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Biomedical subjects

J Siemiatycki

Publications and source records attributed to J Siemiatycki.

At least 19 recordsLinked to original sources
PubMed1992

Oral contraceptives and premenopausal bilateral breast cancer: a case-control study.

We estimated the effect of oral contraceptive (OC) use on premenopausal bilateral breast cancer in a matched case-control study. One hundred forty-four cases were identified from population-based registries of Los Angeles County, California, and of Connecticut and from the major hospitals in Montreal and Quebec City. Matched controls were the unaffected sisters of the cases. When age was included in the model, ever-use of OCs for 1 year or more was associated with an odds ratio 1.7 (95% confidence interval = 1.0-2.9). The odds ratios associated with 1-2, 3-6, and 7 years of use were 1.2 (0.61-2.4), 2.5 (1.2-5.3), and 2.0 (0.93-4.2), respectively. Too few women had used OCs before their first full-term pregnancy or before age 25 for these estimates to be informative. Restricting the analyses to women who had ever given birth yielded an odds ratio for ever-use of OCs of 2.1 (1.0-4.4). The results indicate an increased risk of premenopausal bilateral breast cancer associated with OC use.

Adult↗
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

Gastrointestinal health effects associated with the consumption of drinking water produced by point-of-use domestic reverse-osmosis filtration units.

During a prospective epidemiological study of gastrointestinal health effects associated with the consumption of drinking water produced by reverse-osmosis domestic units, a correlation was demonstrated between the bacterial counts on R2A medium incubated at 35 degrees C and the reported gastrointestinal symptoms in families who used these units. A univariate correlation was found with bacterial counts on R2A medium at 20 degrees C but was confounded by the bacterial counts at 35 degrees C. Other variables, such as family size and amount of water consumed, were not independently explanatory of the rate of illness. These observations raise concerns for the possibility of increased disease associated with certain point-of-use treatment devices for domestic use when high levels of bacterial growth occur.

Canada↗
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

Cancer incidence and risk factors among Montreal residents of Italian origin.

Cancer risks associated with Italian ethnicity were investigated using data from a large case-control study on the aetiology of several cancer sites in the male population of Montreal. Two approaches were taken. First, incidence rates were computed for Italians and for others in the Montreal area using our ascertained cases as numerators and census-derived denominators. Secondly, for respondents to the case-control study, an analysis was carried out with Italian ethnicity as the risk factor and a number of covariates as potential confounders. Out of 4553 incident cases in men aged 35-69, 301 were of Italian origin. As compared with other Montreal males, those of Italian origin had higher incidence rates for cancers of the stomach (p = 0.016, based on 31 cases) and of the colon and rectum (p = 0.102, based on 75 cases) and lower rates for cancer of the lung (p = 0.006) and prostate (p = 0.102, based on 24 cases). For other sites the differences between Montrealers of Italian and non-Italian origins were small. Montreal Italians manifested risks similar to those of the country of origin for cancer of the prostate and similar to the host country for cancers of the colon, rectum and liver. For other sites it was difficult to characterize the pattern because of wide variations among Italian registries. Over 80% of the study subjects in Montreal were interviewed and odds ratios (OR) for Italian ethnicity were estimated for each cancer site using all other sites as controls, adjusting for five potential confounders.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
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↗
PubMed1990

[Time clustering and temporospatial regrouping study of cases of juvenile diabetes in the district of Rhône (1960-1980)].

In order to study the relevance of the influence of environmental factors in Insulin-dependent Diabetes, we dressed a statistical analysis of season-related diabetes (Roger's test and Wallenstein's test). At the same time, we made a statistical analysis of space-time clusters of IDDM patients (Knox method and Mantel method). We noted an illness increase between August and February, although not significantly. The Wallenstein test clearly shows the existence of several significant season-related symptoms. As for the space-time clustering tests, and taking into account the relatively short duration of these environmental factors none in fact allows to assert the existence of such influences.

Adolescent↗
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↗
PubMed1989

Case-control study of IDDM.

Insulin-dependent diabetes mellitus (IDDM) may be caused by a combination of genetic predisposition and environmental insults. However, there are few solid leads concerning human diabetogenic environmental agents. A case-control study was carried out to investigate the possible relationships between IDDM and various biological, chemical, and psychological factors. All 161 cases of IDDM among children aged 0-17 yr occurring in Montreal from 1983 to 1986 were included. The parent of each newly diagnosed diabetic subject was asked to provide the names of two of the child's friends or neighbors who would be age and sex matched to serve as controls. For those unable to do so, matched controls were selected from a hospital emergency room. Parents of cases and controls were interviewed concerning many factors. There was little or no difference between cases and controls with regard to parental smoking habits, exposure to pets, and consumption of meat products high in nitrosamines. In univariate analyses, there was some indication of elevated risk for children who had not been breast-fed, who attended day care or nursery before age 5 yr, who lived in a crowded household at age 3 yr, or who had a history of asthma or eczema, although in multivariate analyses the only variables that had any effect were crowding and day-care attendance. In univariate and multivariate analyses, there was high risk of IDDM among children who had experienced selected stressful life events during the 12 mo preceding onset of IDDM or who had exhibited symptoms of social or psychological dysfunction during that time.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
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↗