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.

Ending the HIV epidemic in the USA: an economic modelling study in six cities

“…We calibrated the model to match the the total number of diagnosed cases (11 calibration targets), new diagnoses (3 targets), and deaths (3 targets) across race and ethnicity groups and HIV risk groups (17 calibration targets in total) and validated against external incidence estimates (overall and among MSM) from 2012-15 for each city. 18 The projected model outcomes showed a good fit to calibration targets according to an overall goodness of fit metric (defined as the weighted sum of the goodness of fit of the individual calibration targets), and model-derived incidence estimates for the years 2012-2015 corresponded with externally estimated uncertainty ranges, showing good external validity. 18 Our calibration and validation process 18 has been documented in detail previously.…”

“…We adapted and calibrated our previous dynamic compartmental HIV transmission model 16,18 to replicate city-level HIV microepidemics in each of our US cities (table 1). Administrative regions (counties) were the main unit of analysis because they correspond to both the lowest level of resource allocation decisions and, in many cases, the finest resolution of available input data.…”

Developing a dynamic HIV transmission model for 6 U.S. cities: An evidence synthesis

“…Furthermore, we included best-quality evidence sources from a narrative review of high-impact, current and diverse HIV models to further inform our initial identification process [164] in order to mitigate the potential correlation between sources. Second, we have not assessed the impact that the uncertainty in poorer quality parameters could have on model recommendations since this was beyond the scope of this study but rather report these findings in work elsewhere [32]. Third, despite a data verification process involving a scientific advisory committee composed of city-specific experts that helped to resolve instances where evidence was of poor representativeness, the number of respondents involved was low.…”

“…HIV transmission can occur through three modes: heterosexual contact, homosexual contact and needle sharing. We specified sexual mixing assortativity between risk groups and race/ethnicity to determine the proportion of sexual contacts within the same group, and varied the level of assortativity across cities [32, 33]. Following HIV infection, individuals transition through various stages beginning with acute infection (three months).…”

Dissemination Science to Advance the Use of Simulation Modeling: Our Obligation Moving Forward

“…Our team’s experience in developing, translating, and disseminating the results of a simulation model for policy decisions in human immunodeficiency virus (HIV) prevention and treatment has been instructive (and humbling). In an effort to set a new standard for transparency, we published separate articles on the evidence synthesis, 3 calibration and validation, 4 baseline projections, 5 cost-effectiveness of individual interventions, 6 and, finally, our cost-effectiveness analysis of different strategies to combat HIV/AIDS in disparate geographic regions. 7 We followed these efforts with a closer examination of the uncertainty in our findings and the value of collecting more information to reduce this uncertainty.…”