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Biomedical subjects

H I Morrison

Publications and source records attributed to H I Morrison.

At least 19 recordsLinked to original sources
PubMed2005

Use of paediatric versus adult oncology treatment centres by adolescents 15-19 years old: the Canadian Childhood Cancer Surveillance and Control Program.

The aim of this study was to evaluate the treatment patterns of adolescents with cancer in Canada to ensure this population is receiving the most appropriate care. The Treatment and Outcome Surveillance (TOS) system was compared with the Canadian Cancer Registry (CCR) to estimate the proportion of adolescents (15-19 years) treated in Canadian paediatric oncology centres from 1995 to 2000 inclusive. Using TOS, the demographic, disease, and clinical characteristics of adolescents treated in paediatric versus adult centres in the Prairies were compared and differences were tested statistically. Approximately 30% of Canadian adolescents with cancer were treated in a paediatric centre. Adolescents treated in an adult centre were older at diagnosis and more likely to have carcinoma or germ cell tumours. The time between symptom onset and first treatment was longer for these adolescents, primarily due to the time between first health-care contact and assessment by a treating oncologist or surgeon. They were less likely to be enrolled in a clinical trial. These results suggest that care for adolescents with cancer in Canada is less satisfactory than for younger children, and can be improved.

Adolescent↗
PubMed2001

Low serum cholesterol concentration and risk of suicide.

Recent reports have suggested a link between low serum total cholesterol and risk of death from suicide. We examined this association using participants in the 1970-1972 Nutrition Canada Survey. We determined the mortality experience of Nutrition Canada Survey participants older than 11 years of age at baseline through 1993 by way of record linkage to the Canadian National Mortality Database. The relation between low serum total cholesterol and mortality from suicide was assessed using a stratified analysis (N = 11,554). There were 27 deaths due to suicide. Adjusting for age and sex, we found that those in the lowest quartile of serum total cholesterol concentration (<4.27 mmol/liter) had more than six times the risk of committing suicide (rate ratio = 6.39; 95% confidence interval = 1.27-32.1) as did subjects in the highest quartile (>5.77 mmol/liter). Increased rate ratios of 2.95 and 1.94 were observed for the second and third quartiles, respectively. The effect persisted after the exclusion from the analysis of the first 5 years of follow-up and after the removal of those who were unemployed or who had been treated for depression. These data indicate that low serum total cholesterol level is associated with an increased risk of suicide.

Adolescent↗
PubMed1999

End-stage renal disease in Canada: prevalence projections to 2005.

BACKGROUND: The incidence and prevalence of end-stage renal disease (ESRD) have increased greatly in Canada over the last 2 decades. Because of the high cost of therapy, predicting numbers of patients who will require dialysis and transplantation is necessary for nephrologists and health care planners. METHODS: The authors projected ESRD incidence rates and therapy-specific prevalence by province to the year 2005 using 1981-1996 data obtained from the Canadian Organ Replacement Register. The model incorporated Poisson regression to project incidence rates, and a Markov model for patient follow-up. RESULTS: Continued large increases in ESRD incidence and prevalence were projected, particularly among people with diabetes mellitus. As of Dec. 31, 1996, there were 17,807 patients receiving renal replacement therapy in Canada. This number was projected to climb to 32,952 by the end of 2005, for a relative increase of 85% and a mean annual increase of 5.8%. The increased prevalence was projected to be greatest for peritoneal dialysis (6.0% annually), followed by hemodialysis (5.9%) and functioning kidney transplant (5.7%). The projected annual increases in prevalence by province ranged from 4.4%, in Saskatchewan, to 7.5%, in Alberta. INTERPRETATION: The projected increases are plausible when one considers that the incidence of ESRD per million population in the United States and other countries far exceeds that in Canada. The authors predict a continued and increasing short-fall in resources to accommodate the expected increased in ESRD prevalence.

Adult↗
PubMed1999

Periodontal disease and risk of fatal coronary heart and cerebrovascular diseases.

