Environmental Health Perspectives Volume 107, Number 6, June 1999

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### An A ss ociation between Fine Particles and A sthma Emergency Department Visits for Children in Seattle Gary Norris, 1 Sharon N. YoungPong, 2 Jane Q. Koenig, 3 Timothy V. Larson, 1 Lianne Sheppard, 4 and James W. Stout 5 1 Department of Civil and Environmental Engineeri ng, University of Washington, Seattle, Washington, USA 2 CH2MHill, Portland, Oregon, USA 3 Department of Environmental Health; 4 Department of Biostatistics; and 5 Department of Pediatrics and Health Services, University of Washington, Seattle, Washington, USA

 Introduction  Methods  Results  Discussion Abstract Asthma is the most common chronic illness o f childhood and its prevalence is increasing, causing much concern for identification of risk factors such as air pollution. We previously conducted a study showing a relationship between asthma visits in all persons < 65 years of age to emergency

departme nts (EDs) and air pollution in Seattle, Washington. In that study the most frequent zip codes of the visits were in the inner city. The Seattle - King Count y Department of Public Health (Seattle, WA) subsequently published a report which showed that the hosp italization rate for children in the inner city was over 600/100,000, whereas it was < 100/100,000 for children living in the suburbs. Therefore, we conducted the present study to evaluate whether asthma visits to hospital emergency departments in the inne r city of Seattle were associated with outdoor air pollution levels. ED visits to six hospitals for asthma and dail y air pollution data were obtained for 15 months during 1995 and 1996. Theassociation between air pollution and childhood ED visits for asthma from the inner cit y

area with high asthma hospitalization rates were compared with those from lower hospital utilization areas. Daily

ED counts were regressed against fine particulate matter (PM) , carbon monoxide (CO) , sulfur dioxide, and nitrogen dio xide using a semiparametric Poisson regression model. Significant associations were found between ED visits for asthma in children and fine PM and CO. A change of 11 μg/m 3 in fine PM was associated with a relative rate of 1.15 [95% confidence interval (CI) , 1.08 - 1.23]. There was no stronger association between ED visits for asthma and air pollution in the higher hospital utilization area than in the lower utilization area. These findings were seen when estimated PM 2.5 concentrations were below the newl y ad opted annual National Ambient Air Quality Standard of 15 μg/m 3

. Key words : air pollution , asthma , carbon monoxide , children , emergency

departments , nitrogen dioxide , particulate matter . Environ Health Perspect 107:489 - 493 (1999) . [Online 6 May 1999] http://ehpnet1.niehs.nih.gov/docs/1999/107p489 -493norris/ abstract.html Address correspondence to J.Q. Koenig, Department of Environmental Health, 357234, University

of Washington, 561A Health Sciences Building, Room 7, PO Box 357234, Seattle, WA 98195 - 7234 USA. Telephone: (206) 543 - 2026. Fax: (206) 685 - 3990. E - mail: jkoenig@u.washington.edu We thank N. May

kut for providing technical advice and the Puget Sound Air Pollution Contro l Agency

for continuing to support air pollution health effects research in the Puget Sound region. We also thank the participating hospitals for their assistance, A. Park of the Seattle King Count y Department of Public Health for the population data, and D.V. Bates for helpful comments regarding the manuscript. Funding for this research was from the Puget Sound Air Pollution Control Agency , Seattle, Washington, and in part from NIEHS Center grant 1 P30 ES 07033. Received 16 November 1998 ; accepted 26 February 1999. 

### Introduction Asthma is the most common chronic illness in children and the cause of most school absences ( 1 ). The rate of hospitalization for asthma has been increasing in children < 18 ye ars of age ( 2 ). The primary increases in asthm a morbidity are observed in minority populations in urban areas ( 3 ). When focusing on the inner cit y, 8 - 12% of children under 18 years of age have asthma ( 4 ). Man y airborne factors can aggravate asthma, including cigarette smoke ( 5 ), dust mites, molds, col d air, animal dander ( 6 ), and cockroaches ( 7

