Defining high HIV incidence subgroups of Australian
homosexual men: implications for conducting HIV
prevention trials in low HIV prevalence settings
IM Poynten,1F Jin,1GP Prestage,1JM Kaldor,1S Kippax2and AE Grulich1
1National Centre in HIV Epidemiology and Clinical Research, University of New South Wales, Sydney, New South Wales,
Australia and2National Centre in HIV Social Research, University of New South Wales, Sydney, New South Wales, Australia
The aim of the study was to assess whether subpopulations with sufficiently high HIV incidences for
HIV prevention trials can be identified in low HIV incidence settings such as Australia.
In a community-based cohort study of HIV-negative homosexually active men in Sydney, Australia,
potential risk factors associated with an annual HIV incidence of ?2 per 100 person-years (PY) were
identified. A stepwise procedure ranked these factors according to HIV incidence, to create a ‘high-
incidence’ subgroup of participants. Willingness to participate in HIV prevention trials was assessed.
Although the incidence in the cohort overall was only 0.78 per 100 PY, nine risk variables were
associated with an HIV incidence of 2 per 100 PY or greater. Stepwise inclusion of these variables
revealed a ‘high-incidence’ subgroup of men representing 24% of the total follow-up time with a
combined HIV incidence of 2.71 per 100 PY, who reported at least one of three risk factors in the past
6 months. These men were more willing than others to participate in vaccine and antiretroviral
therapy HIV prevention trials.
These findings demonstrate that it is possible to identify high HIV incidence subpopulations in low-
incidence settings such as Australia, and these men are of above average willingness to participate in
HIV prevention trials.
Keywords: biomedical prevention, clinical trials, HIV, HIV incidence, pre-exposure prophylaxis,
Accepted 21 January 2010
A range of biomedical HIV prevention technologies are
under clinical development, including vaginal and rectal
microbicides, pre-exposure prophylaxis (PREP) and vac-
cines . A number of these agents have reached the stage
of large-scale effectiveness trials [2,3]. It is generally
accepted that to measure the effectiveness of the preven-
tion intervention with adequate power and achievable
sample sizes, such trials require populations with high HIV
incidences of around 2% or more per year [4,5].
Most communities with a high incidence of HIV
infection are found in resource-poor countries. There is
an urgent need for prevention interventions in these
settings, where the social, economic and public health
consequences of the HIV pandemic have been enormous.
For these reasons, the focus of many HIV intervention trials
has moved to the developing world . All published
vaginal microbicide [6–15] and PREP effectiveness trials
 and almost all ongoing trials have been conducted
solely in resource-poor countries [2,3]. HIV vaccine trials,
in contrast, have generally been conducted in both
resource-rich and resource-poor countries [17–20].
There are only a small number of communities in
resource-rich settings where the HIV incidence is higher
than 2% per year. In Australia, the incidence of HIV
Correspondence: Dr Isobel Mary Poynten, National Centre in HIV
Epidemiology and Clinical Research, Level 2, 376 Victoria Street,
Darlinghurst, NSW 2010, Australia. Tel: 161 2 9385 0900; fax:
161 2 9385 0920; e-mail: email@example.com
HIV Medicine (2010), 11, 635–641
r 2010 British HIV Association
infection is relatively low, and among men who have sex
with men (MSM), the group most affected by HIV, the
incidence is o1% . However, the incidence of HIV
infection among gay men is increasing in Australia, as it is
in MSM around the world [22,23]. Even in Australia, the
prevalence and incidence of HIV infection is as high in
some MSM communities as it is in resource-poor countries
. There is the potential to identify cohorts of these gay
men, at high risk of HIV infection, of sufficient size to
enable the conduct of HIV prevention trials .
Prevention research in both resource-poor and resource-
rich settings is necessary. Population-specific information
on effectiveness and acceptability is essential to provide
guidance for policy makers and health-care providers .
