Modeling the intraurban variability of ambient traffic pollution in Toronto, Canada.

The objective of this paper is to model determinants of intraurban variation in ambient concentrations of nitrogen dioxide (NO2) in Toronto, Canada, with a land use regression (LUR) model. Although researchers have conducted similar studies in Europe, this work represents the first attempt in a North American setting to characterize variation in traffic pollution through the LUR method. NO2 samples were collected over 2 wk using duplicate two-sided Ogawa passive diffusion samplers at 95 locations across Toronto. Independent variables employed in subsequent regression models as predictors of NO2 were derived by the Arc 8 geographic information system (GIS). Some 85 indicators of land use, traffic, population density, and physical geography were tested. The final regression model yielded a coefficient of determination (R2) of .69. For the traffic variables, density of 24-h traffic counts and road measures display positive associations. For the land use variables, industrial land use and counts of dwellings within 2000 m of the monitoring location were positively associated with NO2. Locations up to 1500 m downwind of major expressways had elevated NO2 levels. The results suggest that a good predictive surface can be derived for North American cities with the LUR method. The predictive maps from the LUR appear to capture small-area variation in NO2 concentrations. These small-area variations in traffic pollution are probably important to the exposure experience of the population and may detect health effects that would have gone unnoticed with other exposure estimates.

The relationship between parental occupation and bone cancer risk in offspring.

BACKGROUND: Bone cancers in children are serious and highly fatal conditions, yet relatively little is known about their causes or methods of prevention. METHODS: The relationship between parental occupation and bone cancer in offspring was explored in a case-control study. Cases were identified from the Ontario Cancer Registry; population-based controls were matched on sex and age. Data were collected from their parents through the use of a mailed self-administered questionnaire. RESULTS: The odds ratio estimates (OR) for bone cancer were elevated for fathers in the social sciences (OR = 2.5, 95% confidence interval [CI]: 0.7-8.4). Risk of Ewing's sarcoma was significantly high among children with fathers in social sciences (OR = 6.2, 95% CI: 1.6-24.5) and mothers in teaching (OR = 3.1, 95% CI: 1.1-8.7) or farming (OR = 7.8, 95% CI: 1.9-31.7). Osteosarcoma risk was increased for fathers in farming (OR = 2.1, 95% CI: 0.8-5.7), and mothers in managerial and administrative work (OR = 2.3, 95% CI: 0.6-8.1), and product fabricating, assembling, and repairing (OR = 2.0, 95% CI: 0.6-7.2). CONCLUSIONS: Certain methodological problems plague studies of bone cancer in children (e.g. small studies, low statistical power, analysis of multiple occupational categories, difficulty in identifying specific carcinogenic agents). These associations require further investigation, especially as elevated risks have been reported previously for agricultural occupations.

A cohort study of mortality among Ontario pipe trades workers.

AIMS: To study mortality in a cohort of members of the United Association of Journeymen and Apprentices of the Plumbing and Pipe Fitting Industry of the United States and Canada and to compare results with two previous proportional mortality studies. METHODS: A cohort of 25,285 workers who entered the trade after 1949 was assembled from records of the international head office. Mortality was ascertained by linkage to the Canadian Mortality Registry at Statistics Canada. Standardised mortality ratios were computed using Ontario general population mortality rates as the reference. RESULTS: There were significant increases in lung cancer mortality rates (SMR 1.27; 95% CI 1.13 to 1.42). Increased lung cancer risk was observed among plumbers, pipefitters, and sprinkler fitters. Increased risk was observed among workers joining the Union as late as the 1970s. A random effects meta-analysis of this study and the two PMR studies found significant increases in oesophageal (RR 1.24; 95% CI 1.00 to 1.53), lung (RR 1.31; 95% CI 1.19 to 1.44), and haematological/lymphatic (RR 1.21; 95% CI 1.08 to 1.35) malignancies. CONCLUSIONS: The mortality pattern is consistent with the effects of occupational exposure to asbestos. Increased risk due to other respiratory carcinogens such as welding fume cannot be excluded. There are substantial amounts of asbestos in place in industrial and commercial environments. The education and training of workers to protect themselves against inhalation hazards will be necessary well into the future.