). Additionally , increases in air pollution are associated with exacerbation of asthma as measured b y decreased lung function values and respiratory s ymptoms ( 8 - 10 ), shortness of breath ( 11 ), emergency

department (ED) visits ( 12 - 18 ), and hospitalizations ( 19 , 20 ). Thus there is concern that air pollution is aggravating childhood asthma ( 21 , 22 ). Seattle, Washington, is a hilly coastal cit y with a moderate climate. Itis currentl y incompliance with all U.S. Environmental Protection Agency (EPA) air pollution standards. In Seattle, three studies have been conducted that found associations between the exacerbation of asthma and airborne particulate matter (PM). A study conducted during the heating season in a wood smo ke impacted area found a significant association between decreased lung function in elementary school children with asthma and dry light scattering ( sp ), a measure of fine PM ( 8 ). Another study carried out in Seattle from 1989 to 1990 found significant associations between both PM 10 μm in aerody namic diameter (PM 10 ) and light - scattering values (parti cles approximately 1.0 μm) and ED visits for asthma for patients aged 65 ye ars and younger ( 12 ). Most recently , a study of hospital admissions for asthma found an estimated 4 - 5 % increase in admission rate associated with several measures of PM air pollution [PM 10 , particulate matter 2.5 μm in aerody namic diameter (PM 2.5 ), and the coarse fraction PM 10 - PM 2.5 ] ( 20 ). Sources of PM in Seattle include wood smoke, gasoline and diesel vehicles, resuspended road dust, and industry ( 23 ). A source apportionment study

of PM 10 in Seattle in 1991 - 1992 found that during the heating season, 80% of PM in residential areas originated from wood - burning devices ( 24 ). Concentrations of all measured air pollutants have been decreasing in Seattle over the last decade (25 ). The Seattle - King County Health Department (Seattle, WA) carried out a survey from 1987 to 1996 on asthma hospitalization rates for children in Seattle and surrounding areas using the Comprehensive Hospital Abstract Reporting System and found > 50% higher hospitalization rates in central and southeast Seattle (the inner city) as compared to other districts around Seattle ( 26 ). The present study

examined whether there was a stronger association between air pollution and ED visits for asthma for children in the inner city area than for other children in Seattle using the same hospitals and found that there was not. 

### Methods Health data. Daily

ED visits for asthma were obtained from six hospitals in central and southeast Seattle from 1 September 1995 to 31 December 1996. Permission for use of the hospital data was obtained from the University of Washington Human Subjects Office in Seattle. Four of the six hospitals were downtown; the other two were located within 12 km of central Seattle (Figure 1). The total number of daily visits were compiled based on the International Classification of Disease, Ninth Revision (World Health Organization, Geneva) codes for asthma (493.01 - 493.99). Only data for patients under the age of 18 who lived in a 36 - zip code region were used. The zip code region contained the six hospitals and was limited to an area between the air monito ring stations to the north and south of the central area identified in the hospitalization survey (Figure 1). The 36 zip codes in that region were divided into a high and low utilization density based on the childhood ED visits for asthma. The top 20th percentile zip codes were designated as the high ED asthma utilization areas (seven zip codes). The rest of the zip codes were designated as the low ED asthma utilization areas (29 zip codes). The association between air pollution and ED asthma visits was eva luated for the entire study region (36 zip codes), as well as separatel y for the high and low ED utilization regions (Figure 1).Figure 1. Map of study area showing the air pollution monitoring sites and the high and low emergency

department asthma utilization regions. Abbreviations: PM 10 , particulate matter 10μm in aerodynamic diameter; sp , dry light scattering. *Additional station that operat ed from February 1996 to January

