Cohort Profile: The ONtario Population Health and Environment Cohort (ONPHEC)

Chronic diseases, including cardiovascular disease, diabetes mellitus, cancers and neurological disorders, constitute the most important global burden on disease, accounting for 68% of deaths and 54% of disability- adjusted life years (DALYs) each year.1,2 With increasing life expectancy, the impacts of chronic diseases will continue to rise.3 To reduce the substantial burden of chronic diseases, intervening on their major risk factors is the most cost-effective approach.4 Among various modifiable risk factors, environmental factors are increasingly being recognized as playing important roles in the development of a number of chronic diseases.5 The World Health Organization (WHO) has estimated that approximately 24% of DALYs and 23% of deaths are attributable to five environmental risk factors: outdoor air pollution; indoor air pollution; exposure to lead; climate change; and lack of access to clean water, sanitation and hygiene.6 Environmental exposures may also yield beneficial effects on human health. For example, living in greener neighbourhoods may contribute to improvements in psychological well-being,7–9 increased physical activity10 and reduced obesity11 and overall mortality.12 Many environmental risk factors, such as ambient air pollution and noise, are ubiquitous and can lead to large public health impacts. However, to quantify their health impacts, large cohorts are usually required, as the effect sizes of these exposures at the individual level are relatively small compared with risk factors such as tobacco smoking (for example, smoking increases the risk of lung cancer mortality by 15-fold).13 Recent advances in the volume and variety of electronic health records, and the rate at which they can be merged and analysed in the era of Big Data, provide an opportunity to create very large cohorts to acquire new insights into the environmental burden of chronic diseases.14,15 The ONtario Population Health and Environment Cohort (ONPHEC) is a large, retrospective cohort in the province of Ontario, Canada (population of 10.8 million in 1996),16 created in 2014 by linking multiple large-scale health administrative databases. Comprising virtually the entire Canadian-born population of Ontario who were 35 years or older in 1996 (∼ 4.9 million), with a follow-up until 2014, the primary objectives of ONPHEC are to investigate the independent and combined effects of environmental stressors (such as air pollution, traffic-related noise) on the incidence of chronic diseases and their interactions with ‘healthy’ environmental factors (e.g. green areas). Secondary objectives of ONPHEC include the following: to determine the effects of environmental exposures on the long-term survival of adults with selected chronic diseases; to quantify the burden of disease from adverse environmental factors; to evaluate the impacts of changes in environmental exposure on disease risk such as moving to less polluted neighbourhoods or vice versa; and to identify population subgroups who are most susceptible to the effects and who are disproportionately exposed to environmental stressors. Ontario represents an ideal setting to examine these impacts, for multiple reasons. First, information on the incidence of major chronic diseases such as acute myocardial infarction (AMI), heart failure, diabetes and dementia is available for virtually the entire population of Ontario, using multiple chronic disease databases, some of which have been populated starting as early as the mid 1980s.17–19 Long-term historical data for environmental exposures, such as ambient air pollution and meteorological conditions, are also available with complete spatial coverage across Ontario.20,21 With a retrospective cohort design, ONPHEC provides an efficient and statistically powerful way to investigate the impact of environmental exposures on the onset of chronic diseases. Second, Canada routinely conducts population-based health surveys to collect data on health behaviour and determinants of health, such as smoking, obesity and diet, using a representative sample of the population.22,23 ONPHEC augments health administrative data with these survey data, thus allowing for a two-stage cohort design to combine the strengths of health administrative data (that is large statistical power) and population-based health surveys (that is rich information on person-level risk factors for major chronic diseases). This design allows for indirect control of important risk factors such as smoking and obesity, that are often unavailable in large observational studies, especially those using administrative databases.24 Third, Ontario has generally good environmental conditions, but there are also large spatial variations in their exposures. This provides an opportunity to develop exposure-response functions at relatively low levels of environmental exposures, which will have important public health implications globally. For example, average levels of ambient air pollution in Ontario are considerably lower than in many cities in the USA and Europe, and are well below the WHO air quality guidelines.25,26 Fourth, Ontario is the most populous and ethnically diverse province in Canada, with a population that represents more than 200 ethnic origins.27 With demographic characteristics comparable to the USA and many European countries, findings from ONPHEC will be highly generalizable to populations in many other regions. ONPHEC is a retrospective cohort that was created in 2014. It comprises all residents of Ontario who on 1 April 1 1996: (i) were alive and were between 35 and 100 years of age; (ii) had a recorded birth date and sex; (iii) had a valid health card number; and (iv) were Canadian-born individuals. To better characterize long-term