About the OCS

About the OHTN Cohort Study

Established in 1996, the Ontario HIV Treatment Network Cohort Study (OCS) is the largest community-governed HIV cohort in Ontario and is one of the largest cohort studies in North America. It represents a diverse group of Ontarians living with HIV including men and women of different ages, sexual orientations and ethnicities. For more than 20 years, the OCS has produced research evidence to support cutting-edge initiatives that have advanced HIV care and improved the quality of life of people living with HIV.


Eligibility criteria

From 1995 to present, over 6,500 people living with HIV have been enrolled. Right now, approximately 3,700 are active participants at 13 HIV clinics across the province. People are eligible to participate in the OHTN Cohort Study if they have laboratory evidence of HIV infection and are patients at a participating clinic. Children under the age of 16 years and adults incapable of providing informed consent are ineligible.


What kind of data does the OCS collect?

The OHTN Cohort Study collects:

  1. Clinical data obtained through participants’ clinic records,
  2. Psychosocial and behavioural data collected through an interviewer-administered standardized questionnaire, and
  3. Serological and viral load test data collected by the Public Health Ontario Laboratory. All of the data in the OHTN Cohort Study is anonymized and cannot be linked back to the participant.


Data anonymity

The Ontario HIV Treatment Network will only collect, use and disclose anonymized participant information for the purpose of scholarly research that contributes to an improved understanding of HIV, that contributes to improved treatment for people living with HIV, and/or that helps people living with HIV get better access to care. “Scholarly research” is defined as research that aims at establishing fact, principles, or generalizable knowledge that are of social value and intended to be publicly disseminated. Scholarly research must be consistent with established ethical standards and principles.


Can OHTN Cohort Study data be linked with external databases?

One of the goals of the OHTN Cohort Study is to maintain a rich and comprehensive dataset by establishing and supporting linkages with other data sources including multi-cohort collaborations. OCS data can be linked with external databases and studies. There is an annual linkage with the Institute for Clinical and Evaluative Sciences (IC/ES), which includes health services utilization, mortality and other provincial databases. The OHTN will only authorize a linkage through the review and approval of a Research Project Proposal.


What are the goals of the OHTN Cohort Study?

The goals of the OHTN Cohort Study are:

  • To maintain a rich and comprehensive dataset
  • To promote collaboration and synergy in developing and addressing research questions
  • To share knowledge gained through OCS research


Governance committee

The OHTN Cohort Study is a collaborative, community-driven study. Its administrative committees include scientists, clinicians and other health-care providers, policymakers and persons living with HIV. The Scientific Steering Committee and Priority Population Working Groups oversee the scientific direction of the OHTN Cohort Study. The OHTN Cohort Study Governance Committee, which is made up of stakeholders in the Ontario HIV community, evaluates each project proposal for its community relevance and ethics of the intended data use, and recommends policies relating to data security and confidentiality. The OHTN Cohort Study is funded by the provincial government as part of the core operations of the Ontario HIV Treatment Network.

Contact study coordinator Eliot Winkler at ewinkler@ohtn.on.ca if interested in joining the OCS Governance Committee.


OCS Committee Co-Chairs:

  • Adrian Betts, (AIDS Committee of Durham Region)
  • Martin McIntosh (Regional HIV/AIDS Connection & OAN)


  • Muluba Habanyama (OHTN Board rep.)
  • Rodney Rousseau (OHTN Board rep.)
  • Tracy Conway (Community)
  • Mark McCallum (Community)
  • Toney DiPede (Community)
  • Jasmine Cotnam (Canadian Aboriginal AIDS Network)
  • Alison Bray (Ontario Aboriginal HIV/AIDS Strategy)
  • Viviana Santibañez (Latinos Positivos Toronto)
  • Mary Ndung’u (Africans in Partnership Against AIDS)
  • Sam Ocen (Community)
  • Alan Li (Regent Park Community Health Centre)
  • Barry Adam (Community)
  • Julia Kimmaliardjuk (Community)


OHTN Cohort Study Team

  • Abigail Kroch Ph.D. M.P.H

    Principal Investigator

    Abigail Kroch is the Director of Data and Applied Science Impact at the OHTN. In addition to her work with OCS, she supports HIV surveillance activities through the Ontario HIV Epidemiology and Surveillance Initiative (OHESI). She works to generate epi data describing the HIV epidemic in Ontario, then translate this data into KTE products directed at government, community, and clinical stakeholders. These products help to plan, implement and evaluate programs to improve the provincial HIV prevention, engagement and care cascade. She is an assistant professor at the Dalla Lana School of Public Health at University of Toronto in the Division of Clinical Public Health and is an adjunct scientist at Public Health Ontario.

  • Ann Burchell Ph.D.