Is brain cancer an occupational disease of cardiologists?

OBJECTIVE: To assess the plausibility of radiation as a cause of the statistically unusual event of two cardiologists in Toronto, Ontario who were diagnosed with brain tumours in 1997. DESIGN: Computation of the expected occurrence of brain cancer in Ontario cardiologists and review of the epidemiological literature pertaining to radiation and brain cancer. DATA SYNTHESIS: The occurrence of these two cases is a statistically unusual event--a 'cluster'. There are several plausible explanations for this cluster. First, this may be a chance occurrence, and the tumours may have no causative factors in common. Second, the cause may be radiation exposure. A connection to occupational radiation exposure is biologically plausible, but risk assessment suggests that it is unlikely that this effect would have been observable in the small population of Ontario cardiologists. CONCLUSIONS: Initiation of brain tumours during cardiac fluoroscopic procedures is plausible. Physicians are reminded to practise radiation safety methods during fluoroscopic procedures. The diagnosis of two additional brain tumours in Canadian interventional cardiologists during the past 10 years would confirm the occupational causation theory. The author invites physicians to report knowledge of the diagnosis of brain tumours in Canadian cardiologists to the author or to the editors.

Silicosis surveillance in Ontario from 1979 to 1992.

This paper reports the detection rates of silicosis among silica-exposed persons first exposed to dust in 1950 or later and still employed in 1979 or later in the province of Ontario. The rate varied strongly with latency, being less than two new cases per 10 000 examinations during the first two decades from first exposure, reaching two new cases per 1000 examinations at 27 years from first exposure, and averaging between two and four new cases per 1000 examinations thereafter. A Poisson regression analysis found that the silicosis rate in the interval after 30 years from first exposure was more than 16 times higher than the rate prior to 20 years from first exposure. There was no significant difference in the diagnosis rates among the workers in the mining, primary metal, and nonmetallic mineral industries sectors. The rate of silicosis was higher among smokers than among never smokers (rate ratio 1.54).

Obesity, cigarette smoking and the cost of physicians' services in Ontario.

BACKGROUND: This report uses population-based individual-level data to compute direct estimates of the costs of physicians' services in Ontario in relation to Body Mass Index (BMI) and smoking. METHODS: Subjects were 2,170 respondents to the National Population Health Survey who approved linkage to the Ontario Health Insurance Plan. RESULTS: The mean per capita cost of physicians' services in Ontario increased by $8.90 (95% CI: $1.90-$15.60) for each unit increase in BMI and by $1.75 (95% CI: $0.11-$3.40) for every year of daily smoking. The annual attributable cost of smoking and overweight among residents of Ontario, aged 40-79, was estimated at $275,000,000. CONCLUSIONS: Overweight and smoking are responsible for large costs to the health care system. The cost of public health initiatives could be easily recovered if they were successful in making only moderate changes to the levels of smoking and body weight in the population.

Silicosis, radon, and lung cancer risk in Ontario miners.

The presence of radiographic silicosis was assessed as a risk factor for lung cancer in a cohort and case-control study of miners in the Ontario Silicosis Surveillance Database. Subjects were 328 miners with silicosis matched on age to 970 miners with normal radiographs. In a cancer incidence follow-up, there was a significant excess of lung cancer among miners with silicosis (Standardized Incidence Ratio 2.55; 95% Confidence Interval 1.43-8.28). Miners with normal radiographs had lung cancer incidence about the same as the Ontario average (Standardized Incidence Ratio 0.90; 95% Confidence Interval 0.51-1.47). In a matched case-control analysis of lung cancer, cumulative radon exposure was associated with lung cancer risk (increase in odds ratio 0.4% per WLM; 95% Confidence Interval -0.3% to 1.1%). When the presence of silicosis was added to the model, silicosis was a highly significant risk factor for lung cancer (Odds Ratio 6.99 95% Confidence Interval 1.91-25) and the risk factor for radon was diminished (increase in Odds Ratio -0.5% per WLM; 95% confidence Interval -1.4% to 0.4%). This finding suggests that additional study is warranted before concluding that radon risk factors derived from mining populations do not need to be modified for application to the general population.

