Unprotected sex eight times more common in serious relationships than casual ones, US gay youth study finds

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The strongest single predictor of not using condoms in anal sex in a group of young US gay men was that the relationship was regarded as ‘serious’, a study has found. Unprotected sex was eight times more likely in serious relationships than in casual encounters.

This study, conducted conducted by Northwestern University in Illinois, USA (Mustanski) reinforces previous findings that over two-thirds of HIV transmissions between US gay men happen between primary sex partners and only a third between casual partners (Sullivan).

In this study, the researchers comment, “there was almost no unprotected sex occurring in relationships classified as casual”. This suggests that HIV prevention strategies amongst US gay men may need to focus more on HIV risk and safer-sex negotiation within couples than on individual risk-taking decisions.


statistical significance

Statistical tests are used to judge whether the results of a study could be due to chance and would not be confirmed if the study was repeated. If result is probably not due to chance, the results are ‘statistically significant’. 

longitudinal study

A study in which information is collected on people over several weeks, months or years. People may be followed forward in time (a prospective study), or information may be collected on past events (a retrospective study).


The result of a statistical test which tells us whether the results of a study are likely to be due to chance and would not be confirmed if the study was repeated. All p-values are between 0 and 1; the most reliable studies have p-values very close to 0. A p-value of 0.001 means that there is a 1 in 1000 probability that the results are due to chance and do not reflect a real difference. A p-value of 0.05 means there is a 1 in 20 probability that the results are due to chance. When a p-value is 0.05 or below, the result is considered to be ‘statistically significant’. Confidence intervals give similar information to p-values but are easier to interpret. 


Studies aim to give information that will be applicable to a large group of people (e.g. adults with diagnosed HIV in the UK). Because it is impractical to conduct a study with such a large group, only a sub-group (a sample) takes part in a study. This isn’t a problem as long as the characteristics of the sample are similar to those of the wider group (e.g. in terms of age, gender, CD4 count and years since diagnosis).


The study of the way people think, behave and interact. Psychological therapies are based on talking and working with people to understand the causes of mental health problems and develop strategies to deal with them. Psychologists have specialist training but are not medical doctors.

The study

The current study included 122 young men (aged 16-20) who had sex with men (MSM). Two-thirds classed themselves as gay and nearly a quarter bisexual while the remaining 11% used other categories (queer, questioning etc.) They were a subset of Project Q2, a longstanding longitudinal study of gay youth that has already uncovered high levels of mental ill-health and suicidal behaviour.

The group was recruited by means of ‘snowball sampling’ whereby a number of participants were initially identified by outreach and then encouraged to recruit others (and given $10 for each recruit). Participants were not recruited according to whether they had risky sex or not.

The researchers conducted three surveys of sexual partnerships, risk behaviour and other factors during the previous six months. These occurred at the start of the study and then six and twelve months later. Participants were paid $40 for each interview, and the retention rate was about 90%. Data was available for 117 participants who between them reported a total of 416 sexual partners (3.5 each on average).

The participants’ mean age was 18.5 years and 23% were under 18.

Half of the group described themselves as African-American, just under one in five as white, one in eight as Hispanic and one in nine as multiracial. Six per cent (seven individuals) reported knowing they had HIV; 81% had ever tested for it and 60% said they had taken a test in the last six months.

Only two participants reported knowingly having had sex with an HIV positive partner – this was so uncommon that whether status knowledge influenced safer-sex decisions could not be established.


Half (49%) of participants reported being in a serious relationship at the time of asking, defined as having “someone you feel committed to above all others”, and 80% reported having had at least one over the study period. Twelve per cent had had a female partner (serious or otherwise) during this time.  

Despite commitment being reported frequently, truly long-term relationships were not common: only 8% of participants reported having the same partner six months later. During the 18-month study period 20% of participants reported no ‘serious’ relationship, 23% one, 27% two, and 28% three or more, to a maximum of five.

One factor that may be important for HIV transmission was that, in this gay youth group, the majority of participants’ partners were older than they were – on average two years older.

Violence within relationships was not uncommon – 11% reported being ‘hit, slapped, punched or hurt’ by their partner – but non-consensual sex less so – only two individuals reported forced sex.

The study found an average of 5.74 episodes of unprotected sex within each sexual partnership they had.

Being in a relationship regarded as serious was, by a long way, the strongest predictor of having unprotected sex. This was 7.82 times more likely to happen within a serious relationship than in a casual one (a 682% increase), and was highly statistically significant (p=<0.001).

This association became even more significant when the 12% of partnerships that were with women were eliminated: unprotected sex was ten times more likely within male/male relationships regarded as serious than in ones not thought so.   

Two other factors were associated with more than twice the risk of unprotected sex but were less significant. Participants reporting sex with a woman were 2.9 times more likely to report unprotected sex, but this finding was not statistically significant and could have been due to chance (p=0.25). Forced sex was associated with a 5.5 times greater risk of reporting unprotected sex but, while this was statistically significant, as reported above, forced sex was uncommon.     

Having a relationship that lasted more than six months increased the risk of unprotected sex by 62%, drug use prior to sex by 45%, and  violence within the relationship by 88%.

Unprotected sex was related to the age of partners. There was a 20% increased likelihood of unprotected sex per one-year increase in a partner’s age, relative to the participant, and unprotected sex was six times more common with partners who were five or more years older. A recent US study (Hurt) found that having a partner five or more years older than themselves doubled their risk of HIV infection.  Given that HIV prevalence in gay men increases sharply during the early 20s and especially in African men, this may be a major contributing factor in HIV acquisition.

The researchers in their introduction note that relationships can be ‘serious’ for negative as well as positive reasons: people can feel trapped in a relationship because they feel dominated or because they perceive no-one else is available, as well as because they want the relationship to last.

They tested the influence of these emotional factors and found that while “wanting the relationship to last” wasassociated with unprotected sex (twice the risk), feeling trapped within a relationship was not. If the relationship was known to be open (partner having sex with others), unprotected sex was 32% less likely.

There was a hint that power dynamics might influence safer sex choices in that unprotected sex was 32% more likely if participants reported that their partner “usually got his/her way” in disputes, though this was only marginally significant (p=0.05).


The researchers comment that “Our findings suggest that serious relationships are the context in which most unprotected sex is occurring in our sample of urban, primarily racial-minority, young MSM...This points to serious relationships as being a potentially powerful context for prevention.”

However, they add, “Before such interventions can be developed, more formative research will be required to understand how to address the relatively frequent turnover in serious relationships at this age.”

And they warn that while serious relationships may be an HIV risk factor, there are many “other emotional and health benefits that can come with being in a close and positive romantic relationship.”


Mustanski B and Newcomb ME. Relationship characteristics and sexual risk-taking in young men who have sex with men. Health Psychology, early online edition. DOI: 10.1037/a0023858. 2011.

Sullivan PS et al. Estimating the proportion of HIV transmissions from main sex partners among men who have sex with men in five US cities. AIDS 23(9):1153-62. 2009.

Hurt CB et al. Sex with older partners is associated with primary HIV infection among men who have sex with men in North Carolina. JAIDS 54(2):185-90. 2010.