Biomedical subjects

R Dewar

Publications and source records attributed to R Dewar.

At least 37 records · Page 2Linked to original sources

PubMed1992

Occupational exposure to sulfuric acid in southern Ontario, Canada, in association with laryngeal cancer.

A case-referent study, designed to test associations between asbestos, nickel, and the development of laryngeal cancer, was conducted in southern Ontario in 1977-1979. The cases were individually matched to neighborhood referents for gender and age. This constituted the primary study. Personal interviews had secured tobacco, alcohol, and detailed work histories. To 183 of the male pairs was added retrospective assessments of sulfuric acid exposure for each job, blind of disease status; this constituted the data base for an augmented secondary analysis. Logistic regression revealed statistically significant odds ratios when tobacco and alcohol were controlled. Exposure-response gradients were strongly positive with odds ratios in the range of 1.97 [95% confidence interval (95% CI) 0.63-6.13] for short duration-low level exposure through 6.91 [95% CI 2.20-21.74] for long duration-higher level exposure employing progressively more specific definitions of exposure. Asbestos as a confounder and the interaction terms examined were nonsignificant. These findings are corroborative of those of other studies.

Adult↗

PubMed1991

A retrospective study of myocardial infarction occurring in elderly patients in a coronary care unit.

Myocardial infarction is a major cause of morbidity and mortality particularly in the elderly. Coronary Care Unit monitoring has resulted in the improvement in prognosis in all age groups. In this study, the clinical course and outcome of 204 consecutive patients with acute myocardial infarction aged over 65 years is retrospectively analysed. All patients were managed in a Coronary Care Unit operating a needs related policy. Those under 75 years (120 patients) were compared to those over that age (84 patients). The groups differed in terms of clinical presentation, cardiac enzymatic rise and response to drug therapy. However they had similar complication rates, morbidity and mortality.

Age Factors↗

PubMed1991

The apex cardiac beat: not a reliable clinical sign in elderly patients.

To assess its reliability as a marker of cardiomegaly in elderly patients, we compared a clinical assessment of heart size with that calculated from chest radiography. In 100 hospitalized subjects of median age 78 years, the apex beat was palpable in only 35% and its palpability declined with increasing age. Even when palpable, the apex beat had low specificity (74%) and sensitivity (69%) as a marker of cardiomegaly and its positive predictive value (69%) and negative predictive value (74%) were poor. The clinical assessment of heart size in elderly hospitalized patients should be interpreted with caution.

Age Factors↗

PubMed1991

A randomized trial to evaluate the risk of gastrointestinal disease due to consumption of drinking water meeting current microbiological standards.

BACKGROUND: This project directly and empirically measured the level of gastrointestinal (GI) illness related to the consumption of tapwater prepared from sewage-contaminated surface waters and meeting current water quality criteria. METHODS: A randomized intervention trial was carried out; 299 eligible households were supplied with domestic water filters (reverse-osmosis) that eliminate microbial and chemical contaminants from their water, and 307 households were left with their usual tapwater without a filter. The GI symptomatology was evaluated by means of a family health diary maintained prospectively by all study families over a 15-month period. RESULTS: The estimated annual incidence of GI illness was 0.76 among tapwater drinkers compared with 0.50 among filtered water drinkers (p less than 0.01). These findings were consistently observed in all population subgroups. CONCLUSION: It is estimated that 35% of the reported GI illnesses among the tapwater drinkers were water-related and preventable. Our results raise questions about the adequacy of current standards of drinking water quality to prevent water-borne endemic gastrointestinal illness.

Adolescent↗

PubMed1990

Measuring blood pressure in the elderly: does atrial fibrillation increase observer variability?

