Non-subtype B infections becoming more prevalent in HIV-positive gay men in UK

The HIV subtypes with which gay men in the UK are infected are becoming increasingly diverse, investigators report in the online edition of AIDS. Although HIV-1 subtype B remains the most common type of the virus infecting gay men in the UK, the proportion of infections involving non-B subtypes has increased dramatically.

“This study provides evidence that in the UK there has been an increase in non-B clade HIV infections in MSM [men who have sex with men] since the start of the epidemic,” comment the investigators.

There are several genetically distinct subtypes of HIV, and historically these have been confined to particular geographic regions or risk groups. Among gay and other men who have sex with men in Europe, subtype B predominates.

However, some small studies have shown that the prevalence of non-B subtypes amongst European gay men is increasing.

Investigators therefore wished to describe the frequency of non-B subtypes amongst gay men in the UK, monitoring trends from 1980 through to 2007. They also wished to see if any demographic characteristics were associated with an increased risk of infection with non-B subtypes.

A total of 8058 blood samples from HIV-positive gay men taken and stored in the UK HIV Drug Resistance Database were analysed by the researchers.

Overall, 437 infections (5%) involved non-B subtypes. This included 102 subtype C infections, and 53 infections with subtype A.

Most (69%) of the men with non-B infections were white, and 42% were born in the UK. The distribution of non-B subtypes was similar in UK-born white men and the remaining patients.

The prevalence of non-B subtypes was very low before 1996, but then increased to between 7 and 9% in the period after 2002. However, this prevalence increased sharply to 13% in 2007.

As regards ethnicity, 13% of black and 11% of Asian gay men were infected with non-B strains of HIV. A quarter of the black men and none of the Asian men were born in the UK.

Almost all (96%) non-B infections in gay men were located in south-east England.

In “multivariate” analysis, the factors significantly associated with infection with non-B subtypes were later year of diagnosis (p < 0.001), black African ethnicity (p < 0.001), and non-European country of birth (p = 0.01). Patients aged under 25 were also significantly more likely than those in the 25 to 39 age group to have non-B infection (p = 0.01).

The investigators also found that UK-born white gay men diagnosed after 2002 were 8.5 times more likely to be infected with a non-B subtype than those diagnosed before 1996.

“The increasing prevalence of non-B HIV-1 within MSM (both overall and within UK-born MSM) is suggestive that HIV acquisition within this population may be occurring in the UK,” comment the investigators, adding “segregation of clades of HIV are becoming less distinct”.

The investigators are uncertain about the clinical significance of their findings, concluding, “the impact of introducing non-B HIV-1 infection to a formerly B clade restricted population on clinical outcome or vaccine efforts is unclear. The former is controversial and the latter highlights the need for a cross-clade prophylactic vaccine.”