Here we explore whether subpopulations with sufficiently
high incidences of HIV infection for HIV prevention trials
can be readily identified in a low HIV incidence setting
such as Australia, by assessing incidence in cohort
subgroups, and analysing data on willingness to participate
The Health in Men study (HIM)
The HIM study was a community-based prospective cohort
study of HIV-negative homosexually active men in Sydney
conducted as a vaccine preparedness cohort study . The
methodology for the HIM study has been published
previously [26,27]. The study recruited participants from
June 2001 to December 2004. Interviews were conducted
from June 2001 to June 2007. Written informed consent
was obtained from all potential study participants prior to
enrolment. The HIM study received ethics approval from
the University of New South Wales.
All participants underwent annual structured face-to-
face interviews on a wide range of topics, including sexual
relationships and practices and injecting drug use.
Serological testing for HIV was performed annually using
a combined antigen/antibody test (AxSYM, HIV Antigen/
Antibody Combo; Abbott Diagnostics, Abbott Park, IL,
USA). At approximately 6 months between annual face-to-
face interviews, information on sexual relationships and
practices and injecting drug use in the past 6 months was
collected via a short version telephone interview. Quanti-
tative sexual behaviour data were collected. Printed HIV
prevention information was available for study participants
in the interview waiting area, but no formal HIV risk
reduction counselling was provided during the study.
Incident HIV infections were identified through diag-
noses at the annual study visit and by linkage with the
national HIV register. The final match against the national
HIV register and the final study interviews occurred in June
2007. HIV seroconversion was identified through matching
for 13 participants and, for these individuals, no beha-
vioural data were available at the time of estimated
infection. For seven participants in whom the estimated
date of infection was less than 12 months after the last
interview, information obtained from the last interview was
carried forward for risk factor analysis. Six participants
whose estimated dates of infection were more than 12
months later were excluded from risk factor analysis.
Statistical analysis was performed using STATA 10.0 (STATA
Corporation, College Station, TX, USA). For HIV incidence,
total person-years (PY) were calculated as the time from
study entry to the estimated date of HIV seroconversion.
With the exception of circumcision, all risk factors were
examined as time-dependent covariates.
Factors associated with an HIV incidence of ?2 per 100
Potential risk factors that defined subgroups of the HIM
cohort in which the annual HIV incidence was ?2 per 100
PY, as a starting point, were identified. It should be noted
that the subgroups were not mutually exclusive, as
participants could potentially report more than one risk
factor in a 6-month period, so that a person could fall into
multiple risk factor groups. Risk factors examined that had
been identified in univariate analysis and reported in
previously published research from the HIM study included
any previous nonoccupational post-exposure prophylaxis
(NPEP) use , circumcision status , and any of the
following in the past 6 months: reported unprotected anal
intercourse (UAI) with a known HIV-positive partner,
receptive UAI with a casual partner , having an HIV-
positive regular partner , anal sexually transmitted
infections (STIs) , use of oral erectile dysfunction
medications and recreational drug use . In some cases
[27,30], the definition of risk behaviours used in published
reports was slightly modified and the data reanalysed to
provide a more pragmatic definition of risk groups. For
example, in a previous publication, the risk associated with
receptive UAI was stratified by whether or not ejaculation
had occurred , but for the current analysis, any report
of receptive UAI with a casual partner was included.
Demographic factors such as age, income and education
level were also examined . Other risk factors for higher
HIV incidence were identified from other published sources
and examined within the HIM cohort. These included
number of sexual partners in the past 6 months [32,33,34],
636 IM Poynten et al.
r 2010 British HIV Association HIV Medicine (2010) 11, 635–641
alcohol consumption , previous hepatitis B virus (HBV)
infection  and injecting drug use . For each risk
factor, the HIV incidence was calculated as the number of
HIV seroconversions divided by the total PY of follow-up
for participants who reported/experienced that risk factor.