    Ann Burchell is an epidemiologist and Scientist with the Department of Family and Community Medicine and Li Ka Shing Knowledge Institute at St. Michael’s Hospital, Toronto. She holds degrees in epidemiology from the University of Toronto (MSc) and McGill University (PhD) and has academic appointments as Assistant Professor, Dalla Lana School of Public Health, University of Toronto; Adjunct Professor, Division of Cancer Epidemiology, McGill University; and Adjunct Scientist, Institute for Clinical Evaluative Medicine, Toronto.

Scientific Team

  • Hamilton Health Sciences Centre

    Dr. Philippe El-Helou

    Dr. El-Helou is an assistant professor in the Division on Infectious Diseases of the Department of Medicine at McMaster University and plays a role in both the undergraduate and residency programs. He is also a co-director of the Special Immunology Services Clinic at the McMaster University Medical Center and the head of the Service of Infectious Diseases at St. Joseph’s Healthcare.

  • Elevate NWO

    Holly Gauvin

    Elevate NWO, formerly AIDS Thunder Bay, is a community-based organization that provides hepatitis C, HIV and harm reduction services to communities in northwestern Ontario and hosts one of the 15 hepatitis C teams funded by the Ontario Ministry of Health and Long-term Care.

  • Women’s Health in Women’s Hands

    Wangari Tharao

    Wangari Tharao is Director of Research and Programs at the Women’s Health in Women’s Hands Community Health Centre in Toronto. She served as co-chair of the African and Caribbean Council on HIV/AIDS in Ontario from 2004 to 2010. She is currently co-chair of the Governing Council of the African and Black Diaspora Global Network on HIV and AIDS, a network she co-founded during the International AIDS conference held in Toronto in 2006.

  • Ottawa General Hospital

    Dr. Curtis Cooper

    Dr. Curtis Cooper trained at the University of Saskatchewan (MD 1994). He received certification in Internal Medicine in 1997 and in Infectious Diseases in 1999 while at the University of Manitoba. He completed an HIV Research Fellowship and Masters of Epidemiology in 2002 while at the University of Ottawa. He is currently an Associate Professor with the University of Ottawa, Infectious Diseases Consultant with the Ottawa Hospital Division of Infectious Diseases, Associate Clinical Researcher with the Ottawa Health Research Institute and Director of the Ottawa Hospital and Regional Viral Hepatitis Program.

  • Maple Leaf Medical Clinic

    Dr. Frederic Crouzat

    Fred received his medical degree from the University of Ottawa in 1998, and did his residency training in Toronto at St Michael’s Hospital. It was here that Fred focused on HIV and inner city medicine. Since completing his residency in 2000, his focus continues to be HIV primary care; however, he sought further specialization training in addiction medicine and is certified to prescribe methadone.

  • Sunnybrook Hospital

    Dr. Nisha Andany

    Dr. Andany earned a Bachelor’s of Science Degree at the University of Waterloo before completing her Doctor of Medicine and specialty certifications in General Internal Medicine and Adult Infectious Diseases at the University of Toronto. She was a research student at both the Women’s College Research Institute and the Mount Sinai Hospital, both in Toronto.

  • St. Michael’s Hospital

    Dr. Gordon Arbess

    Dr. Gordon Arbess is a Staff Physician in the Department of Family & Community Medicine at St. Michael’s Hospital in Toronto. He specializes in HIV Primary Care and has an extensive clinical HIV practice. He is the Clinical Director of the HIV/AIDS program. He is the Director of the HIV Fellowship program. Dr. Arbess is on Faculty at the University of Toronto.

  • Toronto General Hospital

    Dr. Sharon Walmsley

    Dr. Sharon Walmsley is a professor of medicine in the Department of Medicine at the University of Toronto and a senior scientist at the Toronto General Research Institute. She is also the assistant director of the Immunodeficiency (HIV) Clinic at the Toronto General Hospital. In 2017 she was appointed as a member of the Order of Canada.

  • Sudbury Regional Hospital

    Dr. Roger Sandre

    Dr. Sandre is a practicing Infectious Disease Specialist at Health Sciences North in Sudbury. He completed his Medical School and Internal Medicine training at McMaster University and Infectious Disease training at the University of Alberta in Edmonton. He is the Medical Director of the Antimicrobial Stewardship Program at Health Sciences North and the Medical Director of the Infection Control Program and the regional HIV Program in North Eastern Ontario. He is involved in several HIV clinical trials in Canada and is an Assistant Professor with the Northern Ontario School of Medicine – teaching both medical students and residents.