BACKGROUND: Recent reports have implicated periodontal disease as a risk factor for coronary heart disease (CHD). METHODS: A retrospective cohort study was conducted using participants in the 1970-1972 Nutrition Canada Survey (NCS). The mortality experience of male and female NCS participants aged 35-84 years without self-reported CHD (n = 10,368) or cerebrovascular disease (CVD) (n = 11,251) was determined through 1993. The relation between dental health and the risk of fatal CHD and CVD was assessed using Poisson regression modeling. RESULTS: In total, 466 CHD and 210 CVD deaths were observed; missing confounder data reduced these numbers to 416 CHD and 182 CVD deaths. Adjusted for age, sex, diabetes status, serum total cholesterol, smoking, hypertensive status, and province, we found a statistically significant association between periodontal disease and risk of fatal CHD. Rate ratios (RR) of 2.15 [95% confidence interval (CI) 1.25-3.72) and 1.90 (95% CI 1.17-3.10) were observed for severe gingivitis and edentulous status, respectively. Non-statistically significantly increased RRs of 1.81 and 1.63 were observed for severe gingivitis and edentulous status for CVD. CONCLUSIONS: These data indicate that poor dental health is associated with an increased risk of fatal CHD.

Adult↗
PubMed1999

Health consequences of smoking among Canadian smokers: An update.

The expected number of deaths in four hypothetical Canadian cohorts (male current smokers, male never-smokers, female current smokers and female never-smokers) was examined by constructing abridged life tables. The expected number of premature deaths (before age 70) among lifelong smokers was found to be about twice that expected among lifelong never-smokers for both males (2.3) and females (1.9). The higher number of premature deaths in the smoking cohorts resulted mainly from cancer and coronary heart disease. The results of this paper highlight the dramatic impact that smoking has on premature mortality.

Adolescent↗
PubMed1998

Suicide mortality and pesticide use among Canadian farmers.

BACKGROUND: An exploratory, case-control study was used to investigate a new hypothesis about suicide among farm operators. This hypothesis suggested a biologically plausible link between exposures to certain pesticides and the occurrence of suicide among farm operators. These analyses were based on data from the Canadian Farm Operator Cohort. METHODS: Canadian male farm operators who committed suicide between 1971-1987 (n = 1,457) were compared with a frequency matched (by age and province) sample of control farm operators (n = 11,656) who were alive at the time of death of individual cases. Comparisons focused on past exposures to pesticides reported to the 1971 Canada Census of Agriculture. RESULTS: Multivariate logistic regression analyses indicated no associations between suicide and (1) acres sprayed with herbicides, (2) acres sprayed with insecticides, and (3) the costs of agricultural chemicals purchased; after controlling for important covariates. There was, however, a suggestive increase in risk for suicide associated with herbicide and insecticide spraying among a subgroup of farm operators who were most likely to be directly exposed to pesticides: OR = 1.71 (95% CI = 1.08-2.71) for 1-48 vs. 0 acres sprayed. Additional risk factors that were identified included seasonal vs. year-round farm work (OR = 1.68; 95% CI = 1.15-2.46); and high levels of paid labor on the farm (e.g., OR = 1.61; 95% CI = 1.24-2.10, for > 13 vs. 0 weeks per year). Factors that were protective included marriage (odds ratio (OR) = 0.69; 95% confidence interval (CI) = 0.58-0.81), having more than one person resident in the farm house (e.g., two vs. one person; OR = 0.62; 95% CI = 0.42-0.92); and higher levels of education (e.g., postsecondary vs. primary; OR = 0.40; 95% CI = 0.17-0.96). CONCLUSIONS: This study does not provide strong support for the main hypothesis under study, that exposure to pesticides is an important risk factor for suicide among farmers. Although secondary to the main hypothesis, a number of other risk factors for suicide were suggested. These have implications for the future study and targeting of suicide prevention programs in rural Canada.

Adult↗
PubMed1998

End-stage renal disease projections for Canada to 2005 using Poisson and Markov models.