1997. Atmospheric data . Air quality data were obtained from the Puget Sound Air Pollution Control Agency

(Seattle, WA) and the state of Washington Department of Ecology (WDOE, Oly

mpia, WA). Daily

PM 10 and dry

light scattering data ( sp ) were available at three sites -- north, central, and south Seattle. Dry light scattering coefficient obtained from an integrating nephelometer most efficientl y measures particles between 0.2 and 0.9 μm ( 27 ), which makes it a measure of the concentration of PM < 1 μm. Carbon monoxide (CO) values were obtained from four sites within the Seattle study region. Sulfur dioxide (SO 2 ) concentrations were measured at one site in central Seattle. Nitrogen dioxide (NO 2 ) and ozone data were obtained from the WDOE for a site in central Seattle and at a site 20 km east of Seattle, respectively . Because the health data collected for this study onl y covered one ozone season (April - Oct ober) there were sufficient ozone data for our model. In addition, the photochemical belt where ozone concentrations are measured is 20 km east of the area where children in this study resided. For pollutants measured at multiple sites, a daily arithmetic average was calculated and used in the time - series analy ses. The appropriate averaging time for each pollutant was based on national and state air quality standards. A 24 - hr average was used for measures of PM. A 1 - hr average was used for SO 2 to reflect the WDOE 1 - hr standard of 400 ppb for SO 2 . Because there is only an annual National Ambient Air Quality Standard (NAAQS) for NO 2 , we selected the daily maximum 1 hr and daily average concentration for this pollutant. A number of studies have used the daily maximum 1 hr NO 2 concentration for time - series analy ses ( 14 , 15 , 28 ). We assumed that CO was a general indicator of the build up of air pollution and we used an averaging time that matched the PM measurements (24 hr). Dew point temperature and average dail y temperature data were collected from the Seattle Tacoma International Airport b y the National Oceanic and Atmospheric Administration National Climatic Data Center (Figure 1); 24 - hr averages were used forthese meteorologic variables.

Statistical analysis . The ED visits for asthma were regressed on predictor and confounding variables using a semiparametric Poisson regression model, a method of choice in recent studies ( 20 , 29 ). All anal yses were conducted with the S - PLUS statistical package (StatSci, Seattle , WA) using a generalized additive model ( 30 ). Base models were first constructed that adjusted for potential confounding factors using day - of - week indicator variables, smooth functions for time trends, temperature, and dew point temperature. The smooth function for time trends used a smoothing spline ( 31 ) that was approximately equivalent to a 2 - month moving average. The degrees of freedom for the smoothing splines for temperature and dew point temperature were selected based on minimizing the degree of fr eedom adjusted deviance ( 32 ). After the base models were created for each of the three utilization areas (high, low, and entire area), the air pollution exposure variables were evaluated b y adding them individually into the model. The final models were eva luated for overdispersion and autocorrelation. Additionally , the assumption of a linear dose response was evaluated using a smooth function. The ED visits for asthma were assumed to be precipitated by either the same - day

air pollution or air pollution lev els up to 4 day s before the visit (0 - to 4 - day lags). These lag times are consistent with that reported b y Cann y and colleagues ( 33 ) who found 84% of the asthmatic children had sy mptoms for 72 hr or less prior to arrival to the ED. 

### Results Table 1 shows a summary of pollutant concentrations in this study . Table 2 summarizes the correlations between the exposure variables that were used. The PM 10 and light - scattering measurements were highly correlated ( r = 0.82). CO was also correlated with these PM measur ements, but not with NO 2 or SO 2 . An additional nephelometer was placed in south Seattle prior to this study to determine whether the inner city area fine PM values correlated with the other fixed PM monitors (Figure 1). The light - scattering measurements fr om the inner cit y monitor were highl y correlated with the other monitors in the network, with a correlation coefficients ranging from 0.75 to 0.85.

The average number of ED visits for asthma in our study for children < 18 years of agewas 1.8 per day , with a maximum of nine visits on any day . This number is low because we restricted the study ar ea to the inner city and surrounding areas. The age distribution of the ED visits for asthma in children < 18 ye ars of age is shown in Table 3. The majority of the ED visits were for children younger than 5 years of age. This age group accounted for 55 and 54% of the asthma visits for the high and low utilization regions, respectively . When comparing asthma ED visits between the two study areas, the high utilization area accounted for 41% of all the asthma ED visits (seven zip codes).

