If someone is adhering well to HIV medication, has had an undetectable viral load for more than six months and has no other sexually transmitted infections, the chance of passing HIV on to someone is in effect close to zero.
If the viral load is at undetectable levels, it means that there is a very small amount of HIV in the blood, and in the bodily fluids exchanged during sex. With an undetectable viral load, in many cases this means that the risk of passing HIV on is in effect close to zero.
THE PARTNER STUDY
The PARTNER study reported that despite 44,500 incidents of sex (vaginal and anal) there were NO transmissions of HIV where the positive partner had an undetectable viral load. This study is still continuing for gay and bisexual men. UK guidelines now recommend that HIV consultants talk about how being on treatment can reduce the risk of sexually transmitting HIV. This is sometimes referred to as 'Treatment as Prevention'. That is prescribing treatment as a means to reduce the amount of HIV in the body in order to minimise the risk of HIV being passed from one person to another. Condoms are still important if people have concerns about other sexually transmitted infections.
If someone is not on treatment, the viral load and the CD4 count may be factors that determine when the doctors think it is appropriate to start doing so. However, current UK guidelines state that anyone living with HIV can start treatment when they feel that the time is right. You can talk to your HIV consultant about this.
It is very important to take the medication exactly as prescribed and attend clinic appointments to monitor viral load levels.