BACKGROUND: End-stage renal disease (ESRD) incidence and prevalence are increasing in many countries worldwide. Due to the high cost of therapy, predicting future numbers of patients requiring dialysis and transplantation is necessary for health care planners. Projecting therapy-specific chronic disease prevalence is inherently problematic, and examples of suitable models and their application are sparse. When applied, rarely was the adequacy of such models evaluated. METHODS: We describe and illustrate a method for projecting therapy-specific ESRD prevalence in Canada for 1995-2005 using data obtained from the Canadian Organ Replacement Register. The projections combine the Poisson model for incidence rates and a Markov model for patient follow-up. Model adequacy is empirically validated by data-splitting. RESULTS: Large increases in ESRD prevalence are expected in Canada, with an average annual increase of 6.9% projected for 1995-2005. Upon validation, the projection model based on 1981-1987 data was able to predict 1994 prevalence within 1%, while projected therapy-specific prevalences closely approximated those observed. CONCLUSIONS: Therapy-specific ESRD prevalence was successfully projected using Poisson and Markov models. Where multistate prevalence forecasts are required, the method could be augmented for application to various other chronic diseases.

Adult↗
PubMed1998

Radon-progeny exposure and lung cancer risk in a cohort of Newfoundland fluorspar miners.

Although radon is a well-established lung carcinogen, there are uncertainties concerning the exposure-response relationship, whether exposures in early life are particularly hazardous, and how smoking affects the risks associated with radon exposure. A cohort study of the mortality experience of 1,743 underground fluorspar miners and 321 surface workers from 1950 to 1984 reported previously has been extended to include 6 additional years of follow-up (1985-1990). A statistically significant relationship was noted between radon-progeny exposure and risk of lung cancer mortality. Our analysis found no effect for age at first exposure. Attained age was strongly predictive of excess relative risk (ERR) per working level month (WLM) of radon exposure, falling from 0.025 for those aged less than 50 years to 0.002 for those 70 years or older. An inverse exposure-rate effect was also observed, wherein for equal total exposure, a high exposure rate (and short duration) is less harmful than a low exposure rate (and long duration). The ERR/WLM increased from 0.0019 for exposures of less than 10 years to 0.0076 for exposures of 20 or more years. The analysis of time-since-exposure windows revealed a greater ERR/WLM for exposures received in more recent periods, similar to the result for time since last exposure. Excess relative risks per WLM were higher for current smokers than for nonsmokers (never and former smokers). Analyses were consistent with a multiplicative relationship between radon-progeny exposure and current smoking and the risk of lung cancer. The assessment of radon exposure and lung cancer risk should incorporate the effects of exposure rate, time since exposure, smoking status and attained age.

Adult↗
PubMed1998

Physical activity, physical fitness, and risk of dying.

We examined the relation between physical activity, physical fitness, and all-cause mortality in a national population-based study of Canadians. We followed men and women ages 20-69 years who had participated in the Canada Fitness Survey between 1981 and 1988. We assessed risk factors for 6,246 men and 8,196 women using multivariate Poisson regression analysis. At baseline, all subjects were asymptomatic according to self-reported screening questions for cardiovascular disease. Men who expended > or =0.5 kilocalories per kilogram of body weight per day (KKD) experienced a 20% decline in risk of mortality [rate ratio (RR) = 0.82; 95% confidence interval (CI) = 0.65-1.04] when compared with subjects expending <0.5 KKD. We observed a 30% decline in risk of mortality among women expending > or =3.0 KKD relative to those expending <0.5 KKD (RR = 0.71; 95% CI = 0.45-1.11). Similar patterns of risk were evident for both men and women when analyses were restricted to participation in nonvigorous activities. Those who perceived themselves to be of less than average fitness were at increased risk of mortality (male RR = 1.64, 95% CI = 1.21-2.22; female RR = 1.66, 95% CI = 1.21-2.26). Subjects with undesirable cardiorespiratory fitness levels were more likely to die, compared with those having recommended fitness levels (RR = 1.52; 95% CI = 0.72-3.18). Fifty-three per cent of men and 35% of women reported participating in a vigorous activity. The relation between daily energy expenditure and risk of mortality in these subjects could not be evaluated, as there were few deaths. Nonetheless, our results among participants reporting no vigorous activities support the hypothesis that there is a reduction in mortality risk associated with even modest participation in activities of low intensity.

Adult↗
PubMed1998

Comorbid survival among elderly male participants of the Canada health survey: relevance to prostate cancer screening and treatment.

