Public messages and campaigns about the dangers of unsafe sex do not appear to be getting through to men who have sex with men, the researchers say – particularly the young ones.

By investigating the genetic profile of the virus in more than 500 newly screened patients over nine years, scientists in Belgium have identified clusters of people with type B virus – not the one that is most prevalent in Africa.

Those infected are almost all white, male, gay and young, they say. These men also tend to have other sexual diseases, such as syphillis, which suggests that they are involved in unsafe sexual behaviour and are not using condoms.

The research was carried out by scientists at Ghent University in Belgium, and there is every indication that their findings hold true for the UK. Nick Partridge, the chief executive of the Terrence Higgins Trust, said that gay men were the group most at risk of HIV infection in the UK.

The Health Protection Agency (HPA), which monitors HIV numbers in the UK, warns every year of the rising rate of infections among men who have sex with men (MSM). In its last full report, for 2009, it said that the rate of infection among gay men remained high, even though there had been a slight overall drop.

HIV infection can go unnoticed for years, but the HPA report said one in five of those diagnosed had become infected within the previous six months – suggesting recent risky behaviour was to blame.

A 2008 report specifically on HIV among men who have sex with men said there were around 32,000 living with HIV in the UK. Just under half of all new diagnoses were among men who had sex with men, and 82% of the infections were probably acquired within the UK.

The Belgian researchers, Kristen Chalmet and colleagues from the Aids Reference Laboratory at Ghent University, found one “striking and alarming” cluster of cases. Over the nine years of the study, 57 men acquired genetically very similar viruses, they say. Eight of them did so in the last year. “Members of this cluster are significantly younger than the rest of the population and have more chlamydia and syphilis infections,” they write today, in the open access journal BioMed Central Infectious Diseases.

Even excluding that group from the study, there was still a relationship between HIV infection and contracting syphilis, which suggested risky sexual behaviour.

The study found two main types of HIV, but their analysis found that those infected with the two sub-types were “significantly different populations”. The vast majority of cases of infection within Belgium were sub-type B cases, and those infected were most often men who have sex with men. The non-B cases were more likely to be in heterosexuals and to have been acquired abroad.

“We clearly demonstrate that, despite the existence of prevention programmes, easily available testing facilities and a supposedly broad public awareness of the infection and its possible routes of transmission, MSM still account for the majority of local onward transmissions,” they write.

“Continuous efforts to sustain prevention programmes targeting MSM are definitely needed.”

Nick Partridge echoed the call for targeted campaigns. “Gay men are still the most at risk of HIV infection in the UK. We also know that more than a quarter of people with HIV in the UK are currently undiagnosed, and they’re far more likely to pass the virus on than those who know they have it.” “Targeted HIV prevention programmes are key to reducing the numbers of new infections each year. But we’d also argue for innovative testing services to better diagnose men who’ve been at most risk.”

Professor Pat Cane, head of the HPA’s antiviral unit, said work done in the UK with the Medical Research Council, “has shown that there are two predominant sources of HIV circulating in the UK at the moment – one in men who have sex with men (HIV1, sub-type B) and the other associated with sub-Saharan Africa (non B, HIV1).”

Guardian 7/9/2010