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Informed by the local epidemiology of HIV, access to PrEP in Australia has been pragmatically targeted to MSM at increased risk of HIV acquisition. Criteria for increased HIV risk were originally defined based on the evidence from the Sydney-based Health in Men (HIM) study (8).

The Table 3.1 summarises the main factors associated with an increased risk of HIV acquisition among gay and bisexually identified men in the Sydney-based HIM study (8). Four factors were associated with HIV incidence of above 1.8 per 100 person-years; these factors formed the criteria for identifying people at high risk of HIV acquisition. Two more factors with an HIV incidence above 1.0 and below 1.8 per 100 personyears formed the criteria for identifying people at medium HIV acquisition risk. Although the HIM study collected data from 2001 to 2007 and HIV notification trends have changed since then, the same factors are likely to remain relevant to HIV transmission and its prevention today, and these factors were validated as eligibility criteria in an analysis of data from the Victorian PrEPX study (9) and continue to guide PrEP prescribing throughout Australia.

Table 3.1 Factors associated with elevated risk of HIV acquisition among men who have sex with men in the Health in Men (HIM) study, Australia, 2001–2007 (8)

Note that while the HIM study uses the terminology of ‘gay and bisexual men’, this guideline uses ‘men who have sex with men’ to focus on behaviour, rather than identity

CI: confidence interval; CLAI: condomless anal intercourse; HIV: human immunodeficiency virus; PrEP: pre-exposure prophylaxis

Of note, due to the specifics of data collection for the HIM study, not all indicators were available to support each individual eligibility criterion for PrEP. Some indicators were collected in different forms, or had a different denominator or reference period. Most importantly, the HIV viral load of HIV-positive regular partners is now known to have a significant impact on HIV transmission (10-12), and data on the HIV viral load of the source partners were not collected in the HIM study. Similarly, infectious syphilis was uncommon in the HIM cohort and was not associated with HIV transmission. However, its incidence has increased greatly since 2007 in Australia. Syphilis is associated with an increased risk of HIV among MSM globally (13, 14), and is therefore included in the PrEP suitability assessment. Drug use is another important factor that influences sexual behaviour and HIV risk acquisition and that has emerged since the HIM study. Methamphetamine use has been associated with increased risk of HIV infection in high-income countries internationally (15). In Australia associations have been observed between injecting drug use and sexual risk taking (16) with a higher incidence of drug use initiation occurring in younger versus older MSM (17). Finally, the reference period for PrEP suitability assessment is set up in these guidelines to reflect behaviour over the previous 3 months whereas the HIM study addressed behaviour over the previous 6 months (8). In addition, the epidemiology of drug use has changed in MSM in Australia (15-19).

The 2017 ASHM PrEP guidelines classified a person’s risk of HIV acquisition as high or low based on criteria from the HIM study (8). The 2017 guidelines recommended that an individual had to report HIV risk in the 3 months before commencing PrEP and that the individual anticipated that they would have HIV risk in the 3 months after commencing PrEP. Individual’s risk of HIV acquisition were classified as high or low based on evidence from the HIM study (8). Additionally, in the 2017 guidelines, clinicians were invited to consider offering PrEP on a case-by-case definition to people who did not meet high- or medium-risk criteria.

Importantly, the 2019 ASHM PrEP guidelines no longer classify a person’s risk of HIV acquisition as high or low and no longer require that an individual demonstrate HIV risk in the previous 3 months. Instead the 2019 guidelines provide behavioural examples of what would make a person suitable for PrEP, including whether a person’s quality of life would be likely to improve if they were offered PrEP, e.g. people with high levels of anxiety about HIV acquisition. (see Suitability for PrEP).

Overall, the epidemiological data highlight the need to strengthen the current strategies for HIV prevention especially in Indigenous populations, overseas-born MSM where HIV rates are rising and heterosexuals, which would include expanding and promoting the uptake of PrEP by all eligible people.

The PrEP suitability criteria that are provided in these guidelines are not intended to limit or deny access to PrEP to any person who seeks it. Instead, they are intended to help identify and actively recommend PrEP to people suitable for PrEP and to guide clinicians in their discussions about PrEP with patients who are uncertain about their HIV risk and need for PrEP use (see Suitability for PrEP).