Biomedical subjects

Daniel Krewski

Publications and source records attributed to Daniel Krewski.

79 records · Page 5Linked to original sources

PubMedDate not supplied

Health and air quality: directions for policy-relevant research.

The NERAM International Colloquia series is a program of five annual meetings involving scientists, regulators, industry representatives, and other stakeholder groups to improve the linkage between emerging scientific evidence on the population health impacts of exposure to particulate matter and clean air policy decisions. Health and Air Quality 2001, the first meeting in the colloquium series, focused on the findings of prospective cohort studies of particulate air pollution and mortality and implications for risk management. A further objective of the colloquium was to identify research directions to reduce information gaps and uncertainties faced by policy makers. This article discusses priority themes for future research to generate evidence in support of policy decisions to improve air quality and population health. These research themes include development of population health indicators to characterize the public health burden of air pollution; individual exposure and outcome studies to the currently available database on the association between air pollution and adverse health effects; identification of sensitive subpopulations; techniques to assess the independent effects of individual pollutants on population health; comparative risk assessment; methods for characterization and communication of uncertainty in risk estimates; effectiveness of policy interventions to guide allocation of limited population health protection resources; improved predictions of the benefits of interventions through appropriate economic analyses: targeted interventions; and approaches for effective stakeholder engagement in risk management policy decisions. Future meetings in the NERAM Colloquium series will provide a forum for discussion of the current state of knowledge and policy implications of findings associated with these key research themes.

Air↗

PubMedDate not supplied

Managing the microbiological risks of drinking water.

The microbiological contamination of drinking water supplies can have serious health consequences for consumers, and this has been dramatically illustrated in recent years by two disease outbreaks in Canada. In this paper, some factors that can influence the microbiological quality of drinking water and its management are examined. Frameworks have been proposed that help to clarify the main elements of health risk assessment and risk management, and, in accordance with these, risks can be logically characterized, evaluated and controlled. A protocol has been developed for microbiological risk assessment and a risk management framework now guides the development of Canada's national guidelines for drinking-water quality. Monitoring of indicator organisms and the application of adequate water treatment are the primary means recommended in the Canadian guidelines to safeguard health from the presence of water-borne pathogens. Understanding the biological characteristics of microbial pathogens is necessary for assessing their impact on community health and appraising the rationale behind drinking-water testing methods and their limitations. Improvements in health surveillance, monitoring, and risk characterization and application of concepts such as multiple barriers (source-to-tap) and total quality management should contribute to better management of the microbiological quality of drinking water.

Canada↗

PubMedDate not supplied

Mortality and long-term exposure to ambient air pollution: ongoing analyses based on the American Cancer Society cohort.

This article provides an overview of previous analysis and reanalysis of the American Cancer Society (ACS) cohort, along with an indication of current ongoing analyses of the cohort with additional follow-up information through to 2000. Results of the first analysis conducted by Pope et al. (1995) showed that higher average sulfate levels were associated with increased mortality, particularly from cardiopulmonary disease. A reanalysis of the ACS cohort, undertaken by Krewski et al. (2000), found the original risk estimates for fine-particle and sulfate air pollution to be highly robust against alternative statistical techniques and spatial modeling approaches. A detailed investigation of covariate effects found a significant modifying effect of education with risk of mortality associated with fine particles declining with increasing educational attainment. Pope et al. (2002) subsequently reported results of a subsequent study using an additional 10 yr of follow-up of the ACS cohort. This updated analysis included gaseous copollutant and new fine-particle measurements, more comprehensive information on occupational exposures, dietary variables, and the most recent developments in statistical modeling integrating random effects and nonparametric spatial smoothing into the Cox proportional hazards model. Robust associations between ambient fine particulate air pollution and elevated risks of cardiopulmonary and lung cancer mortality were clearly evident, providing the strongest evidence to date that long-term exposure to fine particles is an important health risk. Current ongoing analysis using the extended follow-up information will explore the role of ecologic, economic, and, demographic covariates in the particulate air pollution and mortality association. This analysis will also provide insight into the role of spatial autocorrelation at multiple geographic scales, and whether critical instances in time of exposure to fine particles influence the risk of mortality from cardiopulmonary and lung cancer. Information on the influence of covariates at multiple scales and of critical exposure time windows can assist policymakers in establishing timelines for regulatory interventions that maximize population health benefits.

