A Questionnaire Study of Respiratory Health in Areas of High and Low Ambient Wood Smoke Pollution

PEDIATRIC ASTHMA, ALLERGY & IMMUNOLOGY
Volume 4, Number 3, 1990
Mary Ann Liebert, Inc., Publishers
A Questionnaire Study of Respiratory Health in Areas
of High and Low Ambient Wood Smoke Pollution
KATHERINE G. BROWNING, M.S., JANE Q. KOENIG, Ph.D.,
HARVEY CHECKOWAY, Ph.D., TIMOTHY V. LARSON, Ph.D., and
WILLIAM E. PIERSON, M.D.
ABSTRACT
A cross-sectional questionnaire study was conducted to determine whether there were
differences in the prevalence of respiratory symptoms between residents of high and of low
wood smoke pollution areas. Six hundred questionnaires were mailed to households in each
area asking about respiratory symptoms, such as cold, cough, and congestion and wheezing.
The response rate was 57% (325 households) in the high wood smoke area and 51% (257
households) in the low wood smoke area. There were no statistically significant differences
between symptoms in the two areas when all age groups were combined for analysis. However,
there was a trend toward more symptoms in children aged 1-5 years in the high wood smoke
area both in an initial questionnaire, which asked about history of symptoms, and in the
follow-up questionnaires, which asked about symptoms during the preceding 2 weeks. In
particular, for congestion and wheezing, the percentage reported for the initial questionnaire
in the high wood smoke area was 46.4 vs 28.6 in the low wood smoke area. This difference was
29.4 vs 0.0 during the second follow-up period. This pattern was not seen in the other age
groups. It is concluded that this study supports the work of others who have suggested that
wood smoke air pollution aggravates symptoms of respiratory disease in preschool children,
despite an apparent absence of effect at older ages.
INTRODUCTION
energy costs, the number of Americans using woodburning devices for home
has increased dramatically over the past few years. Intense particulate matter pollution has
resulted in some communities where substantial amounts of residential wood combustion occur. Health
concerns about wood smoke pollution have prompted citizens in several states to seek regulation of
Because
heating
of increasing
wood-burning devices/"
on
The use of wood stoves produces both indoor and outdoor pollution. Two recent studies'2·3' have focused
the relationship between respiratory illness in children and the use of wood-burning stoves in the home.
Departments of Environmental Health, Epidemiology, Pediatrics, and Civil Engineering, University of Washington,
Seattle, Washington.
183
BROWNING ET AL.
However, neither indoor nor outdoor air pollution from wood smoke was measured in these studies. To date,
no studies have been published that have sought to evaluate the effect of community wood smoke pollution on
the prevalence of respiratory illness.
The object of this study was to evaluate the relationship between ambient wood smoke pollution and
symptoms of respiratory illness. The approach used was a cross-sectional questionnaire study conducted
during the 1987-1988 winter heating season in Seattle, Washington. Ambient air monitoring data exist for
1986-1987 and for the winter of the study. Prevalence of respiratory symptoms was compared between adults
and children living in neighborhoods with high measured levels of ambient wood smoke pollution and adults
and children living in neighborhoods with lower measured levels of such pollution. A pattern of increased
respiratory symptoms was seen in young children who lived in the high wood smoke area.
METHODS
Initial and follow-up questionnaires were sent to 600 households in each of two study neighborhoods in a
developed residential suburb of Seattle. Selection of neighborhoods was based on analysis of ambient air
monitoring data obtained during the 1986-1987 heating season. One of the investigators (TVL) provided
maps that correlated location with ambient wood smoke concentrations. The area selected as having high
wood smoke levels was characterized by lower elevation and the presence of valleys and creek drainages. The
area selected as having lower wood smoke levels was characterized by higher elevation and the presence of
ridges and hills.
Identification of households within the selected areas was accomplished by use of current year reverse
directories.(4) Streets selected were classified by the directories as high or medium-high income areas.
Multiple family dwellings (apartment houses and addresses with letter or unit number suffixes) and businesses
were excluded.
