Acute effect of air pollution on respiratory complaints, exhaled NO and biomarkers in nasal lavages of allergic children during the pollen season

Locations of Adolescent Physical Activity in an Urban Environment and Their Associations with Air Pollution and Lung Function

Rationale: Physical activity while being exposed to high concentrations of air pollution may lead to greater inhalation of pollutant particles and gases. Thus, owing to features of the built city environment, specific locations where physical activity take place may put individuals at increased risk for harmful inhaled exposures leading to decrements in lung function.Objectives: The objectives were to determine locations throughout an urban landscape where children engage in moderate to vigorous activity (MVA). We hypothesized that outdoor activity would be associated with increased exposure to air pollution and reduced lung function.Methods: Children aged 9-14 years living in New York City (NYC) (n = 151) wore global positioning system devices and wrist accelerometers for two 24-hour periods. Time-stamped global positioning system points and accelerometer data were aggregated and mapped using ArcGIS to determine locations where children engaged in MVA. Location-specific particulate matter <2.5 microns and nitrogen dioxide (NO₂) was determined based on land use regression models of street-level pollution. Temporal air pollution exposure was determined based on daily concentrations collected at one central site in NYC. Forced expiratory volume in 1 second (FEV₁), forced vital capacity (FVC), and forced expiratory flow, midexpiratory phase (FEF_25-75) were collected following each 24-hour period. Data were analyzed using multivariable linear regression models to examine associations between MVA time and both lung function and air pollution in separate models. Additionally, a multiplicative interaction term (MVA time × season) was included to test whether the association between MVA time and lung function outcomes varied by warmer versus colder months.Results: On average, children spent less MVA time outdoors (38.2 ± 39.6 min/d) compared with indoors (71.9 ± 74.7 min/d, P < 0.01), regardless of season. The majority of outdoor MVA occurred along sidewalks and roadbeds (30.2 ± 33.3 min/d, 76.9% of outdoor) where annual average concentrations of NO₂ were relatively high. Interquartile range (IQR) increase in outdoor MVA time (44 min) was associated with higher levels of annual average NO₂ (P < 0.01) but not particulate matter <2.5 microns. In warmer months, for IQR increase in outdoor MVA time, children had 1.41% lower FEV₁/FVC (95% confidence interval [95% CI], -2.46 to -0.36) and 4.40% lower percent predicted FEF_25-75 (95% CI, -8.02 to -0.78). These results persisted even after adjustment for location-specific annual average concentrations of NO₂. No association was observed between MVA time and lung function in colder months (P > 0.05), and a formal test for interaction (MVA time × season) was significant (P value for interaction = 0.01 and 0.03 for FEV₁/FVC and FEF_25-75, respectively).Conclusions: Children in NYC spent less time active outdoors compared with indoors. Outdoor activity was greatest near traffic sources and associated with higher annual average concentrations of NO₂. In warmer months, outdoor activity was associated with lower lung function, but this association did not appear to be mediated by higher exposure to outdoor pollution during exercise.

Is short-term exposure to grass pollen adversely associated with lung function and airway inflammation in the community?

BACKGROUND

The association between grass pollen exposure and early markers of asthma exacerbations such as lung function changes and increase in airway inflammation is limited. We investigated the associations between short-term grass pollen exposure and lung function and airway inflammation in a community-based sample, and whether any such associations were modified by current asthma, current hay fever, pollen sensitization, age, and other environmental factors.

METHODS

Cross-sectional and short-term analyses of data from the Melbourne Atopy Cohort Study (MACS) participants (n = 936). Lung function was assessed using spirometry. Airway inflammation was assessed by fractional exhaled nitric oxide (FeNO) and exhaled breath condensate pH and nitrogen oxides (NOx). Daily pollen counts were collected using a volumetric spore trap. The associations were examined by linear regression.

RESULTS

Higher ambient levels of grass pollen 2 days before (lag 2) were associated with lower mid-forced expiratory flow (FEF_25%-75% ) and FEV₁ /FVC ratio (Coef. [95% CI] = -119 [-226, -11] mL/s and -1.0 [-3.0, -0.03] %, respectively) and also 3 days before (lag 3). Increased levels of grass pollen a day before (lag 1) were associated with increased FeNO (4.35 [-0.1, 8.7] ppb) and also at lag 2. Adverse associations between pollen and multiple outcomes were greater in adults with current asthma, hay fever, and pollen sensitization.

