Summer Learning Institute in Interdisciplinary HIV Research MaRS Centre, Toronto, July 13-17, 2009

1. Population Health and Cohort Research Robert Hogg, PhD Simon Fraser University, Faculty of Health Sciences BC Centre for Excellence in HIV/AIDS Summer Learning Institute in Interdisciplinary HIV Research MaRS Centre, Toronto, July 13-17, 2009

2. Overview • Objective • Readings • Population Health • Epidemiology • Study Design • Descriptive, analytical, experimental and observational • Measures of Association

3. Objective • To review the basic concepts of population health, epidemiology and study design

4. Readings • National Center for Chronic Disease Prevention and Health Promotion, US Centres for Disease Control and Prevention, EXCITE, Epidemiology in the Classroom. An introduction to epidemiology.www.cdc.gov/excite/classroom/intro_epi.htm)

5. Population health

6. Definition Population health is an approach to health that aims to improve the health of the entire population and to reduce health inequities among population groups. In order to reach these objectives, it looks at and acts upon the broad range of factors and conditions that have a strong influence on our health. - Public Health Agency of Canada

7. Canada versus United States Life expectancy at birth (years, both sexes)

8. Canada versus United States Life expectancy at birth (years, both sexes)

9. Explanation? • Why does Canada have a higher life expectancy than the United States?

10. Variation in life expectancy by US county

11. Income It took the poorest fifth of urban Canadians until the mid-1990s to reach the life expectancy experienced by the richest fifth 25 years earlier.

12. Key elements of a Population Health approach • Address the determinants of health: The range of individual and collective factors and conditions (and their interactions) that have been shown to correlate with health status.

13. Determinants of health • Income and Social Status • Social Support Networks • Education • Employment/Working Conditions • Social Environments • Physical Environments • Personal Health Practices and Coping Skills • Healthy Child Development • Biology and Genetic Endowment • Health Services • Gender • Culture

14. Problem

15. Population and those affected Total population = 1,307, total affected = 805, and proportion affected = .620

16. Create a theory • Class time 5 minutes • Describe the data (best way you can) • Note variations between groups • Why did they occur? • What is the event?

17. The Titanic • What is the event? Sinking of the Titanic • Why did it occur? Ship hit an ice berg and there were not enough life boats

18. Variations in those affected • Men more than women Women and children were generally put on life boats first. • Variation by class First class had better access to life boats

19. Epidemiology

20. What is epidemiology? • “The study of epidemics” Concise Oxford Dictionary, 1964 • “The study of the distribution and determinants of disease in humans” MacMahon and Pugh, 1970 • “The science of the occurrence of illness” Miettinen, 1978 • “The study of the distribution and determinants of health related states and events in specified populations and the application of this study to control the health problems” John Last, Dictionary of Epidemiology, 2001 • Simply: • Who gets disease? • Why do they get it? • And what can we do about it?

21. What is epidemiology? • Considered a cornerstone methodology of public health research. • Highly regarding in evidence-based medicine for determining optimal treatment approaches. • Each disease condition has its own “culture” of application of epidemiological tools, but all rest on the same foundation of epidemiological principles and methods. • Examples: • Infectious disease epidemiology • Environmental epidemiology • Chronic disease epidemiology • Injury epidemiology • Molecular epidemiology • Genetic epidemiology

22. Purposes of epidemiology • Determine the extent of disease in a population. • e.g., What is the prevalence of Hepatitis C among injection drug users in the Downtown Eastside of Vancouver? • Assess risks of exposure on developing disease. • e.g., What is the risk of exposure to Baby Tylenol in infancy on the likelihood of developing childhood asthma? • Identify the cause of new syndromes (e.g., HIV causes AIDS) • e.g., What was the cause of the unusually high incidence of Kaposi’s sarcoma among homosexual men in San Francisco in the early 1980s? • Study the natural history and prognosis of disease • e.g., In the absence of chemotherapy, how long do people survive after a diagnosis of lung cancer?

23. Purposes of epidemiology • Determine whether treatment “x” is effective • e.g., Is the herbal remedy Echinacea an effective treatment against the common cold? • Identifying practical disease prevention strategies and determining whether they are effective • e.g., What is the effect of municipal smoking bylaws on the prevalence of smoking and incidence of lung cancer? • Identifying health service use needs and trends • e.g., What is the prevalence and incidence of HIV/AIDS in British Columbia and what proportion of infected individuals will require antiretroviral therapy by 2015?

