THE HIV REPRODUCTION NUMBER IN THE UNITED STATES: ESTIMATION AND IMPACT OF CARE CONTINUUM INTERVENTIONS

Purpose:

We assessed the potential for HIV elimination in the United States, i.e., decreasing the HIV reproduction number to less than 1, and we evaluated the most effective improvements in the HIV care continuum to achieve this goal.

Methods:

We used the HIV Optimization and Prevention Economics (HOPE) compartmental model to estimate the HIV reproduction number in the United States from 2006 to 2015. In this model, we stratified the population by transmission group, race/ethnicity, age, circumcision status, and HIV risk level and the HIV-infected subpopulations by disease progression and continuum of care stage. Transition rates among the approximately 4,000 subpopulations were based on the literature, expert opinion, and model calibration methods, ensuring that this model closely reflected both demographics critical to the spread of HIV and HIV infection in the United States between 2006 and 2010.

We estimated the HIV control reproduction number, R_c, using the next generation matrix method (NGM). R_c is an estimate of the average number of secondary infections from an infected person in a completely susceptible population calculated under the additional assumption that the susceptible population may be taking steps to prevent HIV acquisition.

We conducted a sensitivity analysis to find the degree of change from a base-case R_c in 2015 that would occur by altering model transition rates associated with the HIV care continuum such as being diagnosed with HIV, linked to care, and achieving viral load suppression (VLS). 

Results:

The estimated values of R_c were 1.46 and 1.50 for the periods 2006 - 2010 and 2011 – 2015, respectively. Holding other aspects of the care continuum constant, we found that R_c was insensitive to changes in rates related to diagnosis (% deviation from the base case R_c:  [-1%, 1%]) and linkage to care [-9%, 6%], but was significantly affected by rates related to VLS [-47%, 106%] (Figure 1). Substantially decreasing the VLS dropout rate was the only measure that reduced the value of R_c to less than one.

Conclusions:

Current progress of HIV-infected persons along the care continuum is not sufficient to result in the potential elimination of HIV in the United States (R_c < 1). To achieve this goal, ensuring that HIV-infected persons achieve and maintain VLS will be an important focus.