exposure to environmental factors, we excluded individuals who had resided in Ontario for fewer than 5 years on cohort entry, yielding a total of population of 4 854 759 individuals. We chose 1 April 1 1996 as the date of cohort inception to allow for a 5-year look-back window to establish residential history and to accrue a reasonably long follow-up period until 2014 (the end of follow-up). The study population was constructed using the Ontario Registered Persons Database, a registry of all Ontario residents who have ever had a health card number.28 Because Ontario has a single-payer health insurance system, the registry is an ideal sampling frame that covers the entire target population. Figure 1 outlines the creation of ONPHEC. Creation of the ONtario Population Health and Environment Cohort (ONPHEC). Another important feature of ONPHEC is that a representative sample of this cohort also participated in the 1996/97 cycle of the National Population Health Survey (NPHS) or the 2000/01, 2003, 2005, or 2007/08 cycles of the Canadian Community Health Survey (CCHS), and they agreed to share and link their responses to health administrative databases via their health card number. These surveys are conducted routinely by Statistics Canada and provide detailed data on variables such as smoking, alcohol use, obesity and household income.22,23 These surveys cover all household residents aged 12 years or older, excluding individuals living on First Nations Reserves, Canadian military bases or certain remote regions of Québec.22,23 Ontario response rates for these surveys ranged from 73.4% to 92.8%.22,23 Because ONPHEC was created using the population registry, once included in the cohort, individuals remain in it until death or termination of Ontario health insurance (due to moving out of the province). Follow-up is continuous, with annual updates of the health administrative databases that track important information such as vital status, clinical events and residential postal codes for all cohort members. This is achieved through deterministic record linkage across multiple health administrative databases, using a unique, encoded identifier, thereby protecting individual privacy. To date, ONPHEC has linked data across 20 health administrative, chronic disease and environmental databases (Figure 2). A description of each database is provided in Supplementary Data, available at IJE online. As new data become available for these datasets, the follow-up for ONPHEC will be further extended beyond 2014. Data linkage to create ONPHEC cohort. All the health administrative and health survey data are held and linked at the Institute for Clinical Evaluative Sciences (ICES), located at Sunnybrook Health Sciences Centre in Toronto, Ontario.17 Under Ontario’s Personal Health Information Protection Act, ICES researchers are allowed to link encoded population-based health databases for conducting research following stringent privacy and security policies and practices. The institutional review board at Sunnybrook Health Sciences Centre has approved all ongoing studies under ONPHEC. The primary outcomes of ONPHEC are cardiovascular disease, diabetes and neurodegenerative disease, which were selected based on previous evidence linking environmental exposures to these specific outcomes.29–35 To ascertain their incidence, we used existing chronic disease databases including the Ontario Hypertension Database, the Ontario Congestive Heart Failure Database, the Ontario Myocardial Infarction Database and the Ontario Diabetes Database. More recently, we have developed province-wide databases for three major neurodegenerative diseases (dementia, parkinsonism and multiple sclerosis). Each of these databases has been populated using health administrative data that are routinely collected by the Ontario government for the purpose of health care system administration.17 These chronic disease databases have been validated through chart review and found to have high sensitivity and specificity (for example, the Ontario Diabetes Database has a sensitivity of 86% and specificity of 97%).19,36–40 Algorithms for populating each of these chronic disease databases are provided in Table 1. Additionally, record linkage to the Office of the Registrar General Death Database provides cause-specific mortality information. Case definitions of selected chronic diseases using Ontario health administrative data Hypertension: ICD-9 401-405; ICD-10 code I10-I13 or I15. Myocardial infarction: ICD-9 code 410; ICD-10 code I21. Congestive heart failure: ICD-9 code 428; ICD-10 code I50. Diabetes: ICD-9 code 250; ICD-10 code E10-E14. Dementia: ICD-9 code 046.1, 290.0-290.4, 294, 331.0, 331.1, 331.5; ICD-10 code G30, F00-F03. Parkinsonism: ICD-9 code 332.0-332.1; ICD-10 code G20, G21.0-G21.4, G21.8-G21.9, G22, F02.3. Multiple sclerosis: ICD-9 code 340; ICD-10 code: G35. Case definitions of selected chronic diseases using Ontario health administrative data Hypertension: ICD-9 401-405; ICD-10 code I10-I13 or I15. Myocardial infarction: ICD-9 code 410; ICD-10 code I21. Congestive heart failure: ICD-9 code 428; ICD-10 code I50. Diabetes: ICD-9 code 250; ICD-10 code E10-E14. Dementia: ICD-9 code 046.1, 290.0-290.4, 294, 331.0, 331.1, 331.5; ICD-10 code G30, F00-F03. Parkinsonism: ICD-9 code 332.0-332.1; ICD-10 code G20, G21.0-G21.4, G21.8-G21.9, G22, F02.3. Multiple sclerosis: ICD-9 code 340; ICD-10 code: G35. At the individual level, using record linkage of administrative databases and health surveys we have obtained data such as age, sex, marital status, height, weight, smoking status, daily physical activity and selected pre-existing medical conditions (such as angina, arrhythmia). At the community level, we have derived contextual variables such as average education and unemployment rate, using information from the 