Cohort Profile: The Ontario Mental Health and Intersectionality Data Surveillance (Ontario-MINDS) Cohort

The Ontario Mental health and Intersectionality Data Surveillance (Ontario-MINDS) retrospective cohort was established to address the lack of longitudinal population-based data on child and youth mental health. The cohort includes youth born between 1992 and 1996 who resided in the province at any point prior to 12 years of age (N = 831 957), created using population-based health administrative data. The cohort includes sub-cohorts: (i) the MOMBABY sub-cohort, which includes linkages to maternal socio-demographic and clinical data, and (ii) a migrant sub-cohort, which identifies first- and second-generation migrants by using linkages to immigration data. The cohort is followed up to age 30 years in the health administrative data to ascertain health service contacts for mental and substance-use disorders, with continuous follow-up for 87.5% of the cohort as of 2022. Incident cases of psychotic disorder have also been identified. The data holdings include numerous socio-environmental variables, such as neighbourhood-level marginalization indicators and migrant status. The application of validated algorithms has enabled us to identify factors such as multimorbidity and health service encounters for adverse childhood experiences, and primary data linkages have facilitated the exploration of novel exposures, such as green space and air pollution throughout childhood. Collaborations with investigators interested in life-course approaches to youth physical and mental health are welcomed. Use of the Ontario-MINDS cohort may be granted with the permission of the principal investigator (PI) to those who meet pre-specified criteria for confidential access. Please contact the project PI with any inquiries ([email protected]). The twenty-first century has brought a burgeoning recognition of the central role of mental health and illness to overall population health. Mental and substance-use disorders are among the top five leading contributors to the global burden of illness, largely owing to the young age at first onset [1]. It is estimated that one in five adolescents has a mental or substance-use disorder that will persist into adulthood [2] and nearly 75% of lifetime mental disorders have an onset before the age of 25 years [3]. Among children and youth, mental and substance-use disorders are the leading contributor to the total burden of illness in high-income countries and are responsible for the largest proportion of years lived with disability [4, 5]. However, these estimates do not reflect the full impact of these illnesses on the young people affected. The first onset of mental and substance-use disorders typically occurs during adolescence and early adulthood [3], which may lead to disruptions in social, academic, and professional development. If left untreated, mental disorders among children and adolescents may recur and become chronic [6, 7], potentially leading to poor trajectories into adulthood. These public health impacts are further compounded by the 7- to 10-year reduction in life expectancy faced by people with mental and substance-use disorders, largely attributable to the high prevalence of comorbid physical health conditions and a 12-fold higher risk of suicide [8]. Suicide is currently the second-leading cause of death among young people between 15 and 24 years of age in Canada [9] and >75% of youth suicides involve a history of depression [10]. Mental and substance-use disorders among children and youth are expected to become one of the most pressing public health challenges of our time [4]. However, efforts to address the substantial public health burden of these conditions are hindered by a lack of longitudinal population-based data [11]. The Ontario Mental health and Intersectionality Data Surveillance (Ontario-MINDS) cohort is a population-based retrospective cohort of Ontario children born between 1992 and 1996. The overarching aim of this research programme is to begin to fill the gap in longitudinal population-based research on mental and substance-use disorders among Canadian children and youth. With funding from the Children’s Health Research Institute in London, Ontario, the cohort was created in 2022 by using multiple linked health administrative databases housed at ICES (formerly the Institute for Clinical Evaluative Sciences), which is an independent, non-profit research institute that collates data from the Ontario healthcare system. The Ontario-MINDS cohort includes youth born between 1992 and 1996 who were either born in Ontario or who resided in the province at any point prior to 12 years of age (N = 831 957)—the latter group would include youth who moved to Ontario from other provinces as well as first-generation migrants who landed in Ontario. We selected 12 years of age to ensure the availability of at least one childhood data point for everyone in the cohort. To build the cohort, we identified all people registered for the Ontario Health Insurance Plan (OHIP) with a birth date between 1 January 1992 and 31 December 1996. We excluded people for whom the start of OHIP eligibility occurred after age 12 years, people who were no longer eligible for OHIP by age 12 years, and where death occurred on or before the 12th birthday. We also