Introduction: This thesis prospectively evaluated the cognitive and functional outcomes and health-related quality of life of children admitted urgently to a Pediatric Intensive Care Unit (PICU) at the Hospital for Sick Children. Methods: The primary outcome was the Vineland Adaptive Behavioural Scale (VABS-2) measured at 1-month and secondary outcomes were health-related quality of life, daily functioning, and caregiver perceptions. Results: 56 children and 66 caregivers were enrolled; 42 (75%) patients and 49 (74%) caregivers completed the 1-month assessment. Children in the PICU had a mean VABS-2 score of 85(+25). Daily functioning outcomes did not significantly change from baseline to 1-month. In comparison to baseline, children had significantly reduced health-related quality of life at 1-week but no significant change was found at 1-month. Discussion: Children surviving PICU have significant cognitive morbidity and reduced health-related quality of life that is exacerbated by more intense modes of resuscitation and increasing severity of illness.

Some antibiotics, including co-trimoxazole, inhibit warfarin’s metabolism and may be associated with greater risk of hemorrhage in warfarin-treated patients. This thesis examines the risk of upper gastrointestinal (UGI) hemorrhage in older patients receiving warfarin and antibiotics commonly used to treat urinary tract infections, with a focus on co-trimoxazole. This population-based nested case-control study using Ontario healthcare databases, identified residents aged 66 years or older continuously on warfarin (n=134,637). Cases were those hospitalized with UGI hemorrhage (n=2151). Cases were nearly 4 times more likely than controls to have recently received co-trimoxazole (adjusted odds ratio (OR), 3.84; 95% confidence interval (CI) 2.33 – 6.33). Ciprofloxacin was also associated with an increased risk (adjusted OR 1.94; 95% CI 1.28 – 2.95), but no significant association was observed with amoxicillin, ampicillin, nitrofurantoin or norfloxacin. Among older patients receiving warfarin, co-trimoxazole is associated with a significantly higher risk of UGI hemorrhage than other commonly used antibiotics.

OBJECTIVE: To examine the past-year prevalence and frequency of condom use and to identify correlates of condom use among young, unattached heterosexual Ontarians. METHODS: Descriptive statistics and multiple logistic regression were used to analyze the 1996/97 Ontario Health Survey (OHS), a cross-sectional, random digit-dialling (RDD) survey of 36,892 Ontario residents of households with a telephone line. RESULTS: Between 1996 and 1997, 61.3% (95% CI=58.5%-64.1%) of the study sample (aged 15-44, n=1,949) reported consistent (always) condom use and 11.8% (95% CI=10.2%-13.5%) reported never using condoms. Significant correlates included, for both sexes, health planning region, age, ethnic origin, and type of smoker; for females only, socio-economic status, age at first sexual intercourse, and past-month oral contraceptive use ; and for males only, number of past-year sexual partners, HIV testing history, and past-year frequency of religious attendance. CONCLUSIONS: Findings constitute a cross-sectional component for examining the long-term trend of condom use in Ontario.

Objectives: The objectives of this study were two-fold: (1) to describe the epidemiology of childhood fractures in Ontario; (2) to determine if having a fracture in childhood is associated with an increased risk of having a future fracture. Methods: This was a population-based retrospective cohort study using Ontario health administration data. Children aged 0 to 15 years were grouped according to baseline fracture status. Associations between predictors and future fracture were assessed using Poisson and Cox PH regression. Results: 43,154 Ontario children experienced a baseline fracture (17.5 per 1000 child years). Children with a baseline fracture had a 60% higher rate of fracture during 7 years of follow-up after adjustment for sex, rurality, history of previous fracture and the occurrence of head injury and soft-tissue injury. Conclusions: The occurrence of a baseline fracture is associated with an increased rate of future fracture irrespective of age at time of baseline fracture.

Some antibiotics, including co-trimoxazole, inhibit warfarin’s metabolism and may be associated with greater risk of hemorrhage in warfarin-treated patients. This thesis examines the risk of upper gastrointestinal (UGI) hemorrhage in older patients receiving warfarin and antibiotics commonly used to treat urinary tract infections, with a focus on co-trimoxazole. This population-based nested case-control study using Ontario healthcare databases, identified residents aged 66 years or older continuously on warfarin (n=134,637). Cases were those hospitalized with UGI hemorrhage (n=2151). Cases were nearly 4 times more likely than controls to have recently received co-trimoxazole (adjusted odds ratio (OR), 3.84; 95% confidence interval (CI) 2.33 – 6.33). Ciprofloxacin was also associated with an increased risk (adjusted OR 1.94; 95% CI 1.28 – 2.95), but no significant association was observed with amoxicillin, ampicillin, nitrofurantoin or norfloxacin. Among older patients receiving warfarin, co-trimoxazole is associated with a significantly higher risk of UGI hemorrhage than other commonly used antibiotics.

OBJECTIVE: To examine the past-year prevalence and frequency of condom use and to identify correlates of condom use among young, unattached heterosexual Ontarians. METHODS: Descriptive statistics and multiple logistic regression were used to analyze the 1996/97 Ontario Health Survey (OHS), a cross-sectional, random digit-dialling (RDD) survey of 36,892 Ontario residents of households with a telephone line. RESULTS: Between 1996 and 1997, 61.3% (95% CI=58.5%-64.1%) of the study sample (aged 15-44, n=1,949) reported consistent (always) condom use and 11.8% (95% CI=10.2%-13.5%) reported never using condoms. Significant correlates included, for both sexes, health planning region, age, ethnic origin, and type of smoker; for females only, socio-economic status, age at first sexual intercourse, and past-month oral contraceptive use ; and for males only, number of past-year sexual partners, HIV testing history, and past-year frequency of religious attendance. CONCLUSIONS: Findings constitute a cross-sectional component for examining the long-term trend of condom use in Ontario.

