Newly adopted risk behaviours predict HIV infections in Portuguese gay men

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Changes to an individual’s risk profile – including starting to have unprotected sex with a steady partner, a partner being diagnosed with HIV and having a new diagnosis of syphilis – are associated with an increased risk of HIV seroconversion in the following months, according to an analysis of incidence in a cohort of Portuguese gay men, reported in Eurosurveillance last week.

These markers were more predictive than behavioural or demographic factors noted when individuals entered the cohort. The results suggest that when clinical or prevention services note such new events, more intensive prevention services should be offered. They also underline how quickly HIV infection can occur when HIV is highly prevalent and individuals change their behaviours.

The Portuguese data are published alongside a French survey which found that large numbers of respondents had no discernible prevention strategy.


The data come from men testing for HIV at CheckpointLX, a community testing service in Lisbon. An open cohort was formed of men who tested negative at their first visit, agreed to complete behavioural questionnaires and returned for at least one more test. A total of 804 men who have sex with men met these criteria between 2011 and 2014, providing data for a total of 893 person years.


odds ratio (OR)

Comparing one group with another, expresses differences in the odds of something happening. An odds ratio above 1 means something is more likely to happen in the group of interest; an odds ratio below 1 means it is less likely to happen. Similar to ‘relative risk’. 

detectable viral load

When viral load is detectable, this indicates that HIV is replicating in the body. If the person is taking HIV treatment but their viral load is detectable, the treatment is not working properly. There may still be a risk of HIV transmission to sexual partners.


The transition period from infection with HIV to the detectable presence of HIV antibodies in the blood. When seroconversion occurs (usually within a few weeks of infection), the result of an HIV antibody test changes from HIV negative to HIV positive. Seroconversion may be accompanied with flu-like symptoms.



A sexually transmitted infection caused by the bacterium Treponema pallidum. Transmission can occur by direct contact with a syphilis sore during vaginal, anal, or oral sex. Sores may be found around the penis, vagina, or anus, or in the rectum, on the lips, or in the mouth, but syphilis is often asymptomatic. It can spread from an infected mother to her unborn baby.


A sexual risk reduction strategy for gay men having anal sex without a condom. Different sexual positions are adopted according to HIV status: the HIV negative man takes the insertive role (‘top’) and the HIV-positive man the receptive role (‘bottom’).


Men in the cohort had an average age of 30, most self-identified as homosexual, one-quarter were born outside Portugal and most had previously tested for HIV. At baseline, 44% reported unprotected sex with casual partners and 72% with a steady partner.

Each year, 2.8% of men acquired HIV. This is a little higher than in some other studies of European gay men and may reflect the service’s ability to reach men at higher risk of infection.

A number of factors were associated with acquiring HIV. The researchers paid particular attention to changes in behaviours, for example not reporting a behaviour at the first visit but subsequently reporting it. After statistical adjustment, the following factors were associated with seroconversion during follow-up:

  • Newly reporting having unprotected sex with a steady partner – odds ratio 3.8
  • Consistently reporting unprotected sex with casual partners – odds ratio 3.6
  • Newly reporting having sex with an HIV-positive partner – odds ratio 6.0
  • Newly reporting that a sexual partner had been diagnosed with HIV or had disclosed his HIV-positive status – odds ratio 5.2
  • Reporting an HIV-positive steady partner – odds ratio 3.3
  • A new case of syphilis – odds ratio 4.7

Men who had an HIV-positive steady partner and started to have unprotected sex with him were 17 times more likely to acquire HIV.

In contrast, behavioural factors noted when men entered the cohort were not associated with seroconversion. These factors included partner numbers, the venues used to meet sexual partners, use of PEP and sexual role during anal sex. Demographic factors such as age, education and sexual identity weren’t relevant either.

The authors conclude that short-term contextual and behavioural changes fuel the high incidence seen in this urban cohort.


Over 10,000 gay men living in France were recruited on dating websites, gay news websites, Facebook and a gay magazine to complete a survey in 2011. Of these, 6665 answered all questions relevant to this analysis and are included in the figures that follow.

Average age was 37, three-quarters were university educated, half had a steady male partner, a quarter regularly used sex-on-premises venues and one-in-seven had had a sexually transmitted infection in the previous year.

The researchers were interested in the ways in which participants managed risk during anal intercourse. As well as consistent condom use, this could involve seroadaptive behaviours such as serosorting (only having unprotected sex with men of the same HIV status) and seropositioning (if having unprotected sex with a partner of a different HIV status, the HIV-negative man always being ‘top’ and the HIV-positive man ‘bottom’). Men who had other behaviours were described as having no discernible prevention practice.

Among those who had never tested for HIV, 50% reported consistent condom use, 34% no discernible prevention practice and 16% no anal intercourse.

Among men who believed they were HIV negative, 55% reported consistent condom use, 21% no discernible prevention practice, 16% exclusive seroadaptive behaviours, and 8% no anal intercourse.

Turning to men with diagnosed HIV, the researchers separated those likely to be infectious and those who were not.

Among men who had either a detectable viral load or a recent sexually transmitted infection, 55% didn’t have any discernible prevention practice, 30% reported exclusive seroadaptive behaviours, 13% consistent condom use and 2% no anal intercourse.

Among men with well-controlled HIV, 45% were described as not having any discernible prevention practice, 30% reported exclusive seroadaptive behaviours, 22% consistent condom use and 3% no anal intercourse.

But it could be objected that men living with HIV who have an undetectable viral load and no sexually transmitted infections are highly unlikely to pass on HIV, so the ‘no discernible prevention practice’ label is unhelpful. These men were, in effect, preventing HIV transmission through their adherence to HIV treatment.

It’s also noticeable that those with well-controlled HIV were more likely to consistently use condoms than men with uncontrolled infection (a detectable viral load or a recent sexually transmitted infection).

The researchers analysed the characteristics of the men of all HIV statuses who don’t appear to have a clear prevention strategy in place. They were more likely to have had more than ten partners in the past year, to regularly use sex-on-premises venues and to regularly use dating websites than other participants. Especially among HIV-negative men, they appear to be more socially vulnerable than others – less educated, younger and living away from the big cities.

Men living with HIV who were described as having no discernible strategy were more likely to have been diagnosed after the year 2000 than earlier in the epidemic. The authors say this points to a generational shift, with barebacking and ‘treatment optimism’ having become more prevalent in recent years.


Meireles P et al. Incident risk factors as predictors of HIV seroconversion in the Lisbon cohort of men who have sex with men: first results, 2011–2014. Eurosurveillance. 2015;20(14):pii=21091. (Full text freely available).

Velter A et al. Sexual and prevention practices in men who have sex with men in the era of combination HIV prevention: results from the Presse Gays et Lesbiennes survey, France, 2011. Eurosurveillance. 2015;20(14):pii=21090. (Full text freely available).