CONCLUSION

Grass pollen exposure was associated with eosinophilic airway inflammation 1-2 days after exposure and airway obstruction 2-3 days after exposure. Adults and individuals with asthma, hay fever, and pollen sensitization may be at higher risk.

Outdoor pollen-related changes in lung function and markers of airway inflammation: A systematic review and meta-analysis

BACKGROUND

Experimental challenge studies have shown that pollen can have early and delayed effects on the lungs and airways. Here, we qualitatively and quantitatively synthesize the evidence of outdoor pollen exposure on various lung function and airway inflammation markers in community-based studies.

METHODS

Four online databases were searched: Medline, Web of Science, CINAHL and Google Scholar. The search strategy included terms relating to both exposure and outcomes. Inclusion criteria were human-based studies published in English that were representative of the community. Additionally, we only considered cross-sectional or short-term longitudinal studies which investigated pollen exposure by levels or season. Study quality assessment was performed using the Newcastle-Ottawa scale. Meta-analysis was conducted using random-effects models.

RESULTS

We included 27 of 6551 studies identified from the search. Qualitative synthesis indicated associations between pollen exposure and predominantly type-2 inflammation in both the upper and lower airways, but little evidence for lung function changes. People with ever asthma and/or seasonal allergic rhinitis (SAR) were at higher risk of such airway inflammation. Meta-analysis confirmed a positive relationship between pollen season, eosinophilia and eosinophil cationic protein (ECP) in people with ever SAR but the results between studies were highly variable. Heterogeneity was reduced after further subgrouping by age, and the forest plots indicated that eosinophilic airway inflammation to outdoor pollen exposure increased with age.

CONCLUSION

Among people with ever asthma and ever SAR, exposure to increased ambient pollen triggers type-2 upper and lower airway inflammation rather than a non-specific or innate inflammation. These findings can lead to the formulation of specific pollen immunotherapy for susceptible individuals. Future research should be directed towards investigating lagged associations and effect modifications using larger and more generalized populations.

SYSTEMATIC REVIEW REGISTRATION

CRD42020146981 (PROSPERO).

Association between lung function of school age children and short-term exposure to air pollution and pollen: the PARIS cohort

BACKGROUND

Daily levels of ambient air pollution and pollen may affect lung function but have rarely been studied together. We investigated short-term exposure to pollen and air pollution in relation to lung function in school-age children from a French population-based birth cohort.

METHODS

This study included 1063 children from the PARIS (Pollution and Asthma Risk: an Infant Study) cohort whose lung function and FeNO measurements were performed at age 8 years old. Exposure data were collected up to 4 days before testing. We estimated daily total pollen concentration, daily allergenic risk indices for nine pollen taxa, as well as daily concentrations of three air pollutants (particulate matter less than 10 µm (PM₁₀), nitrogen dioxide (NO₂), ozone (O₃)). Children with similar pollen and air pollution exposure were grouped using multidimensional longitudinal cluster analysis. Associations between clusters of pollen and air pollution exposure and respiratory indices (FEV₁, FVC, FeNO) were studied using multivariable linear and logistic regression models adjusted for potential confounders.

RESULTS

Four clusters of exposure were identified: no pollen and low air pollution (Cluster 1), grass pollen (Cluster 2), PM₁₀ (Cluster 3) and birch/plane-tree pollen with high total pollen count (Cluster 4). Compared with children in Cluster 1, children in Cluster 2 had significantly lower FEV₁ and FVC levels, and children from Cluster 3 had higher FeNO levels. For FEV₁ and FVC, the associations appeared stronger in children with current asthma. Additional analysis suggested a joint effect of grass pollen and air pollution on lung function.

CONCLUSION

Daily ambient chemical and biological air quality could adversely influence lung function in children.

Proximity to major roadways and asthma symptoms in the School Inner-City Asthma Study

BACKGROUND

Traffic proximity has been associated with adverse respiratory health outcomes. Less is known about the combined impact of residential and school exposures on pediatric asthma.

OBJECTIVE

We sought to use spatial analysis methodology to analyze residential and school proximity to major roadways and pediatric asthma morbidity.

METHODS

The School Inner-City Asthma Study (n = 350) recruited school-aged children with asthma. Each participant's school and home addresses were geocoded, and distances from major roadways were measured to calculate a composite measure accounting for both home and school traffic exposure. Generalized estimating equation models were clustered by subject and adjusted for age, race/ethnicity, sex, income, environmental tobacco smoke, controller medication, upper respiratory tract infections, and seasonality.

