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.

Undetectable is the standard of care and is the definition for the treatment "working". Viral load is checked regularly after starting treatment. If it doesn't become undetectable quickly with first line meds, there may be compliance or resistance issues and treatment approach is changed. With current protocols the main reason for treatment failure is mental health/substance abuse interfering with adherence.

The studies on transmission are using sero-discordant couples who are not using condoms. The evidence/confidence has been building over time with multiple studies in which no transmissions were observed.

http://www.catie.ca/en/catienews/2016-09-06/negligible-risk-...

The HPTN 052 randomized study was halted early because the evidence so strongly favored the treatment arm. In the PARTNER observational study, no transmissions were observed in the study at all. The evidence is very strong.

Not a professional, but my wife has HIV (and I don't), so I have a personal interest in the subject.

> How many people taking retrovirals have undetectable levels of HIV?

According to my wife's doctor, most of them. And if that changes, they attempt to adjust treatment to return to that state.

BTW, undetectable appears to mean 20 copies of viral DNA per ml of blood.

> Are those people using condoms?

Well, we were, for many years. But we wanted children, and so after her doctor actually encouraged us we conceived them the old-fashioned way. I really, really enjoyed sex without a condom after so many years, I must say.

Now we have all the children we want, and we ought to go back to condoms, but I find myself wondering about the risk vs. reward. I suppose we'll go back to condoms, but I yearn to forgo them -- it's just less intimate. I wonder how other couples feel.