How can there be a level of HIV viral load that will make infecting others impossible?

Question

I just read about a court case where someone was acquitted for "being dangerous to the surrounding" by having unprotected sex when diagnosed with HIV.

The reasoning was that since this person was medicated, (s)he had too low levels of viruses to be infectious. How can that be? 1 virus should be enough to infect someone, shouldn't it?

I understand/guess that the risk of infection "per virus" might be very low and that, if you "want" the risk for infection to be higher than, say, 1 %, you need to be exposed to millions (or something like that) of viruses. But still, as long as you can transmit more than zero viruses to your surroundings, you must be infectious, mustn't you?

Answer 1

As per the US CDC non-detectable viral load means effectively no transmission possible (there are not many absolutes in medical sciences).

See also: https://www.cdc.gov/hiv/risk/art/index.html

Numerous campaigns have been created on these findings:

• http://www.aidsmap.com/about-hiv/undetectable-viral-load-and-transmission-information-people-hiv
• https://www.preventionaccess.org/undetectable