[tatterdemalion]

The PARTNER study studied 767 serodiscordant couples, with the HIV positive partner undetectable. All participating couples did not use condoms at least some of the time. They found zero cases in which the undetectable partner infected the negative partner.

http://www.aidsmap.com/No-one-with-an-undetectable-viral-loa...

Frequent testing and early intervention are very effective to achieving an undetectable viral load. The adoption of these as public health policy, as well as making available of prophylactic measures for at risk populations, has been effective at combating the spread of HIV - e.g. in San Francisco, where infection rate has been declining significantly over the last 5 or so years.