Area-based socio-economic status (SES) measures are frequently used in epidemiology. Such an approach assumes socio-economic homogeneity within an area. To quantify the agreement between area-based SES measures and SES assessed at the individual level, we conducted a cross-sectional study of 943 children who resided in 155 small enumeration areas and 117 census tracts from 18 schools in Montreal, Quebec. We used street address information together with 1986 census data and parental occupation to establish area-based and individual level SES indicators, respectively. As compared with the SES score determined at the level of the individual, 13 different area-based SES indices classified the children within the same quintile 28.7% (+/- 2.8%) of the time. The discrepancy was within one quintile in 35.3% (+/- 2.3%) of cases, two quintiles in 20.6% (+/- 3.6%), three quintiles in 11.3% (+/- 4.2%) and four quintiles in 4.1% (+/- 0.2%). In conclusion, we observed a substantial discrepancy between area- based SES measures and SES assessed at the individual level. Caution should therefore be used in designing or interpreting the results of studies in which area-based SES measures are used to test hypotheses or control for confounding.
An epidemic of hepatitis B occurring in a rural area of Nova Scotia in 1988 and 1989 was investigated. This epidemic identified injection drug use (IDU) as the major determinant of transmission and was the first highly visible indication of IDU in rural Nova Scotia. Contact-tracing was used to identify 186 injection drug users (IDUs), of whom 153 (82%) were interviewed. Of 133 (72%) IDUs who underwent serological testing, 78 had serological evidence of hepatitis B infection. Using epidemiological criteria, 57 IDUs formed a cluster of hepatitis B infections. Using logistic regression techniques, age (O.R. = 1.1), the total number of IDU-contacts named (O.R. = 1.1), and the number of hepatitis B seropositive IDU-contacts named (O.R. = 1.3), were identified as risk factors predictive of an IDU being a cluster case. The characterization of this epidemic may be useful as a model for the spread of hepatitis B and other viral infections among IDUs in rural areas.
To compare health care expenditure and health status for patients with systemic lupus erythematosus (SLE) between nations with distinct mechanisms for funding and delivering health care services.
Seven hundred eight patients with SLE from 2 centers in each of 3 countries (Canada 229, United States 268, United Kingdom 211) underwent physician assessment of disease activity and damage and reported on physical and psychosocial well being, satisfaction, social support, and health resource utilization. To compare overall utilization, constant prices (1997 Canadian dollars) were applied across countries for each service, enabling diverse resources to be collapsed into a single expression.
After adjusting for important patient covariates, Canadian, compared to American and British patients, reported significantly superior health status in 3 of 8 Medical Outcome Survey Short Form-36 (SF-36) subscales, the SF-36 physical component summary score, and the visual analog scale of general health status. There was no consistent trend in patient satisfaction. Overall annual resource utilization did not vary significantly, with mean annual per patient expenditures (adjusted for demographics, disease duration, activity, damage, social support, health status, patient satisfaction, and age and sex adjusted country-specific SF-36 general population norms) totalling $4853, $5285, and $4760 for Canada, US, and the UK, respectively. However, within each resource category, differences were observed. Canadians saw more specialists than the British, the British more generalists. Canadians and Americans were more frequent users of the emergency room; Americans of laboratory/imaging procedures. Canadians had higher hospital costs than Americans.
After adjustment, Canadian patients reported better well being than their counterparts. Despite considerable differences in the mechanisms of health care funding and service mixture, overall resource utilization did not vary significantly between the countries, although there was a trend towards more intense use of inpatient services in Canada and outpatient services in the United States.
Associations among disease conditions, bone mineral density, and prevalent vertebral deformities in men and women 50 years of age and older: cross-sectional results from the Canadian Multicentre Osteoporosis Study.