1996, 2001, 2006 and 2011 Canadian censuses. Selected characteristics of ONPHEC at cohort entry are presented in Table 2. Additional individual-level information for cohort members who participated in the population-based health surveys is provided in Appendix B (available as Supplementary data at IJE online). Individual- and neighbourhood-level characteristics of the ONtario Population Health and Environment Cohort (ONPHEC) Values are percent or mean ± standard deviation. Based on data linkage across health administrative and chronic disease databases. Among a representative sample of respondents (N≈100,000) to the 1996/1997 cycle of the NPHS or the 2000/2001, 2003, 2005, or 2007/2008 cycles of the CCHS. Body mass index is the weight in kilograms divided by the square of the height in meters. Average daily energy expenditure of participants in their leisure activities (such as walking, bicycling). For each activity, energy expenditure was estimated using frequency and time per session and the value of metabolic energy cost expressed as a multiple of the resting metabolic rate. At the Canadian census tract level. Census tracts are small, relatively stable geographic areas that usually have a population between 2,500 and 8,000 persons. The legal age to work in Canada is 14 years. It is a standard practice in Canada Census to collect and report labour force information among those who are aged 15 years or above. Individual- and neighbourhood-level characteristics of the ONtario Population Health and Environment Cohort (ONPHEC) Values are percent or mean ± standard deviation. Based on data linkage across health administrative and chronic disease databases. Among a representative sample of respondents (N≈100,000) to the 1996/1997 cycle of the NPHS or the 2000/2001, 2003, 2005, or 2007/2008 cycles of the CCHS. Body mass index is the weight in kilograms divided by the square of the height in meters. Average daily energy expenditure of participants in their leisure activities (such as walking, bicycling). For each activity, energy expenditure was estimated using frequency and time per session and the value of metabolic energy cost expressed as a multiple of the resting metabolic rate. At the Canadian census tract level. Census tracts are small, relatively stable geographic areas that usually have a population between 2,500 and 8,000 persons. The legal age to work in Canada is 14 years. It is a standard practice in Canada Census to collect and report labour force information among those who are aged 15 years or above. Among ONPHEC members, approximately 27% (∼1.4 million) died during the follow-up period 1996 to 2014, with cardiometabolic disease as the most common underlying cause of death (Figure 3). Long-term trends of the incidence of six selected chronic diseases are displayed in Figure 4. The incidence of dementia among females aged > 65 years increased markedly from 14.6 per 1000 in 1996 to 45.3 per 1000 in 2012, whereas the incidence of some other diseases such as parkinsonism and AMI remained relatively constant over time. Annual number of deaths, by the underlying cause, in the ONtario Population Health and Environment Cohort (ONPHEC), 1996-2011. Annual incidence rates of six selected chronic diseases (A: acute myocardial infarction, B: congestive heart failure, C: hypertension, D: diabetes, E: dementia, F: parkinsonism) for the ONtario Population Health and Environment Cohort (ONPHEC), 1996-2012. We have developed a variety of environmental exposure data,10,21,41–50 using state-of-the-art methods, including satellite-based remote sensing44 and land-use regression models.51 These exposure data are assigned spatially to cohort members using their annual six-character postal code addresses during follow-up. Six-character postal codes in urban areas represent the centroid of the blocks in which the cohort members live. We included exposures to major air pollutants, including fine particulate matter (particles with aerodynamic diameter <2.5 μm, PM2.5), measures of oxidative potential for particulate matter (mean glutathione depletion and mean ascorbic acid depletion), ultrafine particles (<0.1μm), nitrogen dioxide and ozone. PM2.5 has been associated with various health effects, such as increased cardiovascular mortality.30 Oxidative potential is a novel measure of air pollution exposure, which provides an assessment of regional differences in the ability of PM2.5 to cause oxidative stress, a mechanism thought to play an important role in air pollution health effects.52,53 We are currently evaluating if regional differences in PM2.5 oxidative potential may contribute to regional differences in PM2.5-associated health effects, using ONPHEC. Additional information on air pollutant exposure data is provided in Appendix C (available as Supplementary data at IJE online). In addition, we have information on various meteorological conditions such as air temperature and precipitation from all weather stations across Ontario during the study period.21 Previous studies have demonstrated that both short-term (in days) and longer-term (months or years) variations in temperature increase morbidity and mortality.33,54 Further, spatial variations in traffic-related noise in Toronto, the largest city in Ontario, were derived using exposure surfaces developed from continuous measures of noise from population-based surveys conducted in 2012-13.49 Additionally, we have on hand different measures of green space using land use/classification data and satellite-based normalized difference index was as the between the difference between the and to the of the with more green The data the entire province are available at and spatial As new environmental exposure data become we will continue to link to the cohort. statistical have been to the cohort. First, to examine the between