Ranking of high-incidence strata
A stepwise procedure was used to rank the factors
described above according to the incidence in subgroups
defined by the factor. First, the factor associated with the
highest incidence was identified, the HIV incidence was
recorded and then participants in the cohort who reported
the factor were excluded from further analysis. The
incidence in each of the remaining risk factor subgroups
was then recalculated in the remaining individuals. On
each occasion when HIV incidence in the remaining risk
factor subgroups was recalculated, the incidence in that
stratum changed after the participants above were ex-
cluded. Again, the factor associated with the highest
incidence was identified, the HIV incidence was recorded
and then participants with this factor were excluded from
subsequent analysis. This process was repeated until no
subgroup could be identified in which the incidence
exceeded 1.5 per 100 PY. With each step, PY and number
of HIV seroconversions were summed across the included
factors, and a combined HIV incidence was calculated.
Willingness to participate in HIV prevention efficacy
As the HIM study was designed as a vaccine preparedness
study, a large number (53) of questions on participants’
attitudes towards HIV vaccine trials were asked annually
from 2001 onwards. In contrast, only one question on how
likely they would be to participate in a trial to test the
effectiveness of a rectal microbicide (‘very unlikely’,
‘unlikely’, ‘likely’, ‘very likely’ or ‘don’t know’) and one
question on how likely they would be to participate in a
trial to test the effectiveness of antiretroviral drugs (ARVs)
in preventing HIV infection (‘very unlikely’, ‘unlikely’,
‘likely’, ‘very likely’ or ‘don’t know’) were asked annually,
from 2006 onwards.
The participants’ response to willingness questions in the
final year was included in order to capture their most
recent views on participation in trials. Willingness to
participate in rectal microbicide trials and trials using
ARVs to prevent HIV infection was analysed by logistic
regression, comparing participants in the high incidence
subgroup with the rest of the HIM cohort. Although many
questions concerning HIV vaccines were asked in the HIM
study, there was no specific question on willingness to
participate in HIV vaccine trials. For this reason, factor
analysis was used to develop a scale to represent will-
ingness to participate in HIV vaccine trials. This was based
upon previously published factor analysis of HIV vaccine
attitudes in Sydney [36,37]. The three items included in the
willingness to participate in HIV vaccine trials scale were:
‘I would participate in an HIV vaccine trial even if
I thought the vaccine might not work’, ‘I want to take part
in HIV vaccine trials because I think it will benefit me
personally’ and ‘Gay men have nothing to lose by
participating in an HIV vaccine trial’.
To confirm the suitability of the scale for use in the HIM
study, the three questions were entered into an exploratory
factor analysis, and a reliability coefficient (Cronbach
a-value) was calculated for all participants who responded
to the questions. As with the questions on willingness to
participate in rectal microbicide trials and trials using ARVs
to prevent HIV infection, the participants’ last response was
included in order to capture their most recent views on
participation in trials. Mean scale scores for ‘high-incidence’
subgroups were compared with the mean scale scores for
the remainder of the cohort, using the t-test statistic. Where
the response was ‘Don’t know’, the value for the mean of the
response to the question was used.
A total of 1427 participants were enrolled in the HIM study
between June 2001 and December 2004. The median age at
enrolment was 35 years, with age ranging from 18 to 75
years. The majority (95.2%) of participants self-identified
as gay or homosexual. The cohort was highly educated,
with more than half (51.9%) holding university or post-
graduate qualifications, and 21.6% with tertiary diploma or
technical and further education degrees. Nearly two-thirds
of participants (913; 65.7%) were somewhat or very
involved in the gay community in Sydney. By the end of
the study in 2007, there were 53 HIV seroconversions
identified, giving an overall HIV incidence of 0.78 per 100
PY [95% confidence interval (CI) 0.59–1.02]. The total
follow-up time was 5161 PY, and the median was 3.9 years
per participant. Risk factor analysis was performed on 47 of
the 53 HIV seroconverters who had sexual behaviour data
available within 12 months of seroconversion.
