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A rapid increase in pre-exposure prophylaxis (PrEP) use by gay men in Melbourne and Sydney has been accompanied by an equally rapid decrease in consistent condom use, according to an article published online today in The Lancet HIV. The changes in behaviour between 2016 and 2017 occurred across the gay community, not only in PrEP users – a significant increase in condomless sex with casual partners was observed in HIV-negative men who were not taking PrEP.

The decline in consistent condom use with casual partners is likely to fuel debate about the long-term impact of PrEP, but it is important to note that the proportion of gay men reporting precautionary behaviours with casual partners remained constant – around 70% either always used condoms, took PrEP, had an undetectable viral load or did not have anal sex. However, there has been a substantial shift in the ways in which HIV-negative Australian gay men protect themselves from HIV.

Professor Martin Holt of the University of New South Wales and colleagues analysed data from the annual Melbourne and Sydney Gay Community Periodic Surveys to look at sexual behaviour before (2013-2016) and after (2017) the large-scale roll out of PrEP in publicly funded projects across the states of Victoria and New South Wales. Data from the five surveys conducted between 2013 and 2017, with a total of 16,827 gay and bisexual men, were analysed.

Each year, men who reported sex with male partners in the past five years were recruited at gay venues or events, or through Facebook advertising. It is important to note that while these are the largest regular surveys of gay men in Australia and use a consistent approach each year, the same individuals are not tracked from survey to survey. These are repeated, cross-sectional surveys, rather than a longitudinal cohort. This means that the researchers do not know how an individual behaved before he began using PrEP.

Participants’ sexual practices with casual partners over the previous six months were classified as one of the following:

• no anal sex
• consistent condom use
• condomless anal sex by HIV-positive men on treatment with an undetectable viral load
• condomless anal sex by HIV-negative men on PrEP
• any condomless anal sex by HIV-positive men who weren’t on treatment or didn’t have an undetectable viral load
• any condomless anal sex by HIV-negative men who weren’t on PrEP.

The latter two behaviours were considered to be risky for HIV, whereas the first four were classified as safer sex. As the researchers considered aggregated data over a six-month period (rather than data about specific sexual events), a man who used a condom 99 times but had condomless sex once during the previous six months would be described as having ‘condomless sex’.

Two-thirds of the respondents were of Anglo-Australian ethnicity, their mean age was 36, over half were university educated, two-thirds were in full-time employment, and the vast majority identified as gay. In terms of HIV status, 81% were HIV negative, 10% HIV positive and 10% untested.

In 2013, 2014 and 2015, each year 2% of men said that they had been prescribed and used PrEP in the past six months. In 2016, this increased to 7%, and then in 2017 to 24%. The researchers think that this dramatic increase in PrEP use is the largest and most rapid recorded in any large jurisdiction.

The main analysis concerned sexual practices with casual partners. This also showed a rapid increase in the use of PrEP – from 1% in 2013 to 5% in 2016, and then jumping to 16% in 2017 (p = <0·0001).

This was matched by a decline in consistent condom use. It was reported by 46% of men having casual partners in 2013, 42% in 2016 and 31% in 2017 (p = <0·0001).

This change does not simply reflect less condom use in men taking PrEP. There was a wider decline in consistent condom in the community – in a sub-analysis limited to HIV-negative and untested men not on PrEP who had casual partners, consistent condom use decreased from 49% in 2013 to 46% in 2016, and then to 40% in 2017 (p = <0·0001).

There was a substantial increase in the number of condomless sex acts that were protected by antiretroviral-based prevention, whether that was an HIV-positive man with an undetectable viral load or an HIV-negative man taking PrEP.

Among those having sex with casual partners, this proportion increased from 16% in 2013, to 25% in 2016, and 44% in 2017.

And the proportion having sex which posed a minimal risk of HIV transmission (condom use, no anal sex, PrEP or undetectable viral load) did not change. As the researchers say: “Despite what seems to be community-level risk compensation (decreasing condom use coincident with increasing PrEP use), the overall level of safe sex by gay and bisexual men in Melbourne and Sydney was sustained at around 70%.”

The researchers sum up their findings: “The rapid uptake of PrEP by gay and bisexual men in Melbourne and Sydney during its early implementation has been accompanied by an equally rapid decrease in consistent condom use.”

But HIV diagnoses did not increase as a result. The researchers point out that the changes coincided with a historic decrease in the number of new diagnoses in gay men in both Victoria (down 16% between 2016 and 2017) and New South Wales (down 11%). These trends are probably the result of a gradual increase in the number of gay men who know their status through HIV testing and who achieve undetectable viral load with HIV treatment – as well as the rapid scale-up of PrEP.

“The rapid increase in PrEP use seems to have outweighed the rapid decrease in condom use in this early phase of PrEP implementation,” comment the authors.

Whereas other studies have tracked the sexual behaviour of PrEP users, this study is notable for observing a decrease in condom use in the wider community, in non-PrEP users. This could be described as ‘community-level risk compensation’.

Why might men not taking PrEP use condoms less often? The authors suggest that this could be because they perceive that condomless sex has become less risky due to the widespread use of PrEP. An individual may feel confident that a partner who is taking PrEP will not have HIV, or may feel that because of PrEP, HIV infection has generally become less prevalent.

Only one other study has previously observed this. In San Francisco between 2011 and 2014, PrEP use by HIV-negative men increased from 0% to 9·6% while consistent condom use decreased from 30·5% to 17·5%.

This issue will need to be factored into mathematical modelling of the impact of PrEP. “The beneficial effect of PrEP on HIV epidemics might have been overestimated, particularly in settings in which it was assumed that condom use would be sustained in MSM [men who have sex with men] not using PrEP.”

The researchers also argue that there should be investment in community education campaigns while PrEP is scaled up. These should support the use of condoms within the context of a diversity of HIV prevention practices.

“Our findings suggest that the rapid uptake of PrEP disrupted condom use at a community level,” commented Martin Holt. “However, it’s too early to tell the long-term effects of increasing PrEP use and declining condom use on HIV diagnoses in Victoria and New South Wales.”

Holt M et al. Community-level changes in condom use and uptake of HIV pre-exposure prophylaxis by gay and bisexual men in Melbourne and Sydney, Australia: results of repeated behavioural surveillance in 2013–17. The Lancet HIV, online ahead of print June 2018. (Abstract.)