Current as at: Wednesday 2 June 2021
Contact page owner:
Centre for Epidemiology and Evidence