RESULTS

The majority of participants (62%) attended schools within 100 m from major roadways, and 40% also resided within 100 m of major roadways. In multivariate analyses major roadway proximity was independently associated with increased asthma symptom days. At greater than the threshold of 100 m, children had 29% less odds of a symptom day over the past 2 weeks for each 100-m increase in distance from a major roadway (odds ratio, 0.71; 95% CI, 0.58-0.87; P < .01). Children farther from a major roadway also had significantly less reported health care use (odds ratio, 0.63; 95% CI, 0.47-0.85; P < .01) and were significantly less likely to have poor asthma control (odds ratio, 0.80; 95% CI, 0.69-0.94; P < .01). There was not a meaningful association between distance to a major roadway and lung function outcomes.

CONCLUSIONS

Proximity to a major roadway, a composite measure of home and school exposure but primarily driven by home exposure, was associated with greater asthma morbidity. More studies are needed to evaluate the independent effect of school distance to a roadway on asthma morbidity.

POLLAR: Impact of air POLLution on Asthma and Rhinitis; a European Institute of Innovation and Technology Health (EIT Health) project

Allergic rhinitis (AR) is impacted by allergens and air pollution but interactions between air pollution, sleep and allergic diseases are insufficiently understood. POLLAR (Impact of air POLLution on sleep, Asthma and Rhinitis) is a project of the European Institute of Innovation and Technology (EIT Health). It will use a freely-existing application for AR monitoring that has been tested in 23 countries (the Allergy Diary, iOS and Android, 17,000 users, TLR8). The Allergy Diary will be combined with a new tool allowing queries on allergen, pollen (TLR2), sleep quality and disorders (TRL2) as well as existing longitudinal and geolocalized pollution data. Machine learning will be used to assess the relationship between air pollution, sleep and AR comparing polluted and non-polluted areas in 6 EU countries. Data generated in 2018 will be confirmed in 2019 and extended by the individual prospective assessment of pollution (portable sensor, TLR7) in AR. Sleep apnea patients will be used as a demonstrator of sleep disorder that can be modulated in terms of symptoms and severity by air pollution and AR. The geographic information system GIS will map the results. Consequences on quality of life (EQ-5D), asthma, school, work and sleep will be monitored and disseminated towards the population. The impacts of POLLAR will be (1) to propose novel care pathways integrating pollution, sleep and patients' literacy, (2) to study sleep consequences of pollution and its impact on frequent chronic diseases, (3) to improve work productivity, (4) to propose the basis for a sentinel network at the EU level for pollution and allergy, (5) to assess the societal implications of the interaction. MASK paper N°32.

Coarse Fraction Particle Matter and Exhaled Nitric Oxide in Non-Asthmatic Children

Coarse particle matter, PM_coarse, is associated with increased respiratory morbidity and mortality. The aim of this study was to investigate the association between short-term changes in PM_coarse and sub-clininal airway inflammation in children. Healthy children aged 11 years from two northern Swedish elementary schools underwent fraction of exhaled nitrogen oxide (FENO) measurements to determine levels of airway inflammation twice weekly during the study period from 11 April–6 June 2011. Daily exposure to PM_coarse, PM_2.5, NO₂, NOx, NO and O₃ and birch pollen was estimated. Multiple linear regression was used. Personal covariates were included as fixed effects and subjects were included as a random effect. In total, 95 children participated in the study, and in all 493 FENO measurements were made. The mean level of PM_coarse was 16.1 μg/m³ (range 4.1–42.3), and that of O₃ was 75.0 μg/m³ (range: 51.3–106.3). That of NO₂ was 17.0 μg/m³ (range: 4.7–31.3), NOx was 82.1 μg/m³ (range: 13.3–165.3), and NO was 65 μg/m³ (range: 8.7–138.4) during the study period. In multi-pollutant models an interquartile range increase in 24 h PM_coarse was associated with increases in FENO by between 6.9 ppb (95% confidence interval 0.0–14) and 7.3 ppb (95% confidence interval 0.4–14.9). PM_coarse was associated with an increase in FENO, indicating sub-clinical airway inflammation in healthy children.

Adopting Clean Fuels and Technologies on School Buses. Pollution and Health Impacts in Children

RATIONALE

More than 25 million American children breathe polluted air on diesel school buses. Emission reduction policies exist, but the health impacts to individual children have not been evaluated.