OBJECTIVE: To compare the interobserver and intraobserver variability of blood pressure measurements in geriatric patients in atrial fibrillation and in sinus rhythm. DESIGN: Prospective assessment of blood pressure measurements carried out in random order in two groups of elderly patients by five doctors unaware of the aims of the study. SETTING: Acute assessment wards for geriatric medicine, Cardiff Royal Infirmary. PATIENTS: 50 Elderly patients in sinus rhythm and 50 in atrial fibrillation. MAIN OUTCOME MEASURES: Interobserver and intraobserver variability of blood pressure measurements in the two groups expressed as the coefficient of variability and compared by the Mann-Whitney U test. RESULTS: Interobserver variability was significantly greater in the patients with atrial fibrillation for both systolic and diastolic pressures. Intraobserver variability was significantly greater in the atrial fibrillation group for diastolic pressures but the difference was not significant for systolic pressures. These differences were not related to pulse rate, age, or level of blood pressure. CONCLUSIONS: The findings suggest that in the presence of atrial fibrillation physicians' interpretations of Korotkoff sounds are less uniform, which may have important clinical implications. Possibly a standardised methodology may overcome this problem.

Aged↗

PubMed1990

Silica and cancer associations from a multicancer occupational exposure case-referent study.

A multicancer site, multifactor case-control study was undertaken to generate hypotheses about possible occupational carcinogens. Eligible cases, comprising all incident cases of cancer at 14 sites who were male, aged 35-70 and resident in Montreal, were subjected to probing interviews designed to obtain detailed lifetime job histories and information on potential confounders. Each job history was reviewed by a team of chemists who translated it into a history of occupational exposures. These occupational exposures were then analysed as potential risk factors in relation to the sites of cancer included. Over 3700 cases were interviewed and processed. For each site of cancer analysed as a case series, controls were selected from subjects with cancer at the other sites covered in the study. This report concerns the associations between silica exposure and each site of cancer. In initial screening analyses, there were significantly elevated odds ratios for silica and stomach cancer and for silica and non-adenocarcinoma lung cancer. More detailed analyses confirmed these associations, though there was no evidence of a dose-response relationship for stomach cancer. For lung cancer, there were significantly elevated risks in those with high-level long-term exposure. These results, which took into account several potential confounders including cigarette smoking and asbestos exposure, lend credence to the hypothesis that silica exposure increases the risk of lung cancer, and suggest the possibility of an effect on stomach cancer.

Adult↗

PubMed1989

Cancer risks due to occupational exposure to formaldehyde: results of a multi-site case-control study in Montreal.

A case-control study was undertaken in Montreal to investigate the possible associations between occupational exposures and cancers of the following sites: oesophagus, stomach, colo-rectum, liver, pancreas, lung, prostate, bladder, kidney, melanoma and lymphoid tissue. In total, 3,726 cancer patients and 533 population controls were interviewed to obtain detailed lifetime job histories and information on potential confounders. Each job history was translated into a history of occupational exposures. Because of current concerns about formaldehyde carcinogenicity, we carried out a special analysis of the association between exposure to formaldehyde and each type of cancer covered by this study. Separate statistical analyses were carried out for each type of cancer using population controls as well as a control series drawn from among the other cancer sites in the study. Although nearly a quarter of all subjects had undergone occupational exposure to formaldehyde, the levels of exposure were in general quite low. There was no persuasive evidence of an increased risk of any type of cancer among men exposed to these levels of formaldehyde. However, the possibility of a small increase in risk could not be ruled out.

Adult↗

PubMed1989

Cancer risks associated with 10 inorganic dusts: results from a case-control study in Montreal.

