Development and Calibration of a Dynamic HIV Transmission Model for 6 US Cities

Abstract

Background. Heterogeneity in HIV microepidemics across US cities necessitates locally oriented, combination implementation strategies to prioritize resources. We calibrated and validated a dynamic, compartmental HIV transmission model to establish a status quo treatment scenario, holding constant current levels of care for 6 US cities. Methods. Built off a comprehensive evidence synthesis, we adapted and extended a previously published model to replicate the transmission, progression, and clinical care for each microepidemic. We identified a common set of 17 calibration targets between 2012 and 2015 and used the Morris method to select the most influential parameters for calibration. We then applied the Nelder-Mead algorithm to iteratively calibrate the model to generate 2000 best-fitting parameter sets. Finally, model projections were internally validated with a series of robustness checks and externally validated against published estimates of HIV incidence, while the face validity of 25-year projections was assessed by a Scientific Advisory Committee (SAC). Results. We documented our process for model development, calibration, and validation to maximize its transparency and reproducibility. The projected outcomes demonstrated a good fit to calibration targets, with a mean goodness-of-fit ranging from 0.0174 (New York City [NYC]) to 0.0861 (Atlanta). Most of the incidence predictions were within the uncertainty range for 5 of the 6 cities (ranging from 21% [Miami] to 100% [NYC]), demonstrating good external validity. The face validity of the long-term projections was confirmed by our SAC, showing that the incidence would decrease or remain stable in Atlanta, Los Angeles, NYC, and Seattle while increasing in Baltimore and Miami. Discussion. This exercise provides a basis for assessing the incremental value of further investments in HIV combination implementation strategies tailored to urban HIV microepidemics.

Keywords: HIV/AIDS; dynamic transmission model; epidemiological projection; model calibration; model validation.

Figure 1.

Model schematic diagram. The schematic shows the 19 compartments that constitute each of the 42 population groups in the model. A key for the symbols denoting transitions within the model is available in the Supplementary Appendix.

Figure 2.

Model fit of new diagnoses for calibration. (A) ATL: Atlanta; (B) BAL: Baltimore; (C) LA: Los Angeles; (D) MIA: Miami; (E) NYC: New York City; (F) SEA: Seattle; 95% CI: 95% credible interval. MSM: men who have sex with men (excluding MSM-PWID)

Figure 3.

Model external validity and status quo projections for the rate of new incidence. Year 2012-2015: calibration period; Year 2016-2040: projection period; Year 2021-2040: evaluation period. (A) ATL: Atlanta; (B) BAL: Baltimore; (C) LA: Los Angeles; (D) MIA: Miami; (E) NYC: New York City; (F) SEA: Seattle.