An initial mailed questionnaire containing 38 questions and a follow-up questionnaire with 6 questions
were developed from the standardized respiratory questionnaire of the American Thoracic Society's
Epidemiology Standardization Project.(5) The initial questionnaire included questions on personal character¬
istics, such as age, gender, and occupation. Other information collected included primary and secondary heat
sources, frequency of wood stove use, cigarette smoking history, and history of asthma, hay fever, bronchitis,
and emphysema. Questions regarding respiratory symptoms included questions about symptoms of a mild,
moderate, or severe nature. Questions about mild symptoms asked about the presence of cough or congestion
with colds. Questions about moderate symptoms asked about attacks of respiratory illness each year,
occasional wheezing with colds, or other episodes of wheezing. Questions about severe symptoms asked
about coughing on most days or nights, congestion apart from colds, and wheezing most days or nights.
Questions also were asked about school or work absences due to respiratory illness and doctor visits or
medication use due to respiratory illness.
The follow-up questionnaire, which was sent at two different periods, included questions pertaining only to
respiratory symptoms: presence of cough, cold, congestion and wheezing, absence from school or work due
to respiratory illness, and doctor visits or medication use for respiratory illness. The respondents were asked
if these symptoms or events had occurred during the preceding 2 weeks.
Instructions specified that the person filling out the questionnaire provide information about himself or
herself (adult) and one child closest to the age of 10 if there were children in the household.
The initial questionnaire was mailed early in December 1987. Those households that returned the initial
questionnaires and signed approved consent forms were sent the first follow-up questionnaire during the first
week of January 1988. The second follow-up questionnaire was sent to the same households during the first
week of February.
Symptom prevalence was compared between high and low wood smoke areas by means of calculations of
prevalence ratios and associated 95% confidence intervals.(6)
Ambient air measurements were taken in both areas during the study period, using Harvard samplers for
particulate matter less than 10 µ concentration (PM10) and 1590 series nephelometers for light scattering.
Light scattering values are highly correlated (r 0.97) with PM10 at these sites during the heating season.
=
184
RESPIRATORY HEALTH AND WOOD SMOKE AIR POLLUTION
RESULTS
Study subjects
Response rates for the initial questionnaire were 57% (325 households, including 455 individuals) in the
high wood smoke area and 51 % (257 households, including 368 individuals) in the low wood smoke area. The
percent of households that responded to the initial and both follow-up questionnaires was 37% in the high
wood smoke group and 34% in the low wood smoke group. Not all households responded to both the first and
second follow-up questionnaires, however. The response rate for the first follow-up questionnaire was 64% in
the high wood smoke group and 38% in the low wood smoke group. For the second follow-up, the rates were
54% and 69%, respectively.
The age distributions were similar in both areas. Approximately 18% more females than males participated
in the study. The job classifications were similar for both groups. Forced air heating systems predominated,
with more oil than gas users in the high wood smoke area (35 vs 18%) and more gas than oil users (49 vs 26%)
in the low wood smoke area. Households using wood stoves were very similar, 14% in the high and 13% in the
low wood smoke area. There was a similar prevalence of cigarette smoking in each area, 9.3% in the high and
13% in the low wood smoke area. No association was seen between smoking and symptoms in either area
(probably due to the low prevalence rate of smoking).
History of chronic respiratory disease
The prevalence of individuals in each area reporting a history of respiratory disease was similar in the two
except among children aged 1-5 years. Among children 1-5 years old, the most notable difference
between groups was for history of bronchitis; 14.3% of children in the high wood smoke area were reported
to have bronchitis compared to 0.0% in the low wood smoke area. Among children 6-14 years old, more
children in the low wood smoke area had histories of asthma (15.5%) and bronchitis (5.2%) than did children
in the high wood smoke area (8.2% and 1.6%, respectively). Adults in the age 15-64 years category were very
similar in their history of respiratory disease. Adults in the age 65 and older category in the low wood smoke
area had a higher prevalence of emphysema (6.1%) and bronchitis (14.6%) than did adults in the high wood
smoke area (1.6% and 11.1%, respectively).
areas
24 hr average
Light Scattering Values
(October, 1987 March, 1988)
-
-
E
2
w
»
10
8
6
4
2
0
High Wood S noke An a
Wood S noke Art
a
^ *
to
·
-
S·
io
6
4
0
-
'QjJ/vMJ/^U^^_
o
to
·
M
m
evj
cm
w
DATE
FIG. 1. Light scattering values (24 hour means) vs time in high and low wood smoke areas. Light scattering in this study
is a surrogate for PM10
185
BROWNING ET AL.
