‘Out’ vs. ‘hidden’ – how HIV transmission patterns differ in men who have sex with men

12 July 2018

Men who don’t disclose same-sex sexual behaviour have different HIV transmission patterns compared to other men who have sex with men (MSM) and heterosexual men.

Gay men chatting

A recent UK study reveals that men who do not disclose same-sex sexual behaviour are more likely to have relations with men who also choose not to disclose their sexual behaviors. As such, these men are less likely to be in the close sexual networks that can accelerate HIV transmission – known as HIV clusters.

One explanation suggested for this by the study authors might be that non-disclosed MSM have fewer sexual partners than men who are open about having sex with men. They may also use condoms more consistently or have sex with lower-risk partners.

In the study, researchers mapped the HIV transmission network using a phylogenetic analysis of 14,405 people living with HIV – including 8,452 self-identified MSM, 1,341 self-identified heterosexual men and 1,743 self-identified heterosexual women.

But among the men who identified as heterosexual, 249 were linked clusters of male-to-male sex, suggesting they had not disclosed same-sex behaviour to clinical staff.

The findings also indicate that non-disclosed MSM are more likely to be black than men who are open about same sex behaviour. These results echo findings that black gay men in the UK are less likely to disclose their sexuality than white gay men.

They found that non-disclosed MSM are more likely to act as a ‘transmission bridge’ between other MSM and heterosexual women.  It had previously been thought that women were the transmission link between the two male populations, however, the study shows only 4% of transmission chains follow this pattern.

This echoes research from large USA cities on the role bisexually plays in HIV transmission.

In the UK, although heterosexual men are more likely to test for HIV at a later stage of infection than MSM, the researchers found no difference in testing rates between the disclosed and non-disclosed men who have sex with men.

This suggests non-disclosed MSM might be testing for HIV more regularly than heterosexual men, despite identifying with this group.

The study suggests that men who do not disclose same-sex behaviour might be underestimating their risk of HIV infection and could benefit from an HIV prevention campaign.

However, for such an intervention to be effective, it will need to be targeted differently to traditional campaigns for men who have sex with men. In particular, encouraging people to build trusting relationships with their health-care provider, in which they feel able to disclose their sexual behaviour, could be a valuable focus.

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Written by Hester Phillips