Effect of short-term exposure to low levels of gaseous pollutants on chronic obstructive pulmonary disease hospitalizations

We examined the associations between gaseous pollutants and hospitalization for chronic obstructive pulmonary diseases (COPD) among elderly people living in Vancouver, British Columbia, Canada, a city in which ambient air pollution levels are relatively low. We regressed the logarithm of daily counts of acute COPD hospitalization during the 5-year period from 1994 to 1998 on the daily mean levels of each pollutant, after accounting for seasonal and subseasonal fluctuations, non-Poisson dispersion, and weather variables. Nitrogen dioxide and carbon monoxide were significantly associated with hospitalization for COPD, and the magnitude of effects was increased slightly with increasing days of exposure averaging, with the relative risk for a 7-day average being 1.11 (95%CI: 1.04, 1.20) and 1.08 (1.02, 1.13) for nitrogen dioxide and carbon monoxide, respectively. There was no significant association between either sulfur dioxide or ozone and COPD hospitalization. The combined relative risk for all four gaseous pollutants on COPD hospitalization was 1.21. The effects of gaseous pollutants on COPD hospitalization were not significant after adjustment for PM(10), although its inclusion did not have a marked effect on the point estimates for relative risks. Nitrogen dioxide has a significant impact on COPD hospitalization. Further studies are needed to separate the effects of single pollutants from the combined effects of the complex mixture of air pollutants in urban atmospheres.     

Sensitivity of the estimated air pollution-respiratory admissions relationship to statistical model choice

The objective of this study was to demonstrate the methodological shortcomings of currently available analytical methods for single-city time series data. We analyzed daily Chronic Obstructive Pulmonary Disease (COPD) and daily asthma hospital admissions in Melbourne, Australia from July 1989 to December 1992. Air pollution data comprised nitrogen dioxide, ozone and sulphur dioxide and air particles index consistent with particulates between 0.1 and 1 microm in aerodynamic diameter. Statistical analyses were performed using generalized linear models, generalized additive models, Poisson autoregressive models and transitional regression models. The estimated effect of nitrogen dioxide on COPD hospital admissions was similar across the different statistical models, RR = 1.06 (95% CI 1.01-1.11). Similarly the estimated effect of nitrogen dioxide on asthma hospital admissions was also consistent, RR = 1.05 (95% CI 1.01-1.09). However, the effects of ozone, air particles index and sulphur dioxide were highly sensitive to model specification for both COPD and asthma hospital admissions. In single-city studies of air pollution and respiratory disease, very different conclusions can be drawn from competing models. Furthermore, real time series data have greater complexity than any of the commonly-used existing models allow. Consequently, single-city studies should use several statistical models to demonstrate the stability of estimated effects.     

On the interpretation of epidemiological studies of ambient air pollution

Studies of the effects of ambient air pollution on human health are complicated by the fact that individuals are exposed to a complex mixture of toxic and non-toxic substances that vary in their make-up in space and in time. It is impossible using standard epidemiological designs to uniquely identify any individual component of air pollution as a causal agent of a health effect because of simultaneous exposure to all or a subset of ambient pollutants. Nevertheless, associations observed for a particular pollutant can be interpreted as a marker of toxicity of the mixture, and regulatory action on judiciously selected pollutants can benefit health, as such actions can modify the complex mixture. This paper argues that we may be able to further our understanding of the effects of air pollution on human health by investigating whether particular mixtures are more toxic through (1) conducting and reporting results for all measured components; (2) possibly characterizing the complex mixture by developing synoptic categorizations of daily air pollution, through cluster or latent profile analysis; (3) a careful analysis of differences in the mixtures between locations; and (4) toxicological studies and controlled studies on humans that make use of factorial designs for various components of the air pollution mixture.     

A critical evaluation of acute ozone epidemiology results

Evidence from controlled human exposure studies demonstrates transient pulmonary functional responses to ozone exposure concentrations near the U.S. primary air quality standard of 0.120 ppm. There have been several recent efforts to document low concentration ozone effects in the epidemiological setting. Quantification of ozone effects under natural conditions of exposure can provide valuable information for risk assessment. However, results of epidemiological studies on acute ozone effects have had a limited role in decisions for air quality standards. This reflects difficulties in the quantitative interpretation of results that are to some extent inherent in the epidemiological approach, such as the difficulty of assessing individual exposures, failure to account for varying activity levels, and confounding by temporal covariates, e.g., temperature and pollen. However, in spite of the limitations of individual studies, when viewed as a group the epidemiological studies are consistent among themselves and with results from chamber studies.     