excluded people with missing or invalid sex, and those who resided outside of Ontario. The date of OHIP eligibility was considered to be the index date. A flow chart showing the derivation of the Ontario-MINDS cohort is presented in Figure 1. Flow chart showing the derivation of the Ontario-MINDS cohort. The Ontario-MINDS cohort includes two sub-cohorts that can be used to address specific research questions: The MOMBABY sub-cohort includes youth who are also linked to the ICES MOMBABY dataset (n = 560 262). The MOMBABY dataset includes information on hospital births in Ontario and facilitates linkages with maternal data within the health administrative datasets. This sub-cohort can be used to examine perinatal exposures (e.g. maternal infection during pregnancy) or to obtain information on maternal socio-demographic or clinical factors (e.g. maternal history of mental illness). The migrant sub-cohort (n = 158 785) includes first-generation migrants who landed in Ontario prior to the age of 12 years (n = 84 785), as well as second-generation migrants whose mothers landed in Ontario after 1985 (n = 74 000). First-generation migrants were identified through linkages with the Immigration, Refugees, and Citizenship Canada’s Permanent Resident Database [Immigration, Refugees and Citizenship Canada (IRCC)-PR] [12]. Second-generation migrants were identified by obtaining maternal data from the MOMBABY database and linking with the IRCC-PR database. ICES is a prescribed entity under Ontario’s Personal Health Information Protection Act (PHIPA), which authorizes the collection of personal health information, without consent, for the purposes of health system analysis and evaluation. The use of the data in this project is authorized under section 45 of PHIPA and does not require review by a research ethics board. The Ontario-MINDS cohort is based on routinely collected health administrative data, which allow the ongoing follow-up of cohort members. Follow-up begins at the start of OHIP eligibility (i.e. the index date) and continues until the termination of OHIP coverage (due to outmigration from Ontario), death, or the end of data availability at ICES. Ongoing updates to the follow-up period are planned as additional years of health administrative data become available. Approximately 12.5% of the cohort (n = 103 664) had been lost to follow-up as of 2022 (Figure 2) and the median follow-up time was 27.4 years (Interquartile Range = 25.8, 29.0). There are no differences in socio-demographic characteristics of youth lost to follow-up (Supplementary Table S1) except that the proportion of first-generation migrants is significantly higher among people lost to follow-up (13.7%) relative to those with complete follow-up (9.7%). Entry and exit into the Ontario-MINDS cohort (N = 831 957), defined based on OHIP eligibility. The ICES data holdings are predominantly derived from the publicly funded healthcare system in Ontario, known as the OHIP, which covers medically necessary services for nearly the entire population. In addition to the standard health system data—including outpatient physician visits, emergency department (ED) visits, hospitalizations, and vital status—ICES has linked a wide range of data holdings from other sectors and population-health surveys. These data holdings are routinely updated, with new linkages regularly available, thus providing a rich source of data on a vast array of exposures, confounding factors, and outcomes; some key variable definitions are described below. The primary outcomes of interest in the Ontario-MINDS cohort are indicators of physician-based health service use for mental and substance-use disorders. Acute care visits include ED visits and hospitalizations, identified based on diagnostic codes. We also identified outpatient physician visits for mental and substance-use disorders by using OHIP billings. The diagnostic codes for the visits are categorized by using a standardized definition developed at ICES [13], which includes the following categories: psychotic disorders, mood or anxiety disorders, other selected disorders (e.g. eating disorders, personality disorders), deliberate self-harm, substance-use disorders, and neurodevelopmental disorders (e.g. autism, attention-deficit/hyperactivity disorder). ICES has also validated an algorithm to identify cases of non-affective psychotic disorders [14, 15]. Suicide and mortality data are available through linkages with the Office of the Registrar General-Deaths Vital Statistics Database. There are numerous variables within the health administrative data that are of interest for advancing our understanding of mental and substance-use disorders among youth. For example, information on neighbourhood-level marginalization derived from census data—known as the Ontario Marginalization Index (ON-Marg) [16]—is linked to the ICES data by using residential postal codes. The ON-Marg provides validated indicators across four dimensions: (i) material resources, which are derived from census items related to income, educational attainment, family structure, and housing—this indicator allows the assessment of socio-economic position; (ii) households and dwellings, which are derived from census items related to types of residences (e.g. owned vs. rented, apartments), household information (e.g. living