Infectious diseases

Progression and Transmission of HIV (PATH), agent-based simulation of the US population for HIV prevention and intervention analyses


NIH R01AI127236, 07/15/2017 – 06/30/2022

Model Access:

(launch in webbrowser) (download) (Work in Progress)


Centers for Disease Control and Prevention


Approximately 1.2 million people in the United States are living with human immunodeficiency virus (HIV) infection. The Centers for Disease Control and Prevention (CDC) reported that the number of diagnoses in 2014 was 40,493 compared with 43,806 in 2010. Estimated annual HIV incidence in 2013 was 39,000 compared with 43,200 in 2010, based on CD4 test results from people with diagnosed HIV and a CD4 depletion model. The goal of the National HIV/AIDS Strategy (NHAS) is to reduce annual HIV incidence by 25% by 2020.
Work at UMass: We are developing agent-based simulation models to identify optimal combination interventions to achieve the NHAS goal.

Technical methods:

agent-based simulation,  network modeling, non-linear neural networks, reinforcement learning, machine learning, probability modeling; Software : Netlogo, MATLAB

Publications and reports:

  1. Progression and Transmission of HIV (PATH 2.0) – Agent-based simulation with dynamic transmission model
    Model Access: (open-access model in preparation)

    1. Gopalappa, C., Farnham, P.G., Chen, Y-H., and Sansom, S.L. Combinations of interventions to achieve a national HIV incidence reduction goal: insights from an agent-based model. AIDS, November 28, 2017 – Volume 31 – Issue 18 – p 2533 to 2539
    2. Gopalappa, C., Farnham, P.G., Chen, Y-H., and Sansom, S.L. Progression and Transmission of HIV/AIDS (PATH 2.0): A New Agent-Based Model to Estimate HIV Transmissions in the United States, Med Decis Making 2017 Feb;37(2):224-233. doi: 10.1177/0272989X16668509 LINK
    3. Cited in Dailey AF, Hoots BE, Hall HI, et al. Vital Signs: Human Immunodeficiency Virus Testing and Diagnosis Delays — United States. MMWR Morbidity and Mortality Weekly Report. Dec 2017;66(47):1300-1306. doi:10.15585/mmwr.mm6647e1
    4. Cited in McCree, D.H., et. al., ‘HIV acquisition and transmission among men who have sex with men and women: What we know and how to prevent it’, Preventive Medicine, Volume 100, April 2017, Pages 132-134.
  2. Progression and Trasmission of HIV (PATH 1.2) – Agent-based simulation without dynamic transmission
    Model Access: (launch in webbrowser) (download)

    1. Farnham, P., Gopalappa, C., Sansom, S., Costs and effectiveness of early versus late treatment in view of recent guidelines for starting treatment at an earlier HIV stage, Division of HIV/AIDS Prevention, Centers for Disease Control and Prevention, JAIDS, 64(2):183-189, 2013.
    2. Cited in the National HIV AIDS Strategy for the United States: Update to 2020, The White House, July 2015 **Cited in the CDC FY 2017 Congressional Justification for Budget Request, Justification of Estimates to the Appropriations Committees, 2016,
  3. Farnham, P.G., Holtgrave, D. R., Gopalappa, C., Angela B. Hutchinson, Stephanie L. Sansom, Lifetime Costs and QALYs Saved from HIV Prevention in the Test and Treat Era, Letter to the Editor, JAIDS, 64(2):e15-e18, 2013
  4. Gopalappa, C., Farnham, P., Hutchinson, A., and Sansom, S., Cost-effectiveness of the National HIV/AIDS Strategy (NHAS) goal of increasing the proportion linking to care at diagnosis, JAIDS, 61 (1):99-105, 2012.