Subclasses of LpA-I in coronary artery disease: distribution and cholesterol efflux ability

To determine the effect of air pollution in Mexico City on respiratory health, patient visits for upper respiratory tract infections were monitored in five clinics. Levels of ozone, nitrogen dioxide, carbon monoxide, and sulfur dioxide, and climatological variables were collected. Correlations of filtered data revealed an association between NO2 and O3 with an increase in visits to clinics because of respiratory problems. Autoregressive analysis indicated that pollutant levels/respiratory visits associations remained significant even after simultaneous inclusion of temperature, suggesting that air pollution was associated with 10 to 16% of the clinic visits. The relative risk indicated that high levels of O3 and NO2 could increase the total number of clinic visits to between 19 and 43% above average. The other pollutants and the control group did not demonstrate significant associations.     

Effect of environmental pollution on medical visits for respiratory infections in children in Mexico City

OBJECTIVE: To model the variability of medical visits by children for respiratory reasons as a consequence of the daily changes in environmental pollution observed in the emergency and family medicine departments of a hospital of the Instituto Mexicano del Seguro Social located in the southwest of Mexico City during 1993. MATERIALS AND METHODS: The correlation between the presence of upper and lower respiratory tract infections and exposure to ozone and nitrogen dioxide was studied. To model this association, the authors used multivariate Poisson regression models with linear and non-linear risk, with lag periods between the environmental measurements and the medical visits of one, two and three days, as well as the average of the measurements of three, five and seven days previous to the visit. RESULTS: The model estimates that an increment of 50 ppb in the daily average of ozone would cause an increase of 9.9% in emergency visits due to high respiratory tract infections during the winter, which could rise to 30% if the increment would last five consecutive days in average. CONCLUSIONS: Results suggest that exposure of children younger than 15 years of age to ozone and nitrogen dioxide significantly affect the number of medical visits for respiratory causes in this part of Mexico City.     

A multifactorial study of patients with asthma. Part 2: air pollution, animal dander and asthma symptoms

As part of a multifactorial computer-assisted study of patients with asthma, the relationship between air pollution, animal dander and asthma symptoms was evaluated. No association was found between four major air pollutants (carbon monoxide, ozone, nitrogen oxides and sulfur dioxide) and asthma symptoms. Patients who owned cats and dogs reported more severe asthma symptoms (p less than .01) than patients who did not own cats and dogs. The evaluations completed to date indicate that daily exposure to cats and dogs accounts for more of the asthma symptoms differences between patients than daily exposure to air pollutants.     

Urban air pollution and emergency admissions for asthma in four European cities: the APHEA Project

BACKGROUND: A study was undertaken to assess the combined association between urban air pollution and emergency admissions for asthma during the years 1986-92 in Barcelona, Helsinki, Paris and London. METHODS: Daily counts were made of asthma admissions and visits to the emergency room in adults (age range 15-64 years) and children (< 15 years). Covariates were short term fluctuations in temperature and humidity, viral epidemics, day of the week effects, and seasonal and secular trends. Estimates from all the cities were obtained for the entire period and separately by warm or cold seasons using Poisson time-series regression models. Combined associations were estimated using meta-analysis techniques. RESULTS: Daily admissions for asthma in adults increased significantly with increasing ambient levels of nitrogen dioxide (NO2) (relative risk (RR) per 50 micrograms/m3 increase 1.029, 95% CI 1.003 to 1.055) and non-significantly with particles measured as black smoke (RR 1.021, 95% CI 0.985 to 1.059). The association between asthma admissions and ozone (O3) was heterogeneous among cities. In children, daily admissions increased significantly with sulphur dioxide (SO2) (RR 1.075, 95% CI 1.026 to 1.126) and non-significantly with black smoke (RR 1.030, 95% CI 0.979 to 1.084) and NO2, though the latter only in cold seasons (RR 1.080, 95% CI 1.025 to 1.140). No association was observed for O3. The associations between asthma admissions and NO2 in adults and SO2 in children were independent of black smoke. CONCLUSIONS: The evidence of an association between air pollution at current urban levels and emergency room visits for asthma has been extended to Europe. In addition to particles, NO2 and SO2--by themselves or as a constituent of a pollution mixture--may be important in asthma exacerbations in European cities.     