METHODS

Using a natural experiment, we characterized the exposures and health of 275 school bus riders before, during, and after the adoption of clean technologies and fuels between 2005 and 2009. Air pollution was measured during 597 trips on 188 school buses. Repeated measures of exhaled nitric oxide (FeNO), lung function (FEV1, FVC), and absenteeism were also collected monthly (1,768 visits). Mixed-effects models longitudinally related the adoption of diesel oxidation catalysts (DOCs), closed crankcase ventilation systems (CCVs), ultralow-sulfur diesel (ULSD), or biodiesel with exposures and health.

MEASUREMENTS AND MAIN RESULTS

Fine and ultrafine particle concentrations were 10-50% lower on buses using ULSD, DOCs, and/or CCVs. ULSD adoption was also associated with reduced FeNO (-16% [95% confidence interval (CI), -21 to -10%]), greater changes in FVC and FEV1 (0.02 [95% CI, 0.003 to 0.05] and 0.01 [95% CI, -0.006 to 0.03] L/yr, respectively), and lower absenteeism (-8% [95% CI, -16.0 to -0.7%]), with stronger associations among patients with asthma. DOCs, and to a lesser extent CCVs, also were associated with improved FeNO, FVC growth, and absenteeism, but these findings were primarily restricted to patients with persistent asthma and were often sensitive to control for ULSD. No health benefits were noted for biodiesel. Extrapolating to the U.S. population, changed fuel/technologies likely reduced absenteeism by more than 14 million/yr.

CONCLUSIONS

National and local diesel policies appear to have reduced children's exposures and improved health.

Noninvasive effects measurements for air pollution human studies: methods, analysis, and implications

Human exposure studies, compared with cell and animal models, are heavily relied upon to study the associations between health effects in humans and air pollutant inhalation. Human studies vary in exposure methodology, with some work conducted in controlled settings, whereas other studies are conducted in ambient environments. Human studies can also vary in the health metrics explored, as there exists a myriad of health effect end points commonly measured. In this review, we compiled mini reviews of the most commonly used noninvasive health effect end points that are suitable for panel studies of air pollution, broken into cardiovascular end points, respiratory end points, and biomarkers of effect from biological specimens. Pertinent information regarding each health end point and the suggested methods for mobile collection in the field are assessed. In addition, the clinical implications for each health end point are summarized, along with the factors identified that can modify each measurement. Finally, the important research findings regarding each health end point and air pollutant exposures were reviewed. It appeared that most of the adverse health effects end points explored were found to positively correlate with pollutant levels, although differences in study design, pollutants measured, and study population were found to influence the magnitude of these effects. Thus, this review is intended to act as a guide for researchers interested in conducting human exposure studies of air pollutants while in the field, although there can be a wider application for using these end points in many epidemiological study designs.

Diesel exhaust but not ozone increases fraction of exhaled nitric oxide in a randomized controlled experimental exposure study of healthy human subjects

BACKGROUND

Fraction of exhaled nitric oxide (FENO) is a promising non-invasive index of airway inflammation that may be used to assess respiratory effects of air pollution. We evaluated FENO as a measure of airway inflammation after controlled exposure to diesel exhaust or ozone.

METHODS

Healthy volunteers were exposed to either diesel exhaust (particle concentration 300 μg/m3) and filtered air for one hour, or ozone (300 ppb) and filtered air for 75 minutes. FENO was measured in duplicate at expiratory flow rates of 10, 50, 100 and 270 mL/s before, 6 and 24 hours after each exposure.

RESULTS

Exposure to diesel exhaust increased FENO at 6 hours compared with air at expiratory flow rates of 10 mL/s (p = 0.01) and at 50 mL/s (p = 0.011), but FENO did not differ significantly at higher flow rates. Increases in FENO following diesel exhaust were attenuated at 24 hours. Ozone did not affect FENO at any flow rate or time point.

CONCLUSIONS

Exposure to diesel exhaust, but not ozone, increased FENO concentrations in healthy subjects. Differences in the induction of airway inflammation may explain divergent responses to diesel exhaust and ozone, with implications for the use of FENO as an index of exposure to air pollution.