Factors associated with an HIV incidence of ?2 per
Risk factors associated with an HIV incidence of more than
2 per 100 PY are summarized in Table 1. In order of
incidence they included reports in the past 6 months of
UAI with a known HIV-positive partner, any injecting drug
Identifying populations for prevention trials 637
r 2010 British HIV Association HIV Medicine (2010) 11, 635–641
use, receptive UAI with a casual partner, any anal STI, both
oral erectile dysfunction medication and methampheta-
mine use, more than 50 casual partners, having an HIV-
positive regular partner, any oral erectile dysfunction
medication use and any psychedelic/hallucinogen use
The remaining risk factors examined had an HIV
incidence of o2 per 100 PY. Circumcision status (HIV
incidence in uncircumcised participants of 1.04 per 100 PY;
95% CI 0.58–1.20) and the use of ‘any recreational drugs’
(0.83 per 100 PY; 95% CI 0.77–1.41) in the past 6 months
were associated with an HIV incidence of approximately
1 per 100 PY. Daily alcohol consumption (1.48 per 100 PY;
95% CI 0.74–2.96) and prior HBV infection (1.24 per 100
PY; 95% CI 0.71–2.19) were each associated with an HIV
incidence of o2 per 100 PY. When demographic factors
including age, education, income and occupation were
examined individually, none was found to be related to an
HIV incidence of ?2 per 100 PY (data not shown).
Identification of high-incidence strata
In total, there were nine risk factors identified with an HIV
incidence of 2 per 100 PY or higher (Table 1). The stepwise
procedure described above was used to rank these nine risk
factors. Thirteen of the total 47 HIV seroconversions were
among men who reported the highest risk behaviour of UAI
with an HIV-positive partner. The group of participants
reporting UAI with an HIV-positive partner were excluded
from the analysis and the incidence in the remaining eight
high-risk groups was recalculated. Receptive UAI with
casual partners was the next highest risk group identified
(2.43 per 100 PY; 95% CI 1.38–4.28), accounting for 12 of
the remaining 34 HIV seroconversions (Table 2). After
exclusion of those men, reported use of both oral erectile
dysfunction medication and methamphetamines had the
highest HIV incidence (1.67 per 100 PY; 95% CI 0.84–3.34).
The combined HIV incidence among men who reported at
least one of these three risk factors (hereafter called the
‘high-incidence’ subgroup) was 2.71 per 100 PY (Table 2),
and included approximately 70% of total seroconversions
(33) and 24% of the total PY of follow-up (1218 PY). When
men reporting any of these three risk factors were excluded,
the HIV incidence was o1 per 100 PY in all remaining men.
Table 1 HIV incidence by risk factors with published estimates from
the Health in Men (HIM) study or other sources
Risk factor in past
per 100 PY
UAI with known HIV-
Any injecting drug use
Receptive UAI with casual
Any anal STI*
Any OEM and
More than 50 casual
Any OEM use
Any previous NPEPz
246.2913 5.28 (3.06–9.09)
7 4.29 (2.05–9.00)
244.476 2.45 (1.10–5.46)
363.418 2.20 (1.10–4.40)
*Neisseria gonorrhoea, Chlamydia trachomatis or anal warts.
wBoth oral erectile dysfunction medication (OEM) and methamphetamine
zAny NPEP use in the past.
CI, confidence interval; NPEP, nonoccupational post-exposure prophylaxis;
STI, sexually transmitted infection; UAI, unprotected anal intercourse.
Table 2 Stepwise analysis of HIV incidence per 100 person-years (PY) for the highest strata of HIV incidence
Risk factor in past 6 months
with highest HIV incidence
Number of HIV
each risk factor (total
no. of seroconversions)
of follow-up for
each risk factor
per 100 PY
per 100 PYw
Step 1 (all variables)
UAI with known
Step 2 (variable above excluded)
Receptive UAI with casual partner
Step 3 (two variables above excluded)
Any OEM and methamphetamine usez
13 (47)246.295.28 (3.06–9.09)246.295.28
12 (34)493.282.43 (1.38–4.28)739.573.38
8 (22)478.66 1.67 (0.84–3.34)1218.232.71
Tests in italics represent the variable with the highest HIV incidence in that stratum.