A multicancer site, multifactor case-control study was undertaken to generate hypotheses about possible occupational carcinogens. Probing interviews were carried out with eligible cases, comprising all incident cases of 20 types of cancer who were male, aged 35-70 years, and a resident in Montreal. The interview was designed to obtain detailed lifetime job histories and information on potential confounders. Each job history was reviewed by a team of chemists and industrial hygienists who translated it into a history of occupational exposures. These occupational exposures were then analyzed as potential risk factors in relation to the sites of cancer included; 3,726 cases were interviewed. For each site of cancer analyzed, controls were selected from among the other sites in the study. This report concerns the associations between the 12 main types of cancer in our series and 10 inorganic dusts that are found mainly in construction and metal industries. All site-exposure combinations were investigated. After intensive control for confounding, nonadenocarcinoma (NAC) of the lung was associated with long duration-high level exposure to silica (odds ratio [OR] = 1.4), excavation dust (OR = 1.9), concrete dust (OR = 2.5), abrasives dust (OR = 1.4), and alumina (OR = 1.5). It was difficult to disentangle the relative effects of those substances, and confounding among them was a distinct possibility. Although residual confounding by some uncontrolled factors may explain the elevated ORs, the results were compatible with the hypothesis of a nonspecific relation between NAC of the lung and respirable inorganic dusts as a class. Other associations that remained suggestive after in-depth analysis were silica and stomach cancer (OR = 1.2) and concrete dust and lymphoma (OR = 2.9).

Adult↗

PubMed1989

Costs and statistical power associated with five methods of collecting occupation exposure information for population-based case-control studies.

The ascertainment of information on past occupational exposure of study subjects is perhaps the main problem in case-control studies of occupational risk factors. Several methods have been proposed and used but little is known of their relative merits. The present study, undertaken in the context of a large ongoing case-control study of occupational cancer in Montreal, was designed to compare the costs of and statistical power to be derived from five plausible methods of data collection: 1) job titles abstracted from routine records, 2) job titles abstracted from routine records and processed through a job exposure matrix to derive exposure data, 3) job titles obtained by interview, 4) job titles obtained by interview and processed through a job exposure matrix to derive exposure data, and 5) job descriptions obtained by interview and processed by a team of experts to derive exposure data. Statistical power of the five methods was derived for 160 hypothetical risk factors, partly on the basis of empirical data from the data set and partly on the basis of some theoretical constructs. The design based on interview and expert evaluation was used as a reference, and the degree of misclassification of other methods was estimated in relation to this reference. For fixed sample size the interview and expert evaluation design was estimated to be much more costly than the others, but it provides much greater statistical power for detecting risks. Under the conditions of this investigation, this design was the most cost-effective. However, it is not clear to what extent this finding is generalizable.

Case-Control Studies↗

PubMed1988

Smoking and degree of occupational exposure: are internal analyses in cohort studies likely to be confounded by smoking status?

Occupational cohort studies are usually carried out without the benefit of information on smoking habits of cohort members. One common approach to avoid confounding bias related to smoking habits is to carry out an internal analysis, comparing workers with different degrees of occupational exposure. The premise behind this approach is that within a cohort there is unlikely to be correlation between degree of exposure and smoking habits. If this were untrue, smoking could confound the disease-exposure relationships. Our purpose was to verify the premise. The study sample consisted of 857 French-Canadian men born between 1910 and 1930, with 11 or fewer years of education, and interviewed around 1980 in the context of an occupational cancer case-control study. For each man we had information on smoking habits, job history, and a history of the chemicals he was exposed to in each of his jobs. We computed two indices of the dirtiness of workers' job histories: one based on the job titles held by the man and a second based on the degree of exposures to workplace substances. There was no correlation between these indices of job dirtiness and smoking history. We also examined the smoking-exposure relationship among the subsets of men who had been occupationally exposed to ten especially noticeable substances. Within the subsets, there was no indication of a consistent difference among the smoking subgroups in level or duration of exposure to these index substances. These findings do not support the view that nonsmokers sought out cleaner job environments than smokers; they imply that internal analyses of "dose-response" in cohort studies are unlikely to be seriously confounded by smoking habits.

Adult↗

PubMed1988

Degree of confounding bias related to smoking, ethnic group, and socioeconomic status in estimates of the associations between occupation and cancer.

