Edinburgh Research Explorer Impact of early antiretroviral treatment on sexual behaviour in the INSIGHT Strategic Timing of Anti-Retroviral Treatment (START) Trial

Background: Antiretroviral treatment (ART) reduces HIV infectiousness, but the effect of early ART on sexual behaviour is unclear. Methods: We assessed, within the START randomised trial that enrolled HIV-positive adults with CD4>500/mm 3 , the effect of early (immediate) versus deferred ART on: (i) condomless sex with HIV-serodifferent partners (CLS-D); (ii) all condomless sex (CLS); (iii) HIV transmission-risk-sex (CLS-D-HIV-risk, defined as CLS-D and: not on ART or started ART <6 months ago or viral load(VL)>200c/mL or no VL in past 6 months), during two year follow-up. Month-12 CLS-D (2010-2014) was the primary outcome. Results: Among 2562 MSM, there was no difference between immediate and deferred arms in CLS-D at month 12 [12.6% versus 13.1%; difference (95% CI):-0.4%(-3.1%, 2.2%),p=0.75] or month 24, or in CLS. Among 2010 heterosexual men and women, CLS-D at month 12 tended to be higher in the immediate versus deferred arm [10.8% versus 8.3%; difference:2.5%(-0.1%, 5.2%),p=0.062]; the difference was greater at month 24 [9.3% versus 5.6%; difference:3.7%(1.0%, 6.4%),p=0.007], at which time CLS was higher in the immediate arm [20.7% versus 15.7%,p=0.013]. CLS-D-HIV-risk at month 12 was substantially lower in the immediate versus deferred arm for MSM [0.2% versus 11.0%; difference:-10.7%(-12.5%, -8.9%),p<0.001] and heterosexuals [0.6% versus 7.7%; difference:-7.0%(-8.8%, -5.3%),p<0.001], due to viral suppression on ART. Conclusions: A strategy of early ART had no effect on condomless sex with HIV-serodifferent partners among MSM, but resulted in modestly higher prevalence among heterosexuals. However, among MSM and heterosexuals, early ART resulted in a substantial reduction in HIV-transmission-risk-sex, to a very low absolute level.


Introduction
In 2015, results were published from the START (Strategic Timing of Antiretroviral Treatment Trial) 1,2 and TEMPRANO 3 randomised trials, demonstrating that a strategy of immediate ART (regardless of CD4 cell count) for people with diagnosed HIV reduced serious morbidity and mortality compared to ART deferral. Guidelines that had previously set CD4 thresholds for ART initiation were changed to recommend ART initiation for all adults with HIV at any CD4 level. [4][5][6] US guidelines had already recommended such a strategy, primarily based on evidence from observational studies. 7 Prior to this conclusive evidence of the clinical benefit of early ART, results had been accumulating regarding the protective effect of ART on HIV transmission. Initially, a number of observational studies demonstrated a marked association between the viral load (VL) of an HIV-positive person and the risk of HIV transmission to an HIV-negative partner. [8][9][10][11][12] In 2011, unequivocal evidence came from the HPTN 052 randomised trial, which demonstrated that use of early ART for the HIV-positive partner of serodifferent couples was associated with a 96% reduction in transmissions to the HIV-negative partner. 13 Subsequently, the PARTNER 14 , PARTNER2 15 and Opposites Attract 16  Together these studies have provided the necessary evidence for assurance that HIV-positive people on ART with undetectable VL cannot transmit HIV (Undetectable=Untransmittable; Prevention Access Campaign). 17 As knowledge regarding the protective effect of VL suppression on HIV infectiousness has been disseminated and publicized, and in particular since the 'Swiss Statement' in 2008, 18 it has been debated whether such knowledge impacts on sexual behaviour and patterns of condom use among people taking ART. [19][20][21] Initially the concern was that if viral suppression on ART led merely to a reduction in (rather than elimination of) HIV transmission risk, any increase by the HIV-positive individual in CLS with HIV-serodifferent partners (CLS-D) could partially negate the benefit of ART. 19,20 Recent findings have provided reassurance on this point, demonstrating no transmission risk in this context. [14][15][16] However an increase in CLS-D associated with ART use may still be concerning in the context of sub-optimal ART adherence, infrequent VL monitoring, inaccurate knowledge of personal VL status 22 or poor knowledge of the importance of viral suppression, a key issue in early treatment. 23 Furthermore, any changes in patterns of CLS overall may have implications for transmission of other sexually transmitted infections (STIs). It is also conceivable that reductions in condom use among HIV-positive people may affect condom use among HIV-negative people with partners of unknown HIV status.
However, it is important to reeavualte this association as patterns of sexual behaviour may have changed with increasing awareness of the protective effect of suppressed VL, paritcularly since publication of HPTN 052 in 2011. 13 Furtherore, now that the protective effect of viral suppression on HIV transmission is assured, it is necessary to consider measures additional to CLS-D, that capture sex with risk of HIV-transmission by accounting for viral suppression. 45,[47][48][49] When considering risk of other STIs, CLS overall is the most relevant measure.
We previously reported on sexual behaviour at enrolment in the START trial. 50 We now assess, separately among MSM and heterosexual individuals, the effect of a strategy of early ART compared to ART deferral on sexual behaviour in the first two years of follow-up, considering: CLS-D at month 12 (the pre-defined primary outcome), CLS, CLS-D with risk of HIV transmission, and other measures.