Atmospheric monitoring
Figure 1 shows light scattering (bsp) data for the high and low wood smoke areas from October 1987
through March 13, 1988. The high wood smoke area had higher bsp levels in all study periods, for both 24
hour average and peak values, than did the low wood smoke area. The equivalent 24 hour average PM10
concentration on a given day followed a similar pattern in both areas but was consistently lower in the low
wood smoke area (p < 0.001). In the low wood smoke area for November and December 1987 and January
1988 the monthly PM10 averages were 36,41, and 22 µg/m3, respectively. For the high wood smoke area, the
monthly average PM10 values were 72, 53, and 41 µg/m3, respectively. The highest 24-hour PM10 values by
month in the low wood smoke area were 56, 59, and 29 µg/m3; in the high wood smoke area, the highest
24-hour values by month were 100, 53, and 127 µg/m3. Chemical analysis of selected filter samples at the
high wood smoke site indicated that on average 70% of the PM10 was wood smoke, and the remainder was
primarily due to diesel exhaust.7
Prevalence
of symptoms
The initial questionnaire was completed from 11/20/87 to 12/15/87, the first follow-up period was from
12/20/87 to 1/10/88, and the second follow-up was from 1/15/88 to 2/7/88. The age-stratified prevalence of
respiratory symptoms reported and the ratios of the prevalence in the high vs low wood smoke areas during the
initial study period are given in Table 1. The most notable differences between areas were seen in the children
ages 1-5. The differences remained consistent in the mild, moderate, and severe symptom category. None of
the differences was statistically significant at the
0.05 level, since the confidence intervals overlapped
the null value of 1.0. However, because of the exploratory nature of this study and the relatively small sample
size, the intent was to look for patterns of response. As shown in Table 1, in the age 1-5 years category, the
largest differences between groups were reported for usually having congestion with cold (46.4% in the high
wood smoke area and 28.6% in the low wood smoke area, ratio 1.62), having occasional wheezing without
a cold (14.3% in the high wood smoke area and 7.1% in the low wood smoke area, ratio
2.01), and usually
without
cold
in
the
wood
smoke
and
0.0%
in
the
low
wood
smoke area).
a
area
having a cough
(7.1%
high
Exclusion of children with asthma did not alter these differences materially.
In adults age 65 and older, contrary to our expectation, the trend was in the opposite direction. Respondents
in the low wood smoke area reported a higher prevalence of symptoms in each category. It was noted earlier
that the prevalence rates of history of bronchitis and emphysema were higher in the low wood smoke area.
Eliminating the emphysema cases from the analysis decreased the difference between areas but did not alter
the trend. There were no consistent patterns in the other two age groups, 6-14 and 15-65 years of age (Ta¬
ble 2).
None of the differences reported for the follow-up periods for children was statistically significant at the
0.05 level (Table 3). There was a trend among children ages 1-5 years in the high wood smoke area to
have higher prevalences of colds (66.7 vs 50%) and congestion and wheezing (23.8 vs 16.7%) in the first
follow-up period. The percentages for the second follow-up period were 41.2 vs 20.0% for cold, 41.2 vs
22.2% for cough, and 29.4 vs 0.0% for congestion and wheezing and absence due to respiratory disease (29.4
=
=
=
=
vs
10.0).
Although this study focused on outdoor air pollution from wood stoves, data regarding indoor use of wood
stoves also were collected. In the high wood smoke area, households with children ages 1-5 years reported
that 28.8% used the wood stove from 3 days a week to daily. In the low wood smoke area, only 7.1% of the
households with children ages 1-5 years reported wood stove use of that frequency. However, except for
coughing without a cold, there was no tendency toward more symptoms in children from homes using wood
stoves,
as
shown in Table 4.
DISCUSSION
This
study has investigated the occurrence of symptoms of respiratory illness in residents of areas with
relatively high and low measured levels of ambient wood smoke pollution. The findings suggest that young
186
RESPIRATORY HEALTH AND WOOD SMOKE AIR POLLUTION
Table 1.