This cross-sectional cohort study of 5566 women and 2187 men 50 years of age and older in the population-based Canadian Multicentre Osteoporosis Study was conducted to determine whether reported past diseases are associated with bone mineral density or prevalent vertebral deformities. We examined 12 self-reported disease conditions including diabetes mellitus (types 1 or 2), nephrolithiasis, hypertension, heart attack, rheumatoid arthritis, thyroid disease, breast cancer, inflammatory bowel disease, neuromuscular disease, Paget's disease, and chronic obstructive pulmonary disease. Multivariate linear and logistic regression analyses were performed to determine whether there were associations among these disease conditions and bone mineral density of the lumbar spine, femoral neck, and trochanter, as well as prevalent vertebral deformities. Bone mineral density measurements were higher in women and men with type 2 diabetes compared with those without after appropriate adjustments. The differences were most notable at the lumbar spine (+0.053 g/cm2), femoral neck (+0.028 g/cm2), and trochanter (+0.025 g/cm2) in women, and at the femoral neck (+0.025 g/cm2) in men. Hypertension was also associated with higher bone mineral density measurements for both women and men. The differences were most pronounced at the lumbar spine (+0.022 g/cm2) and femoral neck (+0.007 g/cm2) in women and at the lumbar spine (+0.028 g/cm2) in men. Although results were statistically inconclusive, men reporting versus not reporting past nephrolithiasis appeared to have clinically relevant lower bone mineral density values. Bone mineral density differences were -0.022, -0.015, and -0.016 g/cm2 at the lumbar spine, femoral neck, and trochanter, respectively. Disease conditions were not strongly associated with vertebral deformities. In summary, these cross-sectional population-based data show that type 2 diabetes and hypertension are associated with higher bone mineral density in women and men, and nephrolithiasis may be associated with lower bone mineral density in men. The importance of these associations for osteoporosis case finding and management require further and prospective studies.
It is common in population screening surveys or in the investigation of new diagnostic tests to have results from one or more tests investigating the same condition or disease, none of which can be considered a gold standard. For example, two methods often used in population-based surveys for estimating the prevalence of a parasitic or other infection are stool examinations and serologic testing. However, it is known that results from stool examinations generally underestimate the prevalence, while serology generally results in overestimation. Using a Bayesian approach, simultaneous inferences about the population prevalence and the sensitivity, specificity, and positive and negative predictive values of each diagnostic test are possible. The methods presented here can be applied to each test separately or to two or more tests combined. Marginal posterior densities of all parameters are estimated using the Gibbs sampler. The techniques are applied to the estimation of the prevalence of Strongyloides infection and to the investigation of the diagnostic test properties of stool examinations and serologic testing, using data from a survey of all Cambodian refugees who arrived in Montreal, Canada, during an 8-month period.
Available data, although fragmentary, indicate that infections impose a large burden on long-term-care facilities (LTCFs) in the United States. Endemic infections occur with frequencies estimated to range between 1.64 and 3.83 million per year. These estimates rival or exceed the annual tally for nosocomial infections in acute-care settings. Infections associated with outbreaks caused by respiratory, gastrointestinal, and antimicrobial-resistant pathogens burden LTCFs even further. As judged by antimicrobial use, transfers to hospital, and mortality figures, infections in LTCFs are not trivial. Moreover, annual costs associated with these infections appear to exceed $1 billion. Recognition of the burden associated with infection in LTCFs helps to identify research priorities for this rapidly growing area of healthcare.
The Medical Outcomes Study 36-item Short Form (SF-36) is a widely used measure of health-related quality of life. Normative data are the key to determining whether a group or an individual scores above or below the average for their country, age or sex. Published norms for the SF-36 exist for other countries but have not been previously published for Canada.
The Canadian Multicentre Osteoporosis Study is a prospective cohort study involving 9423 randomly selected Canadian men and women aged 25 years or more living in the community. The sample was drawn within a 50-km radius of 9 Canadian cities, and the information collected included the SF-36 as a measure of health-related quality of life. This provided a unique opportunity to develop age- and sex-adjusted normative data for the Canadian population.
Canadian men scored substantially higher than women on all 8 domains and the 2 summary component scales of the SF-36. Canadians scored higher than their US counterparts on all SF-36 domains and both summary component scales and scored higher than their UK counterparts on 4 domains, although many of the differences are not large.
The differences in the SF-36 scores between age groups, sexes and countries confirm that these Canadian norms are necessary for comparative purposes. The data will be useful for assessing the health status of the general population and of patient populations, and the effect of interventions on health-related quality of life.
