Studies: transmission between men

As we said in the previous section, only 3% of couples in the HPTN 052 study were male/male, which is not nearly enough to calculate a transmission risk or reduction in risk for MSM. Some other studies about this group are relevant though.

A prospective study examining the effect of antiretroviral treatment on HIV transmission in gay men was first presented in February 2009 to the 16th Conference on Retroviruses and Opportunistic Infections in Montreal,1 with further information presented in April 2009 to the 15th Annual British HIV Association Conference in Liverpool.2 This study, involving 1144 gay men attending an HIV-treatment centre in Brighton between 2000 and 2006, is the first to examine the risk of transmission in a cohort of gay men and other men who have sex with men (MSM).

The investigators used clinical and epidemiological information to identify the factors involved in new HIV infections in gay men and, by performing phylogenetic analysis on the HIV from 859 individuals, 41 'likely transmitters' were identified, 29 (70%) of whom had never taken HIV treatment and nine of whom (22%) had interrupted their treatment at the time of transmission. The study found an association between a higher viral load and a greater risk of HIV transmission, with each tenfold increment in viral load increasing the risk of HIV transmission by 68%.

Taking HIV treatment was associated with a 96% reduction in the risk of HIV transmission. Of the three transmissions on treatment seen during 3556 person-years of follow-up, one is thought to have originated in an individual with an undetectable viral load. No further details are available.

This is not the first recorded case of HIV transmission during sex between men where the infected partner has an undetectable viral load, however. In a case report from Germany, published in August 2008, and confirmed by phylogenetic analysis, a gay man who had maintained an undetectable viral load on treatment since 2000 apparently infected his partner between 2002 and 2004 after reporting unprotected anal intercourse on a number of occasions.3 Neither partner reported a sexually transmitted infection and both reported that their relationship was monogamous.

A study from San Francisco has found that in cases where HIV is transmitted between gay men, there is a strong correlation between the viral load in the infecting person and the viral load in the person infected.4

In this study, gay men with acute HIV infection were matched phylogenetically with infecting partners, as in the Brighton study. Twenty-four recently infected men were matched with 23 source partners, one of whom had infected two people. The average viral load in the recently infected men was 86,332 copies/ml (4.94 logs) and in the source partners was 23,951 copies/ml (4.38 logs).  For every one log (tenfold) rise in the infecting partner’s viral load, the mean viral load of the partners infected increased by 0.43 logs (a 2.7-fold increase).

(To explain more clearly, this would imply that if the average viral load in the infecting men had been 100,000 copies/ml, the average viral load in partners infected would be 128,000 copies/ml, but if the average viral load in source partners had been 10,000 copies/ml, the viral load in infected partners would be 47,500 copies/ml. It is important to emphasise that the viral load in source and infected partners in this study was being measured at different time points in the evolution of their infection – in acute infection in the infected partners and in relatively recent, but chronic, infection in the source partners).

Two or three of the 23 source individuals in this study had been on ARVs at the time of infection, but none had an undetectable viral load when it was measured (minimum 6776 copies/ml3).

In short, treatment seems to reduce the chance of infection between men (and, by the same token, between heterosexuals who have unprotected anal intercourse) to the same degree as it does for vaginal intercourse. Given, however, that the best estimate we have for the per-contact risk of HIV infection via anal intercourse is that the risk of infection is between five and ten times greater than that seen in vaginal intercourse,5 we can speculate that it would take a more profoundly suppressed viral load to render anal intercourse negligibly unsafe than it would to have the same effect with vaginal intercourse.

References

  1. Fisher M et al. HIV transmission amongst men who have sex with men: association with antiretroviral therapy, infection stage, viraemia and STDs in a longitudinal phylogenetic study. Sixteenth Conference on Retroviruses and Opportunistic Infections, Montreal, 2009
  2. Fisher M et al. HIV transmission amongst men who have sex with men: association with infection stage, viraemia and STIs in a longitudinal phylogenetic study. HIV Medicine 10 (Supp 1), 018, 2009
  3. Sturmer M et al. Is transmission of HIV-1 in non-viraemic serodiscordant couples possible? Antiviral Therapy 13:729-732, 2008
  4. Hecht PM et al. HIV RNA level in early infection is predicted by viral load in the transmission source. AIDS 24(7):941-945, 2010
  5. Baggaley RF et al. HIV transmission risk through anal intercourse: systematic review, meta-analysis and implications for HIV prevention. Int J Epidemiol 39(4): 1048-1063, 2010
This content was checked for accuracy at the time it was written. It may have been superseded by more recent developments. NAM recommends checking whether this is the most current information when making decisions that may affect your health.
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This content was checked for accuracy at the time it was written. It may have been superseded by more recent developments. NAM recommends checking whether this is the most current information when making decisions that may affect your health.

NAM’s information is intended to support, rather than replace, consultation with a healthcare professional. Talk to your doctor or another member of your healthcare team for advice tailored to your situation.