The association between air pollution and increased ED visits for a sthma was evaluated in the three utilization regions. Significant associations between increased ED visits for asthma and air pollution were found across the utilization regions (Table 4). Relative rates were calculated for an interquartile range (IQR; 75 - 25th percentile) increase in pollutant concentration. Fine particles measured as light - scattering coefficient ( sp ) were significantl y associated with increased ED asthma visits in children from all three zip code areas with relative rate increases ranging from 1.13 to 1.16 across the study regions. PM 10 and CO had similar relative rates over the study regions and were significantly associated with ED visits for asthma in the low utilization area and in the total study area. The daily 1 - hr maximum SO 2 and NO 2 were not significantly associated with an increase in ED visits for asthma for an y of the study areas. The association between ED visits for asthma and ozone was only

determin ed for the entire study area because of the large number of missing data (45% of the day s). Ozone was not significantly associated with ED visits for asthma; the relative rate was 1.02 [95% confidence interval (CI), 0.98 - 1.05] for an IQR of 4.6 ppb in the maximum daily running 8 - hr average.

Multipollutant models containing either PM measurement (light scattering or PM 10 ), SO 2 , and NO 2 were also anal yzed for the entire study region using a 1 - day lag. CO was excluded from the multipollutant model because it was assumed to be a surrogate for stagnant con ditions. The relative rate for light scattering and PM 10 remained significant with relative rates of 1.17 (CI , 1.08 - 1.26) and 1.14 (CI , 1.04 - 1.26), whereas the SO 2 andNO 2 terms were not significantly associated with an increase in ED visits for asthma (data not shown). The highest PM concentrations were observed during the winter heating season, as was seen in three earlier studies in Seattle ( 8 , 12 , 20 ) (Figure 2). Initial analy ses showed that 24 and 25 December 1995 were influential data points in the regression because of the high measured PM concentrations. To assess the impact of these data, we repeated the anal ys es with and without these 2 day s to evaluate the effect of these at ypicall y high PM concentrations (Figure 2). The relative rates for increase d ED visits for asthma in the entire study area including and excluding 24 and 25 December were 1.11 (C I, 1.02 - 1.20) and 1.14 (CI , 1.05 - 1.24), respectivel y, for an 11.5 - μg/m 3 increase in PM 10 . Relative rates for inclusion and exclusion of those dates for a ssociations with light scattering were 1.10 (CI, 1.04 - 1.17) and 1.15 (CI, 1.07 - 1.23) for an IQR increase. These results show the relative rates remained significant with the inclusion of the influential dates, but the relative rate for light scattering dec reased 5% with the inclusion of the two high concentration points. Additionally , the inclusion of 24 and 25 December 1995 caused the dose - response relationships for light scattering to show nonlinear behavior above values approximately equal to 40 μg/m 3 PM 2.5 . Because these 2 days were holidays, the use of the ED visits for asthma may

have been different from other day s in the study . Based on the high influence and a potential holiday

effect, these 2 day s were not included in our primary analysis.

Figure 2. Time series of PM 10 and PM 2.5 data. Abbrevi ations: PM 2.5 , particulate matter 2.5 μm in aerody

namic diameter; PM 10 , particulate matter 10 μm in aerodynamic diameter.

a Estimated from light - scattering data. 

### Discussion We found significant associations between ED visits for asthma in children and PM 10 , light - scattering measurement of fine PM, and CO. L ight scattering, which is a measure of fine PM primarily

< 1.0 μm in diameter, was significantly associated with ED visits for asthma in all the anal ys es. Additionally , PM 10 and CO were significant predictors of ED asthma visits in the low utilization and for the combined utilization areas. The higher relative risk in this study

as compared to the earlier results by Schwartz and colleagues ( 12 ) may be due to the fact that our population was restricted to individuals under the age of 18, a more susceptible group than the population at large. We reco gnize that ED data from hospitals contain some misdiagnoses. Delfino andassociates ( 34 ) found a good association between hospital summary data and chart review. The majority

of cases in our study

came from a single children's hospital specializing in diagnoses for childhood diseases. The number of visits for the high utilization region (371) was less than the low utilization area (529) and likel y did not achieve statistical significance for PM 10 and CO because of the reduced number of events. Otherwise, the high and low utilization areas did not appear to have different associations between air pollution and increased ED visits for asthma. The estimated numbers of children under 18 years of age in the high utilization area and in the rest of Seattle were 6 ,921 and 100,895, respectively . However, we cannot compare the absolute number of visits for the two utilization areas because a given relative rate increase in ED visits in the high utilization area caused more absolute visits than in the low utilization area. In this study, relative rates for light scattering in the low and high utilization areas were 13 and 16% for an IQR increase of approximately 10 μg/m 3 of fine PM. The light - scattering IQR was converted to represent PM 2.5 gravimetric mass based on co located nephelometer and PM 2.5 monitors at the southernmost PM monitoring site (224 day s, r = 0.86). The average concentration for the 15 - month period of this study was approximately