Notes
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To assess the behavioural and psychosocial effects of screening asymptomatic children at high risk for hyperlipidemia.
Observational study involving prospective longitudinal and cross-sectional portions.
Two tertiary care pediatric lipid clinics in Montreal.
Longitudinal portion: all children aged 4 to 17 years who presented for screening at the lipid clinics between April 1990 and June 1991. Of the 56 eligible children 52 (93%) (and their mothers) agreed to participate, 34 with hyperlipidemia (case subjects) and 18 without hyperlipidemia (control subjects). Thirty-five children (67%) completed 3 assessments over 12 months. Cross-sectional portion: all children aged 4 to 17 years in whom hyperlipidemia had been diagnosed 2 to 5 years earlier at one of the lipid clinics. Of the 58 eligible children 48 (83%) (and their mothers) participated.
For children, mean scores on the Child Behavior Checklist (Behavior Problems subscale) (CBCL), the Children's Depression Inventory (CDI) and the State-Trait Anxiety Inventory for Children (STAIC); for mothers, mean scores on the Beck Depression Inventory (BDI) and the State-Trait Anxiety Inventory (STAI).
In the longitudinal portion of the study, there was no significant difference between the case and control subjects in the mean CDI or STAIC scores at 1 or 12 months. At 1 month after diagnosis the case subjects in the longitudinal portion had a significantly higher mean CBCL score than the children in the cross-sectional component (p = 0.01). With the control group as the reference group, the adjusted odds ratios for a high CBCL score (greater than 62) for the case subjects were 15.5 (95% confidence interval [CI] 2.4 to 99.8) at 1 month and 15.8 (95% CI 1.1 to 223.4) at 12 months. The corresponding values for the children in the cross-sectional component were 1.3 (95% CI 0.3 to 6.2) and 5.0 (95% CI 0.5 to 50.9).
The observed behavioural problems in children with a recent diagnosis of hyperlipidemia were independent of other risk factors, such as age and sex of child and mother's age and BDI score. Our results suggest that identification of hyperlipidemia in children may have harmful psychological effects in the families involved. This evidence strengthens arguments for the exclusion of cholesterol measurement from the periodic health examination of children at moderately high risk.
Comparing the psychometric properties of preference-based and nonpreference-based health-related quality of life in coronary heart disease. Canadian Collaborative Cardiac Assessment Group.
A cross-sectional survey (n = 878) was conducted to compare the psychometric properties of three preference-based and one nonpreference-based health-related quality of life measures among healthy subjects with and without treatment for dyslipidemia and/or hypertension and patients with coronary heart disease (CHD). All measures were stable over a 3 to 6 week period. Compared to the Time Trade-off (TTO) and the Standard Gamble (SG), the Rating Scale (RS) correlated with the SF-36 Health Survey most highly. In contrast to the SF-36 General Health Perception (GHP), the SF-36 Physical Component scale and the RS, the TTO and SG were less able to discriminate CHD patients with various levels of physical disability. Only the SF-36 GHP subscale and the RS were able to differentiate healthy participants from participants receiving dyslipidemia and/or hypertension treatment. Neither the SF-36 Physical or Mental Component scales were able to discriminate these two groups. Overall, these results suggest that unlike the RS, the TTO and the SG, as administered in this study, may not be sufficiently sensitive to measure the impact of primary cardiovascular disease prevention strategies on the health-related quality of life of the participants.
Imprecise values arise when bacterial colonies are too numerous to be counted or when no colonies grow at a specific dilution. Our objective was to show the usefulness of multiple imputation in analysing data containing imprecise values. We also indicate that interval censored regression, which is faster computationally in situations where it applies, can be used, providing similar estimates to imputation. We used bacteriological data from a large epidemiological study in daycare centres to illustrate this method and compared it to a standard method which uses single exact values for the imprecise data. The data consisted of numbers of FC on children's and educators' hands, from sandboxes and from playareas. In general, we found that multiple imputation and interval censored regression provided more conservative intervals than the standard method. The discrepancy in the results highlights both the importance of using a method that best captures the uncertainty in the data and how different conclusions might be drawn. This can be crucial for both researchers and those who are involved in formulating and regulating standards for bacteriological contamination.