Mieke Koehoorn

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Graduate Student Supervision

Doctoral Student Supervision

Dissertations completed in 2010 or later are listed below. Please note that there is a 6-12 month delay to add the latest dissertations.

Epidemiology of chronic disease and multimorbidity for transgender people living with and without HIV (2021)

Introduction: Given limited evidence of the epidemiology of chronic disease and multimorbidity for transgender people living with and without HIV, the purpose of this dissertation was to: 1) systematically review chronic disease burden for transgender populations globally; 2) assess methods for identifying transgender people with and without HIV in administrative data, to facilitate investigation of chronic disease-related and other healthcare utilization for this population; and 3) investigate multimorbidity burden for transgender compared to cisgender people living with HIV. Methods: Systematic review methods were used to review and narratively synthesize the empirical literature on chronic disease among transgender populations, globally. Healthcare records were used to develop and validate a computable phenotype to identity transgender people in a large linked provincial administrative dataset. Longitudinal analysis methods were used to examine multimorbidity prevalence and incidence for transgender compared to cisgender people in North America in a large longitudinal HIV cohort collaborative. Key Findings: The literature on chronic disease among transgender populations is focused on mental and sexual health, with sparse attention to chronic physical health, in particular age-related chronic conditions and inflammation-related disease. Identification of transgender people is feasible in administrative health data, with high specificity, concordance with transgender-specific healthcare utilization, and ability to reliably characterize transgender populations in terms of demographics and chronic disease. Transgender people living with HIV had elevated incidence and prevalence of multimorbidity compared to cisgender people living with HIV, though inconsistently over time and without strong evidence of statistically significant differences by gender identity. Conclusions: High quality evidence of chronic conditions among transgender populations is needed; in particular longitudinal, population-based and representative studies with appropriate comparison groups and rigorous measurement of both transgender status and chronic conditions. Development of validated measures for ascertaining transgender status in administrative data is an important contribution given the limited evidence and the methodological challenges in transgender health research. Given evidence of increased burden of multimorbidity for transgender people living with HIV, future research on chronic co- and multimorbidity for transgender populations is warranted with attention to vulnerabilities by racialization and gender, and the role of intervenable disease risk factors such as smoking.

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Investigating the epidemiology and work disability impacts of anxiety and depression disorders after musculoskeletal injury using linked health data (2020)

Anxiety and depression disorders are common after lost-time musculoskeletal work injury, and may be a modifiable determinant of work disability. Despite this, little evidence exists on the epidemiology or impacts of mental health in the work injury population. This dissertation generated new information on the descriptive epidemiology and work disability impacts of anxiety and depression disorders among workers with lost-time musculoskeletal work injury. Accepted lost-time claims for spine or upper limb strain or sprain work injury were extracted for workers in the Canadian province of British Columbia from 2000 to 2013. Anxiety and depression diagnoses and physician mental health services were identified using physician billing, hospital discharge and prescription data. Analytic approaches included prevalence estimates; multinomial, Cox, and instrumental variable regression models; direct adjusted survival curves; and model stratification by gender. Approximately 1 in 10 men and 3 in 10 women had a recent or current anxiety or depression disorder at the time of injury. Both pre-existing and new onset anxiety and depression disorders were associated with a lower probability of sustained return to work, and pre-existing anxiety was associated with a higher probability of lost-time recurrence after initial return to work. The effect size of the association between pre-existing anxiety and sustained return to work was greater for men than for women, and pre-existing depression was associated with a lower probability of sustained return to work for men but not women. Lastly, instrumental variable methods offer a promising analytic approach to estimate the effects of mental health treatment, based on physician treatment preference, on work disability outcomes for workers with a mental disorder. These findings offer important and novel contributions to our understanding of the prevalence, impacts, and management of anxiety and depression disorders in a lost-time musculoskeletal work injury context. Workers’ compensation benefits and programs intended to improve return to work after musculoskeletal injury should take pre-existing anxiety and depression disorders into consideration, in addition to new onset disorders attributable to the injury; and, gender specific strategies may be warranted to optimize return-to-work outcomes.