In occupational cancer epidemiology, many studies are carried out without access to information on smoking and other potential confounding variables. It is unclear whether such deficiencies are likely to cause serious bias in estimates of cancer-occupation associations. An empiric investigation was carried out to determine the effect of inclusion or exclusion of three variables--smoking, ethnic group, and socioeconomic status--on estimates of odds ratios (OR) between 25 occupations and three types of cancer--lung, bladder, and stomach. Of the 75 associations studied, only one OR was distorted by more than 40% when comparing unadjusted with adjusted estimates; three were distorted by between 30% and 40%; four others by between 20% and 30%. Of the eight associations which were distorted by more than 20%, seven involved lung cancer and one involved bladder cancer; none involved stomach cancer. An additional analysis was carried out on the 25 lung cancer-occupation associations to determine whether the nature of the stratification on smoking (ie, whether crude or "precise" categories were used) gave different OR estimates. The differences in ORs induced by different parametrizations of the smoking variable were relatively small. Our results support the view that relative risks between lung cancer and occupation in excess of 1.4 are unlikely to be artifacts due to uncontrolled confounding. For bladder and stomach cancer, the corresponding cut point may be as low as 1.2. In studies of occupation and cancer, uncontrolled confounding due to smoking and social class may not be as serious a threat to the integrity of results as is sometimes feared.

Adult↗

PubMed1988

Incidence of IDDM in Montreal by ethnic group and by social class and comparisons with ethnic groups living elsewhere.

We examined the incidence of insulin-dependent diabetes mellitus (IDDM) among children aged 0-14 yr in Montreal by social class and by ethnic group from 1971 to 1985. There was a slightly higher risk in wealthier as opposed to poorer classes. This income gradient was more marked in younger than in older children. Children of French extraction had about two-thirds the risk of IDDM of children of other origins, mainly British and other European. This mimics the patterns of risk in Europe, where France is reported to have lower rates than does Britain and Scandinavia. The absolute levels of risks among French Canadian and Jewish Canadian children were about double those reported from France and Israel, respectively. These various results are compatible with the hypothesis that both genetic and environmental factors influence IDDM risk.

Adolescent↗

PubMed1988

Associations between several sites of cancer and ten types of exhaust and combustion products. Results from a case-referent study in Montreal.

A population-based case-referent study provided information on the associations between several types of cancer and 10 types of exhaust and combustion products. All site-exposure combinations were investigated. An increased lung cancer risk, in particular squamous-cell cancers, due to exposure to gasoline and diesel exhausts was found. Among the associations that have not been subject to previous attention, the most promising leads for further investigation are the possible relations between gasoline and diesel exhaust and colorectal cancers, gasoline exhaust and kidney cancer, coal combustion products and pancreatic cancer (and possibly nonadenocarcinoma lung cancer), combustion products of heating oil and prostatic cancer, and natural-gas combustion products and bladder cancer.

Adult↗

PubMed1987

Associations between several sites of cancer and twelve petroleum-derived liquids. Results from a case-referent study in Montreal.

A population-based case-referent study provided information on the associations between several types of cancer and 12 petroleum-derived liquids. All site-exposure combinations were investigated. The most interesting results concerned the following combinations: leaded gasoline-stomach cancer, aviation gasoline-kidney cancer (and the possible implications of this association for a similar effect of unleaded automotive gasoline), mineral spirits-squamous-cell cancer of the lung, diesel fuel-nonadenocarcinoma lung cancer, lubricating oils-squamous-cell lung cancer, cutting fluids-bladder cancer, other mineral oils-bladder cancer, mineral spirits-prostate cancer, diesel fuel-prostate cancer, and lubricating oils-prostate cancer.

Humans↗

PubMed1987

Discovering carcinogens in the occupational environment. Methods of data collection and analysis of a large case-referent monitoring system.