Air pollution and increased levels of fractional exhaled nitric oxide in children with no history of airway damage

Air pollution is associated with a wide range of adverse respiratory events. In order to study the mechanism associated with these effects, the relationships between fractional exhaled nitric oxide (FeNO), a potential marker of airway inflammation, and exposure to air pollution were examined in schoolchildren. FeNO was measured in 104 children (34 asthmatics and 70 non-asthmatics) drawn from the general population simultaneously with air pollution assessments (fine particles with an aerodiameter under 2.5 microm, nitrogen dioxide, acetaldehyde, and formaldehyde, with pumps and passive samplers) in schoolyards and classrooms. Asthmatics exhaled more FeNO than non-asthmatics. FeNO levels were significantly elevated in both asthmatic and non-asthmatic children exposed to high concentrations of formaldehyde, acetaldehyde, and PM(2.5). Differences between high versus low exposure in non-asthmatics resulted in an FeNO increase ranging from 45% for indoor acetaldehyde to 62% for indoor PM(2.5). Stronger associations were found in non-asthmatic children who were atopic, suggesting that atopic children may be more sensitive to air pollution than non-atopic children. Exposure to air pollution may lead to airway inflammation, as measured by FeNO, in schoolchildren. These associations occur even in children with no history of airway damage and seem to be enhanced in atopic subjects.

How can we measure the impact of pollutants on respiratory function in very young children? Methodological aspects

There is increasing evidence that air pollution particularly affects infants and small preschool children. However, detecting air pollution effects on lung function in small children is technically difficult and requires non-invasive methods that can assess lung function and inflammatory markers in larger cohorts. This review discusses the principles, usefulness and shortcomings of various lung function techniques used to detect pollution effects in small children. The majority of these techniques have been used to detect effects of the dominant indoor pollutant, tobacco exposure. However there is increasing evidence that non-invasive lung function techniques can also detect the effects of outdoor air pollution.

Environmental influence on the measurement of exhaled nitric oxide concentration in school children: special reference to methodology

INTRODUCTION

Measuring exhaled nitric oxide (eNO) is a noninvasive and useful method for evaluating the correlation between airway inflammation and air pollution. The method is being used in studies; however, the effects of polluted air on eNO values are poorly understood. If polluted air significantly affects eNO concentrations, then it would be hard to evaluate the concentration of eNO, particularly in epidemiological measurements to detect the effects of airway inflammation, such as that in bronchial asthma. Thus, we hypothesized that short-term exposure to air pollution affects eNO values.

PURPOSE

To study the effects of environmental nitrogen oxides on the measurement of eNO concentration.

SUBJECTS AND METHODS

A total of 19 school children who lived on a large street with heavy traffic with random allocation were studied. Subjects with bronchial asthma were identified with a questionnaire. Suspended particulate matter. including particulate matter with an aerodynamic diameter < or =2.5 microm (PM(2.5)), optical black carbon, nitric oxide (NO), nitric dioxide (NO(2)), and nitrogen oxides (NO(X)), were measured at a fixed place along the street every hour for 11 consecutive days. The concentrations of NO and NO(2) for each subject were measured by an individual 2-pyenyl-4,4,5,5-tetramethylimidazoline-3-oxide-1-oxyl sampler, and the concentration of eNO was measured with the off-line method.

RESULTS

Of 19 subjects, 3 were found to have bronchial asthma. The level of each pollutant for 11 days peaked during the mornings (6;9 a.m.) and evenings (6;9 p.m.) due to traffic jams; average eNO values in healthy subjects and those with asthma were 27.1 +/- 9.7 and 57.7 +/- 18.6 ppb (p=0.098), respectively. It was found that the eNO value remained high when the mean values of various pollutants remained high for 8 hours before the measurements. It was estimated that the mean eNO values increased by 1.08 ppb (95% CI: 0.72;1.45) when the mean NO(X) value for the previous 8 hours reached approximately 10 ppb.

CONCLUSION

We conclude that short-term exposure to polluted air of at least 8 hours before measurement affects eNO values. Therefore, caution should be exercised when measuring eNO value in epidemiological studies.

Ambient and microenvironmental particles and exhaled nitric oxide before and after a group bus trip

OBJECTIVES

Airborne particles have been linked to pulmonary oxidative stress and inflammation. Because these effects may be particularly great for traffic-related particles, we examined associations between particle exposures and exhaled nitric oxide (FE(NO)) in a study of 44 senior citizens, which involved repeated trips aboard a diesel bus.

METHODS

Samples of FE(NO) collected before and after the trips were regressed against microenvironmental and ambient particle concentrations using mixed models controlling for subject, day, trip, vitamins, collection device, mold, pollen, room air nitric oxide, apparent temperature, and time to analysis. Although ambient concentrations were collected at a fixed location, continuous group-level personal samples characterized microenvironmental exposures throughout facility and trip periods.