Air Pollution↗

PubMedDate not supplied

Testing the harvesting hypothesis by time-domain regression analysis. I: baseline analysis.

Although the association between air pollution and daily mortality is well established, the mechanisms by which air pollution results in excess mortality are not yet well understood. In particular, there exists debate over whether air pollution has a direct effect on mortality in the general population or simply shortens the life span of frail individuals, a hypothesis referred to as "harvesting." The goal of this investigation is to test the harvesting hypothesis using the time-domain regression method of Dominici et al. (2003a). We conducted simulations based on a two-compartment model that divides the population into a larger group of healthy individuals and a frail subpopulation. Death from air pollution is assumed to take place in two steps, by first moving from healthy population to the frail pool, then death with probability related to the level of air pollution. Using time-domain analysis, we seek to identify data patterns that would be characteristic of harvesting under different scenarios. For a pure harvesting model, time-domain analysis indicates that mortality is associated with a short-term air pollution episode of less than 2 d if the mean residency time in the frail pool is short. If both entrants and deaths depend on the level of air pollution and the rates of entry to and exit from the frail pool are about the same, the log relative risk estimates are essentially unchanged at all time scales. If pollution affects mortality in the frail pool more than entrants, larger effects will occur at shorter time scales.

Air Pollution↗

PubMedDate not supplied

Testing the harvesting hypothesis by time-domain regression analysis. II: covariate effects.

This article extends the previous work of Fung et al. (2004) investigating the ability of the time-scale log-linear regression model, proposed by Dominici et al. (2003), to detect mortality displacement (sometimes known as harvesting) in time-series data relating air pollution to excess mortality. We conducted a simulation study based on two different compartment models of the death process: pure frailty model and mixed frailty model. We assume that nonaccidental death only affects frail population in a pure frailty model and affects both frail people and other individuals in the mixed frailty model. With a pure frailty model and a moderate-size pollution effect, we identified a characteristic mortality displacement pattern in the different time-scale coefficients of log relative risk. However, once a covariate like temperature was introduced into the model, such a mortality displacement pattern disappeared. Furthermore, a false mortality displacement effect was present in the incorrectly specified model, when temperature was not taken into account. We believe that time-scale regression has limited value for detecting mortality displacement in time-series data.

Air Pollution↗

PubMedDate not supplied

Using willingness to pay to evaluate the implementation of Canada's residential radon exposure guideline.

BACKGROUND: The objective of this investigation was to determine the effectiveness of Canada's residential radon exposure guideline in influencing individuals' health protection decisions. METHOD: Homeowners with known exposure levels in a high residential radon area (Winnipeg, Manitoba) were surveyed to document what they had done and spent to reduce their exposure to radon. The 507 respondents were then re-surveyed to elucidate their response to hypothetical scenarios. Logistic regression was used to model risk reduction decisions as a function of exposure and other explanatory variables. RESULTS: Homeowners were only likely to have taken action to reduce exposure at levels exceeding 1,100 Bq/m3, well above Canada's guideline of 800 Bq/m3. However, when informed of the guideline, respondents indicated they would act at exposures of 702 Bq/m3. INTERPRETATION: The Canadian residential radon exposure guideline, as it has been implemented, has not effectively prompted homeowner actions to reduce exposures to radon.

Air Pollution, Indoor↗

PubMedDate not supplied

Physical inactivity and socioeconomic status in Canadian adolescents.

UNLABELLED: Physical activity is an important determinant of population health. In this paper, we examine levels of physical activity among Canadian adolescents in relation to socioeconomic status. METHODS: Data from the Canadian Community Health Survey, Cycle 2.1, conducted in 2003, were used to evaluate the association between socioeconomic status and physical activity. This survey included 9,294 males between 12 and 20 years of age, and 9,147 females in the same age range. RESULTS: Among adolescents aged 12 to 20 years, 55.9% of males and 39.2% of females were physically active. The proportion of subjects in the active category tended to decrease with age in both males and females. Adolescents from low income families were more physically inactive (odds ratio=1.30, 95% confidence interval=1.29-1.32) than those from high income families. CONCLUSION: Physical inactivity in adolescence represents an important population health issue in Canada. Physical activity levels tended to be higher among males, younger people, and those with higher socioeconomic status. Multi-sectoral policies and initiatives are needed to create environments that promote physical activity among Canadian youth.

Adolescent↗