Changes Following Anticholinesterase Exposures

Evidence from controlled human exposure studies demonstrates transient pulmonary functional responses to ozone exposure concentrations near the U.S. primary air quality standard of 0.120 ppm. There have been several recent efforts to document low concentration ozone effects in the epidemiological setting. Quantification of ozone effects under natural conditions of exposure can provide valuable information for risk assessment. However, results of epidemiological studies on acute ozone effects have had a limited role in decisions for air quality standards. This reflects difficulties in the quantitative interpretation of results that are to some extent inherent in the epidemiological approach, such as the difficulty of assessing individual exposures, failure to account for varying activity levels, and confounding by temporal covariates, e.g., temperature and pollen. However, in spite of the limitations of individual studies, when viewed as a group the epidemiological studies are consistent among themselves and with results from chamber studies.     

On ecological fallacy, assessment errors stemming from misguided variable selection, and the effect of aggregation on the outcome of epidemiological study

In social and environmental sciences, ecological fallacy is an incorrect assumption about an individual based on aggregate data for a group. In the present study, the validity of this assumption was tested using both individual estimates of exposure to air pollution and aggregate data for 1,492 schoolchildren living in the in vicinity of a major coal-fired power station in the Hadera region of Israel. In 1996 and 1999, the children underwent subsequent pulmonary function tests (PFT), and their parents completed a detailed questionnaire on their health status and housing conditions. The association between children's PFT results and their exposure to air pollution was investigated in two phases. During the first phase, PFT averages were compared with average levels of air pollution detected in townships, and small census areas in which the children reside. During the second phase, individual pollution estimates were compared with individual PFT results, and pattern detection techniques (Getis-Ord statistic) were used to investigate the spatial data structure. While different levels of areal data aggregation changed the results only marginally, the choice of indices measuring the children's PFT performance had a significant influence on the outcome of the analysis. As argued, differences between individual-level and group-level effects of exposure (i.e., ecological or cross-level bias) are not necessary outcomes of data aggregation, and that seemingly unexpected results may often stem from a misguided selection of variables chosen to measure health effects. The implications of the results of the analysis for epidemiological studies are discussed, and recommendations for public health policy are formulated.     

Air pollution,socioeconomic position,and emergency hospital visits for asthma in Seoul,Korea

Objective Some epidemiological literature has observed that air pollution effects on health differed across regional or individual socioeconomic position. This study evaluated whether regional and individual socioeconomic position, as indicated by health insurance premiums, modified the effect of air pollution on hospital visits for asthma. Methods Effects of ambient air pollutants (particulate matter, carbon monoxide, sulfur dioxide, nitrogen dioxide, and ozone) on 92,535 emergency out-patient hospital visits for asthma in Seoul, Korea during 2002 were estimated using case-crossover analysis, adjusting for time trend, weather conditions, and seasonality. Next, interactions between air pollutants and Korean National Health Insurance premium (1) for the individual patient and (2) averaged across the patient’s residence district, were entered, first singly then jointly, in the models. Results Relative risks of emergency outpatient hospital visits were all positively and significantly associated with interquartile increases for selected lags for all air pollutants. In the regression model with interaction terms for both individual premium and regional-average premium, associations with all five-air pollutants ranged from 1.03 to 1.09 times higher among the lowest premium districts compared to the highest premium districts. Of all the pollutants, nitrogen dioxide showed the strongest associations in lower premium districts compared to the higher premium districts. Individual socioeconomic position did not modify the associations in either the single or joint interaction models. Conclusion In Seoul, community but not individual socioeconomic conditions modified risk of asthma hospital visits on high air pollution days.     

Controlled human exposures to ambient pollutant particles in susceptible populations

Epidemiologic studies have established an association between exposures to air pollution particles and human mortality and morbidity at concentrations of particles currently found in major metropolitan areas. The adverse effects of pollution particles are most prominent in susceptible subjects, including the elderly and patients with cardiopulmonary diseases. Controlled human exposure studies have been used to confirm the causal relationship between pollution particle exposure and adverse health effects. Earlier studies enrolled mostly young healthy subjects and have largely confirmed the capability of particles to cause adverse health effects shown in epidemiological studies. In the last few years, more studies involving susceptible populations have been published. These recent studies in susceptible populations, however, have shown that the adverse responses to particles appear diminished in these susceptible subjects compared to those in healthy subjects. The present paper reviewed and compared control human exposure studies to particles and sought to explain the "unexpected" response to particle exposure in these susceptible populations and make recommendations for future studies. We found that the causes for the discrepant results are likely multifactorial. Factors such as medications, the disease itself, genetic susceptibility, subject selection bias that is intrinsic to many controlled exposure studies and nonspecificity of study endpoints may explain part of the results. Future controlled exposure studies should select endpoints that are more closely related to the pathogenesis of the disease and reflect the severity of particle-induced health effects in the specific populations under investigation. Future studies should also attempt to control for medications and genetic susceptibility. Using a different study design, such as exposing subjects to filtered air and ambient levels of particles, and assessing the improvement in biological endpoints during filtered air exposure, may allow the inclusion of higher risk patients who are likely the main contributors to the increased particle-induced health effects in epidemiological studies.     