The association between ambient carbon monoxide levels and daily mortality in Toronto, Canada

The role of ambient levels of carbon monoxide (CO) in the exacerbation of heart problems in individuals with both cardiac and other diseases was examined by comparing daily variations in CO levels and daily fluctuations in nonaccidental mortality in metropolitan Toronto for the 15-year period 1980-1994. After adjusting the mortality time series for day-of-the-week effects, nonparametic smoothed functions of day of study and weather variables, statistically significant positive associations were observed between daily fluctuations in mortality and ambient levels of carbon monoxide, nitrogen dioxide, sulfur dioxide, coefficient of haze, total suspended particulate matter, sulfates, and estimated PM2.5 and PM10. However, the effects of this complex mixture of air pollutants could be almost completely explained by the levels of CO and total suspended particulates (TSP). Of the 40 daily nonaccidental deaths in metropolitan Toronto, 4.7% (95% confidence interval of 3.4%-6.1%) could be attributable to CO while TSP contributed an additional 1.0% (95% confidence interval of 0.2-1.9%), based on changes in CO and TSP equivalent to their average concentrations. Statistically significant positive associations were observed between CO and mortality in all seasons, age, and disease groupings examined. Carbon monoxide should be considered as a potential public health risk to urban populations at current ambient exposure levels.     

Asthma presentations to emergency departments in western Sydney during the January 1994 Bushfires

BACKGROUND: From 5 to 12 January 1994, the state of New South Wales suffered from the worst bushfires seen this century. High levels of particulate air pollution were recorded in western Sydney from 7 to 14 January 1994, with nephelometry readings reaching 10.24 beta scat (10(-4)/m) and particulate matter < 10 mu readings peaking at 250.00 micrograms/m3. The aim of this study was to determine whether there was an increase in the proportion of asthma presentations to emergency departments (ED) in western Sydney as a result of the bushfire-generated particulate air pollution. METHOD: We retrospectively analysed the emergency room attendance books for asthma presentations from seven public hospitals serving the Western Sydney and Wentworth Health Areas over two 6-7 week periods, 17 December 1992 to 31 January 1993, and 17 December 1993 to 31 January 1994. Air pollution and meteorological data were obtained from local monitoring stations. RESULTS: The difference in the proportion of all ED presentations that were due to asthma during the week of the bushfire-generated air pollution, compared with the same week 12 months before, after adjusting for baseline changes over the 12-month period, was 0.0067 (95% CI: -0.0007, 0.0141). The maximum daily nephelometry reading was not a significant predictor of the daily number of asthma presentations to ED in any of the Poisson regression models. CONCLUSIONS: The bushfire-generated particulate air pollution in January 1994 did not result in an increase in asthma presentations to ED in western Sydney.     

Mortality and ambient fine particles in southwest Mexico City, 1993-1995

++Epidemiologic studies have focused attention on the health effects of fine particulate air pollutants <2.5 microm in diameter (PM2.5). To further characterize the potential effects of fine particles, we investigated the relationship of air pollution to mortality in Mexico City during 1993-1995. The concentration of PM2.5 was measured on a 24-hr integrated basis; concentrations of NO2 and ozone were measured hourly and reduced to 24-hr means. Daily mortality was determined from death registration records, and Poisson regression was used to model daily death counts as a function of air pollutant levels on the same and previous days, while controlling for temperature and periodic cycles. Without taking other air pollutants into account, a 10 microg/m3 increase in the level of PM2.5 was associated with a 1.4% increase in total mortality, both on the current day and 4 days after exposure [95% confidence interval (CI), 0.2-2.5]. An equivalent increase in PM2.5 was also associated with somewhat larger excesses of deaths among people over 65 years of age and from cardiovascular and respiratory causes, which occurred after a lag of 4 days. The mean concentration of ozone over a 2-day period was associated with a 1.8% increase in mortality from cardiovascular diseases. NO2 was not consistently related to mortality. Fine particles had an independent effect on mortality when modeled simultaneously with other pollutants, and the association of ozone with cardiovascular mortality was strengthened after adjusting for NO2 and PM2.5. These results support previous findings that urban air pollution at current levels leads to excess mortality and suggest that fine particles may play a causal role in producing that excess.     

