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Prevention Research

Brief Report: Changes in Behavior After PrEP Initiation Among Australian Gay and Bisexual Men

Prestage, Garrett PhDa; Maher, Lisa PhDa; Grulich, Andrew PhDa; Bourne, Adam PhDb; Hammoud, Mohamed BPsycha; Vaccher, Stefanie BSca; Bavinton, Benjamin PhDa; Holt, Martin PhDc; Jin, Fengyi PhDa

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JAIDS Journal of Acquired Immune Deficiency Syndromes: May 1, 2019 - Volume 81 - Issue 1 - p 52-56
doi: 10.1097/QAI.0000000000001976
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In Australia, declines in HIV infections have accompanied increases in the proportion of gay and bisexual men (GBM) using HIV pre-exposure prophylaxis (PrEP).1 Nonetheless, rates of recent receptive condomless anal intercourse (CLAI) with casual partners (R-CLAIC) among HIV-negative men who were not using PrEP have remained stable at about 20%.2 This could be because men who previously engaged in R-CLAIC without taking PrEP may be continuing to do so, or that men who had previously not engaged in R-CLAIC may have commenced doing so while others who had previously engaged in R-CLAIC simultaneously initiated PrEP use.

GBM represent the key population group at risk of HIV infection in Australia.3,4 PrEP effectively reduces the risk of HIV infection among adherent GBM by as much as 99%.5 Australia's National HIV Strategy prioritizes GBM for HIV prevention, and PrEP is now offered at minimal cost through public subsidy.4,6,7 Eligibility criteria for access to PrEP include recent (within last 3 months) CLAI with an HIV-positive partner with detectable viral load; recent R-CLAIC; recent use of methamphetamine; or recent diagnosis with a rectal sexually transmissible infection (STI) or syphilis.8

More than 15,000 GBM currently use PrEP in Australia.9 The proportion of HIV-negative GBM in Sydney and Melbourne using PrEP increased rapidly from 2% in 2013 to 24% in 2017.2 Most men who used PrEP in these cross-sectional surveys reported behaviors consistent with PrEP prescribing guidelines, during the same period as their PrEP use.10 Methamphetamine use remained stable with about 1 in 8 reporting use in the previous 6 months.2 In open-label PrEP trials, men who commenced PrEP more often engaged in R-CLAIC over time.11,12 Use of PrEP was associated with higher rates of R-CLAIC in a US cohort of young GBM and a Dutch cohort of GBM.13,14 In a small US clinic-based sample, PrEP use was associated with increased rates of CLAI.15 What is less clear, however, is how PrEP influences sexual behaviors and how the sexual behavior of GBM who commence PrEP compares with the behavior of those who do not use PrEP.

In this article, we use 30-month follow-up data from a cohort of Australian GBM to investigate changes in sexual behavior and drug use after initiation of PrEP compared with men who did not use PrEP.


The methods of the Following Lives Undergoing Change (Flux) study have been described elsewhere.16 Flux is an ongoing online prospective observational cohort study among Australian GBM. Study promotion occurred through online advertising through social media, including popular gay “dating” sites and apps, and Facebook. Once enrolled, participants completed online surveys at study virtual visits at 6-monthly intervals. Participants provided informed consent, and the study was approved by the Human Research Ethics Committee at UNSW Sydney (HC14075).


At each virtual visit, the online questionnaire included demographic items, questions on sexual identity, HIV testing history, and self-reported HIV serostatus. Men described their recent (ie, previous 6 months) methamphetamine use and their PrEP use. Sexual behavior was reported for both regular and casual partners. Data collected therefore included 3 of the 4 eligibility criteria for PrEP in Australia; STI data were not collected.

We also included a previously used measure of social engagement with gay men (gay social engagement; GSE) based on 2 items: proportion of friends who are gay and amount of free time spent with gay men.17 Other measures included the Kalichman sexual sensation-seeking scale.18,19


Men who lived in Australia, aged 16 years or above, were eligible for participation if they were gay- or bisexual-identified or had any sexual contact with another man in the previous year.


Data were analyzed with SPSS version 25 software. Descriptive statistics were used to describe demographic and other characteristics of men who used PrEP. For each virtual visit, we described use of PrEP, and changes in behaviors that met the eligibility criteria for PrEP (except STI diagnoses). Categorical variables were analyzed using Pearson's χ2 test, and t tests were used for continuous variables. We used type I error rate of 5% for these analyses. For overall trends over time, responses at each of the 6 virtual visits were included. The McNemar method for nonparametric tests of 2 related samples was used to examine the significance of univariate relationships between the visit before commencement of PrEP and the visit concomitant with PrEP initiation. For men who never used PrEP, we compared their most recent follow-up visit with the preceding visit.


Overall, 1695 men were enrolled in 2014–2015 and 864 in 2017. Among these 2559 men, 151 were HIV-positive and another 393 were already using PrEP at baseline. Of the remaining 2015 men, 1518 had completed at least one follow-up virtual visit by July 2018 and were included in these analyses. Compared with the 1518 men included here, the 497 excluded men were younger (mean = 29.7 years vs mean = 34.7 years; P < 0.001), less likely to have university-level education (40.7% vs 60.2%; P < 0.001), and had lower GSE scores (Mean = 2.50 vs Mean = 2.73; P < 0.001) but were no more or less likely to engage in R-CLAIC and had similar partner numbers and sexual sensation-seeking scores.

At baseline, the mean age was 34.7 years (SD 13.07; median = 31 years). Participants were mostly university-educated (60.2%) and in full-time employment (58.6%). Three quarters (77.0%) were of Anglo-Celtic background. Most identified as gay (90.4%) or bisexual (7.6%). Most participants (1397, 92.0%) had been tested for HIV.