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A program of research addressing exposure assessment in epidemiological studies of shift work (2017)

BACKGROUNDShift work is common with wide-ranging implications for worker health. It is also complex, presenting challenges for exposure assessment in epidemiological studies and the development of strong evidence to inform health interventions and policies. This dissertation generated new information on the measurement, assignment, and determinants of shift work exposure, in order to address important limitations in this field of epidemiology.METHODSIn Chapter 2, 152 full-shift personal light-at-night measurements were collected from 102 shift workers in emergency services and healthcare to investigate exposure variability and different exposure metrics. In Chapter 3, multiple exposure indicators were constructed for a national survey of nurses (n=11,450) to demonstrate the impacts of exposure assignment on observed relationships between shift work and depression. In Chapter 4, interviews were conducted with 88 employers in one Canadian province to examine determinants of workplace-level shift work policies and practices.RESULTSIn Chapter 2, average light-at-night exposures varied across occupations and settings; between-group variance exceeded between-worker and within-worker variance, and all exposure metrics were moderately-to-highly correlated. In Chapter 3, the strongest relationships between shift work and depression were observed in the model with highest exposure precision, defined by shift timing and rotation intensity, whereas weak relationships were observed in models with lower exposure precision, defined by shift timing or presence/absence of shift work. In Chapter 4, long duration shifts varied by industry and were more likely in large workplaces; shift work education/training was more likely in large workplaces and those without seasonal shift work; and nighttime lighting policies were more likely in workplaces reporting that maintenance, client service needs, or prior nighttime incidents affected shift work.CONCLUSIONSThis dissertation can inform future epidemiological studies of shift work. Chapter 2 identified high-level exposure indicators (e.g., occupation groupings) and flexibility in the choice of highly correlated metrics for light-at-night exposure studies. Chapter 3 showed that increasing the precision of exposure assignment reduced measurement error and effect attenuation for the outcome of depression. Chapter 4 identified determinants of workplace-level shift work policies and practices (e.g., industry, employer size, temporary work, and employer motivations) to consider in future research and interventions.

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Impact of Prior Hysterectomy on Risk of Subsequent Back Injury in Front Line Healthcare Workers (2016)

Low back injury (LBI) is associated with altered core muscle function and studies have validated the role of these deep stabilizing muscles in prevention and treatment of back pain and injury. No previous studies have evaluated the impact of surgery such as abdominal hysterectomy (AH) on these deep stabilizers and the potential for increased risk of LBI following surgery. The aims of this research were to investigate a link between AH and LBI first with administrative health data analysis and then clinically by measuring muscle thickness with rehabilitation ultrasound imaging (RUSI) before and after surgery.A retrospective cohort of 37,057 female frontline healthcare workers, a population at high risk of occupational LBI due to the heavy nature of their work, was extracted. Exclusion of 27,987 due to a history of back pain or injury, prior hysterectomy or failure to meet the provincial residency requirement of five years left a sample size of 9,070. Within this research sample, 634 (7%) had undergone hysterectomy, a prevalence much lower than the published value of 30%. Statistical analysis revealed no increased risk of LBI in this cohort of healthcare workers without prior history of LBI. Clinical RUSI assessment of the core muscles would investigate if this was because there was no change in the muscle function post-surgically. Validity and reliability of RUSI to evaluate core muscle function have been established for intersessions up to two weeks. A group of women not undergoing AH was used to establish reliability over intervals of four, eight and twelve weeks. Intraclass correlations (ICC₃,₁) ranging from 0.75 to 0.90 for measured muscle thickness in the deep abdominal and lumbar muscles exceeded the minimum standard of 0.70 for research purposes. Percent change measures did not meet this standard. A prospective descriptive case series involving nine individuals undergoing AH found post-surgical decreases in measurements of the deep abdominal stabilizers most notably in the participants with a history of previous low back pain/injury or who were obese. These findings support continued investigation of the relationship between AH and LBI including individuals with risk factors such as prior low back pain/injury and/or obesity.

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Solar Ultraviolet Radiation and Outdoor Workers in Canada: A Program of Research on Exposure Assessment, Sun Protection Behaviours and Prostate Cancer Risk (2015)

No abstract available.

The Utilization and Timing of Neuroimaging and the Role of Neurophysiological Techniques in the Diagnostic Evaluation of Transient Ischemic Attack (2014)