Assessing the impact of the local environment on birth outcomes: a case for HLM

Hierarchical linear Models (HLM) is a useful way to analyze the relationships between community level environmental data, individual risk factors, and birth outcomes. With HLM we can determine the effects of potentially remediable environmental conditions (e.g., air pollution) after controlling for individual characteristics such as health factors and socioeconomic factors. Methodological limitations of ecological studies of birth outcomes and a detailed analysis of the varying models that predict birth weight will be discussed. Ambient concentrations of criterion air pollutants (e.g., lead and sulfur dioxide) demonstrated a sizeable negative effect on birth weight; while the economic characteristics of the mother's residential census tract (ex. poverty level) also negatively influenced birth weight.     

Urban air pollution in Latin America and the Caribbean: health perspectives

In the last few years, air pollution has become a major issue in some countries of Latin America and the Caribbean because of urban development and growing industrialization. In addition to industrial processes often concentrated in the cities, vehicle emission and stationary-source fuel combustion are the primary sources of air pollution. Although air-quality standards have been established in some Latin American countries, these are frequently exceeded. Adverse health effects of air pollution have been mainly associated with the following pollutants: sulfur dioxide and particulate matter, photochemical oxidants, nitrogen dioxide and carbon monoxide, and lead. Short-term as well as long-term effects can be expected at levels exceeding WHO guidelines. The Latin American urban areas most affected by anthropogenic pollutant emissions are: the area of S?o Paulo (Brazil), the city of Santiago (Chile) and the metropolitan area of Mexico City. However, situations similar to those prevailing in these cities could well occur in other cities of Latin America and the Caribbean. The population exposed to air-pollutant levels exceeding WHO guidelines can be estimated to 81 million or 26.5% of the total urban population of Latin America and 19% of its total population. These estimates correspond to 30 million children (0-14), 47 million adults (15-59) and 4 million elderly people (60+). To date a very limited number of epidemiological studies have been carried out to determine the potential health effects of air pollutants in Latin America. To obtain a rough estimate, a scenario was hypothesized in which subjects living in cities would be exposed to a given level of air pollutant, using data from the international literature to extrapolate the expected number of events in different strata of the hypothetical population. The estimated health effects are considerable and warrant priority control intervention. This is true although epidemiological studies are needed to evaluate the health impact of specific pollutant compounds as well as their interactions in Latin American populations exposed to high levels of pollution.     

Effects of air pollution on adults with chronic obstructive pulmonary disease

Few studies have been conducted on the effects of air pollution on patients with chronic obstructive pulmonary disease (COPD). During a 14-mo period, 39 Parisian adults with severe COPD were monitored by their physicians. Daily levels of 4 air pollutants were provided by an urban air-quality network. Exacerbation of COPD was associated only with ozone (O3) (odds ratio [OR] = 1.44 for a 10-microg/m3 increase in O3; 95% confidence interval [CI] = 1.14, 1.82), with a lag of 2-3 days. The effect of O3 was greater in patients whose carbon dioxide pressure (PaCO2) was higher than 43 mm Hg (OR = 1.83; 95% CI = 1.36, 2.47) vs. those with a lower PaCO2 (OR = 1.26; 95% CI = 0.90, 1.77). The effect of O3 was unchanged, regardless of the maintenance medications used. The only air pollutant to which patients with severe COPD were particularly sensitive was O3.     

Air pollution and hospital admissions in Sydney, Australia, 1990 to 1994.