24. Descriptive studies

25. Descriptive studies • Research that describes the occurrence of disease and/or exposure • Remember: Person, place and time • Ask: Who?, what?, when?, where? • Example: National Population Health Survey

26. Person • Characteristics of the individuals affected by the disease. • May vary by disease. • age, gender, marital status, race/ethnicity, health status, religion, occupation, socio-economic status, sexual orientation, travel history, education, health status, genetic predisposition, etc.

27. Place • Where did the events take place? • Standard place characteristics include: • Location where the disease was acquired (e.g. country, province, city, postal code) • Description of the location (e.g. type housing, crowded living conditions, proximity to animals) • Surrounding characteristics of the environment (e.g industrial areas, farms)

28. Time • When did the events occur? • When did symptoms first appear • Date of event (day, week, month, year), clock time of event, day versus night, seasonal variation, annual variation, etc.

29. Descriptive studies Case reports / case series • Detailed descriptions usually by a doctor or group of doctors identifying diseases that are unusual/interesting; may be related to unusual exposure

31. Ecological studies • Compare the prevalence of exposures and disease occurrence in populations • Note:observations collected/displayed at the group level may not apply at the individual level

32. South Africa • Wood et al. The Lancet, 2000 • Antiretroviral use has a substantial impact on life expectancy

33. Analytic studies

34. Analytic studies • To evaluate the association between an exposure or characteristic and the development of a particular disease • Three essential characteristics that are examined to study causes of disease: • Host • Agent • Environment

35. Epidemiologic Homeostasis Host Intrinsic traits that influence the risk of exposure, susceptibility once exposed, and the responses to causal factors. Agent Environment

36. Epidemiologic Homeostasis Host Agent Environment Biological, physical, or chemical factors that are necessary for disease occurrence.

37. Epidemiologic Homeostasis Host Agent Environment Extrinsic Factors that determine the level of exposure, likelihood of exposure, and susceptibility to disease once exposed.

38. Epidemiologic Homeostasis Agent, host, and environmental factors interact to determine the distribution of disease in human populations. These factors may to form a steady state (epidemiologic homeostasis) or may readjust to lead to the elimination of disease or epidemics, depending on whether factors favor the host or the agent Host Agent Environment

39. Epidemiologic Homeostasis Paul Farmer: “First you cure the family of TB. Then you start changing the conditions that made them especially vulnerable to TB in the first place.” (p293) Host Haitian family Environment Agent Haiti TB

40. Overview of Analytic Study Designs

41. Experimental

42. Epidemiological Study Designs • Experimental studies – researcher tries to change something and measure the effect on disease outcome – clinical trials, preventive trials • Observational studies – researcher does not intervene in any way

43. Randomized control trial

44. The North American Opiate Medication Initiative (NAOMI) • A clinical trial that examined whether medically prescribed heroin could successfully attract and retain street-heroin users who have not benefited from previous repeated attempts at methadone maintenance and abstinence programs • The trial showed remarkable retention rates and significant improvements in illicit heroin use, illegal activity and health for participants receiving heroin, as well as those assigned to optimized methadone maintenance.

45. Create a trial • What is the outcome? • What is the exposure? • Who is at risk? • What is the intervention/ treatment? • What are the advantages and disadvantages?

46. Observational

47. Observational studies • Measurement of disease occurrence or health outcome • Comparing patterns of exposure and disease outcomes • Identifying risk factors associated with health/disease

48. Observational studies • Measurement of disease occurrence or health outcome • Comparing patterns of exposure and disease outcomes • Identifying risk factors associated with health/disease Can be either descriptive or analytical

49. Cohort Studies • Cohort: any designated group or persons who are followed or traced over a period of time, as in a prospective cohort study • Cohort studies: compare rates of occurrence of disease or death in people with or without a particular exposure

50. CIHR Team in HIV treatment outcomes: The Canadian Observational Cohort (CANOC) Collaboration • This emerging team collaboration is an essential first step to evaluating the impact of antiretroviral care on the health and well being of persons infected with HIV/AIDS across various regions of Canada. • Participating cohorts • BC Centre for Excellence in HIV/AIDS • Clinique Medicale L’Actuel • Canadian Co-infection Cohort Study • EARTH • Maple Leaf Medical Clinic • Montreal Chest Institute IDS • Ontario HIV Treatment Network • Toronto General Hospital • University of Ottawa