12 μg/m 3 PM 2.5 , a concentration below the new EPA annual standard (15 μg/m 3 ). PM 10 was associated with a 14% increase in ED asthma visits for an increase of 12 μg/m 3 PM 10 . The association between increased asthma visits and CO was investigated in Anchorage, Alaska ( 35 ), Reno, Nevada ( 36

), and Seattle ( 20 ). The Anchorage and Reno studies did not find a significant association between ED visits for asthma and CO; however, CO was associated with hospital admissions in Seattle ( 20 ). Th e Reno study used the highest hourly

maximum level in their local air pollution network, and the Anchorage study used the daily average 8 - hr maximum concentration during winter months. The Seattle hospital admission study ( 20 ) used the daily

average of four monitoring stations. In the present study , we used a 24 - hr average of four sites in our study region for the entire 15 months. Because CO has no biologicall y plausible mechanism for the exacerbation of asthma ( 37 ) we interpret it as a general indicator o f air pollution. The significant association between increased ED visits for asthma and CO found in this anal ys is could result from the high correlation between CO and PM 10 (0.74) as well as light scattering (0.74). To explore this possibility , a factor an al ys is of the ph ys ical and chemical nature of air pollution in Seattle was conducted on both the CO and particulate composition data collected previously ( 38 ) at the southernmost PM site in this study . Factor anal ys is with a varimax rotation has been used to both examine the colinearity among the various air pollutant variables and to identify important features of the variability

in these pollutants (Table 5) ( 39 , 40 ). Main et al. ( 38 ) measured the composition of PM 2.5 or fine soil and coarse PM (PM 10 - PM 2.5 ). Coarse and fine soil mass were reconstructed b y adding the mass of the oxides of soil species (Si, Ca, Fe, and Ti) ( 41 ).Using these data we derived three factors which explained 95% of the variance and show

that the variability

in PM 2.5 composition is influenced b y three factors: a ) incomplete combustion products consisting of CO, elemental carbon, organic carbon, and soluble potassium (wood smoke marker); b ) secondary aerosols consisting of ammonium and sulfate; and c ) fine and coarse soil (Table 5). T he light scattering and PM 10 data are correlated with the first factor scores, with correlation coefficients of 0.81 and 0.77, respectivel y. Note that CO is associated with the buildup of incomplete combustion derived products including particulate organic carbon and particulate elemental carbon. This study

did not find a significant association between NO 2 , SO 2 , or ozone and increased ED asthma visits. The NO 2 , SO 2 , and ozone measurements are only taken at one site in the network and may

be subject to a greater degree of exposure misclassification than the CO and PM pollutant measures that represent averages of three to four sites in the study area. In addition, the SO 2 concentrations were low, with a mean dail y 1 - hr maximum concentration of 6 ppb. Other i nvestigators have reported that the peak hourly NO 2 concentration was significantly associated with increased ED visits for asthma during winter months in Northern California ( 15 ) and with increased ED visits and respiratory admissions in Athens, Greece ( 2 8 ). Peak hourl y NO 2 was also associated with increased ED visits for asthma during both the winter and summer months in Barcelona, Spain ( 14 ). The average peak NO 2 concentrations in the Northern California, Athens, and Barcelona studies were 69 ppb, 50 ppb , and 58 ppb, respectively . These concentrations are significantl y higher than the average peak hourl y NO 2 concentration of 35 ppb observed in this study . Our finding of no significant association between ED asthma visits and maximum hourly