RESULTS

In pre-trip samples, both microenvironmental and ambient exposures to fine particles were positively associated with FE(NO). For example, an interquartile increase of 4 microg/m(3) in the daily microenvironmental PM(2.5) concentration was associated with a 13% [95% confidence interval (CI), 2-24%) increase in FE(NO). After the trips, however, FE(NO) concentrations were associated pre-dominantly with microenvironmental exposures, with significant associations for concentrations measured throughout the whole day. Associations with exposures during the trip also were strong and statistically significant with a 24% (95% CI, 15-34%) increase in FE(NO) predicted per interquartile increase of 9 microg/m(3) in PM(2.5). Although pre-trip findings were generally robust, our post-trip findings were sensitive to several influential days.

CONCLUSIONS

Fine particle exposures resulted in increased levels of FE(NO) in elderly adults, suggestive of increased airway inflammation. These associations were best assessed by microenvironmental exposure measurements during periods of high personal particle exposures.

Personal and ambient air pollution is associated with increased exhaled nitric oxide in children with asthma

BACKGROUND

Research has shown associations between pediatric asthma outcomes and airborne particulate matter (PM). The importance of particle components remains to be determined.

METHODS

We followed a panel of 45 schoolchildren with persistent asthma living in Southern California. Subjects were monitored over 10 days with offline fractional exhaled nitric oxide (FeNO), a biomarker of airway inflammation. Personal active sampler exposures included continuous particulate matter < 2.5 microm in aerodynamic diameter (PM2.5), 24-hr PM2.5 elemental and organic carbon (EC, OC), and 24-hr nitrogen dioxide. Ambient exposures included PM2.5, PM2.5 EC and OC, and NO2. Data were analyzed with mixed models controlling for personal temperature, humidity and 10-day period.

RESULTS

The strongest positive associations were between FeNO and 2-day average pollutant concentrations. Per interquartile range pollutant increase, these were: for 24 microg/m3 personal PM2.5, 1.1 ppb FeNO [95% confidence interval (CI), 0.1-1.9]; for 0.6 microg/m3 personal EC, 0.7 ppb FeNO (95% CI, 0.3-1.1); for 17 ppb personal NO2, 1.6 ppb FeNO (95% CI, 0.4-2.8). Larger associations were found for ambient EC and smaller associations for ambient NO2. Ambient PM2.5 and personal and ambient OC were significant only in subjects taking inhaled corticosteroids (ICS) alone. Subjects taking both ICS and antileukotrienes showed no significant associations. Distributed lag models showed personal PM2.5 in the preceding 5 hr was associated with FeNO. In two-pollutant models, the most robust associations were for personal and ambient EC and NO2, and for personal but not ambient PM2.5.

CONCLUSION

PM associations with airway inflammation in asthmatics may be missed using ambient particle mass, which may not sufficiently represent causal pollutant components from fossil fuel combustion.

Low-level ozone exposure and respiratory symptoms in infants

OBJECTIVE

Recent studies indicate that the U.S. Environmental Protection Agency (EPA) ozone standards may not protect sensitive individuals. In this study we examined respiratory effects of ozone in infants who may be vulnerable, particularly if they are children of asthmatic mothers.

DESIGN

Women delivering babies at one of five hospitals in southwestern Virginia between 1994 and 1996 were invited to participate in a cohort study; 780 women enrolled. Ambient air quality data (ozone and particulate matter) were collected at a central monitoring site.

PARTICIPANTS

This analysis is of 691 infants followed for approximately 83 days between 10 June and 31 August 1995 and/or 1996 ; they contributed a total of 52,421 infant-days of follow-up. Mothers were interviewed at enrollment and approximately biweekly to report infants' daily symptoms. Repeated measures logistic regression models were run separately for wheeze, difficulty breathing, and cough. Ozone metrics included 24-hr average, peak 1-hr, and maximum 8-hr average. Analyses were repeated for the 61 infants whose mothers had asthma.

RESULTS

For every interquartile-range increase in same-day 24-hr average ozone, likelihood of wheeze increased 37% [95% confidence interval (CI), 2-84%]. Among infants of asthmatic mothers, same-day 24-hr average ozone increased likelihood of wheeze 59% (95% CI, 1-154%) and of difficulty breathing 83% (95% CI, 42-136%). Maximum 8-hr ozone and peak 1-hr ozone were associated with difficulty breathing, but not wheeze, in infants of asthmatic mothers. Ozone was not associated with cough.

CONCLUSIONS

At levels of ozone exposure near or below current U.S. EPA standards, infants are at increased risk of respiratory symptoms, particularly infants whose mothers have physician-diagnosed asthma.