Nutrient utilization by sheep and performance and carcass characteristics of steers fed crab waste-straw silage

Exacerbations of asthma have been associated with exposure to ozone or particles with a 50% cut-off aerodynamic diameter of 10 microm (PM10). We postulated in this study that the association of summertime air pollution (i.e. ozone and PM10) with acute respiratory symptoms, medication use and peak expiratory flow differs among patients grouped according to asthma severity. During the summer of 1995, effects of ambient air pollution on these parameters were studied in a panel of 60 nonsmoking patients with intermittent to severe persistent asthma. These patients were recruited from our Pulmonary Out-patient Clinic. Subgroup analysis was performed on the degree of hyperresponsiveness and lung steroid use before the start of the study, as indictors for the severity of asthma. Associations of the parameters studied with ozone, PM10, nitrogen dioxide (NO2), sulphur dioxide (SO2) and black smoke were evaluated using time series analysis. Several episodes with increased summertime air pollution occurred during the 96 day study period. Eight hour average ozone concentrations exceeded the World Health Organization (WHO) Air Quality Guidelines (120 microg x m(-3)) on 16 occasions. Daily mean levels of PM10 were moderately elevated (range 16-98 microg x m(-3)). Levels of the other measured pollutants were low. There was a consistent, positive association of the prevalence of shortness of breath (maximal relative risk (RRmax) 1.18) with ozone, PM10, black smoke and NO2. In addition, bronchodilator use was associated with both ozone and PM10 levels (RRmax 1.16). Stratification by airway hyperresponsiveness and steroid use did not affect the magnitude of the observed associations. No associations with peak expiratory flow measurements were found. We conclude that the severity of asthma is not an indicator for the sensitivity to air pollution.     

Aging and life adjustment after spinal cord injury

We studied the short-term effects of Paris winter air pollution (i.e., sulfur dioxide, Black Smoke, suspended particulates with an aerodynamic diameter close to 10 microm, and nitrogen dioxide) in 40 nonsmoking mild to moderate asthmatics (52% male; mean age = 46 y; 90% treated with inhaled steroids). During a 6-mo period, subjects recorded asthma symptoms and three daily peak expiratory flow measurements. Statistical analysis (i.e., generalized estimating equation models that accounted for autocorrelation of responses, weather data, and time trends) revealed consistent and significant associations between the pollutants and asthma attacks and symptoms in the entire study group, especially in the subgroup of individuals who took inhaled beta2 agonists as needed. Pollutants correlated negatively with morning peak expiratory flow in the subgroup that took inhaled beta2 agonists as needed, and they correlated positively with daily variability in asthmatics who received regularly scheduled inhaled beta2 agonists. The effects lingered several days after exposure occurred. Low-level pollution has consistent measurable effects on nonsmoking adults who have well-treated mild or moderate asthma.     

Urban air pollution and cardiopulmonary ill health: a 14.5 year time series study

OBJECTIVES: To examine possible associations between daily concentrations of urban air pollutants and hospital emergency admissions and mortality due to cardiac and pulmonary disease. METHODS: A time series study was conducted in the City of Edinburgh, which has a population of about 450,000. Poisson log linear regression models were used to investigate the relation of the daily event rate with daily air pollution concentrations of sulphur dioxide (SO2) and black smoke from 1981 to 1995, and of nitrogen dioxide (NO2), ozone (O3), carbon monoxide (CO), and particulate matter (PM10) from 1992 to 1995. Adjustments were made for seasonal and weekday variation, daily temperature, and wind speed. RESULTS: The most significant findings were positive associations over the period 1981-95 between black smoke as a mean of the previous three days and daily all cause mortality in people aged > or = 65, and respiratory mortality also in this age group (3.9% increase in mortality for a 10 micrograms/m3 increment in black smoke). For hospital emergency admissions between 1992 and 1995 the two most significant findings (p < 0.05) were for cardiovascular admissions of people aged > or = 65 which showed a positive association with PM10 as a mean of the 3 previous days, and a negative association with O3 as a mean of the previous three days. Analyses of outcomes based on linkage with previous cardiorespiratory emergency admissions did not show substantially different results. CONCLUSION: These data suggest that in the City of Edinburgh, after correction for confounders, there was a small but significant association between concentrations of black smoke and respiratory mortality in the older age group, probably attributable to higher pollution levels in the early part of the study period. There were also generally weak and variable associations between day to day changes in concentrations of urban air pollutants at a single central point and emergency hospital admission rates from cardiac and respiratory disease.     

