Monitoring HIV drug resistance in King County

Background

For people living with HIV, achieving viral suppression through use of antiretroviral (ARV) drugs preserves the health of the person living with HIV and prevents transmission. However, if HIV develops resistance to ARV medications, they may not work as well to prevent severe HIV disease and deaths related to HIV.

Three drug classes are routinely evaluated for resistance: non-nucleoside reverse transcriptase inhibitors (NNRTI), nucleoside reverse transcriptase inhibitors (NRTI), and protease inhibitors (PI). It is recommended that all individuals newly diagnosed with HIV receive NNRTI, NRTI and PI resistance testing. Integrase strand transfer inhibitors (INSTI) are a more recently developed drug class and INSTI resistance testing is currently recommended for people at higher risk of exposure to major INSTI mutations. 1,2 As part of HIV-related public health activities, PHSKC monitors the proportion of newly diagnosed individuals who receive HIV-1 resistance testing following diagnosis and the annual prevalence of ARV resistance.

Multi-class drug resistance (MDR) is defined as higher-level drug resistance in more than one antiretroviral drug class (PI, NRTI or NNRTI). The Stanford University drug resistance database website is used for interpretation of the sequences. “Higher-level resistance” refers to the top two resistance scores returned by Stanford’s tool: “intermediate” and “high-level.”  INSTI resistance is not included in the figure as transmitted resistance has been rare. Since 2016, only two instances of transmitted INSTI resistance were identified among people living with HIV in King County.

Acquired HIV resistance can occur when a person has HIV that is replicating while also taking ARV medications. This can result in HIV mutations that make the current ARV medication ineffective. The figure below shows the proportion of people living with HIV in King County with either transmitted or acquired resistance.