Prevalence of Symptoms (%)
(n
Mild symptoms
1. Usually coughs with cold
High WS
Low WS
Ratioa
=
=
(n
(n
=
=
15-44
(n
(n
63)
59)
=
109)
70)
45-64
(n
(n
=
=
86)
55)
>65
(n
(n
=
=
60)
45)
49.7
45.5
1.09
49.2
40.0
46.2
46.2
0.87
(0.41,2.46)
(0.59, 1.60)
(0.78, 1.53)
(0.73, 1.55)
(0.53, 1.43)
Low WS
Ratio
46.4
28.6
1.62
39.7
37.3
1.06
47.8
51.6
0.93
52.9
47.2
1.12
31.6
41.5
0.76
(95% CI)
(0.53, 4.96)
(0.60, 1.89)
(0.66, 1.29)
(0.77, 1.62)
(0.44, 1.31)
Low WS
Ratio
42.9
42.9
1.00
33.3
39.7
0.84
36.6
38.5
0.95
28.3
31.1
0.91
17.5
33.3
0.53
(95% CI)
(0.38, 2.65)
(0.47, 1.52)
(0.65, 1.40)
(0.56, 1.47)
(0.27, 1.31)
10.0
18.5
0.54
14.8
11.0
1.35
13.6
14.0
0.98
10.3
14.3
0.72
(0.20, 1.48)
(0.67, 2.71)
(0.46, 2.05)
(0.26, 1.99)
40.7
28.6
1.42
31.7
33.9
0.94
30.7
27.3
1.12
29.4
23.8
19.5
22.2
0.88
(0.46, 4.46)
(0.50, 1.74)
(0.72, 1.75)
(0.74, 2.06)
(0.42, 1.82)
14.1
11.7
1.21
11.8
14.3
0.83
15.3
17.5
0.87
(0.62, 2.35)
(0.40, 1.71)
(0.38, 2.02)
10.6
13.8
0.77
9.2
18.1
0.51
11.4
20.0
0.57
(0.16,3.19)
(0.39, 1.51)
(0.24, 1.06)
(0.24, 1.33)
12.7
11.9
1.06
12.3
8.9
1.38
10.8
19.0
0.57
11.5
28.8
0.40
(0.39, 2.95)
(0.66, 2.86)
(0.28, 1.14)
(0.18,0.89)
Moderate symptoms
1. History of asthma
High WS
Low WS
Ratio
7.1
0
(95% CI)
—
2. Occasional wheeze with cold
High WS
Low WS
Ratio
(95% CI)
Severe symptoms
1. Occasional wheeze without cold
High WS
Low WS
Ratio
(95% CD
Low WS
Ratio
14.3
7.1
2.01
9.5
8.5
1.12
—
without cold
(95% CI)
—
—
Ratio of prevalence in
high
1.24
-
7.1
0
Low WS
Ratio
(0.34, 3.68)
4.8
6.8
0.71
3.6
0
(95% CI)
Usually coughs
High WS
1.06
-
(0.22,17.85)
Usually congested without cold
High WS
a
=
49.2
50.8
0.97
Yearly coughs and congestion
High WS
3.
28)
14)
50.0
50.0
1.00
(95% CI)b
Usually congested with cold
High WS
2.
6-14
1-5
(n
Low
3.
Questionnaire
Age group (years)
Symptom severity
and exposure classification
High
2.
Respiratory Illness During Initial
Study Period
of
wood smoke to low wood smoke
b95% confidence interval for prevalence ratio.
187
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BROWNING ET AL.
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RESPIRATORY HEALTH AND WOOD SMOKE AIR POLLUTION
Table 3.