A multi-cancer site, multi-factor, case-referent study was undertaken to generate hypotheses about possible occupational carcinogens. About 20 types of cancer were included. Incident cases among men aged 35-70 years and diagnosed in any of the major Montreal hospitals were eligible. Probing interviews were carried out for 3 726 eligible cases. The interview was designed to obtain detailed lifetime job histories and information on potential confounders. Each job history was reviewed by a team of chemists who translated it into a history of occupational exposures. These occupational exposures were then analyzed as potential risk factors in relation to the sites of cancer included. For each site of cancer analyzed, referents were selected from among the other sites in the study. The analysis was carried out in stages. First a Mantel-Haenszel analysis was undertaken of all cancer-substance associations, stratifying on a limited number of covariates, and, then, for those associations which were noteworthy in the initial analysis, a logistic regression analysis was made taking into account all potential confounders. This report describes the fieldwork and analytical methods.

Carcinogens, Environmental↗

PubMed1986

Associations between several sites of cancer and nine organic dusts: results from an hypothesis-generating case-control study in Montreal, 1979-1983.

A multi-cancer site, multi-factor case-control study was undertaken to generate hypotheses about possible occupational carcinogens. Probing interviews were carried out with over 2,000 subjects. All incident cases of 19 sites of cancer in males aged 35-70 and resident in Montreal were eligible. The interview was designed to obtain detailed lifetime job histories, and information on potential confounders. Each job history was reviewed by a team of chemists who translated it into a history of occupational exposures. These occupational exposures were then analyzed as potential risk factors in relation to the sites of cancer included. For each site of cancer analyzed as a case series, controls were selected from among the other cancer sites in the study. This report concerns the associations between sites of cancer for which there were over 100 cases processed (stomach; colorectal, also analyzed by subsites; lung; prostate; bladder; kidney; non-Hodgkin's lymphoma) and nine organic dusts (wood; paper; grain; flour; fabrics; cotton; wool; synthetics; fur). All site-exposure combinations were investigated. The ones that provided the most interesting leads were lung-wood dust (odds ratio (OR) = 1.5), stomach-wood dust (OR = 1.5), colorectal-synthetic fiber (OR = 1.5), bladder-synthetic fiber (OR = 1.8), non-Hodgkin's lymphoma-cotton dust (OR = 1.9), colon-grain dust (OR = 2.6), prostate-grain dust (OR = 2.2), and prostate-paper dust (OR = 2.0). Only the associations with wood dust, synthetic fibers and cotton dust showed some evidence of "dose-response" with duration of exposure. Because it is such a common exposure and appears to increase lung and stomach cancer risks, wood dust may be responsible for a great deal of occupational cancer.

Adult↗

PubMed1985

The problem of multiple inference in studies designed to generate hypotheses.

Epidemiologic research often involves the simultaneous assessment of associations between many risk factors and several disease outcomes. In such situations, often designed to generate hypotheses, multiple univariate hypothesis-testing is not an appropriate basis for inference. The number of true positive associations in a collection of many associations can be estimated by comparing the observed distribution of p values for the positive associations to a theoretical uniform distribution, or to the observed distribution of negative associations, or to an empiric randomization distribution. None of these approaches, however, will distinguish the true from the false positive associations. Various criteria for selecting a subset of associations to report are considered by the authors, including Bonferoni adjustment of p values, splitting the sample for searching and testing, Bayesian inference, and decision theory. The authors prefer an approach in which all associations in the data are reported, whether significant or not, followed by a ranking in order of priority for investigation using empirical Bayes techniques. Methods are illustrated by application to preliminary data from a study aimed at identifying hitherto unsuspected occupational carcinogens.

Bayes Theorem↗

PubMed1985

Dispersed repetitive DNA sequence of Mucor racemosus.

A dispersed repetitive DNA sequence has been identified within the genome of the fungus Mucor racemosus. Recombinant phage clones, as well as a plasmid harboring the sequence, have been isolated. Examination of cloned fragments comprising part of the repetitive sequence has led to a partial characterization of the element. The sequence has been detected in other Mucor species, and although the apparent number and chromosomal position of the repetitive sequence vary from strain to strain, it is clear that at least portions of the element have been conserved.

DNA, Fungal↗