This study assessed the survival of a nationally representative sample of older Canadian men, taking into account common comorbid conditions. Mortality follow-up between 1978 and 1989 was conducted for male participants of the Canada Health Survey who were at least 60 years of age at baseline. The proportional hazards model and life table methods were used to examine survival by comorbidity status. Comorbid conditions examined included history of stroke and/or heart disease, high blood pressure, chronic bronchitis or emphysema, diabetes and smoking status, but excluded cancer because of small numbers. For those subjects aged 80 and older, comorbidity was not a significant predictor of survival. A large portion of men between the ages of 60 and 79, even those with pre-existing comorbid conditions, survived at least 10 years after interview. In a clinical setting, more detailed information on comorbid conditions can be obtained to better estimate long-term survival. Notwithstanding, our findings may have implications for the administration of population-based health interventions (e.g. the use of prostate-specific antigen [PSA] blood tests for the early detection of prostate cancer). In particular, our results suggest that there may be little benefit in restricting access to PSA screening based on survival probability in men under age 80.

Aged↗
PubMed1997

Two-stage sampling for etiologic studies. Sample size and power.

Preexisting computerized databases are potentially valuable sources of epidemiologic data. Since such databases are infrequently created specifically for etiologic research, data may be available for the exposure of interest and, through record linkage, for the endpoint of interest, but lacking for potential confounders. Because of the size of these databases, two-stage sampling is an efficient alternative to surveying the entire study population for confounder data. At stage 1, information on exposure and disease status is obtained for the entire study population. Confounder data are collected for probability-selected subsamples at stage 2. Logistic regression is performed on the stage 2 samples, with the parameter estimates and variances appropriately corrected to account for the stage 1 data. In this paper, the authors present methods for determining the required stage 2 sample size in the case of categorical exposure and confounding variables. Sample size tables, power curves, and a computer program have been produced to accommodate a binary exposure and a single binary confounder. With the increasing availability of preexisting yet incomplete databases, the potential for use of two-stage sampling will greatly increase in the future. This investigation provides a basis for estimating the number of participants to sample for the collection of confounder data at the second stage.

Case-Control Studies↗
PubMed1997

Hemodialysis versus peritoneal dialysis: a comparison of adjusted mortality rates.

Although kidney transplantation is the preferred treatment method for patients with ESRD, most patients are placed on dialysis either while awaiting transplantation or as their only therapy. The question of which dialytic method provides the best patient survival remains unresolved. Survival analyses comparing hemodialysis and continuous ambulatory peritoneal dialysis/continuous cyclic peritoneal dialysis (CAPD/CCPD), a newer and less costly dialytic modality, have yielded conflicting results. Using data obtained from the Canadian Organ Replacement Register, we compared mortality rates between hemodialysis and CAPD/CCPD among 11,970 ESRD patients who initiated treatment between 1990 and 1994 and were followed-up for a maximum of 5 years. Factors controlled for include age, primary renal diagnosis, center size, and predialysis comorbid conditions. The mortality rate ratio (RR) for CAPD/CCPD relative to hemodialysis, as estimated by Poisson regression, was 0.73 (95% confidence interval: 0.68 to 0.78). No such relationship was found when an intent-to-treat Cox regression model was fit. Decreased covariable-adjusted mortality for CAPD/CCPD held within all subgroups defined by age and diabetes status, although the RRs increased with age and diabetes prevalence. The increased mortality on hemodialysis compared with CAPD/CCPD was concentrated in the first 2 years of follow-up. Although continuous peritoneal dialysis was associated with significantly lower mortality rates relative to hemodialysis after adjusting for known prognostic factors, the potential impact of unmeasured patient characteristics must be considered. Notwithstanding, we present evidence that CAPD/CCPD, a newer and less costly method of renal replacement therapy, is not associated with increased mortality rates relative to hemodialysis.

Adolescent↗
PubMed1997

Coronary heart disease mortality among Newfoundland fluorspar miners.

OBJECTIVES: The association between cumulative radon exposure and coronary heart disease mortality was studied in a retrospective cohort investigation of Newfoundland fluorspar miners. METHODS: Multivariate Poisson regression techniques were used to estimate relative risks of coronary heart disease mortality by level of radon exposure. Relative risks (RR) were adjusted by attained age, calendar period, duration of exposure, and smoking status. Death from coronary heart disease was the outcome measure of interest and was identified by record linkage to the Canadian Mortality Database. RESULTS: An elevated risk of mortality from coronary heart disease was observed among miners with a cumulative radon exposure exceeding 1000 working-level months [RR 1.5, 95% confidence interval (95% CI) 0.77-2.75]. The association between radon exposure and coronary heart disease was not statistically significant according to a test for trend across exposure categories (P = 0.09). The smokers were 1.8 times more likely than the nonsmokers to die from coronary heart disease (95% CI 1.1-2.8). CONCLUSIONS: These results suggest a positive association between coronary heart disease and radon exposure. However, these findings should be interpreted cautiously due to the inability to control for the confounding influence of other known risk factors of coronary heart disease.