Prevalence
of
Acute Respiratory Symptoms (During Previous Week)
Study Period
in
Children
by
Study period
First follow-up
Initial questionnaire
Symptoms and
Age 1High (n 28)
exposure
=
classification
Low
(n
=
14)
Age 6-14
High (n 63)
Age 1-5
High (n 21)
=
Low (n
=
Age 6-14
High (n 35)
=
Low (n
59)
=
Second follow-up
=
5)
Low (n
=
20)
Age 1-5
High (n 17)
=
Low (n
=
9)
Age 6-14
29)
Low (n = 34)
High (n
=
Cold
High WS
Low WS
Ratio3
32.1
(95%CI)b
Cough
High WS
42.9
0.75
24.2
32.2
0.75
66.7
50.0
1.33
36.1
47.6
0.76
41.2
20.0
2.06
58.6
47.2
1.24
(0.27,2.10)
(0.38, .48)
(0.39, 4.58)
(0.33, 1.72)
(0.43, 9.84)
(0.64, 2.42)
25.0
Low WS
Ratio
35.7
0.70
17.5
39.0
0.45
57.1
60.0
0.95
(95% CI)
25.0
33.3
0.75
41.2
22.2
1.85
(0.22, 2.20)
27.6
41.7
0.66
(0.22, 0.92)
(0.27, 3.33)
(0.28, 2.01)
(0.39, 8.85)
(0.28, .56)
23.8
16.7
1.43
8.3
14.3
0.58
29.4
0
17.2
13.9
1.24
(0.17, 12.14)
(0.12, 2.89)
4.8
14.6
0.32
33.3
33.3
1.00
19.4
40.0
0.49
29.4
10.0
2.94
20.7
33.3
.62
(0.06, 1.57)
(0.27, 4.77)
(0.18, 1.34)
(0.35, 25.04)
(0.23, 1.65)
Congestion wheezing
High WS
Low WS
Ratio
—
—
(95% CI)
Absence due
High WS
Low WS
Ratio
—
to
respiratory disease
0
0
(95% CI)
—
aRatio of prevalence in high wood smoke to low wood smoke
95% confidence interval for prevalence ratio.
Table 4.
Moderate symptoms
with cold
44.4
Frequent use"
Infrequent/no useb 50.0
Ratio0
95% CId
0.89
0.40-2.00
Usually congested with cold
55.6
Frequent use
Infrequent/no use 37.5
Ratio
1.48
95% CI
0.71-3.09
Yearly coughs and congestion
33.3
Frequent use
Infrequent/no use 43.8
Ratio
0.76
95% CI
0.28-2.08
a
Frequent use = 3
bInfrequent/no use
History of asthma
Frequent use
Infrequent/no use
Ratio
95% CI
0
3.1
—
Severe symptoms
Occasional wheeze without cold
0
Frequent use
Infrequent/no use 15.6
Ratio
95% CI
Usually congested without cold
0
Frequent use
Infrequent/no use 3.1
Ratio
95% CI
Usually coughs without cold
11.1
Frequent use
Infrequent/no use 3.1
Ratio
3.56
95% CI
0.25-51.41
—
Occasional wheeze with cold
33.3
Frequent use
Infrequent/no use 34.4
Ratio
95% CI
0.97
0.34-2.75
-
—
—
times/ week or more,
10.
less than 3 times/week,
=
=
Ratio of prevalence by frequent to infrequent
d95% confidence interval for prevalence ratio.
c
areas.
Prevalence of Symptoms of Respiratory Illness m in Children Aged 1-5 Years
Comparing Frequency of Wood Stove Usage
Mild symptoms
Usually coughs
(0.36, 4.28)
=
31.
use.
189
BROWNING ET AL.
children (ages 1-5) develop more symptoms of respiratory illness if they live in an area with larger amounts
of wood smoke pollution. For adults over age 65, the trends were generally in the opposite direction, although
increased history of chronic respiratory disease in the low wood smoke area may explain these comparisons.
Ambient wood smoke pollution levels (measured as PM10 concentration and light scattering, which serves
as a surrogate for PM10 in these locations) always were higher in high wood smoke areas. The monthly
averages were highest in both areas during the initial and first follow-up study periods. The highest peak value
for the low wood smoke area was in the first follow-up period (59 µg/m3). For the high wood smoke area, it
was in the second follow-up period (127 µg/m3). Symptoms in the young children also were greatest during
the second follow-up period.
