Estimating the HIV Effective Reproduction Number in the United States and Evaluating HIV Elimination Strategies

Context: The reproduction number is a fundamental epidemiologic concept used to assess the potential spread of infectious diseases and whether they can be eliminated. Objective: We estimated the 2017 United States HIV effective reproduction number, R-e, the average number of secondary infections from an infected person in a partially infected population. We analyzed the potential effects on R-e of interventions aimed at improving patient flow rates along different stages of the HIV care continuum. We also examined these effects by individual transmission groups. Design: We used the HIV Optimization and Prevention Economics (HOPE) model, a compartmental model of disease progression and transmission, and the next-generation matrix method to estimate R-e. We then projected the impact of changes in HIV continuum-of-care interventions on the continuum-of-care flow rates and the estimated R-e in 2020. Setting: United States. Participants: The HOPE model simulated the sexually active US population and persons who inject drugs, aged 13 to 64 years, which was stratified into 195 subpopulations by transmission group, sex, race/ethnicity, age, male circumcision status, and HIV risk level. Main Outcome Measures: The estimated value of R-e in 2017 and changes in R-e in 2020 from interventions affecting the continuum-of-care flow rates. Results: Our estimated HIV R-e in 2017 was 0.92 [0.82, 0.94] (base case [min, max across calibration sets]). Among the interventions considered, the most effective way to reduce R-e substantially below 1.0 in 2020 was to maintain viral suppression among those receiving HIV treatment. The greatest impact on R-e resulted from changing the flow rates for men who have sex with men (MSM). Conclusions: Our results suggest that current prevention and treatment efforts may not be sufficient to move the country toward HIV elimination. Reducing R-e to substantially below 1.0 may be achieved by an ongoing focus on early diagnosis, linkage to care, and sustained viral suppression especially for MSM.