Study population
START was an open-label multicenter randomized trial enrolling 4684 HIV-positive people who had never taken ART and who had a CD4 count above 500 cells/μL, from April 2009 to December 2013. 1 Individuals were randomised to either start ART immediately (early ART) or to defer ART until occurrence of a CD4 cell count below 350 cells/μL or an AIDS event.
The primary endpoint was serious AIDS or non-AIDS morbidity or mortality. On May

Transmission risk behaviour study
Participants were asked to self-complete a transmission risk behaviour questionnaire at baseline, month 4, and every 12 months subsequently. Sexual activity (vaginal or anal sex) during the previous 2 months was ascertained for: men having sex with women; men having sex with men; women having sex with men. 50 All participants who had a risk behaviour questionnaire available within the first two years (at 4, 12, or 24 months) were included in this analysis. All information provided after 15 th May 2015 was excluded. Sexual behaviour measures (two month recall period) were derived at baseline and each follow-up point,  Table 3 footnote for details). Injection drug use transmission risk was defined as having injected drugs in the past two months and having shared needles or other equipment with someone who had negative/unknown HIV status. Transmission risk beliefs were beliefs related to whether a person using HIV treatment who had an undetectable viral load could pass on HIV to another person through unprotected sex. Responses of: "cannot" and "much less likely" were grouped together in contrast to: "a little less likely", "just as likely" and "more likely". The pre-specified primary outcome was CLS-D at month 12. Separate analyses were pre-specified for MSM, and heterosexual men and women (combined). 27 Some measures were considered only for MSM, due to low frequency among heterosexual participants.
Transmission risk behavior forms were updated early in recruitment. Information on CLS-D and CLS-D-HIV-risk was available from original and updated forms; information on all other outcomes was available only from the updated version. Participants were included in an analysis at a specific time point if the relevant behaviour questionnaire was available; treatment of missing values is described in the footnote of Table 3.

Statistical methods
Baseline characteristics, and ART use and viral suppression over follow-up, were summarised according to gender/sexual orientation. Subsequent analyses were carried out separately for: MSM; heterosexual men and women combined. Sexual behaviour and attitude measures were For all comparisons participants were kept in their original randomised group.

Results
Of the 4684 HIV-positive people who were randomised, 112 (2.4%) were excluded from analysis as they had not completed a transmission risk questionnaire during the two year follow-up. Of the remaining 4572 participants there were 2562 MSM, 788 heterosexual men, and 1222 women. Baseline characteristics are shown in Table 1.

Sexual behaviour at baseline
The baseline transmission risk questionnaire was completed by 4504 of 4572 (98.5%) participants (original version N=547, updated version N=3957). Prevalence of CLS in the past two months was 39.2%, 23.8%, and 28.1% among MSM, heterosexual men and women respectively; prevalence of CLS-D was 19.9%, 9.6% and 14.5% respectively. CLS-D-HIVrisk prevalence was identical to CLS-D prevalence (by definition, as no participants were on ART at baseline).  Table 2 shows numbers completing the risk behaviour questionnaire by time point and the prevalence of ART use and VL ≤200 copies/mL, according to randomised arm and gender/sexual orientation. In the immediate arm, the proportion of participants who were on ART remained fairly stable from month 4 to month 24, at around 96-98%. Correspondingly, the prevalence of VL ≤200 copies/mL increased rapidly from baseline to month 4, with some further increase to month 24. In the deferred arm, the proportion on ART increased steadily over follow-up (as more individuals reached eligibility for ART initiation), mirrored by an increase in prevalence of viral suppression. Table 3  Among heterosexual men and women there was some evidence that CLS-D at month 12 was higher in the immediate versus deferred arm: 10 Prevalence of CLS, ≥2 CLS partners, ≥2 CLS-D partners, and insertive CLS-D with ejaculation did not differ by arm at month 12, nor did number of CLS-D acts among those diagnosed >3 months ago who reported CLS-D at baseline. Although prevalence of CLS-D was somewhat higher in the immediate versus deferred arm among heterosexual individuals, the prevalence of CLS-D-HIV-risk at month 12 was much lower in the immediate arm: 0.6% vs 7.7% [difference:-7.0%, 95% CI (-8.8%, -5.3%), p<0.001, Chi-squared test], due to viral suppression on ART.