Summertime haze air pollution and children with asthma

In order to investigate associations between summertime haze air pollution and asthma at an individual level, 52, 58, and 56 children (ages 7 to 13) attending a summer "asthma camp" were followed during the last week of June in 1991, 1992, and 1993, respectively. Most of the subjects had moderate to severe asthma. Daily records were kept of the environmental conditions, as well as of subject medication use, lung function, and medical symptoms. Air pollution was found to be significantly and consistently correlated with acute asthma exacerbations, chest symptoms, and lung function decrements. The pollutant most consistently associated with adverse health consequences was ozone (O3), although associations with sulfates and hydrogen ion suggest a possible role by fine particles as well. Effects were found to be roughly monotonic as a function of O3 concentration. Regression of morning (8:00 A.M.) to afternoon (5:00 P.M.) peak flow change on O3 indicated pulmonary function reductions similar to those previously reported for more active children without asthma. Moreover, analyses also indicated an increased risk of an asthma exacerbation and of experiencing chest symptoms of approximately 40% on the highest pollution day, relative to the mean. Based on these relative risk estimates, a rise in the 1-h daily maximal O3 from 84 ppb to 160 ppb was associated in this group with an increase from 20 to 28 (+/- 2) in the expected number of unscheduled medications administered/day, and from 29 to 41 (+/- 3) in the expected total number of chest symptoms/day. Thus, air pollution can be a major contributor to the respiratory problems experienced by children with asthma during the summer months.     

Characteristics of subjects with a high frequency of emergency visits for asthma

The determinants of frequent visits to the emergency department (ED) for asthma were evaluated in 30 patients who made 2 or more ED visits for asthma (mean, 3.1; range, 2 to 9) over a period of 1 year. They were matched for age, sex, and medication with a control group of asthmatic patients who had made no ED visits within the same period. Evaluation included measurements of expiratory flows (baseline FEV1; PEFR 4 times daily for 3 weeks), airway responsiveness to methacholine, perception of induced bronchoconstriction, and questionnaires on quality of life and knowledge of asthma and its management. In comparison with the control group, the study group showed a trend toward inferior socioeconomic status, education level, and technical abilities (eg, inhaler use). Both groups had similar baseline FEV1, reversibility of airflow obstruction, methacholine-induced changes in expiratory flows, and perception of bronchoconstriction. Diurnal variation in PEFR was slightly increased in the study group. Absenteeism from work or school was higher in the study group but quality of life score was similar to controls. Patients with frequent ED visits showed significantly lesser knowledge of asthma control criteria, as well as an overall trend toward reduced asthma management knowledge and skills. In conclusion, in addition to the previously reported undertreatment of asthma, other factors such as insufficient asthma management knowledge and skills may contribute to frequent ED visits for asthma.     

Chamber exposures of children to mixed ozone, sulfur dioxide, and sulfuric acid

To help assess acute health effects of summer air pollution in the eastern United States, we simulated ambient "acid summer haze" as closely as was practical in a laboratory chamber. We exposed young volunteers who were thought to be sensitive to this pollutant mixture on the basis of previous epidemiologic evidence. Specifically, we exposed 41 subjects aged 9-12 y to mixed ozone (0.10 ppm), sulfur dioxide (0.10 ppm), and 0.6-microm sulfuric acid aerosol (100 +/- 40 microg/m3, mean +/- standard deviation) for 4 h, during which there was intermittent exercise. Fifteen subjects were healthy, and 26 had allergy or mild asthma. The entire group responded nonsignificantly (p > .05) to pollution exposure (relative to clean air), as determined by spirometry, symptoms, and overall discomfort level during exercise. Subjects with allergy/asthma showed a positive association (p = .01) between symptoms and acid dose; in healthy subjects, that association was negative (p = .08). In these chamber-exposure studies, we noted less of an effect than was reported in previous epidemiologic studies of children exposed to ambient "acid summer haze."     