Very few men reported condomless sex with an HIV-positive “boyfriend” whose viral load was detectable (Table 1). PrEP use increased over time and few of those who commenced PrEP subsequently stopped using it. The proportion of men who engaged in R-CLAIC that was protected by PrEP increased while R-CLAIC that was not protected by PrEP declined by 71.7%. Methamphetamine use remained stable at about 1 in 7.

PrEP Eligibility Behaviors and PrEP Use During Each Virtual Visit (N = 1518)

Among the 348 men who initiated PrEP during follow-up, the proportion reporting R-CLAIC increased by 57.4% between the visit before commencing PrEP and the visit when they reported commencing PrEP (Table 2; McNemar < 0.001). Multiple instances of R-CLAIC increased by 87.3%. Group sex increased by 33.7% (McNemar < 0.001). Mean partner number increased from 21.96 in the period before commencing PrEP to 34.55 during the period when they commenced PrEP (p-trend = 0.002).

Behavioral Changes and PrEP Initiation (N = 1518)

Among the 1170 men who never used PrEP, the proportion reporting R-CLAIC remained steady between visits and group sex declined (McNemar = 0.001) (Table 2). Mean partner number also remained steady at 9.31 in the previous survey period and 8.59 during the most recent follow-up (p-trend = 0.185).

Methamphetamine use increased slightly among both PrEP initiators and PrEP nonusers (Table 2).

Men who initiated PrEP were more likely to engage in R-CLAIC than were men who did not, both in the period before PrEP initiation (Table 2; P < 0.001) and in the period during which they commenced PrEP (P < 0.001). They were also more likely to have engaged in group sex and to have used methamphetamine in both survey periods. Mean partner number among men who initiated PrEP was twice that of men who never used PrEP during the period before PrEP initiation (P < 0.001) and almost 4 times as high during the period they commenced PrEP (P < 0.001). Men who initiated PrEP had higher mean scores on the measure of gay social engagement than did men who never used PrEP, both before (3.08 vs 2.66; P < 0.001) and after (3.16 vs 2.65; P < 0.001) PrEP initiation. They also had higher scores on sexual sensation-seeking both before (31.90 vs 28.32; P < 0.001) and after (32.84 vs 28.49; P < 0.001) PrEP initiation.


Uptake of PrEP in this sample of Australian GBM increased dramatically over time and few men subsequently stopped using PrEP. PrEP initiation coincided with significant increases in R-CLAIC, sexual partners, and group sex. Although prevalence of those behaviors was higher among PrEP initiators before commencing PrEP than among men who never used PrEP, their engagement in those behaviors increased substantially coincident with initiation of PrEP. PrEP users effectively became more adventurous than they already were. Men whose behaviors shifted in the direction of greater (perceived) “risk” during the follow-up period may have decided to commence PrEP to minimize the possibility of HIV infection. Alternatively, initiating PrEP may have led to some men becoming less concerned about the need to sustain other methods of risk reduction.

Although more men engaged in R-CLAIC over time, the increased uptake of PrEP means that the proportion of R-CLAIC not protected by PrEP has declined. Among men who did not initiate PrEP, the proportion who engaged in R-CLAIC remained stable over time. Although men who did not initiate PrEP were less likely to engage in “risky” behaviors than men who did, they nonetheless continued to engage in those behaviors at the same rate over time.

Men who initiated PrEP also used methamphetamine at higher rates than men who never used PrEP, but commencing PrEP was only accompanied by small increases in methamphetamine use. “Chemsex” has previously been strongly associated with “sexual risk behavior” and HIV infection among GBM.20–22 That methamphetamine use was not substantially affected by PrEP initiation suggests that post-PrEP changes in behavior were mostly restricted to sex.

Men who initiated PrEP also scored higher on sexual sensation-seeking than men who did not, both before and after they commenced PrEP. Men who participated in intensive sex partying networks, despite being at elevated risk of HIV infection, may nonetheless have been somewhat restrained because of concerns about the risk of HIV infection. Even among high-risk GBM, most men use some forms of risk-reduction most of the time.10,23 Men who do not access PrEP despite being eligible for it are often less consistent over time in their likelihood to engage in the behaviors that make them eligible for PrEP than are the men who initiate PrEP.24 Among men who initiate PrEP, the desire to engage in such behaviors is often felt strongly.25

The initiation of PrEP by men inclined toward more “adventurous” behaviors will certainly reduce their risk of HIV infection. However, whereas, prior to their initiation of PrEP, their more constrained, though still occasionally high-risk sexual behavior may have minimized the possibility of other STIs, after they had initiated PrEP, their increased frequency of R-CLAIC, and of multiple partners may increase exposure to these other infections.26,27 Although this is potentially mitigated by the regular sexual health screening that accompanies PrEP.28 Nonetheless, observed changes in behavior after PrEP initiation were presumably because men felt safe from HIV infection. Distinguishing between perceptions of “safe” and “risky” sex before and after PrEP is an evolving issue.28 Rather than being viewed as increases in risk-taking behavior, these changes need to be understood in the context of changing definitions of “safe sex” and may represent broader changes in gay community “safe sex culture.”29–31

Although this volunteer, online convenience sample was similar in characteristics and behaviors to those of participants in other samples of Australian GBM,4,10,32,33 it may not be representative of all homosexually active men in Australia. Questions referred to the 6-month period before each visit, so we were unable to identify the precise timing of commencement of PrEP in relation to changes in behavior.


PrEP offers a means for some men to engage in sexually adventurous behaviors that they may have previously desired but were cautious about practicing without the protection now offered by PrEP. It is important that all GBM have access to high-quality regular sexual health screening to offset any potential increases in non-HIV STIs that may follow these changes in behavior.


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HIV; pre-exposure prophylaxis; gay men; men who have sex with men; sexual risk behavior; chemsex

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