Выражение встречается в следующем контексте:

Regimens based on ritonavir-boosted PIs may allow less-than-perfect adherence without virologic rebound, according to results of a British Columbia cohort study presented at the 13th Conference on Retroviruses and Opportunistic Infections. However, less than 95% adherence to a combination based on an unboosted PI or NNRTI heightened the risk of viral breakthrough in this cohort.

Заранее спасибо