Differential expression of the p27Kip1 mRNA in IFN-sensitive and resistant cell lines

STUDY OBJECTIVES: In a previous study published by our group, six out of nine subjects with mild allergic asthma were shown to have an enhanced response to allergen challenge following a 1-h exposure in an 0.8-m3 exposure chamber (modified from a body plethysmograph) to an average of 120 parts per billion (ppb) ozone at rest. Other studies failed to confirm this effect. In the present study, using a similar design, we reexamined this effect using a larger group of asthmatics and a larger chamber allowing minimal fluctuations in ozone levels during exposures. DESIGN: Prospective, randomized single-blinded crossover study. SETTING: Pulmonary function laboratory equipped with an exposure chamber. SUBJECTS: Fifteen subjects had mild allergic asthma; 9 men and 6 women; the mean (SD) age was 32.5 (10) years; FEV1 was 3.4 (0.8) L; baseline methacholine provocation concentration causing a 20% fall in FEV1 was (PC20) 3.28 (4.1) mg/mL. INTERVENTIONS: Each participant was exposed, at rest, on 1 day to filtered air and on another day to ozone (mean level=120 ppb) in a larger exposure chamber than the one used in our first study with less variability in ozone level (110 to 130 vs 85 to 175 ppb) using a random, single-blinded design. After each exposure, the subject was challenged with allergen (nine with grass pollen extract and six with ragweed extract) and allergen PC15 was measured. RESULTS: Ozone preexposure did not affect allergen PC15 when compared with clean air preexposure (allergen PC15 dilution 1/114 vs 1/119, respectively). Ozone vs air preexposure resulted in an allergen PC15 that was lower in five subjects, higher in six, and unchanged (within one doubling dose) in four. CONCLUSIONS: At this low level with less variability and lower peaks than our previous study, ozone had no significant effect on airway allergen responsiveness.     

Are non-allergenic environmental factors important in asthma?

OBJECTIVE: To review the roles of viral respiratory tract infections, environmental tobacco smoke and air pollution in asthma. DATA SOURCES: MEDLINE (1992-1995) searches were conducted for publications on asthma, environmental tobacco smoke, ozone, nitrogen dioxide and particulates. STUDY SELECTION: Representative original experimental and epidemiological studies and reviews of viral infections in asthma. DATA SYNTHESIS: Respiratory virus infections are the most common and important trigger of asthma attacks in children and probably also in adults. Their role in promoting development of asthma is not so clear. Exposure to environmental tobacco smoke is almost certainly responsible for some cases of childhood asthma, and can also trigger symptoms of bronchoconstriction in adults with asthma. Exposure to ozone or nitrogen dioxide is associated with symptoms, impaired lung function, bronchial hyperresponsiveness and hospital presentations for asthma. These pollutants may also act as cofactors in the development of allergen-specific bronchial hyperresponsiveness. CONCLUSIONS: Research on preventing upper respiratory viral infections may reduce asthma morbidity. The move to non-smoking workplaces is welcome, but new interventions are needed to prevent young women taking up smoking and subsequently exposing their children. The ambient air quality guideline for ozone should be revised and a health-based guideline for respirable particulates introduced.     

Air pollution and asthma

The role of air pollution in the increased prevalence and morbidity of asthma has been widely debated, but results to date indicate that the normally encountered levels of air pollution are unlikely to contribute to a worsening of asthma. When the levels of sulphur dioxide (SO2) are exceptionally high it is possible that asthmatic patients may have increased symptoms after exertion, since this irritant gas acts as a trigger to bronchoconstriction. There is also evidence that suspended particles may also act as an inciter of asthma symptoms when concentrations are high. Experimentally, ozone in high concentrations may increase airway responsiveness in both normal and asthmatic subjects by inducing airway inflammation, but asthmatic individuals show the same responses as normal subjects and there is little or no evidence to link increases in ambient ozone with an increase in asthma. There is little evidence that nitrogen dioxide (NO2), even at the peak levels recorded, has any significant effect on airway function in normal or asthmatic individuals. Other air pollutants which are present in lower concentrations have not been studied as extensively, but there is no convincing evidence that they cause significant respiratory symptoms in asthmatic patients. It is still possible that combinations of air pollutants may have greater effects on airway function than exposure to a single pollutant, although there is little evidence to support this. Epidemiological evidence provides little support for the idea that atmospheric pollution levels are related to the frequency of asthma symptoms or the frequency of attacks. More importantly, there is no evidence that asthma prevalence or aetiology is related to the level of air pollution. A review of currently available information therefore provides little evidence for the widely expressed view that atmospheric pollution is related to increased prevalence or morbidity of asthma or is related to the causation of asthma.     