Background: Transient ischemic attack (TIA) is an episode of transient focal neurological deficit with an ischemic vascular cause. Neuroimaging can detect ischemia, determine etiologic mechanisms, and identify stroke risk after TIA, and early assessment reduces stroke risk. Despite guidelines recommending imaging, Canadian hospital-based studies have reported underutilization and delays in the use of imaging procedures after TIA. However, as many TIA patients are not evaluated in hospital, population-based studies are required to determine whether imaging use increased after guideline implementation and characterize trends in imaging timing after TIA. Although administrative databases enable population-based studies of procedure utilization and timing, previous studies have been restricted to hospital-based cohorts, as physician claims data lack validity for TIA ascertainment. Further, as many patients are not evaluated acutely, the assessment of alternative techniques may inform the subacute effects of transient ischemia.Methods: In Chapter 2, sensitivity, specificity, and positive predictive value were used to evaluate the validity of multiple algorithms for TIA case ascertainment from physician claims data. Chapters 3 and 4 provided estimates of imaging utilization before and after guideline implementation and trends in imaging timing in population-based TIA cohorts. Chapter 5 used transcranial magnetic stimulation to measure thresholds for intracortical inhibition and facilitation subacutely after TIA and assessed the relationship of these thresholds with clinical features of TIA. Summary of Findings: The algorithms for TIA ascertainment using physicians claims data evaluated in Chapter 2 were not valid, informing the case definition for subsequent population-based analyses. Chapter 3 showed increases in neuroimaging use but overall poor utilization after the implementation of practice guidelines, with differences by modality and diagnostic setting. In Chapter 4, no changes in imaging timing after TIA were observed over the study period. In Chapter 5, alterations in intracortical thresholds after TIA on transcranial magnetic stimulation were observed and correlated with clinical risk scores. Conclusions: This dissertation contributes new knowledge of population-based practices of the use and timing of neuroimaging after TIA and has implications for future research examining barriers for timely access to imaging techniques and the utility of alternative techniques in the diagnostic evaluation of individuals with TIA

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Work-related cardiovascular risk factors among professional firefighters in British Columbia, Canada: an investigation of noise, carbon monoxide and cortisol secretion (2012)

No abstract available.

The demographic, economic and health fabric of mining communities in British Columbia, Canada (2011)

A significant number of communities in British Columbia (BC) are founded on mineral development and are subject to variable economic boom-and-bust cycles with implications for sustainability and community health. There were three main objectives of this multi-method PhD dissertation. The first was to quantitatively examine community level indicators describing economic, sustainability, and demographic characteristics (gained from Canadian Census data) of 31 BC rural resource based communities (with a focus on mining communities) during a period of time (1991 to 2001) when BC resource sectors experienced an economic downturn. The second was to assess the relationship between exposure to declining economic conditions and acute cardiovascular disease, chronic cardiovascular disease, and mental health outcomes in 29 BC rural resource-based using Statistics Canada Labour Force Survey data and Ministry of Health data over the same time period, again with a focus on mining. The third objective was to qualitatively investigate the experiences of health and social service providers using interviews, with respect to community health issues and the boom-bust mining cycle in a Northern remote coal mining community in British Columbia. During the decade under study, demographic and economic indicators indicated that mining communities were dependent on, and vulnerable to, economic activities and identified the need to strategize the sustainability of mining communities in British Columbia. Health data indicated that declining and bust economic conditions had a significant negative impact on the prevalence of acute cardiovascular disease and mental disorders in mining communities. Qualitative data revealed that the mining boom-bust cycle had negative effects on community health issues, and community health service provision. This dissertation concludes by proposing strategic opportunities aimed at the enhancement of mining community health and sustainability for policy-makers, communities, the mining industry and researchers to consider.

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A Comparison of Self-Reported Use of Primary Mental Health Care Versus Provincial Administrative Records (2009)

No abstract available.

Balancing Efficiencies and Tradeoffs in Epidemiological Field Studies: Evaluating EMG Exposure Assessment for Low Back Injury Risk Factors in Heavy Industry (2008)

No abstract available.

The relationship between water and Helicobacter pylori and the burden of related illnesses in the Township of Langley, British Columbia (2008)