Objectives: The objectives of this study were two-fold: (1) to describe the epidemiology of childhood fractures in Ontario; (2) to determine if having a fracture in childhood is associated with an increased risk of having a future fracture. Methods: This was a population-based retrospective cohort study using Ontario health administration data. Children aged 0 to 15 years were grouped according to baseline fracture status. Associations between predictors and future fracture were assessed using Poisson and Cox PH regression. Results: 43,154 Ontario children experienced a baseline fracture (17.5 per 1000 child years). Children with a baseline fracture had a 60% higher rate of fracture during 7 years of follow-up after adjustment for sex, rurality, history of previous fracture and the occurrence of head injury and soft-tissue injury. Conclusions: The occurrence of a baseline fracture is associated with an increased rate of future fracture irrespective of age at time of baseline fracture.

Aboriginal Canadians (First Nations, Métis, and Inuit) have the highest prevalence of overweight and obesity compared to other ethnic groups in Canada. In order to assess the evolution of the problem over time and to understand potential risk factors, three studies were conducted using nationally-representative survey data. Direct comparisons between Aboriginal and non-Aboriginal Canadians from the same surveys provide important perspectives on the magnitude of health disparities that cannot be obtained by small regional studies that dominate the current available literature. Body mass index (BMI) trajectories from 1994 to 2009 were estimated for Aboriginal and non-Aboriginal Canadians. Aboriginal Canadians experienced higher rates of BMI increase over the 14-year period between 1994 and 2009. Rate of BMI increase was specifically higher for Aboriginal adults born in the 1960s and 1970s when compared with non-Aboriginal adults, and later-born cohorts had consistently higher BMI compared with earlier-born cohorts. The role of potentially modifiable lifestyle factors in obesity among Aboriginal and non-Aboriginal youth was also investigated. Compared to non-Aboriginal youth, consumption of fruits/vegetables and dairy products was lower, and more Aboriginal youth were "high" TV watchers. Physical activity participation did not differ between "high" and "low" TV watchers for both groups, and was associated with lowered odds for obesity only among Aboriginal youth. The complex relationship between obesity and socioeconomic status for Aboriginal and non-Aboriginal Canadians was explored. Employment status was strongly and negatively associated with obesity among Aboriginal men and women. Aboriginal men of high socioeconomic status (SES) were most likely to be obese, whereas Aboriginal women of high SES were least likely to be obese. Important descriptive and analytical information on an emerging and serious public health issue among Aboriginal people in Canada can inform the design and planning of intervention programs and development of public health strategies targeted at obesity.

Introduction: This thesis prospectively evaluated the cognitive and functional outcomes and health-related quality of life of children admitted urgently to a Pediatric Intensive Care Unit (PICU) at the Hospital for Sick Children. Methods: The primary outcome was the Vineland Adaptive Behavioural Scale (VABS-2) measured at 1-month and secondary outcomes were health-related quality of life, daily functioning, and caregiver perceptions. Results: 56 children and 66 caregivers were enrolled; 42 (75%) patients and 49 (74%) caregivers completed the 1-month assessment. Children in the PICU had a mean VABS-2 score of 85(+25). Daily functioning outcomes did not significantly change from baseline to 1-month. In comparison to baseline, children had significantly reduced health-related quality of life at 1-week but no significant change was found at 1-month. Discussion: Children surviving PICU have significant cognitive morbidity and reduced health-related quality of life that is exacerbated by more intense modes of resuscitation and increasing severity of illness.

Introduction: The association between smoking and depression has been well established, but the nature of the relationship has not been determined. A synthesis of longitudinal studies examining the onset of smoking and depression among adolescents demonstrated consistent evidence of both smoking predicting depression and depression predicting smoking in multiple populations; however, more work is needed to develop and test the mechanisms associated with the onset of the co-occurrence of smoking and depression. This thesis examines the role of a broad range of potential confounders on the relationship between smoking and depression, and investigates a potential mechanism of effect. Method: Analyses were conducted using the Nicotine Dependence in Teens (NDIT) cohort which included 1293 students initially aged 12-13 years recruited from all grade seven classes in a convenience sample of ten secondary schools in Montreal, Canada surveyed twenty times over five years. Multiple regressions were performed to examine the temporal relationship of potential confounders on the relationship between smoking and depression and to empirically observe variables that could be intermediate on pathways between smoking and depression. A growth curve model was developed to test the effect of perceived self medication on changes in depression scores over time. Results: A concept map of the smoking and depression relationship in the NDIT cohort was developed according to the results of proportional hazard and fixed effect regressions in which friend smoking, stress, and anxiety-associated variables were identified as intermediate variables. Perceived self-medication was associated with decelerated rates of change of depressive symptoms over times, suggesting that smoking may increase mean levels of stress and depressive symptoms, but may offer the perception of control. Conclusion: In concert, this thesis suggests a model in which stress and the perceived control of psychobiological function using cigarettes lead to the development of increased depressive symptoms and increased cigarette use.