Mortality among workers exposed to carbon disulfide.

Mortality experience was investigated at a plant in Ontario that produced viscose rayon, with carbon disulfide as a main raw material. Work-history records for 279 deceased workers at the plant (plant A) were obtained and compared with those for 511 deceased workers at a pulp and paper plant in the same city (plant B). In a proportional mortality analysis, using as a reference the general population of Ontario, at both plants there were fewer deaths from ischemic heart disease than expected (the proportional mortality ratios [PMRs] were 83 at plant A and 95 at plant B) but more deaths than expected from cerebrovascular disease (PMRs were 115 at plant A and 149 at plant B). In a subgroup of plant A workers who had been employed in high-carbon-disulfide exposure areas, deaths from ischemic heart disease were less than expected (PMR = 82), particularly among those who worked in these areas for more than 5 y. Most deaths occurred among those aged 65 y or more. Mortality from strokes, however, was greater than expected (PMR = 207, p < .05); the excess was confined to workers who died at age 65 y or older (PMR = 229, p = .01). Proportional mortality from strokes was also increased in the pulp workers among those who died at age 65 y or older (PMR = 153). In a case-control analysis, the risk of ischemic heart disease at plant A was slightly less than at plant B (odds ratio (OR] = 0.92, 95% confidence interval [CI] = 0.60-1.42), with no association between risk and years worked in high-carbon-disulfide areas (OR/y = 0.99, 95% CI = 0.94-1.03). Among those who died at age 65 y or older, the risk of stroke in the high-exposure subgroup was (a) increased significantly, compared with other plant A workers (OR = 4.92, 95% CI = 1.66-14.65); and (b) increased slightly, compared with plant B workers (OR = 1.37, 95% CI = 0.83-2.26). These results suggested an unusually low risk of strokes among other plant A workers. The risk of stroke was associated with years in high-carbon-disulfide areas (OR/y = 1.03, 95% CI = 0.96-1.1 0). The observed increase in proportional mortality from strokes may represent a chance finding, but a causal role for exposure cannot be excluded.

Body mass index and quality of life in a survey of primary care patients.

BACKGROUND: The prevalence of overweight and obesity is increasing and contributes to the burden of ill health in the community. The impact of obesity on health-related quality of life has been less well studied than how it affects physical morbidity and mortality. METHODS: A survey of health-related quality of life using the 12-item Short Form (SF-12) of the Medical Outcomes Study Short Form-36 was mailed to patients attending a family medicine clinic. Multiple regression analyses were used to investigate the relationships between scores on the mental and physical components of the SF-12 and body mass index (BMI) while controlling for age, sex, and family income. RESULTS: Responses were received from 565 subjects (53%). The relationships among BMI and quality of life in the mental and physical domains were nonlinear. Quality of life scores were optimal when BMI was in the range of 20 to 25 kg per m2. CONCLUSIONS: The National Heart, Lung, and Blood Institute has published evidence-based clinical guidelines for the identification, evaluation, and treatment of overweight and obesity in adults. Subjects with BMI in the range 18.5 to 24.9 kg per m2 are classified as having normal weight. These observations suggest that achieving a weight in this range will maximize the patient's subjective sense of well-being.

Use of "time windows" to investigate lung cancer latency intervals at an Ontario steel plant.

This paper describes an application of the time windows method to an examination of the temporal pattern of lung cancer risk among steel workers. Case-control methodology was utilized. The cases were 36 men who had died of lung cancer and the controls were 289 men who had died of any other cause. The number of years of employment in the steel pouring area was used as a surrogate measure of exposure. The data were examined by contingency table analysis and by logistic regression, which permitted adjustment for exposures in multiple time windows and the use of continuous, rather than categorical, measures of exposure. It was found that lung cancer risk was associated with exposures occurring between 18 and 30 years before death. It cannot yet be determined whether this time course reflects a biological response or the temporal pattern of exposure to an as yet unidentified toxic agent.

Leukemia after exposure to benzene: temporal trends and implications for standards.