*Stepwise addition of person-years for each risk factor.
wStepwise calculation of HIV incidence (accumulated number of HIV seroconversions divided by accumulated number of person-years).
zReporting use of both oral erectile dysfunction medication (OEM) and methamphetamine.
CI, confidence interval; UAI, unprotected anal intercourse.
638 IM Poynten et al.
r 2010 British HIV Association HIV Medicine (2010) 11, 635–641
Association between willingness to participate in
prevention trials and HIV incidence
A total of 844 HIM participants responded to the question
on willingness to participate in rectal microbicide trials.
Among this group, 29% of the 244 ‘high-incidence’
participants were willing to participate in rectal micro-
bicide trials compared with 23% of the remaining cohort
[odds ratio (OR) 1.38; 95% CI 0.97–1.95; P50.073]. When
the 233 men who reported that they did not know how
likely they were to participate were excluded, 40% of ‘high-
incidence’ men were willing to participate compared with
32% of the remainder of the responding cohort (OR 1.44;
95% CI 0.99–2.10; P50.056). Of the 895 HIM participants
who responded to the question on willingness to participate
in trials using ARVs to prevent HIV infection, men in the
‘high-incidence’ subgroup were significantly more willing
to participate compared with the rest of the respondents,
both when the 69 men who reported that they did not know
how likely they were to participate were included (51 and
41%, respectively; OR 1.52; 95% CI 1.13–2.05; P50.006)
and when they were excluded (55 and 44%, respectively;
OR 1.54; 95% CI 1.13–2.11; P50.006).
Factor analysis of participants’ last responses to the three
questions about willingness to participate in HIV vaccine
trials confirmed the reliability of the scale (Cronbach
a50.72). A total of 1218 participants responded at least
once to all three questions and the mean of the total score
was 8.15 [standard deviation (SD) 2.10]. The 324 men in the
‘high-incidence’ subgroup had a higher mean score on the
scale (8.39; SD 1.97) than the remaining 894 participants
(8.06; SD 2.14; P50.01), indicating that they were more
willing to participate in HIV vaccine trials.
Despite an overall HIV incidence in this cohort of
Australian gay men of less than 1 per 100 PY, a readily
identified subgroup comprising approximately a quarter of
the cohort had an HIV incidence of 2.7 per 100 PY. Men in
this ‘high-incidence’ subgroup were significantly more
willing than others to participate in HIV prevention trials
using ARVs or vaccines. These findings confirm that there
are populations in low-incidence settings such as Australia
who have sufficiently high HIV incidence and are willing
to take part in HIV prevention trials, including those of the
newer biomedical prevention technologies.
In the HIM cohort, nine overlapping risk variables were
associated with an HIV incidence of ?2 per 100 PY. Three
of these risk variables were included in the final ‘high-
incidence’ subgroup: UAI with a known HIV-positive
partner, receptive UAI with casual partners, and reporting
use of both oral erectile dysfunction medication and
methamphetamines. Over a quarter of all HIV seroconver-
sions (13; 27.7%) were in men reporting the highest risk
factor, UAI with a known HIV-positive partner (HIV
incidence 5.3%). Based on this finding, it may seem
appropriate to target only these men for HIV prevention
trials. However, these men accounted for only 4.8% of total
HIM follow-up. Thus, the target population is small and
recruiting sufficient numbers for an HIV prevention trial
would probably be difficult. By adding the two next
highest risk behaviours (receptive UAI with casual partners
and reporting use of oral erectile dysfunction medication
and methamphetamines), while maintaining an HIV
incidence of 2.7 per 100 PY per year, the size of the
population at risk was greatly increased to 24% of the
cohort. With an HIV incidence of 2.7 per 100 PY, HIV
prevention trials among this group of men may be feasible.
