Assessment of Viral Suppression by Various Retention in Care Measures and Viral Load Monitoring Patterns among a Cohort of HIV-Infected Patients in Washington, DC Open Access
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Background: For HIV-infected patients, retention in care is critical for viral suppression; however, there is no optimal method for measuring retention. The impact of differential viral load monitoring frequency on sustained viral suppression is also understudied. The research conducted intended to validate and expand on previous findings concerning the effects of different retention measures and viral load monitoring patterns on viral suppression using data from the DC Cohort, a longitudinal, observational study of HIV-infected patients receiving care at 13 clinics in Washington, DC. Methods: We calculated and compared the following retention measures: no 6-month gaps in care, 4-month visit constancy, the Institute of Medicine (IOM) measure defined as >2 visits at least 90 days apart in a 12-month period, and the Health and Human Services (HHS) measure defined as >1 visit in each 6-month interval in 24-months with >60 days between visits. The average amount of time between consecutive viral load tests was calculated to estimate viral load monitoring frequency. Cox proportional hazards regression and Poisson regression were used to model relationships between retention and achievement of viral suppression, retention and virologic failure, and viral load monitoring frequency and virologic failure. Viral suppression was defined as undetectable viral load and virologic failure was defined as viral load >200 copies/ml. Each outcome was modeled as a recurrent event. Results: DC Cohort participants experienced moderate to high retention and the majority were able to achieve and sustain viral suppression over time. Increases in 4-month visit constancy, IOM, and HHS retention measures were significantly associated with increased rates of achievement of viral suppression. None of the retention measures was associated with decreased rate of virologic failure early in follow up, but having no gaps in care >6 months was associated with an increased rate of virologic failure among participants virally suppressed at study entry. Later in follow up, visit constancy and IOM measures were associated with decreased rates of subsequent virologic failure among participants who achieved viral suppression, but only the IOM measure was associated with decreased failure among participants virally suppressed at enrollment. There was no difference in virologic failure rates by viral load monitoring frequency for DC Cohort participants who were virally suppressed and had a baseline CD4 count >300 at consent.Conclusion: The relationship between retention and achievement of viral suppression was consistent for most of the retention measures, validating prior research. For the relationship between retention and virologic failure, our results varied depending on how retention was measured, whether or not participants were virally suppressed at study entry, and amount of time following consent. Further follow up is needed to determine whether these patterns are maintained over time. Our findings support the revised HHS treatment guidelines that recommend reduced viral load monitoring for patients who have been virally suppressed with a CD4 count >300 for at least 2 years. In terms of clinical care and policy implications, recommendations for visit frequency and different retention measures may need to be tailored to specific patient populations.