Antiretroviral therapy may be stabilising HIV epidemic in Danish gay men

The use of antiretroviral treatment appears to have stabilised the HIV epidemic in Danish gay men, even though rates of risky sex have increased, research published in the online edition of the Journal of Acquired Immune Deficiency Syndromes suggests.

“While unsafe sex among MSM [men who have sex with men] has increased substantially and the number of HIV-positive MSM living in Denmark has enlarged, the incidence of HIV diagnoses in this population has remained stable for more than a decade,” write the authors. “Our findings indicate that this paradox is due to effective antiretroviral therapy and not increased awareness of safe sex.”

The investigators believe that the HIV epidemic in Danish gay men is being sustained by undiagnosed people and diagnosed people who are not yet on antiretroviral therapy.

There is growing interest in the use of HIV treatment as prevention. Studies conducted in heterosexual people show that the risk of sexual transmission of the virus is negligible if a patient is on HIV treatment and has an undetectable viral load.

Data showing the impact of antiretroviral therapy on the HIV epidemic in gay and other MSM are largely lacking.

However, investigators in Denmark hypothesised that antiretroviral therapy was indeed preventing new infections in gay men.

They examined three data sources to see if this was indeed the case. These sources provided information on: HIV prevalence and the number of new diagnoses; the sexual risk behaviour of gay men; and the incidence of syphilis.

Between 1995 and 2009, there was a median of 93 new HIV diagnoses in gay men per year. There was evidence of a modest decline in new diagnoses in the late 1990s, followed by a vague increase until 2005, when the number of new diagnoses stabilised.

Other surveillance data showed that the number of undiagnosed infections in the country remained largely unchanged at approximately 500 people.

During the period of the study, there was a 75% increase in the number of HIV-positive gay men who were alive and living in Denmark from 1035 in 1995 to 1813 in 2010.

Over the same period, the number of HIV-positive gay men with a viral load above 400 copies/ml fell from 1035 to 262.

The investigators calculated that HIV incidence in gay men (Cohort Community Reproductive Rate, or CCRR) was 0.099 in 1995. This fell steadily through the late 1990s and stabilised at 0.071 from 2005 onwards.

This fall in HIV incidence was accompanied by an increase in the proportion of HIV-positive men with virologic suppression.

It was apparent that this stabilising of the epidemic was due to antiretroviral therapy rather than changes in sexual behaviour.

Data from the annual Sex Lives Survey showed there were year-on-year increases in unsafe sex. Respondents reported an increasing number of partners with whom they had anal sex (p < 0.01), increased frequency of unprotected anal intercourse (p < 0.01) and an increase in the number of partners of unknown HIV status (p < 0.01).

Men with diagnosed HIV infection were significantly more likely to report risky sexual behaviour than HIV-negative men.

Syphilis surveillance data also suggested that gay men were having more risky sex. The annual number of diagnoses increased from just 2 in 1995 to 208 in 2009.

“The present study suggests that successful implementation of HAART [highly active antiretroviral therapy] has had a major impact on HIV incidence among MSM,” comment the investigators.

The investigators believe there are two sources of new infections: diagnosed patients who are not yet taking antiretroviral treatment and a constant pool of approximately 500 undiagnosed infections.

“Earlier models have suggested that there may be a balancing point at which increasing levels of high risk sexual behaviour performed by a large number of undiagnosed/untreated HIV-positive MSM offsets the effect of early/regular HIV-testing…and subsequent treatment of those diagnosed as HIV-positive,” note the researchers. “This point seems to have been reached among MSM in Denmark in the early 2000s.”

They therefore conclude “additional measures to diminish the pool of MSM who are at risk of transmitting HIV should focus both on earlier initiation of HAART and enhanced testing, especially of MSM engaged in sexual risk behaviour”.

Cowan SA et al. Stable incidence of HIV diagnoses among Danish MSM despite increased engagement in unsafe sex. J Acquir Immune Defic Syndr, online edition. DOI: 10. 1097/QAI.0b013e31825af90, 2012.