Viral Loads vs Tranmissability

[timfreo]

This may be esoteric or moot question due to the range of impacting factors, but it's been bugging me for ages; at what concentration of virus does the likelihood of transmission move from say "possible" to "probable" to "almost certain" , as just examples. 

The measurement of an Undetectable level is often also described as Untransmissable. A VL moving from a level of 20 copies/ml, or say UD, to 200 copies, then it may become tranmissable but very unlikely. What if that the increases to 2,000 copies, then 20,000, then 200,000 etc etc. How does the potential for infection curve, on a graphical representation, increase? 

Viral load is a concentration measurement of copies per ml. When the entire range of potential concentration levels are needed to be displayed on a "page",  they are factorised, on a log scale X10, etc

[BootmanLA]

3 hours ago, timfreo said:

This may be esoteric or moot question due to the range of impacting factors, but it's been bugging me for ages; at what concentration of virus does the likelihood of transmission move from say "possible" to "probable" to "almost certain" , as just examples. 

The measurement of an Undetectable level is often also described as Untransmissable. A VL moving from a level of 20 copies/ml, or say UD, to 200 copies, then it may become tranmissable but very unlikely. What if that the increases to 2,000 copies, then 20,000, then 200,000 etc etc. How does the potential for infection curve, on a graphical representation, increase? 

Viral load is a concentration measurement of copies per ml. When the entire range of potential concentration levels are needed to be displayed on a "page",  they are factorised, on a log scale X10, etc

I do not believe there is a "regularly found in nature" viral load level that would be described as "almost certain" for transmission. While you're correct that there's a general increase in risk of transmission starting with "essentially zero" for an undetectable VL and rising along with the VL. But even when a person has an uncontrolled HIV infection, there's still a much better than average chance that a single sex act will not infect another person (absent that person himself already having a weakened immune system).

As for what the shape of that curve is, between the extremes of "undetectable" and "uncontrolled HIV infection with a VL in the high 6 figures or higher", there just isn't evidence to graph it, and frankly, it would essentially be a waste of resources that could be far better spent on other, actual serious issues. 

[garsento]

One 2000 paper looking at straight couples in Uganda found a sharp fall in HIV transmission rates depending on viral load, with people with under 400 copies per millimetre not being linked to any transmissions.

 

 

[garsento]

[think before following links] https://pubmed.ncbi.nlm.nih.gov/10738050/

[think before following links] https://i-base.info/guides/testing/viral-load

^ This is from the study I mentioned yesterday.

The recent studies on undetectability in same-sex couples were working from an assumption of 200 copies per millilitre as the upper limit of undetectability.