OBJECTIVES: This study examined the effects of outdoor air pollutants on daily hospital admissions in Sydney, Australia. METHODS: A time-series analysis of counts of daily hospital admissions and outdoor air pollutants (1990 to 1994) was performed, by means of Poisson regression that allowed for overdispersion and autocorrelation. RESULTS: An increase in daily maximum 1-hour concentration of nitrogen dioxide from the 10th to the 90th percentile was associated with an increase of 5.29% (95% confidence interval = 1.07, 9.68) in childhood asthma admissions and 4.60%(-0.17,9.61) in chronic obstructive pulmonary disease (COPD) admissions. A similar increase in daily maximum 1-hour particulate concentration was associated with an increase of 3.01% (-0.38, 6.52) in COPD admissions. An increase from the 10th to the 90th percentile in daily maximum 1-hour nitrogen dioxide, daily maximum 1-hour ozone, and daily mean particulate was associated with an increase in heart disease admissions among those 65 years and older of 6.71% (4.25, 9.23), 2.45% (-0.37, 5.35), and 2.82% (0.90, 4.77), respectively. Heart disease and childhood asthma were primarily associated with nitrogen dioxide; COPD was associated with both nitrogen dioxide and particulates. CONCLUSIONS: Current levels of air pollution in Sydney are associated with increased hospitalization for respiratory and heart disease.     

Long-term exposure to outdoor air pollution and the prevalence of asthma: meta-analysis of multi-community prevalence studies

The effect of outdoor air pollution on variations in asthma prevalence is unclear. We have conducted a meta-analysis of multi-community studies to evaluate and quantify the evidence for an association between community levels of pollution and asthma prevalence. We identified peer-reviewed articles reporting associations between community levels of air pollution and the prevalence of wheeze symptom or asthma diagnosis which were based on five or more communities. Associations were investigated by meta-analysis and by analysis of the direction and statistical significance of estimates. We identified 21 studies of more than five communities (range 6 to 62). The proportion of studies reporting at least one significantly positive association was 43% but, of the total of 178 pollution-outcome estimates, only 11% were statistically significantly positive. Thirteen studies reported associations with pollution analysed as a quantitative variable, and these results were meta-analysed. For period prevalence (mainly wheeze symptom), the results were null: Random effects estimates (95% confidence intervals) for the odds ratios of nitrogen dioxide, particulate matter with aerodynamic diameter <10 μm, ozone and sulphur dioxide were 1.00 (0.95, 1.06), 1.00 (0.94, 1.07), 1.01 (0.96, 1.07) and 1.03 (0.97, 1.09), respectively. For lifetime prevalence (mainly asthma diagnosis), the random effects estimates were similar: 1.00 (0.99, 1.01), 0.99 (0.96, 1.02), 1.06 (0.98, 1.14) and 1.00 (0.96, 1.05), respectively. We found no evidence of an association between community levels of outdoor air pollution and asthma prevalence.     

An air pollution model for use in epidemiological studies: evaluation with measured levels of nitrogen dioxide and benzene

The aim of the study was to evaluate the predictions derived from the Danish Operational Street Pollution Model (OSPM) when the input data are obtained by simple methods that could be used in large-scale epidemiological studies. The model calculations were thus compared with passive sampler measurements of nitrogen dioxide and benzene at 103 street locations in Copenhagen, Denmark, and at 101 locations in rural areas. Data on traffic and street configuration were collected by means of a simple registration scheme in which forms were filled out by local municipal authorities. Meteorological data were derived from routine measurements at Copenhagen airport, and data on background air pollution were based on a simple empirical model. Differences in air pollution levels between rural areas and Copenhagen and differences in nitrogen dioxide concentrations at various locations in Copenhagen were well reproduced by the OSPM. The correlation coefficients (r) between the measured and the predicted half-year average concentrations of nitrogen dioxide in Copenhagen were between 0.75 and 0.80 for various degrees of precision of the input data for the model. The results indicate that the OSPM used with the presented methods for generation of input data might be useful in assessing long-term exposure to air pollutants in epidemiological studies.     

Confounding in air pollution epidemiology: the broader context

Recent research appropriately suggests that caution is warranted when interpreting long-term trends of improving air quality and trends in reduced mortality rates as causal because of concerns about confounding. The use of long-term time trends as the primary source of exposure variability, however, has been avoided in most air pollution epidemiology studies. Multiple studies, using different study designs that exploit various temporal and spatial dimensions of exposure variability, have observed reasonably consistent and coherent associations between particulate air pollution and cardiopulmonary health. It's possible that these air pollution studies have experienced "epidemiological bad luck" with multiple confounders that are inadequately controlled for and coincidentally cause spurious correlations that are coherent across the different study designs. To be consistent with the overall epidemiologic results, these confounders must correlate with pollution across various dimensions of time and space and be stronger risk factors for cardiopulmonary disease than for other disease. The more likely explanation of recent air pollution epidemiology is that air pollution, especially fine particulate and related pollution, has measurable effects on cardiopulmonary health.     