Meta-analysis and dose-response functions of air pollution respiratory effects

A Meta-analysis was conducted on 107 original epidemiological papers published between 1980 and 1993 on the respiratory health impact of suspended particles, sulfur dioxide, ozone and nitrogen dioxide. These are the usual air quality indicators that are monitored in urban ambient air. The range of exposures that were studied (averages and 90th percentiles are respectively up to 88, 83, 124 and 53 mu/m3 (averages) and 180, 147, 234 and 131 micrograms/m3 (90th percentile) for each of the four pollution indicators) allowed assessment of dose-response functions for irritative pulmonary conditions (cough and/or asthma episodes) and respiratory function (FEVI and peak expiratory flow). The dose-response functions seem linear in the range of observed concentrations, with nitrogen dioxide showing the least consistent association across different health indicators. When applied to exposures measured as a 100 micrograms/m3 increase of pollutant's concentrations compared to low background values, the average relative risks of airway irritation (cough and/or asthma épisodes) range, according to the pollutant, from 1.08 to 1.47; average relative decreases of respiratory function amount to 1.1 to 2.2%. The effects are most often stronger among young subjects. The results of this study, when applied to air pollution concentrations in the range of values that were observed in this study, should foster health risk assessment studies in places where population air pollution exposures are available.     

Inhibition of neutrophil apoptosis and modulation of the inflammatory response by granulocyte colony-stimulating factor in healthy and ethanol-treated human volunteers

Nitrogen dioxide levels were measured in 80 homes in the Latrobe Valley, Victoria, Australia, using passive samplers. Some 148 children between 7 and 14 yr of age were recruited as study participants, 53 of whom had asthma. Health outcomes for the children were studied using a respiratory questionnaire, skin prick tests, and peak flow measurements. Nitrogen dioxide concentrations were low, with an indoor median of 11.6 microgram/m3 (6.0 ppb), and a maximum of 246 microgram/m3 (128 ppb). Respiratory symptoms were more common in children exposed to a gas stove (odds ratio 2.3 [95% CI 1. 0-5.2], adjusted for parental allergy, parental asthma, and sex). Nitrogen dioxide exposure was a marginal risk factor for respiratory symptoms, with a dose-response association present (p = 0.09). Gas stove exposure was a significant risk factor for respiratory symptoms even after adjusting for nitrogen dioxide levels (odds ratio 2.2 [1.0-4.8]), suggesting an additional risk apart from the average nitrogen dioxide exposure associated with gas stove use. Atopic children tended to have a greater risk of respiratory symptoms compared with nonatopic children with exposure to gas stoves or nitrogen dioxide, but the difference was not significant.     

Traffic-related NO2 and the prevalence of asthma and respiratory symptoms in seven year olds

The aim of this study was to determine whether outdoor nitrogen dioxide (NO2) was associated with the prevalence of asthma and respiratory symptoms. In eight nonurban communities, 843 children resident for a minimum of 2 yrs were studied. Since industrial sources of air pollution were at least 20 km away from the study communities, NO2 was considered to primarily indicate traffic-related air pollution. NO2 was recorded at central monitors, and the 3 yr mean exposure was calculated. Asthma and respiratory symptoms were assessed according to the International Study on Asthma and Allergy in Childhood. Prevalence of asthma at some time ("ever asthma") was associated with long-term NO2. In parallel with increasing levels of NO2 (community specific 3 yr mean 6.0-17.0 parts per billion (ppb)), asthma prevalence was 2.5, 1.4, 1.6, 2.3, 3.4, 3.6, 7.6 and 8.5%, respectively (p=0.002 for trend). The prevalence odds ratios (PORs) for "ever asthma", following adjustment for gender, age, parental education, passive smoke exposure, type of indoor heating, and parental asthma, were 1.28 (95% confidence interval (95% CI) 0.20-7.98), 2.14 (95% CI 0.40-11.3) and 5.81 (95% CI 1.27-26.5), when each of two communities with low, regular and high NO2, respectively, were compared with the two communities with very low NO2. For symptoms "wheeze" (adjusted PORs for increased NO2: 1.47, 1.23 and 2.27) and "cough apart from colds" (adjusted PORs for increased NO2: 1.49, 1.93 and 2.07), a similar trend was seen. In this study a significant relationship was observed between traffic-related nitrogen dioxide and the prevalence of asthma and symptoms. Whether this association is causal has to be tested in longitudinal studies.