Comparison of randomised arms according to baseline factors: CLS-D at month 12
The odds ratio (95% CI) of CLS-D at month 12 for the immediate versus deferred strategy was 0.96 (0.76, 1.22) for MSM and 1.34 (0.98, 1.82) for heterosexual men and women (the latter adjusted for gender). (Figure 1). Among MSM, there was no evidence that the intervention effect on CLS-D varied across subgroups. Among heterosexual men and women, the intervention effect (higher CLS-D at month 12 in the immediate versus deferred arm) was greater among participants aged <40 years (p=0.035 for interaction). Table 3 and Figure 2 show the prevalence of sexual behaviour measures by time point and randomised arm. The additional baseline estimates exclude participants diagnosed for less than three months.

Time since randomisation and sexual behaviour
Prevalence of CLS-D fell from revised baseline to month 4 in both arms, among MSM and heterosexuals. By month 24, prevalence had increased back towards the revised baseline level for MSM in both arms, and for heterosexuals in the immediate arm. For heterosexuals in the deferred arm, prevalence of CLS-D continued to fall throughout follow-up, resulting in higher CLS-D prevalence in the immediate versus deferred arm at month 24  Similar patterns over time were apparent when CLS was considered (Table 3 and Figure 1b).
Prevalence of CLS-D-HIV-risk decreased over time from month 4, as participants started ART (Table 3 and Figure 1c). As expected this decrease was particularly dramatic in the immediate ART group, resulting in substantial differences in CLS-D-HIV risk between randomised groups at months 12 and 24.

Transmission risk beliefs
At month 12, participants in the immediate arm were more likely than those in the deferred arm to indicate a belief that a person on HIV treatment with undetectable VL cannot, or is much less likely, to transmit HIV when having unprotected sex: 48 Table   3). Similar differences between arms were apparent at month 24 (Table 3).   transmission. This was based on data from the Partners Prep study which indicated a reduced but residual transmission risk persisting during the first 6 months of ART, due to incomplete viral suppression in blood and genital compartments. 23 In practice, and with newer ART drugs, viral suppression and subsequent protection may be attained at an earlier stage after ART initiation. But also of note, the difference between arms in CLS-D-HIV-risk attenuated from month 12 to month 24, and this would continue to occur as more individuals in the deferral arm started ART. In terms of STI transmission risk, the strategy of early ART resulted in a modest increase in prevalence of CLS among heterosexual individuals at year two only. However, less than 2% of heterosexual participants reported more than one CLS partner in the recall period. Risk of STI acquisition and transmission may be less concerning in this context. Incidence of bacterial STIs was not assessed in START.

