How does HIV Spread in Heterosexuals?

We receive many enquiries on our Sexual Health Forum about the mechanism of spread of HIV in heterosexuals.

People sending in queries are often panic-stricken about minor sexual activities and the risk of possible spread of HIV from an infected individual to them. The risk of spread of HIV from an HIV-infected individual to another in the absence of unprotected penetrative (vaginal and /or anal) is exceedingly low to almost impossible.

A study reported in the New England Journal of Medicine (Viral Load and Heterosexual Transmission of Human Immunodeficiency Virus Type 1; Quinn et al; Vol 342:921-929; March 30, 2000, Number 13) examined the relationship between risk and rate of transfer of HIV depending on "viral load". Viral load is the term used to describe the amount of virus detectable in a particular body fluid and is usually referred to as particles per ml of blood.

The article identified the other factors which might influence how HIV was spread and these were:-

Frequency of unprotected sexual activity
Types of sexual contact
use or otherwise of condoms
circumcision in males
the presence or otherwise of other Sexually Transmitted Infections or Diseases
The study identified 415 heterosexual couples where one was HIV positive and the other HIV negative (HIV discordant couples). 55% of the males were HIV positive and 45% of the females were HIV positive. The study went on for 30 months. 22% of the originally HIV negative people then became HIV positive during this time. The spread rate was the same between HIV positive men and HIV negative women as between HIV negative men and HIV positive women.

Peak rates of spread were observed in younger individuals between 15 and 19 years old.

The study found that the main determinant of whether an HIV positive person would spread HIV and infect another person with whom they had sex was the amount of virus they had in their system at the time - the amount of their viral load. The study found that in people with undetectable viral loads there were no seroconversions in the previously HIV negative people studied. In addition, the cut off point seems to be around 1500 or so copies per ml.

What does this mean?

It seems to suggest that HIV infection occurs most commonly when people who already have HIV have a high viral load - a high amount of virus particles in their system. This is important because:-

It makes the need to have regular HIV test very important if you are having unprotected sex with others because in the early stages of HIV, viral load tends to be very high and this seems to be the time when most new infections might be passed on.
In addition, it is reassuring that because large amounts of virus are required to cause infections in others it is likely that activities we call low risk such as oral sex will be likely to be virtually no-risk in people on successful treatment which aims to reduce the amount of virus to undetectable levels.

Posted by Freedomhealth