alone, marital status), and population in- and outmigration—these map directly onto commonly used indicators of area-level social fragmentation [17]; (iii) age and labour force, which are derived from census items related to the economic vitality of the area, including the proportion of the population who are older adults and children, as well as people unable to work due to disability; and (iv) racialized and newcomer populations, which are derived from census items related to visible minority groups and migrant status. We can also apply existing algorithms to identify other determinants of mental and substance-use disorders. For example, we have applied the Johns Hopkins Adjusted Clinical Groups System to the outpatient and hospitalization data to identify comorbid physical health conditions and multimorbidity [18]. We have also adapted existing algorithms for identifying adverse childhood experiences in health administrative data [19], which have enabled us to identify people who had health service encounters for experiences of abuse, neglect, or household dysfunction during childhood. Finally, primary data linkages will enable us to explore novel antecedents of mental and substance-use disorders. For example, we have linked data from the Canadian Urban Environmental Health Research Consortium (https://canue.ca). This primary data linkage will allow us to explore the cumulative effects of environmental factors throughout childhood, such as green space and air pollution, on the subsequent risk of mental and substance-use disorders during adolescence and early adulthood. Socio-demographic characteristics of the Ontario-MINDS cohort at 12 years of age are presented in Table 1. Most youth entered the cohort prior to age 4 years, meaning that we can ascertain exposures of interest throughout most of the childhood. Based on linkages to IRCC data, 10.2% of the cohort are first-generation migrants and 8.9% of the cohort are second-generation migrants. Within the migrant sub-cohort, 16.8% of first-generation migrants (9.0% of total sub-cohort) arrived in Canada with refugee status and the most common regions of birth were South Asia (14.4%), East Asia (12.0%), Europe (8.7%), and North Africa and the Middle East (7.9%). Characteristics of the Ontario-MINDS cohort at age 12 years (N = 831 957) Values not summing to 100% are due to missing data (<2.5% per variable). Characteristics of the Ontario-MINDS cohort at age 12 years (N = 831 957) Values not summing to 100% are due to missing data (<2.5% per variable). Throughout childhood, adolescence, and early adulthood (follow-up to 2022), 70.6% of the Ontario-MINDS cohort had at least one physician visit with a diagnostic code for a mental or substance-use disorder and 6.2% had at least one acute care encounter (ED or hospitalization). The 6-month prevalence of any visit for a mental or substance-use disorder was 10.5%, which aligns with estimates of physician-based mental health service use from other youth samples in Ontario [20]. A summary of the diagnoses assigned to the visits is presented in Figure 3. More than half of the cohort (55.8%) had at least one visit related to mood or anxiety disorders throughout childhood, adolescence, and early adulthood. Other common reasons for encounters with physician-based services included other mental disorders (29.7%) and neurodevelopmental disorders (26.8%). The incidence of non-affective psychotic disorder in the study cohort was 137.3 per 100 000 person-years (95% confidence interval = 135.3, 139.4), which is aligned with other Canadian estimates of the incidence of psychotic disorders for this age group obtained from health administrative data [15, 21]. Frequency of health service use for mental and substance-use disorders among youth in the Ontario-MINDS cohort (N = 831 957) by diagnosis assigned to the visit. Event rates represent children with at least one visit for each diagnosis group. We currently have several projects underway to explore childhood antecedents to youth mental and substance-use disorders by using the Ontario-MINDS cohort, with a particular focus on socio-environmental exposures and intersectional approaches. In one study, we have modelled trajectories of neighbourhood-level income throughout childhood (Figure 4) and examined the association with subsequent use of health services for mental and substance-use disorder up to age 25–30 years. We found clear socio-economic gradients in the use of acute care services for mental and substance-use disorders, but few differences in outpatient visits. In a separate study, we have used the Ontario-MINDS cohort to estimate the risk of psychotic disorders among first- and second-generation migrant groups—this represents the first Canadian data to date on second-generation migrant groups showing no excess risk of psychotic disorder overall, relative to non-migrants, in contrast to international evidence [22]. Trajectories of neighbourhood income quintile from birth to age 12 years, identified by using longitudinal latent class models. The Ontario-MINDS cohort represents the largest Canadian birth cohort to date [23], with comprehensive coverage of youth born between 1992 and 1996, and continuous follow-up to age 25–30 years. Furthermore, the cohort is dynamic, allowing in-migration up to age 12 years, meaning that first-generation