Ambient air pollution and cardiovascular emergency department visits in potentially sensitive groups

Limited evidence suggests that persons with conditions such as diabetes, hypertension, congestive heart failure, and respiratory conditions may be at increased risk of adverse cardiovascular morbidity and mortality associated with ambient air pollution. The authors collected data on over 4 million emergency department visits from 31 hospitals in Atlanta, Georgia, between January 1993 and August 2000. Visits for cardiovascular disease were examined in relation to levels of ambient pollutants by use of a case-crossover framework. Heterogeneity of risk was examined for several comorbid conditions. The results included evidence of stronger associations of dysrhythmia and congestive heart failure visits with comorbid hypertension in relation to increased air pollution levels compared with visits without comorbid hypertension; similar evidence of effect modification by diabetes and chronic obstructive pulmonary disease (COPD) was observed for dysrhythmia and peripheral and cerebrovascular disease visits, respectively. Evidence of effect modification by comorbid hypertension and diabetes was observed in relation to particulate matter less than 10 microm in aerodynamic diameter, nitrogen dioxide, and carbon monoxide, while evidence of effect modification by comorbid COPD was also observed in response to ozone levels. These findings provide further evidence of increased susceptibility to adverse cardiovascular events associated with ambient air pollution among persons with hypertension, diabetes, and COPD.     

Comparing meta-analysis and ecological-longitudinal analysis in time-series studies. A case study of the effects of air pollution on mortality in three Spanish cities

STUDY OBJECTIVE: The objective of this paper is to introduce a different approach, called the ecological-longitudinal, to carrying out pooled analysis in time series ecological studies. Because it gives a larger number of data points and, hence, increases the statistical power of the analysis, this approach, unlike conventional ones, allows the complementation of aspects such as accommodation of random effect models, of lags, of interaction between pollutants and between pollutants and meteorological variables, that are hardly implemented in conventional approaches. DESIGN: The approach is illustrated by providing quantitative estimates of the short-term effects of air pollution on mortality in three Spanish cities, Barcelona, Valencia and Vigo, for the period 1992-1994. Because the dependent variable was a count, a Poisson generalised linear model was first specified. Several modelling issues are worth mentioning. Firstly, because the relations between mortality and explanatory variables were non-linear, cubic splines were used for covariate control, leading to a generalised additive model, GAM. Secondly, the effects of the predictors on the response were allowed to occur with some lag. Thirdly, the residual autocorrelation, because of imperfect control, was controlled for by means of an autoregressive Poisson GAM. Finally, the longitudinal design demanded the consideration of the existence of individual heterogeneity, requiring the consideration of mixed models. MAIN RESULTS: The estimates of the relative risks obtained from the individual analyses varied across cities, particularly those associated with sulphur dioxide. The highest relative risks corresponded to black smoke in Valencia. These estimates were higher than those obtained from the ecological-longitudinal analysis. Relative risks estimated from this latter analysis were practically identical across cities, 1.00638 (95% confidence intervals 1.0002, 1.0011) for a black smoke increase of 10 microg/m(3) and 1.00415 (95% CI 1.0001, 1.0007) for a increase of 10 microg/m(3) of sulphur dioxide. Because the statistical power is higher than in the individual analysis more interactions were statistically significant, especially those among air pollutants and meteorological variables. CONCLUSIONS: Air pollutant levels were related to mortality in the three cities of the study, Barcelona, Valencia and Vigo. These results were consistent with similar studies in other cities, with other multicentric studies and coherent with both, previous individual, for each city, and multicentric studies for all three cities.     

Health effects of ambient air pollution – recent research development and contemporary methodological challenges

Exposure to high levels of air pollution can cause a variety of adverse health outcomes. Air quality in developed countries has been generally improved over the last three decades. However, many recent epidemiological studies have consistently shown positive associations between low-level exposure to air pollution and health outcomes. Thus, adverse health effects of air pollution, even at relatively low levels, remain a public concern. This paper aims to provide an overview of recent research development and contemporary methodological challenges in this field and to identify future research directions for air pollution epidemiological studies.     

大气污染暴露对肝功能指标影响的流行病学研究进展

随着全球环境污染问题日趋严峻,大气污染对健康的影响已受到广泛关注。越来越多的证据表明,大气污染物可能通过直接或间接作用影响肝脏功能,改变肝功能指标水平。流行病学研究是评价大气污染健康效应的重要方法。目前国内外已逐渐开展大气污染暴露对肝功能指标影响的流行病学研究,但不同研究的结论不一致。本文从长期暴露和短期暴露两方面综述了大气污染对肝功能指标影响的流行病学研究进展,并指出现有研究存在的不足,为今后开展此类研究提供建议。