Transcript Asthma and the Environment - Northern Arizona University

Risk Factors for Asthma
Mary Ellen Gordian MD
MPH
Institute for Circumpolar
Health Studies
University of Alaska
Anchorage
What is Asthma?
Asthma is a chronic respiratory disease
characterized by:
• eosinophilic inflammation of the airways;
• bronchial hyper-responsiveness to stimuli.
Different Types of Asthma
• Allergic asthma is associated with allergy as much
as 80% of childhood asthma is related to allergy.
• Intrinsic asthma is not associated with allergy.
• Post-infective asthma occurs after a lower
respiratory infection. Frequently clears by age 5.
Known Risk Factors for Asthma
• Family history – genetic predisposition
• Environmental tobacco smoke
• Combination of family history and
environmental tobacco smoke exposure is
additive.
World Wide Increase in Asthma
• Multi-center surveys show that asthma is
increasing worldwide.
• Greatest increases in “westernized”
English-speaking countries.
• Urban areas have more asthma cases than
rural areas.
• Increase in both children and adults.
Asthma Rates
Asthma Increasing
Australia
Costa Rica
New Zealand
Oman
Peru
Singapore
United Kingdom
United States
No Asthma Increase
Albania
Estonia
Indonesia
Latvia
Uzbekistan
The Icon of Westernization
What is
westernization?
Individualization
Independence
Initiative
and your own car!
Allergens associated with Asthma
• Dust mite allergy has been associated with
asthma.
• Cockroach allergen are common in inner
city children, associated with asthma.
• Molds have been implicated.
• Animal allergens (cat is ubiquitous)
• Children with allergy have increased risk of
asthma.
So why the increase in
ALLERGIC RESPONSES!
To survive in an environment full of foreign
protein antigens, animals developed a method
of response that minimized the energy needed
to encounter non-infectious protein.
Recognition and minimal responsetolerogenic response
Cytokine IL-10 dampens immune responses.
What is Causing the Increase?
• Dietary Hypothesis
Changes in diet result in increased susceptibility to
allergic response.
• Hygiene Hypothesis
Increased cleanliness reduces level of endotoxin
which changes the immune system
• Adjuvant Hypothesis
Exposure to petroleum exhaust fumes changes the
immune system
Concerns for Dietary Hypothesis
•
•
•
•
Reduction in locally grown food.
Increases in chemically treated food.
Salt intake is increased.
Omega 3 fatty acids reduce allergic
response in animals.
• Early intake of cow’s milk protein or soy
protein may increase risk of allergy.
Hygiene Hypothesis
Environmental exposure to endotoxin
has a crucial role in the developing
immune system driving the immune
response from cell-mediated
immunity (inflammation)
to antibody production.
Hygiene Hypothesis
• Children living on farms have less risk of
allergy and asthma.
• Children in daycare have decreased risk.
• Children with older siblings less risk.
• Children with animal pets have less risk.
• Increased amount of endotoxin exposure in
farm homes, and homes with dogs
Adjuvant Theory
The exposure to traffic pollution results in
changes in the immune system which
promotes cell-mediated Th2 immunity
characterized by inflammation.
There is direct experimental evidence for this.
Evidence for Adjuvant Theory
• Children living near to freeways in Holland
have greater symptoms, reduced FEV1.
• Children hospitalized for asthma live near
high traffic areas as compared to children
hospitalized for GI problems in U.K.
• Children living near traffic have more
cough in Japan.
Laboratory Evidence
• People experimentally exposed to diesel
exhaust (DE) have 16 x greater response to
ragweed allergen than people not exposed.
• People exposed to DE make IgE to new
antigen exposure, while people not exposed
make IgA, IgG, but not IgE.
Mary Ellen’s Theory
• Petroleum exhaust affects the tolerogenic
response, reduces IL-10 and promotes
allergic responses----Not proven yet
What are we doing in Alaska?
• Survey of Anchorage parents of children in
kindergarten and first grade in 13 schools
regarding asthma diagnoses, symptoms,
demographics, home environment and
family history.
• Over 1100 surveys received. Minorities well
represented. All socioeconomic classes
represented. Geographically distributed.
Study Design
• 13 schools representing a range of traffic
exposure and socioeconomic demographics
• All kindergarten and first-grade students
received surveys at registration, or in the
classroom. (50-85% response rate)
• Traffic data collected from state
• Traffic measured on roads with no data.
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Traffic Variables
• Nearest intersection to home is located on map.
• Buffer zones 100 meters and buffer zones of 300
meters around intersection are drawn and the
length of each road falling within buffer is
measured.
• The length within the buffer is multiplied by the
average daily traffic on that road in that segment.
Baseline Characteristics of Children between 5 and 7 years
No Asthma
Parental Asthma
No
Yes
Smoker in Home
No
Yes
Family Income
<$20K
$20-49K
$50-100K
>$100K
Gender
male
female
Asthma
Asthma rate p-value
<0.001
734
151
53
50
6.7%
24.9%
0.066
631
290
69
46
9.9%
13.7%
0.018
189
375
253
63
36
48
19
9
16.0%
11.3%
7.0%
12.5%
0.314
470
449
64
50
12.0%
10.0%
Categorization of Traffic Exposure at 100-meter Buffer
No Asthma
Asthma
Total
Asthma rate
______________________________________________________
Exposure
Low
636
75
711
10.5%
Medium
231
28
259
10.8%
High
60
13
73
17.8%
927
116
1043
Regression results of 100-meter buffer and 300-meter buffer
100-meter Buffer
300-meter buffer
OR (95%CI)
Exposure
Low
Medium
High
Parental Asthma
No
Yes
Smoker in home
No
Yes
Family Income
<$20K
$20-49K
$50-100K
>$100K
Gender
male
female
p-value
0.068
Referent
1.06 (0.64, 1.77)
2.38 (1.19, 4.76)
OR (95%CI)
Referent
1.37 (0.85, 2.23)
2.74 (1.35, 5.56)
<0.001
Referent
4.27 (2.74, 6.65)
<0.001
Referent
4.30 (2.75, 6.72)
0.203
Referent
1.34 (0.86, 2.10)
0.177
Referent
1.37 (0.87, 2.15)
0.183
Referent
0.72 (0.43, 1.21)
0.49 (0.26, 0.93)
0.81 (0.33, 1.94)
0.256
Referent
0.76 (0.45, 1.28)
0.52 (0.27, 1.01)
0.89 (0.37, 2.17)
0.351
Referent
0.81 (0.53, 1.25)
p-value
0.024
0.338
Referent
0.81 (0.53, 1.25)
Some Unexpected Findings
• A great many children do not live in the
neighborhood school boundaries.
• Children diagnosed with asthma have an
increased number of respiratory illnesses.
• There is variation in asthma rates between
schools, highest 20%, lowest 6%.
Conclusions
• Children exposed to high traffic volumes have two
and a half times greater risk of being diagnosed
with asthma.
• The effect size of high traffic volume within 3
blocks of home is as great or greater than having a
smoker in the house.
• Residential housing and schools should be
protected from high traffic areas.