Risk behaviour related to injection drug use
Two previous randomised trials have assessed the impact of ART on sexual transmision risk; 47,48 neither supported the hypothesis that ART use leads to increased condomless sex. In the SMART trial (2002)(2003)(2004)(2005)(2006), the prevalence of 'high-risk behaviour' (CLS-D or injecting risk behaviour) was similar compared between the continuous ART and CD4-guided episodic ART arms. 47 Among the subgroup who were not on ART at baseline, there was a reduction in high-risk behaviour in the first two years in the continuous compared to episodic ART arm.
More recently ,in the TEMPRANO-ANRS12136 trial of immediate versus deferred ART initiation (2008-2012), the proportion of participants reporting CLS-D was similar when compared between randomised arms at year one. 48 Many observational studies have assessed the association between ART and sexual behaviour among people with diagnosed HIV,  including two meta-analyses 29,32 and some studies in low/middle income countries. 41,43,45 The vast majority found no association of ART use or viral suppression with CLS-D, or found ART was in fact associated with lower levels of CLS-D. A few studies reported different findings overall, or in specific subgroups or analyses. Among sexually active women in the US Women's Interagency HIV Study (1996)(1997)(1998)(1999)(2000)(2001), consistent condom use was less likely to be reported after ART initiation compared to pre-ART, in some adjusted models. 24  among participants who were virally suppressed compared to those not on ART. 26 In a French study (2000)(2001)(2002)(2003)(2004)(2005)(2006)(2007)(2008)(2009), in more recent years, ART use and suppressed VL were associated with CLS-D among HIV-diagnosed heterosexual men with steady partners. 27 In the UK ASTRA study , prevalence of CLS-D among MSM on ART was higher for those with self-reported undetectable VL compared to those without. 28 Finally, a subsidiary analysis in one of the aforementioned meta-analyses found that an undetectable VL was associated with slightly higher sexual risk-taking. 29 Therefore previous literature suggested that, in some contexts, condom use may be influenced by knowledge of viral suppression, but the effect may be modest, and evidence is relatively weak in light of all relevant studies. These current results from START are the most contemporary (2010-2015) but seem broadly consistent with this synopsis, showing that starting ART may have modestly reduced condom use among heterosexuals. Although the combined heterosexual group was the predefined population of analysis, the pattern of results was broadly similar when men and women were examined separately (data not shown). The results from START and the other randomised trials have advantage that confounding is minimized in the comparison of the groups randomised to start or defer ART. It should also be noted that, as in the TEMPRANO trial, this START analysis addresses a slightly different question to the observational studies, as it evaluates the impact of starting ART on sexual behaviour over two years among people with high CD4 counts. In most of the observational comparisons, people on ART varied in terms of time since starting treatment and CD4 count; conceivably impact on sexual activity and condom use may vary according to these factors. Indeed there was evidence of significant variation in transmission risk beliefs by recruitment setting, which differed for MSM and heterosexuals. MSM from high income countries were more likely than those from low/middle income countries to express belief in a strong protective effect of viral suppression, whereas for heterosexuals there was some evidence of the opposite effect (belief more prevalent in low/middle income settings). The trial was carried out over a period of considerable change with regard to scientific evidence available on this issue, and publicity surrounding it, and these complex trends are likely to reflect this.
Increasing emphasis on the "U=U" message 17 may be leading to further changes in transmission risk beliefs and patterns of condom use; it is likely that the full effect of the current research evidence is yet to be apparent.
Among MSM, in both the immediate and deferred treatment arms, CLS-D prevalence fell from randomization to months 4 and 12, and subsequently increased back towards the revised baseline levels by year two. Among heterosexual participants, a similar but less marked decline in CLS-D occurred from revised baseline to month 4. Other studies have reported on temporary reductions in sexual risk for MSM following HIV diagnosis, 53,54 and so a similar pattern may have occurred for those individuals in START who were newly diagnosed at trial entry. In addition, for all participants, trial participation and regular contact with health care professionals and services, may have had a moderating effect on levels of condomless sex.
Limitations of this study include the possibility of error or bias arising from self-reported sexual behaviour and incomplete or missing questionnaires, though 12 month response rates were high and similar between randomised arms, and questionnaires were self-completed.
Participation in a trial with repeated monitoring of behavioural outcomes may have influenced condom use or it's reporting. The measure of HIV-transmission risk sex assumes that the latest VL is applicable to the entire two-month recall period.
In conclusion, a strategy of early ART did not impact on levels of serodifferent condomless sex among MSM and resulted in a small increase among heterosexual individuals. However in both groups, the strategy had a substantial favourable impact on HIV transmission risk behaviour at one year and is therefore likely to result in a marked reduction in new HIV infections in the initial period. The modest increase in condomless sex among the heterosexual group suggests the importance of continuing to monitor sexual behaviour as ART use expands, in order to understand any impact on other sexually transmitted infections.
Patterns of condomless sex may have changed with increasing promotion of the U=U message since the START trial was conducted. *112 of 4684 randomised participants were not included in the sub-study as they did not complete the transmission risk behavior questionnaire at any of the three follow-up time points (months 4, 12 and 24). ~Missing values: n=57 for time since diagnosis; n=8 for baseline VL. BL=baseline   For denominators by time point and p values comparing randomised arms, see Table 3.