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Seth Welles, PhD, ScD

Seth Welles

Professor of Epidemiology
Epidemiology and Biostatistics
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BA, Biology, Boston University; PhD, Cellular Biology, Boston University; ScD, Epidemiology, Harvard School of Public Health


Dr. Welles conducts research and mentors students in studies of infection and chronic disease, including viral carcinogenesis and HIV/AIDS. His earliest epidemiologic work was focused on studies of immune suppression and adult T-cell leukemia/lymphoma caused by the human T-cell lymphotropic virus type I (HTLV-I). Subsequently, he worked as an epidemiologist and biostatistician with the AIDS Clinical Trials Group to assess the utility of using molecular markers of HIV antiretroviral drug resistance, HIV-1 viral load, and CD4 cell number as prognostic and surrogate markers of clinical disease.

Currently, Dr. Welles studies psychosocial risk for HIV infection and STDs among sexual and gender minority (SGM) adults and adolescents, including gay and bisexual men, and transgender women. Most of his work is focused on methodologic challenges involved with reducing bias when evaluating the impact of sexual orientation/same-sex behaviors on HIV and STI acquisition: These studies involve both adjustment of misclassification of orientation and/or sexual behavior as the impact of misclassification on HIV risk assessment, as well as constructing complex agent-based models to evaluate the impact of prevention strategies (such as PrEP, HIV seroadaptive behaviors, and treatment of HIV infection as prevention) on HIV and STI acquisition and transmission.

Dr. Welles welcomes both Masters and Doctoral students with strong quantitative/analytic skills, who are passionate about HIV prevention.

Sponsored Research:

A Randomized, Double Blind, Phase 2B Study Testing the Efficacy and Safety of AGS-004 (dendritic cell vaccine) on Host Control of HIV Replication during Analytical Treatment Interruption (NIH/NIAID; Role: Co-Investigator)

Long-acting, self-administered HIV therapy with the CCR5 antibody PRO 140 (NIH/NIAID; Role: Co-Investigator)

HCV Cancer Vaccines (PA Department of Health & Human Services; Role: Co-Investigator)

Identification of risk factors for Clostridium difficile infection at Hahnemann University Hospital (Pfizer; Role: Co-Investigator)

Establishing Evidence for Peer Group Support and Asset Building Among Families with Young Children on TANF: Ensuring Fidelity & Producing Indicators (Annie E. Casey Foundation; Role: Co-Investigator)

Recent Student Projects


Impact of Pre-exposure Prophylaxis on HIV Transmission in the Context of Condom Use, Treatment as Prevention, and Seroadaptive Practices (agent-based modeling)

Daily Doxycycline Use to Prevent Syphilis Infection among MSM Receiving PrEP (agent-based modeling)

Bias Adjustment Techniques and HIV Sexual Risk Estimation

  • Bayesian approaches when evaluating racial disparities in HIV risk among men who have sex with men (MSM)

  • To Be or Not To Be: Men Who Have Sex with Men and Bayesian Correction of Misclassification
  • Health-Related Quality of Life in the Era of Highly Active Anti-Retroviral Therapy in a large United States Military Cohort of Individuals Living with Human Immunodeficiency Virus

  • Mental health and cardiovascular disease among Sexual and Gender Minorities

  • On Individual and Community-Level Determinants of Pertussis and Flu Incidence and Vaccination
  • The Role of Hormone Therapy on Cardiovascular Disease among Transgender Men and Women in Philadelphia


A Retrospective Case-Control Study of Hospital-Acquired Clostridium difficile Infection

  • Youth Asthma Epidemiologic Surveillance in Croix-des-Bouquets, Haiti

  • Periodontitis and Alzheimer’s Disease: Inflammation as a Mediator

  • An Investigation of Body Art and Blood Borne Viruses in Philadelphia
  • Comparison of Confirmed and Unconfirmed Antibody-Positive Hepatitis C Cases in Philadelphia

  • Evaluating the Effectiveness of the “Take Control Philly” Condom Mailing Distribution Program
  • Attitudes Towards Sexual Minorities and HIV among Residents of the Russian Federation

Research Interests

  • Cancer
  • Clinical Trials
  • Community Engaged Research
  • Data Analysis Methods
  • Global health or International health
  • Health Disparities
  • Infectious Disease
  • Mental health and Behavioral health
  • Reproductive or Sexual Health
  • Statistical Modeling
  • Substance use
  • Violence and Trauma


Tran NK, Goldstein ND, Welles SL. Bias Adjustment Techniques Are Underutilized in HIV Sexual Risk Estimation: A Systematic Review.  Int J Env Res Publ Health 2018; 15(8)

LeVasseur MT, Goldstein ND, Olivieri-Mui B, Welles SL. The Effect of PrEP on HIV Incidence Among Men Who Have Sex With Men in the Context of Condom Use, Treatment as Prevention, and Seroadaptive Practices. JAIDS 2018; 77:31-40.

Roth AM, Aumaier BL, Welles SL, Gross R , Szep Z, Martinez-Donate AP, Chavis M, Van Der Pol B.  An Exploration of Factors Impacting Preexposure Prophylaxis Eligibility and Access Among Syringe Exchange Users. Sex Trans Dis 2018; 45:217-221

Levine EC, Martinez O, Mattera B, Wu E, Arreola S, Rutledge SE, Newman B, Icard L, Muñoz-Laboy M, Hausmann-Stabile C, Welles S, Rhodes SD, Dodge BM, Alfonso S, Fernandez MI, Carballo-Diéguez A. Child Sexual Abuse and Adult Mental Health, Sexual Risk Behaviors, and Drinking Patterns Among Latino Men Who Have Sex With Men. J Child Sex Abuse 2017; 18:1-17.

Wu L, Sell R, Roth A, Welles SL. Association of Sexual Minority Identity with Cardiovascular Disease is Mediated by Mental Health Disorders. Prev Med 2018 Mar;108:123-128

LeVasseur MT, Goldstein ND, Welles SL. A public health perspective on HIV/AIDS in Africa: Victories and unmet challenges.  Pathophysiology 2014; 21: 237-56.

Baliban SM, Michael A, Shammassian B, Mudakha S, Khan AS, Cocklin S, Zentner I, Latimer BP, Bouillaut L, Hunter M, Marx P, Sardesai NY, Welles SL, Jacobson JM, Weiner DB, Kutzler MA. An Optimized, Synthetic DNA Vaccine Encoding the Toxin A and Toxin B Receptor Binding Domains of Clostridium difficile Induces Protective Antibody Responses In Vivo. Infect Immun 2014; 82:4080-91

Sweet T, Polansky M, Welles SL. Mediation of HIV/STI Risk by Mental Health Disorders Among Persons Living in the United States Reporting Childhood Sexual Abuse. JAIDS 2013; 62:81-9

Sweet T, Welles SL.  Associations of sexual identity or same-sex behaviors with history of childhhod sexual abuse and HIV/STI risk in the United States. JAIDS 2012; 59:400-8.

Politch JA, Mayer KH, Welles SL, O'Brien WX, Xu C, Bowman FP, Anderson DJ. Highly active antiretroviral therapy does not completely suppress HIV in semen of sexually active HIV-infected men who have sex with men. AIDS 2012; 26:1535-43.