long-term exposure to environmental factors and incidence of chronic diseases, we spatial that were developed by of This for the that health among individuals living in the or are more than for individuals living and that these may be by variables included in the Second, to the interactions between risk factors (e.g. and to provide information that is more for public health we have an With this interactions can be as a from of the effects (that is risk of exposures. the of the can be as with each level of exposure a certain level of Third, to control for important individual-level risk factors such as and diet, which are often unavailable in large cohort studies using administrative databases, we an indirect developed by ONPHEC This is a that can of risk factors or and for multiple This on information on the between and risk factors from data (e.g. a and the between the risk factors and survival from existing The indirect on the of the the data from a representative sample of the study cohort, ONPHEC allows for better control of risk Fourth, we a risk to characterize the of exposure-response between environmental exposures and various chronic To date, we have the between ambient air pollution and the incidence of selected diseases. In we ONPHEC members who participated in the population-based health surveys between 1996 and Among we that for increase in exposure to the incidence of diabetes increased by In we that the onset of was associated with long-term exposure to PM2.5 in Ontario, with an adjusted of per increase in More recently, through record linkage of ONPHEC with the For we all in Ontario an We estimated that increase in exposure to PM2.5 was associated with a increase in risk of deaths, increase in deaths from heart disease and increase in These to of deaths being attributable to PM2.5 among AMI We also that exposure to ambient had a impact on deaths compared with that from high in Ontario, and that the largest impact of temperature was on especially among individuals than 65 we are currently the spatial and trends of major neurodegenerative diseases, the of on morbidity and the combined effects of green space and air pollution on the long-term survival of living with cardiovascular diseases, the burden of low and high ambient on the risk of from cardiovascular diseases and diabetes and evaluating the between dementia and long-term exposure to air The major strengths of ONPHEC include large and of the entire Canadian-born population of Ontario who were 35 years or older in 1996 This the potential for increasing We also achieved virtually complete follow-up of all ONPHEC members by deterministic record linkage using unique, encoded In addition, there are population-based databases available in Ontario that of major chronic diseases. a of environmental exposure data are available across As new health information and environmental data become they can be into ONPHEC for with a follow-up of ONPHEC provides a way to study the environmental burden of chronic diseases. the generally good environmental conditions in Ontario and relatively large in their exposures, ONPHEC a opportunity to investigate the health impacts of environmental exposures at relatively low This cohort has First, to many large ONPHEC have detailed information on some important risk factors such as smoking and mass index for all cohort members. However, with a two-stage cohort design in which health administrative data are with population-based health survey data, ONPHEC allows for better control of the potential of risk factors on effect Second, the of disease onset is to individuals who have a previous history of of these events at of the cohort members may have However, is to the risk such of disease is to be by exposures to environmental risk factors such as air Third, as in many cohort studies, it is to exposures to environmental risk factors such as daily activity may have an important on total exposure to environmental risk However, a population survey that Canadian adults who resided in major cities during on average over of their time each at and we were to track vital and incidence of chronic diseases among individuals they out of we individuals if they for health are highly in that linkage of ONPHEC with on clinical risk factors or environmental exposure the with in a The ONtario Population Health and Environment Cohort (ONPHEC) is a large, retrospective cohort in the province of Ontario, Canada, that was created in 2014 to investigate the independent and combined effects of various environmental exposures on the development and of chronic diseases. ONPHEC comprises virtually the entire Canadian-born population in Ontario who were 35 years or older in 1996 million) and multiple Big Data (e.g. large-scale health administrative databases, satellite-based environmental and novel statistical Follow-up extended until 2014 through individual-level record linkage to databases of and A of ONPHEC is the two-stage cohort health administrative data are with population-based health survey data on major risk factors for chronic diseases from a representative sample of ONPHEC. ONPHEC information on incidence and mortality from major chronic diseases, including cardiovascular diseases, diabetes and neurodegenerative diseases. ONPHEC a variety of environmental exposure developed by the using state-of-the-art such as satellite-based remote are highly the with Supplementary data are available at IJE online. for ONPHEC is provided by the Canadian of Health and Health Canada and This study was by the Institute for Clinical Evaluative Sciences (ICES), which is by an annual from the Ontario of Health and of this are based on data and information and provided by the Canadian Information Health Institute The and in this represent the of or of

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