SO 2 is consiste nt with the earlier Seattle study ( 12 ) and the study

in Barcelona ( 14 ). The lack of a significant association between ED visits for asthma and ozone in this study

may be due to the large number of missing measurements. In summary , this study

found a small but significant association between air pollution and increased ED visits for asthma in children in Seattle. PM and CO concentrations in this study were associated with increased childhood ED visits for asthma and represent the daily variation in incomple te combustion products including elemental carbon and organic carbon. Results from this study of a susceptible subpopulation show significant increases of ED asthma visits for children with daily PM 2.5 concentrations substantially below the newly adopted N ational Ambient Air Quality Standard of 15 μg/m annually ( 42 ).[ References Listed in PubMed ] References and Notes 1. Hill RA, Standen PJ, Tattersfield AE. Asthma, wheezing, and school absence in primary schools. Arch Dis Child 644:246 - 251 (1989). 2. Gergen PJ, Weiss KB. Changing patterns of asthma hospitalization among children: 1979 to 1987. J Am Med Assoc 264:1688 - 1692 (1990). 3. Moore CM, Ahmed I, Mouallem R, May W, Ehlayel M, Sorensen RU. Care of asthma: allergy clinic versus emergency room. Ann Al le rgy Asthma Immun ol78:373 - 380 (1997). 4. Crain EF, Weiss KB, Bijur PE, Hersh M, Westbrook, Stein REK. An estimate of the prevalence of asthma and wheezing among inner - city children. Pediatrics 94:356 - 364 (1994). 5. Azizi BHO, Zulkifli HI, Kasim MS. Indoor air pollution and asthma in hospitalized children in a tropical environment. J Asthma 32:413 - 418 (1995). 6. Burr ML, Limb ES, Andrae S, Barry DM, Nagel F. Childhood asthma in four countries: a com parative survey. Int J Epidemiol 2 3:341 - 347 (1994). 7. Rosenstreich DL, Eggleston P, Kattan M, Baker D, Slavin RG, Gergen P, Mitchell H, McNiff - Mortimer K, Lynn H, Ownby D, et al. The role of cockroach allergy and exposure to cockroach allergen in causing morbidity among inner city children with asthma. N Engl J Med 336:1356 - 1 363 (1997). 8. Koenig JQ, Larson TV, Hanley QS, Robelledo V, Dumler K, Checkoway H, Wang SZ, Lin D, Pierson WE. Pulmonary function change s in children associated with fine particulate matter. Environ Res 63:26 - 38 (1993). 9. Romieu I, Meneses F, Ruiz S, S ie nra JJ, Huerta J, White MC, Etzel RA. Effects of air pollution on the respiratory health of asthmatic children living in Mexico City. Am J Respir Crit Care Med 154: 300 - 307 (1996). 10. Peters A, Dockery DW, Heinrich J, Wichmann HE. Short - term effects of particulate air pollution on respiratory morbidity in asthmatic children. Eur Respir J 10: 872 - 879 (1997). 11. Ostro B, Lipsett MJ, Mann JK, Braxton - Owens H, White MC. Air pollution and asthma exacerbations among African - American children in Los Angeles. Inhal Toxicol 7: 711 - 722 (1995). 12. Schwartz J, Slater D, Larson TV, Pierson WE, Koenig JQ. Particulate air pollution and hospital emergency room visits for asthma in Seattle. Am Rev Respir Dis 147:826 - 831 (1993). 13. Bates DV, Baker - Anderson M, Sizto R. Asthma attack periodicity: a study of hospital emergency visits in Vancouver. Environ Res 51:51 - 70 (1990). 14. Castellsague J, Sunyer J, Saez M, Anto JM. Short - term association between air pollution and emergency room visits for asthma in Barcelona. Th orax 50:1051 - 1056 (1995). 15. Lipsett M, Hurley SB, Ostro B. Air pollution and emergency room visits for asthma in Santa Clara County, California. Envi ron Health Perspect 105:216 - 222 (1997). 16. Delfino RJ, Murphy - Moulton AM, Burnett RT, Brook JR, Beckla ne MR. Effects of air pollution on emergency room visits for respiratory illnesses in Montreal, Quebec. Am

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