The objectives of this dissertation are to (1) propose a conceptual framework describing the role of water in H. pylori transmission; (2) construct a database of water system and environmental characteristics using a geographic information system (GIS); (3) investigate the prevalence and incidence of H. pylori-related illnesses; and (4) examine the association between water system and environmental variables and H. pylori infection. The setting for this work was the Township of Langley, British Columbia. Based on findings from epidemiological and microbiological studies, a conceptual model of water’s role in H. pylori transmission was developed (Chapter 2). A population-based approach was employed in the construction of the GIS database to assign the risk factors outlined in the model to each Township resident (Chapter 3). Using administrative health services records for H. pylori-related illness, the average annual prevalence of gastric cancer, peptic ulcer disease and gastritis was 20, 450 and 1,777 cases per 100,000 population respectively, and average annual incidence was 13, 268 and 899 cases per 100,000 respectively. There was a significant decrease in the prevalence and incidence of peptic ulcer disease and the incidence of gastritis in the study population over the follow-up period, however, the costs to the health care system remained high (Chapter 4).In a nested case-control study, variables from the GIS database were linked to a database of serological results used to ascertain positive H. pylori infection. H. pylori infection was associated with mixed water source (adjusted OR = 0.63, versus groundwater only) and non-residential land use (adjusted OR=1.58, versus residential) among younger cases (Chapter 5). Odds ratios diminished in the older age groups, suggesting the presence of a cohort effect and that the exposures investigated were most relevant for younger individuals.The findings highlight possible transmission routes, relevant within the Canadian (and North American) context and evidence for public health interventions with regards to water supply and land use. Further, the methodology linked a variety of administrative data to cover all residents of the study area and assigned environmental variables over time, and can serve as a model for other environmental epidemiologic studies.

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Master's Student Supervision

Theses completed in 2010 or later are listed below. Please note that there is a 6-12 month delay to add the latest theses.

Investigating factors associated with medicinal cannabis use among military veterans (2022)

The first part of this thesis is a literature review that summarizes the current scientific evidence on factors associated with medicinal cannabis use among military veterans, responding to a priority Veterans Affairs Canada (VAC) evidence need on the use of medicinal cannabis to inform the delivery of this health benefit and program for veterans. It was found that cannabis use among military veterans is associated with multiple sociodemographic/economic, health-related and military services characteristics, but most consistently with mental health related conditions and with combat related military characteristics. However, much of the existing literature on cannabis use among veterans is from cross-sectional study designs, and the body of literature would be strengthened by future cohort or longitudinal study designs. The second part is a feasibility study demonstrating the utility of the linkage of VAC data and the procedures for using these data for research purposes, including a descriptive study that investigates the use of VAC data to summarize the population of Canadian veterans who receive cannabis for medical purposes (CMP). The highest average amount of CMP per authorization was observed among veterans in their 30s, those who were male, those who were separated/divorced/widowed, those who resided in New Brunswick, Newfoundland and Labrador and Manitoba, those with an approved pensionable condition for mental health and hearing conditions, those who were junior non-commissioned members (JrNCM), with land environment at the time of release and with less than 20 years of service. The third and final part of this thesis is an epidemiological study using multivariable models to examine the complex profile of sociodemographic/economic, health-related and military service characteristics associated with VAC medicinal cannabis authorization dosage (4 to 10 grams versus 3 grams or less) prescribed for Canadian regular force veterans. The strongest associations with a higher authorization amount were observed for veterans receiving benefits for mental health conditions, by province of residence, and for more recent year of authorization; as well as for veterans who were younger and male gender, actively participating in a rehabilitation program, with land environment at the time of release, and who had an involuntary release from service.

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Certification in hazardous industries : an evaluation of the British Columbia Faller Training Standard (2011)

Manual tree falling is historically one of the most hazardous occupations in British Columbia (BC). In an effort to reduce injury rates in this trade, WorkSafeBC implemented regulations requiring mandatory safe work practice training and certification known as the BC Faller Training Standard (BCFTS). The goal of this thesis was to assess if mandatory certification is associated with changes in injury rates and risk of injury for manual tree fallers.Two studies were conducted to determine effects of certification: 1) a comparison of manual tree faller specific injury rates for each forest region of BC during pre and post certification periods and 2) a comparison of the individual level risk of injury associated with certification status for a cohort of manual tree fallers. Annual injury rates representing the number of injuries/10,000,000m³ wood for each BC forest region were constructed using workers’ compensation data obtained from WorkSafeBC and wood harvest volume data from the Ministry of Forests and Range. The individual level relative risk (RR) of injury associated with certification status was determined using WorkSafeBC workers compensation data linked to a cohort listed in the BC Forest Safety Council faller registry.The injury rate study indicated that following implementation of mandatory safe work practice certification, acute injury rates in the Coast Forest Region dropped from 33.5 injuries/10,000,000m³ in 2006 to 25.8 injuries/10,000,000m³ in 2008. The cohort study based on experienced fallers who obtained grandfathered certification found that individual level risk of injury did not change significantly (RR=1.11, 95%CI 0.58,2.14) for the year immediately following certification compared to the year before certification. Combining these two study outcomes suggests the BCFTS may have an effect in the region of the province with the highest level of manual tree falling, although the individual level risk analysis suggests that the effects may take longer to be realized in the industry as a whole.

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