  • St. Joseph’s Health Care – London

    Dr. Michael Silverman

    Dr. Silverman received his medical degree and Residency in Internal Medicine at the University of Toronto. He carried out his fellowship in Infectious Diseases at the University of Manitoba in Winnipeg, and an HIV post-doctoral fellowship (1991-2) at the University of California, San Francisco, USA. He established the Positive Care Clinic in Whitby, Ontario (the regional HIV/Hepatitis clinic) and the Durham Regional Tuberculosis Clinic in Ajax.

  • Windsor Regional Health Clinic

    Dr. Jeff Cohen

    Dr. Jeff Cohen is the medical director of the HIV Care Program at the Windsor Regional Hospital. He graduated from McGill University with honours in biochemistry, and went on to attend the McMaster University Medical School.

  • University of Ottawa Health Services

    Elizabetha Lavoie

    Elizabeth Lavoie is a Nurse Practitioner registered with the College of Nurses of Ontario, and has over 15 years of experience working in primary health care. Currently, Elizabeth works for the University of Ottawa Health Services, with a focus on treating patients living with HIV. Elizabeth has worked in a wide variety of roles within the health care field, including: emergency room, smoking cessation, international development, SARS crisis management and much more.

  • Hotel Dieu Hospital Kingston

    Dr. Jorge Martinez-Cajas

    Dr. Martinez-Cajas is an Assistant Professor in the Department of Medicine in the Division of Infectious Diseases with a cross-appointment to the Department of Biomedical and Molecular Sciences at Queen’s University, having joined the Faculty in January 2009. He completed a three year research CTN fellowship at the McGill AIDS Centre in 2008 where he worked on antiretroviral drug resistance with Dr. Mark Wainberg.

OHTN Cohort Study Staff

  • Eliot Winkler M.Sc. B.Sc.
    Coordinator, Data & Applied Science Impact

    Eliot works as a Coordinator in the Data and Applied Science Impact Unit at the OHTN, coordinating the OHTN Cohort Study as well as the Ontario HIV Epidemiology Surveillance Initiative (OHESI). Eliot is a member of the HIV Mental Health Network Steering Committee and his personal research interests include accessibility to mental health resources and service utilization and availability for people living with HIV. Eliot is a graduate of the Clinical Anatomy MSc program at the University of Western Ontario and previously worked as a Clinical Research Coordinator in the Nephrology department at Toronto General Hospital.

  • Tsegaye Bekele M.P.H
    Senior Analyst, Biostatistics

    Tsegaye Bekele is a Senior Analyst, Biostatistics with several years of experience in statistical analyses. He provides analytical support to the OCS and his research interests include social determinants of health, childhood trauma, addiction and mental health, and health-related quality of life.

  • Sean Colyer D.V.M. M.Sc

    Sean was born and raised in Northwestern Ontario. He holds a Master’s degree in Public Health from McGill University and completed his practicum with the Momentum (Engage) Health Study in Vancouver. Before training to be an epidemiologist, Sean practiced veterinary medicine in Toronto.

  • Lucia Light, Ph.D. M.P.H.

  • Nahid Qureshi M.B.B.S. M.P.H
    Lead, Clinical Data

    Nahid Qureshi is a clinical data analyst. She is responsible for improving the quality of OCS data. She holds a Master’s in Public Health specializing in health informatics and data management from Mahidol University, Thailand. She is also an internationally trained medical doctor (MBBS) and is currently completing her MSc in Biostatistics at Dalla Lana School of Public health, University of Toronto. Nahid is also an oracle certified associate and trained in R, SAS, SPSS and Qualtrics programming.

  • Maya Kessler Ph.D.
    Lead, Epidemiologist

    Maya Kesler is the lead epidemiologist for the Data and Applied Science Impact unit at the Ontario HIV Treatment Network (OHTN). Previously she was a Post-Doctoral Fellow in the Cruiselab at the Factor Inwentash Faculty of Social Work, University of Toronto. She holds a PhD in Epidemiology from the Dalla Lana School of Public Health, University of Toronto, a Master’s of Science in Epidemiology from Johns Hopkins Bloomberg School of Public Health and an Honours Bachelors of Science in Bioethics and Biological Anthropology from the University of Toronto.

  • Wesley Jordan Oakes Ph.D.
    Lead, Data & Applied Science Impact

    Wesley Jordan Oakes is the Lead of Data and Applied Science Impact at the OHTN. He is responsible for supporting the planning and implementation of the OHTN Cohort Study’s Scientific Protocol and Research Policies. His work focuses on developing community-specific knowledge products, collaborations and evidence-based approaches that drive provincial HIV prevention activities and engagement in the Care Cascade. He is a member of the TPH Research Ethic Board and holds a M.Phill form the School of Oriental and African Studies (SOAS), University of London. He is scheduled to defend his Ph.D in Anthropology from York University this summer.