Adult↗
PubMed1997

Estimating lung cancer mortality from residential radon using data for low exposures of miners.

Some recent estimates of lung cancer risk from exposure to radon progeny in homes have been based on models developed from a pooled analysis of 11 cohorts of underground miners exposed to radon. While some miners were exposed to over 10,000 working level months (WLM), mean exposure among exposed miners was 162 WLM, about 10 times the exposure from lifetime residence in an average house and about three times the exposure from lifetime residence at the "action level" suggested by the U.S. Environmental Protection Agency. The extrapolation of lung cancer risk from the higher exposures in the miners to the generally lower exposures in the home is a substantial source of uncertainty in the assessment of the risk of indoor radon. Using the pooled data for the miners, analyses of lung cancer risk were carried out on data restricted to lower exposures, either <50 WLM or <100 WLM. In the pooled data, there were 115 lung cancer cases among workers with no occupational WLM exposure and 2,674 among exposed miners, with 353 and 562 lung cancer cases in miners with <50 WLM and <100 WLM, respectively. Relative risks (RRs) for categories of WLM based on deciles exhibited a statistically significant increasing trend with exposure in each of the restricted data sets. In the restricted data, there was little evidence of departures from a linear excess relative risk model in cumulative exposure, although power to assess alternative exposure-response trends was limited. The general patterns of declining excess RR per WLM with attained age, time since exposure and exposure rate seen in the unrestricted data were similar to the patterns found in the restricted data. Risk models based on the unrestricted data for miners provided an excellent fit to the restricted data, suggesting substantial internal validity in the projection of risk from miners with high exposures to those with low exposures. Estimates of attributable risk for lung cancer (10-14%) in the U.S. from residential radon based on models from the unrestricted data were similar to estimates based on the data for miners receiving low exposures.

Air Pollutants, Radioactive↗
PubMed1996

Serum folate and risk of fatal coronary heart disease.

OBJECTIVE: To assess the relationship between serum folate level and the risk of fatal coronary heart disease (CHD) among men and women. DESIGN: Retrospective cohort study with serum folate levels measured from September 1970 to December 1972, with follow-up through 1985. SETTING: Participants in the Nutrition Canada Survey. PARTICIPANTS: A total of 5056 Canadian men and women aged 35 to 79 years with no history of self-reported CHD. MAIN OUTCOME MEASURE: Fifteen-year CHD mortality. RESULTS: A total of 165 CHD deaths were observed. We found a statistically significant association between serum folate level and risk of fatal CHD, with rate ratios for individuals in the lowest serum folate level category (<6.8 nmol/L [3 ng/mL]) compared with the highest category (>13.6 nmol/L [6 ng/mL]) of 1.69 (95% confidence interval, 1.10-2.61). CONCLUSIONS: These data indicate that low serum folate levels are associated with an increased risk of fatal CHD.

Adult↗
PubMed1995

Lung cancer in radon-exposed miners and estimation of risk from indoor exposure.