migrant groups are also included in the sample. Linkages with hospital birth records also enable the ascertainment of maternal socio-demographic and clinical information for a subset of the cohort. The number of research questions that can be explored in the linked health administrative data is vast and this data platform will enable innovative lines of inquiry to be pursued. This work will advance public health approaches to mental and substance-use disorders among youth by providing information for population-health surveillance, identifying determinants of illness and disparities across population subgroups, and supporting improvements in mental health services and systems of care. Despite these strengths, several limitations to the data should be noted. Our ascertainment of service contacts for mental and substance-use disorders are limited to physician-based services, meaning that we have missed service contacts with other types of mental health service providers, such as psychologists and social workers. This is particularly an issue for contacts that occurred prior to age 18 years, as child and adolescent mental health services are delivered across multiple sectors [13]. Future planned linkages with data from the Ontario Ministry of Children, Community, and Social Services, as well as existing linkages with population-health surveys, will enhance our ability to further explore use of non-physician-based mental health services. In addition, although we are able to identify cases of non-affective psychotic disorder by using a validated algorithm [14], we are limited in our ability to identify cases of other types of mental and substance-use disorders. This is due to a lack of specificity in the diagnostic codes used in the outpatient data, which only include three digits, whereas four digits are needed to distinguish between some types of mental disorders. As such, our outcomes are predominantly focused on health service use for mental and substance-use disorders, rather than diagnosed cases. Finally, we are unable to identify fathers in the health administrative data, as the hospital birth records in MOMBABY do not include paternity information. Consequently, we are unable to identify second-generation migrants for whom the father had a history of migration and we cannot account for paternal risk factors or history of mental illness in our analyses. However, we can identify siblings born to the same mother within the MOMBABY sub-cohort. The Ontario-MINDS cohort is held securely in coded form at ICES. Collaborations with investigators who are interested in life-course approaches to youth physical and mental health are welcomed, particularly collaborations that could facilitate linkages with other datasets containing information on socio-environmental exposures or clinical outcomes. Legal data-sharing agreements between ICES and its data providers prohibit ICES from making the dataset publicly available; however, use of the Ontario-MINDS cohort may be granted with the permission of the principal investigator (PI) for those who meet pre-specified criteria for confidential access, available at www.ices.on.ca/DAS. Please contact the project PI with any inquiries ([email protected]). ICES is a prescribed entity under Ontario’s PHIPA, which authorizes the collection of personal health information, without consent, for the purposes of health system analysis and evaluation. The use of the data in this project is authorized under section 45 of PHIPA and does not require review by a research ethics board. We are grateful to Lixia Zhang for analytic support on this work. This study was supported by ICES, which is funded by an annual grant from the Ontario Ministry of Health (MOH) and the Ministry of Long-Term Care. This document used data adapted from the Statistics Canada Postal CodeOM Conversion File, which is based on data licensed from Canada Post Corporation, and/or data adapted from the Ontario Ministry of Health Postal Code Conversion File, which contains data copied under license from ©Canada Post Corporation and Statistics Canada. Parts of this material are based on data and/or information compiled and provided by CIHI, Ontario MOH, and IRCC. The analyses, conclusions, opinions, and statements expressed herein are solely those of the authors and do not reflect those of the data sources; no endorsement is intended or should be inferred. We thank the Toronto Community Health Profiles Partnership for providing access to the Ontario Marginalization Index. Study conception and acquisition of funding: K.K.A. Input on cohort creation and included variables: K.K.A., R.R., M.R., J.E., B.L. Cohort creation and data analysis: B.L. Drafting of manuscript: K.K.A., R.R. Revising manuscript for intellectual content: M.R., J.E., B.L. Final approval of published version: K.K.A., R.R., M.R., J.E., B.L. Supplementary data is available at IJE online. Conflict of interest: None declared. The creation of the Ontario-MINDS cohort was funded by the Children’s Health Research Institute (London, Ontario) and by a Petro Canada Young Innovator Award (to K.K.A.). K.K.A. is supported by a Tier 2 Canada Research Chair in Public Mental Health Research. The authors declare that AI tools were not used in the preparation of this manuscript.

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