HIV risk from single contact may be higher than thought

Keith Alcorn, Keith Alcorn
Published: 05 March 2001

The risk of HIV transmission from activities like unprotected anal intercourse with new partners may be dangerously underestimated by long-term studies of serodiscordant partners, a leading researcher into the sexual transmission of HIV said today.

Speaking at the Fifth International Congress on Drug Therapy in HIV Infection, Dr Pietro Vernazza of the Cantonal Hospital, St Gallen, Switzerland, said:

“We’re citing these studies all the time, but I think it’s time we re-considered other data”.

Although long-term partner studies have shown that the risk of male to female or female to male transmission from a single episode of sexual intercourse may be as little as 0.3%, Vernazza points to single contact studies in commercial sex workers which have shown transmission rates of 3.1% - 8.2% from women to men, and rates in excess of 50% per episode in men to women.

He argues that long-term partner studies do not factor in the protective effect of any HIV-specific immunity that develops in partners who are repeatedly exposed to HIV but remain uninfected. Several studies in commercial sex workers and other individuals repeatedly exposed to HIV have shown that HIV-specific cytotoxic T-lymphocyte responses to HIV are detectable in these individuals, despite no evidence of HIV infection.

“The highest risk of transmission probably lies in the first few contacts” said Pietro Vernazza.

Risk of transmission during structured treatment interruptions

Vernazza also presented a case history which is likely to have a strong influence on advice about structured treatment interruptions – a case of sexual transmission during an STI by a man with previously undetectable viral load.

The man, who had had undetectable viral load prior to the treatment interruption, had been having unprotected sexual intercourse with his female partner prior to the STI. Two weeks after the STI, his female partner reported an acute viral illness, and tests revealed that she had become infected with HIV.

Together, we can make it happen

We can end HIV soon if people have equal access to HIV drugs as treatment and as PrEP, and have free choice over whether to take them.

Launched today, the Community Consensus Statement is a basic set of principles aimed at making sure that happens.

The Community Consensus Statement is a joint initiative of AVAC, EATG, MSMGF, GNP+, HIV i-Base, the International HIV/AIDS Alliance, ITPC and NAM/aidsmap

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.