The study aims to determine the prevalence of drug resistance mutation (DRM) in virally suppressed HIV infection, and the impacts of regimen change and the presence of low level viremia. Adults living with HIV infection on antiretroviral therapy (ART) with full viral suppression would be recruited. Cases are patients planning for regimen switch, while controls are those with and without low level viraemia (LLV) not planned for switch. Blood samples would be collected before and after switch. Sequencing would be performed to identify DRM present in HIV-1 proviral DNA.

Aim/objectives: With the aim of determining the impact of antiretroviral regimen and switch on archived HIV-1 drug resistance mutation (DRM), the study's objectives are, to: (a) estimate the prevalence of DRM in virally suppressed HIV infection; (b) assess changes in archived resistance before and after switch; and (c) identify predictors of archived DRM after regimen switch.

Design: A prospective observational study

Setting: All HIV specialist clinic services in Hong Kong

Methods: Adults living with HIV infection on antiretroviral therapy (ART) with full viral suppression who are planned for regimen switch would be recruited. Controls are patients with and without low level viraemia (LLV) not planned for switch, matched by antiretroviral regimen. Blood samples would be collected before switch, shortly and then 2-3 years after switch. Nanopore sequencing would be performed to identify DRM present in HIV-1 proviral DNA. Transcription of relevant clinical record data would be made to contribute to statistical and phylogenetic analyses

Main outcome measures: Change in DRM frequency between baseline and followups at (a) short term and long term; (b) occurrence of virological failure and time to failure; (c) difference in DRM frequency between presence and absence of LLV, and switched and non-switched patients.

Anticipated outcome: The study results would determine if archived resistance clearance would change following ART switch, identify factors associated with persistence of archived resistance, and inform management on the application of proviral DNA testing in clinical practice.

Inclusion Criteria:

• Patients living with HIV who are (a) aged 18 or above, (b) on antiretroviral therapy, (c) has viral load <20 copies/mL at 2 time points for ≥6 months, (d) planning regimen switch.
• Patients for inclusion in the control group meet the same criteria (a) but they are not planned for switch. Controls include patients with low level viremia (LLV) as defined as ≥2 consecutive viral load level between 21 and 200 copies/mL in the preceding 2 years.

Exclusion Criteria:

• Patients living with HIV who (a) are pregnant, (b) have virologic failure, (c) are suffering from concurrent opportunistic infections, (d) are prisoners , (e) are unable to give consent, and (f) have mental illnesses.

Patients living with HIV and who are attendees of HIV specialist clinics in the public service in Hong Kong

Individual data are protected as per provision of the approval of the Ethics Committee