The results of this study are consistent with other reported research on the health effects of particulate
matter. A study in Steuben ville, Ohio, found a positive correlation between decreased lung function in
children and increased concentrations of total suspended particulate matter (TSP) and sulfur dioxide (S02).<8)
The lung function decreases lasted for 1-2 weeks after exposure. A similar study in the Netherlands followed
lung function measurements in 179 children aged 7-11 years while TSP and S02 were monitored.<9> The study
found 3%-5% reductions in lung volume measurements during air pollution episodes when high concentra¬
tions of these pollutants were present. These authors reported that the lung function changes persisted for
about 16 days after the period of elevated air pollution. In our study, the questionnaires reflect an exposure lag
of about 2 weeks at most, but based on the other studies, the lag could have been greater in some cases. In both
the Steuben ville and Netherlands studies, S02 concentrations as well as PM were elevated. Thus, determining
the unique contribution of PM on the lung function decrements is difficult. In the Seattle airshed in the winter,
S02 levels are very low (monthly arithmetic averages ranged from 0.004 to 0.016 ppm during 1986). Thus the
only elevated air pollutant measured in our study was PM10. A recently published article also showed that rates
of respiratory illness and symptoms were elevated among children living in cities with high particulate matter
pollution/10' This study found, in children slightly older than in the present study (10—12 years of age), a
significant association between both bronchitis and chronic cough (odds ratios 2.5 and 3.7, respectively) and
particulate matter less than 15 µ in diameter. The contribution from wood smoke was not reported.
The question of exposure effects resulting from ambient air pollution is a difficult one. Results obtained at
fixed monitoring stations may not be truly representative of exposures throughout a geographical region/11'
We sought to minimize this variability by having monitoring stations in each area, selecting areas that had
overall geographical similarity and selecting households located in geographically similar subareas of each
study area. Mobile monitoring also was used throughout the high wood smoke area.
The relationship between ambient PM]0 concentrations and actual personal exposures has been studied by
Spengler et al.( '2) They found that ambient concentrations were poorly correlated with personal exposures and
that indoor concentrations of PM10 frequently were higher than outdoor concentrations. The indoor
concentrations were highest in the homes of smokers. They did not specifically examine the relationships
between wood stove use or ambient wood smoke pollution and indoor concentrations of PM,0.
Larson et al./7) however, studied indoor-outdoor fine particle mass concentration relationships. In a
building with an electric furnace, the indoor fine particle mass concentration was approximately 70% of the
outdoor fine particle mass concentration. The conclusion was that particles and reactive gases penetrate
buildings, and consequently even the indoor environment of homes not using wood stoves will be polluted by
ambient wood smoke pollution/7' This supports our data that show no association between personal use of a
wood stove and respiratory symptoms but did show a pattern of increased symptoms associated with high
levels of community outdoor wood smoke that could pollute the indoor environment.
A limitation of the present study is the relatively low questionnaire return rate. Mail questionnaire surveys
in particular present concerns about response selectivity. Persons receiving the questionnaire have the chance
to look at the entire questionnaire before making decisions about responding. People who are interested in the
subject of the questionnaire may be more likely to respond/4' We did send a postcard to nonrespondents in an
attempt to determine the reasons for not responding. Fifty percent of those who returned the postcard stated
that they were "too busy." Demographically, the nonrespondents who returned the card were not different
from respondents. The socioeconomic level in the communities involved in our study was well above average.
People in upper socioeconomic strata are more likely to have better access to health care, to be able to afford
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RESPIRATORY HEALTH AND WOOD SMOKE AIR POLLUTION
housing, and may be healthier overall than those in lower socioeconomic strata. In addition,
cigarette smoking is generally thought to be more prevalent among lower socioeconomic groups.
In conclusion, the results of this study indicate that some differences existed in the prevalence of respiratory
symptoms in high wood smoke pollution areas vs low wood smoke pollution areas. These patterns of response
were most pronounced for children in the 1-5 years of age group. No such pattern of response was seen when
in-home wood stove use was used as the surrogate exposure variable. Because of the small sample size and
lack of personal monitoring data, the results of this study should be regarded cautiously. However, the
patterns of response indicate that the health effects of wood smoke air pollution warrant further evaluation.
better diet and
ACKNOWLEDGMENT
This
study was supported by a grant from the American Lung Association of Washington.
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Address reprint requests to:
Jane Q. Koenig, Ph.D.
Department of Environmental Health
SC-34
University of Washington
Seattle, WA 98195
191