Can HIV be transmitted if viral load is undetectable?
We know that several factors complicate the relationship between serum viral load and degree of infectiousness. The correlation of HIV viral load in blood and in the genital tract is relatively weak. There is an overall effect, averaged across people, that antiretroviral therapy reduces blood and genital (semen, vaginal fluid) viral load. But there is not a one-to-one correspondence! Some individuals have relatively high viral loads in their semen while having relatively low viral loads in their blood, and vice versa. There also seems to be greater variation of the concentration of HIV in the genital tract than in the blood, both from one person to another and within one person at different times.