BACKGROUND: Radioactive radon is an inert gas that can migrate from soils and rocks and accumulate in enclosed areas, such as homes and underground mines. Studies of miners show that exposure to radon decay products causes lung cancer. Consequently, it is of public health interest to estimate accurately the consequences of daily, low-level exposure in homes to this known carcinogen. Epidemiologic studies of residential radon exposure are burdened by an inability to estimate exposure accurately, low total exposure, and subsequent small excess risks. As a result, the studies have been inconclusive to date. Estimates of the hazard posed by residential radon have been based on analyses of data on miners, with recent estimates based on a pooling of four occupational cohort studies of miners, including 360 lung cancer deaths. PURPOSE: To more fully describe the lung cancer risk in radon-exposed miners, we pooled original data from 11 studies of radon-exposed underground miners, conducted a comprehensive analysis, and developed models for estimating radon-associated lung cancer risk. METHODS: We pooled original data from 11 cohort studies of radon-exposed underground miners, including 65,000 men and more than 2700 lung cancer deaths, and fit various relative risk (RR) regression models. RESULTS: The RR relationship for cumulative radon progeny exposure was consistently linear in the range of miner exposures, suggesting that exposures at lower levels, such as in homes, would carry some risk. The exposure-response trend for never-smokers was threefold the trend for smokers, indicating a greater RR for exposure in never-smokers. The RR from exposure diminished with time since the exposure occurred. For equal total exposure, exposures of long duration (and low rate) were more harmful than exposures of short duration (and high rate). CONCLUSIONS: In the miners, about 40% of all lung cancer deaths may be due to radon progeny exposure, 70% of lung cancer deaths in never-smokers, and 39% of lung cancer deaths in smokers. In the United States, 10% of all lung cancer deaths might be due to indoor radon exposure, 11% of lung cancer deaths in smokers, and 30% of lung cancer deaths in never-smokers. This risk model estimates that reducing radon in all homes exceeding the U. S. Environmental Protection Agency's recommended action level may reduce lung cancer deaths about 2%-4%. These estimates should be interpreted with caution, because concomitant exposures of miners to agents such as arsenic or diesel exhaust may modify the radon effect and, when considered together with other differences between homes and mines, might reduce the generalizability of findings in miners.

Adult↗
PubMed1995

Radon and cancers other than lung cancer in underground miners: a collaborative analysis of 11 studies.

BACKGROUND: Exposure to the radioactive gas radon and its progeny (222Rn and its radioactive decay products) has recently been linked to a variety of cancers other than lung cancer in geographic correlation studies of domestic radon exposure and in individual cohorts of occupationally exposed miners. PURPOSE: This study was designed to characterize further the risks for cancers other than lung cancer (i.e., non-lung cancers) from atmospheric radon. METHODS: Mortality from non-lung cancer was examined in a collaborative analysis of data from 11 cohorts of underground miners in which radon-related excesses of lung cancer had been established. The study included 64,209 men who were employed in the mines for 6.4 years on average, received average cumulative exposures of 155 working-level months (WLM), and were followed for 16.9 years on average. RESULTS: For all non-lung cancers combined, mortality was close to that expected from mortality rates in the areas surrounding the mines (ratio of observed to expected deaths [O/E] = 1.01; 95% confidence interval [CI] = 0.95-1.07, based on 1179 deaths), and mortality did not increase with increasing cumulative exposure. Among 28 individual cancer categories, statistically significant increases in mortality for cancers of the stomach (O/E = 1.33; 95% CI = 1.16-1.52) and liver (O/E = 1.73; 95% CI = 1.29-2.28) and statistically significant decreases for cancers of the tongue and mouth (O/E = 0.52; 95% CI = 0.26-0.93), pharynx (O/E = 0.35; 95% CI = 0.16-0.66), and colon (O/E = 0.77; 95% CI = 0.63-0.95) were observed. For leukemia, mortality was increased in the period less than 10 years since starting work (O/E = 1.93; 95% CI = 1.19-2.95) but not subsequently. For none of these diseases was mortality significantly related to cumulative exposure. Among the remaining individual categories of non-lung cancer, mortality was related to cumulative exposure only for cancer of the pancreas (excess relative risk per WLM = 0.07%; 95% CI = 0.01-0.12) and, in the period less than 10 years since the start of employment, for other and unspecified cancers (excess relative risk per WLM = 0.22%; 95% CI = 0.08-0.37). CONCLUSIONS: The increases in mortality from stomach and liver cancers and leukemia are unlikely to have been caused by radon, since they are unrelated to cumulative exposure. The association between cumulative exposure and pancreatic cancer seems likely to be a chance finding, while the association between cumulative exposure and other and unspecified cancers was caused by deaths certified as due to carcinomatosis (widespread disseminated cancer throughout the body) that were likely to have been due to lung cancers. This study, therefore, provides considerable evidence that high concentrations of radon in air do not cause a material risk of mortality from cancers other than lung cancer. IMPLICATIONS: Protection standards for radon should continue to be based on consideration of the lung cancer risk alone.

Adult↗