CALIBRATING DYNAMIC COMPARTMENTAL MODELS OF HUMAN IMMUNODEFICIENCY VIRUS IN THE UNITED STATES

Purpose:

   We calibrated two dynamic compartmental models of human immunodeficiency virus (HIV) disease progression and transmission in the United States to evaluate different assumptions regarding the impact of antiretroviral therapy (ART) on persons living with HIV.

Method:

   The two models have similar structures but different assumptions with regards to the effects of ART on disease progression. In Model 1, we assumed that persons living with HIV/AIDS (PLWH) treated with ART experienced no disease progression while their HIV RNA viral load was suppressed (VLS), and, when not VLS, disease progression equivalent to that among PLWH never treated with ART. In Model 2, PLWH exposed to ART experienced slower (but non-zero) disease progression before and after VLS. Both models were calibrated to approximate the percentage of PLWH diagnosed, percentage of PLWH prescribed ART (Model 1) or VLS (Model 2), and HIV incidence reported in surveillance data. They were both then recalibrated to estimate additional targets: HIV prevalence and deaths among PLWH.

Result:

   Model 1 and Model 2 were able to meet all their initial calibration targets. However, we found that, when the additional targets were considered, Model 1’s structure consistently underestimated HIV prevalence and overestimated deaths among PLWH. Only Model 2 could be parameterized to simultaneously target those outcomes. 

Conclusion:

   To correctly calibrate to the relatively low number of deaths among HIV-infected persons in the United States and a prevalence of approximately 1 million infected persons, our model comparison showed that exposure to ART must be high, and the benefits of that exposure must extend to persons whose viral load is not suppressed, given the relatively small proportion of persons who achieve VLS at any one point in time. The model comparison also illustrated the necessity of calibrating to multiple targets in these analyses.