BACKGROUND: Benzene is a human leukemogen. Risk assessment, and the setting of occupational and environmental standards, has assumed that risk is constant in time after a unit of exposure. Leukemia risk is known to vary with time after exposure to ionizing radiation. METHODS: A matched case-control study of leukemia risk in relation to the temporal pattern of benzene exposures was performed using data from the National Institute of Occupational Safety and Health. RESULTS: Leukemia risk following exposure to benzene varied with time in a manner similar to that following exposure to ionizing radiation. More recent exposures were more strongly associated with risk than were more distant ones. There was no significant relation between leukemia death and benzene exposures incurred more than 20 years previously. CONCLUSIONS: Recent analyses of specific occupational and environmental carcinogens, including benzene and radon, have indicated that cancer risk tends to decline as the time from exposure increases. This suggests that standards for the control of occupational or public risk must be selected to control exposures over a narrower time frame than the usual lifetime one. In the case of benzene, it would appear that risk is attributable primarily to exposures incurred during the previous 10 to 20 years, with exposures in the most recent 10 years being the most potent. To limit risk, exposures must be controlled during that interval. It is important that epidemiologists explore the temporal pattern of risk in their studies to facilitate the risk assessment of other carcinogens.

Silica, silicosis, and lung cancer: a risk assessment.

BACKGROUND: To investigate exposure-response relationships for silica, silicosis, and lung cancer. METHODS: Quantitative review of the literature identified in a computerized literature search. RESULTS: The risk of silicosis (ILO category 1/1 or more) following a lifetime of exposure at the current OSHA standard of 0.1 mg/m(3) is likely to be at least 5-10% and lung cancer risk is likely to be increased by 30% or more. The exposure-response relation for silicosis is nonlinear and reduction of dust exposures would have a greater than linear benefit in terms of risk reduction. Available data suggests that 30 years exposure at 0.1 mg/m(3) might lead to a lifetime silicosis risk of about 25%, whereas reduction of the exposure to 0.05 mg/m(3) might reduce the risk to under 5%. CONCLUSIONS: The lifetime risk of silicosis and lung cancer at an exposure level of 0.1 mg/m(3) is high. Lowering exposures to the NIOSH recommended limit if 0.05 mg/m(3) may have substantial benefit.

Occupational associations with lung cancer in two Ontario cities.

A death certificate based case-control study of lung cancer in two Ontario cities was performed to estimate the risk of lung cancer attributable to occupation in Ontario, and to estimate the proportion of occupational lung cancers receiving compensation from the Workers' Compensation Board. Occupation and industry were identified from the death certificate. A priori occupations for analysis were those whose members had received compensation for occupational cancer from the Ontario Workers' Compensation Board. Population attributable risks were computed using the relative risks observed in this study and employment data from the 1986 Census of Canada. Subjects were all men (N = 967) between the ages of 45 and 75 years resident in the cities of Hamilton and Sault Ste-Marie who died of lung cancer from 1979 to 1988. Controls (2,821) were matched on age, year of death, and city of residence. In agreement with other studies, an increased risk of lung cancer was observed for workers in the construction sector, for miners, and for truck drivers. It was estimated that only a small proportion of lung cancers attributable to occupation are compensated in Ontario. It is believed that many occupational cancers go uncompensated because of the failure to file claims, rather than because claims are rejected by Compensation Boards. Physicians are in a position to advise patients about the possibility of compensable disease and to act as advocates for them. By recognizing compensable illness, physicians have the opportunity to ease the financial burden of patients and their families. The challenge is a difficult one, but it is well worth pursuing.

Lung cancer among steelworkers in Ontario.

A population-based case-control study was carried out to follow up observations of increased lung cancer risk in the steel pouring areas of two Ontario steel mills. Study subjects were all men, aged 45-75 years, who died of lung cancer in the cities of Hamilton or Sault Ste-Marie, Ontario from 1979-1988. Nine hundred sixty-seven lung cancer victims were matched with 2,827 control subjects who died of other causes. Work histories were provided by the employers of steelworkers. In comparison with other residents of their cities, the relative risk of death from lung cancer was 0.85 (95% confidence interval [CI]: 0.58-1.23) for steelworkers in Sault-Ste Marie and was 1.10 (95% CI: 0.89-1.37) for steelworkers in Hamilton. In internal comparisons within the steel companies, increased lung cancer risk was observed among foundry, coke oven, and pouring pit workers. Retrospective hygiene assessment suggested that the increased risk of lung cancer among steel pourers might be related to the use of tar-based mold coating agents or to exposure to mineral fibers.