The sample size necessary for each study arm in a
randomized controlled HIV prevention trial to show 50%
efficacy of an intervention after 1 year of follow-up would
be 1853, assuming a significance level of 95% and a power
of 80%. If the entire HIM population was recruited, with an
incidence of 0.78 per 100 PY, the sample size would
increase to over 6500 per study arm. Men at high risk of
HIV in the HIM study were more willing to participate in
HIV prevention trials of vaccines and ARVs. Although not
quite significant, there was a trend towards greater
willingness to participate in rectal microbicide trials among
men at higher risk of HIV infection (P50.056) when only
men who had definite opinions on participation were
included. This association between an increased risk of HIV
infection and willingness to participate in HIV prevention
trials has been consistently identified in MSM who are
potential trial participants, both in Australia  and in
other countries [34,35,38–41]. The combination of high
HIV incidence and increased willingness to participate in
trials further indicates the suitability of such a population
for prevention trials.
This study had the strength of being a large-scale
prospective cohort study and was primarily community-
based, with only 4% of participants recruited from clinics.
Although not necessarily representative of all Australian
gay men, a wide variety of recruitment strategies were used
to reach a broad sample of the homosexual community.
Detailed information on UAI behaviour was collected,
which allowed the differentiation of partner- and position-
specific practices from all UAI acts and the creation of
precise definitions of risk variables. The prospective
biannual collection of behavioural data minimized recall
There were several limitations in this study. The question
on willingness to participate in trials using ARVs to prevent
Identifying populations for prevention trials 639
r 2010 British HIV Association HIV Medicine (2010) 11, 635–641
HIV infection potentially included men’s attitudes to PREP
and/or NPEP trials. However, as the intervention is the
same (oral antiviral therapy), it is feasible that men’s
attitudes towards participation in PREP and NPEP trials
would be similar. Because of the design of the study
questionnaire, different methods were used to assess
willingness to participate in vaccine trials and in trials of
ARVs or rectal microbicides. Although the results were not
directly comparable, they all indicated greater willingness
to participate in ‘high-incidence’ men. Finally, the ques-
tions on willingness to participate in rectal microbicide and
trials of ARVs to prevent HIV infection were asked only in
the final 2 years of the study period (2006–2007).
In Australia and in other low-incidence resource-rich
settings , HIV vaccine efficacy trials including MSM
have already been conducted. Population-specific informa-
tion is also needed for other HIV interventions such as
PREP and microbicides in these settings. We have
demonstrated here that the selection of well-defined and
pragmatic eligibility criteria led to the identification of a
cohort of Australian gay men at high risk of HIV infection,
who were more willing than men at lower risk of HIV
infection to be involved in HIV prevention trials. Targeted
recruitment strategies would aid in enrolling sufficient
numbers of men to make these trials feasible. Effectiveness
trials of all HIV biomedical prevention technologies could
be undertaken in low HIV prevalence resource-rich settings
such as Australia. Such research is necessary to provide
effectiveness and acceptability data in the at-risk commu-
nities who may use these interventions.
The authors thank all the participants, the dedicated HIM
study team and the participating doctors and clinics.
Conflicts of interest: The authors have no conflicts of
Sources of support: The National Centre in HIV
Epidemiology and Clinical Research and the National
Centre in HIV Social Research are funded by the Australian
Government Department of Health and Ageing. The Health
in Men Cohort study was funded by the National Institutes
of Health, a component of the US Department of Health and
Human Services (NIH/NIAID/DAIDS: HVDDT Award N01-
AI-05395), the National Health and Medical Research
Council in Australia (Project grant 400944), the Australian
Government Department of Health and Ageing (Canberra)
and the New South Wales Health Department (Sydney).
M.P. is supported by a National Health and Medical
Research Council (NHMRC) Public Health Postgraduate
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