Radium in drinking water and the risk of death from bone cancer among Ontario youths.

OBJECTIVE: To determine whether residents of Ontario who are exposed to radium 226 naturally occurring in drinking water are at increased risk of bone cancer. DESIGN: A population-based case-control study of records from death and birth registries. Water samples were obtained from residences at the time of birth and of death. SETTING: Ontario. PARTICIPANTS: All Ontario-born people under the age of 26 years who died of bone cancer between 1950 and 1983. Control subjects were those who died of any other disease matched by age, sex and year of death. OUTCOME MEASURES: Radium exposure distributions and estimation of risk. RESULTS: An association was found between death from bone cancer and exposure to radium at the birthplace residence in concentrations of 7.0 mBq/L or more (odds ratio 1.58, 90% confidence interval [CI] 1.01 to 2.50; p = 0.047). There was a statistically significant exposure-response relation (p = 0.045). The increase in risk was similar for the main types of childhood bone cancer: osteosarcoma, Ewing's sarcoma and chondrosarcoma. CONCLUSIONS: The estimated risk at these exposure levels is much higher than would be predicted. The association may be spurious, the point estimates of risk may be too high, or risk factors derived from other exposure circumstances may not be valid for exposure to radium beginning in the prenatal period. Should the findings be confirmed, consideration might be given to removing radium from drinking-water sources.

Silicosis surveillance in Ontario: detection rates, modifying factors, and screening intervals.

The Province of Ontario has had a surveillance program for workers in dusty industries for almost 70 years. This paper reports the detection rates of silicosis among 68,701 silica-exposed individuals who were first exposed to dust in 1950 or later, and who were still employed in 1979 or later. The detection rate varied strongly with latency, being less than two new cases per 10,000 examinations during the first two decades from first exposure, reaching two new cases per 1,000 examinations at 27 years from first exposure, and averaging between two and four new cases per 1,000 examinations thereafter. The silicosis incidence rate among miners was only about half that among foundry workers. Cigarette smoking was also found to be a risk factor for the diagnosis of silicosis. These data were used to model the detection rate of new cases of silicosis as a function of the time interval between examinations, and results are presented for examination cycles between 2 and 10 years.

Record linkage as a research tool for office-based medical care.

OBJECTIVE: To explore the feasibility of linking records to study health services and health outcomes for primary care patients. DESIGN: A cohort of patients from the Family Medicine Centre at Mount Sinai Hospital was assembled from the clinic's billing records. Their health numbers were linked to the Ontario Hospital Discharge Database. The pattern of hospital admission rates was investigated using International Classification of Diseases (ICD) codes for primary discharge diagnosis. A pilot case-control study of risk factor management for stroke was nested in the cohort. SETTING: Family medicine clinic based in a teaching hospital. PARTICIPANTS: A cohort of 19,654 Family Medicine Centre patients seen at least once since 1991. MAIN OUTCOME MEASURES: Admission rates by age, sex, and diagnosis. Numbers of admissions for individual patients, time to readmission, and length of stay. Odds ratios for admission for cerebrovascular disease. RESULTS: The 19,654 patients in the cohort had 14,299 discharges from Ontario hospitals in the 4 years from 1992 to 1995, including 3832 discharges following childbirth. Some patients had many discharges: 4816 people accounted for the 10,467 admissions excluding childbirth. Excluding transfers between institutions, there were 4975 readmissions to hospital during the 4 years, 1392 (28%) of them within 28 days of previous discharge. Admissions for mental disorders accounted for the greatest number of days in hospital. The pilot study of risk factor management suggested that acetylsalicylic acid therapy might not be effective for elderly primary care patients with atrial fibrillation and that calcium channel blocker therapy might be less effective than other therapies for preventing cerebrovascular disease in hypertensive primary care patients. CONCLUSIONS: Record linkage combined with data collection by chart review or interview is a useful method for studying the effectiveness of medical care in Canada and might suggest interesting hypotheses for further investigation.