Exposure to traffic related air pollution and the onset of childhood asthma: is there a connection?

1. Session: New perspectives on vulnerable groups
Does traffic-related air pollution
cause childhood asthma?
Haneen Khreis1, Charlotte Kelly1,2, James Tate1, Roger Parslow3
and Karen Lucas1
1 Institute for Transport Studies, 2 Leeds Institute of Health Sciences, 3 Leeds Institute of
Cardiovascular and Metabolic Medicine, University of Leeds
Changing Perspectives: 1st International Conference
on Transport and Health, London, 6 – 8 July 2015

2. 50 years of asthma: UK trends from 1955 to 2004
Trends in the prevalence of a diagnosis of asthma ever in children. m, month; y, year. Source: Anderson et al. (2007)

3. Why such steady and rapid increases?
“… the increase in disease must
be attributable to a change in
as-yet unknown environmental
factors… ” (Cookson, 2004, p. 979)
Source: Brook (2012)

4. Does children’s exposure to traffic-
related air pollution increase their
risks of developing asthma?
Meta-analysis
Case study - The Born in Bradford
Systematic review
Provide data
Learn and apply lessons

5. Does children’s exposure to traffic-related air pollution increase
their risks of developing asthma?
3. Include studies which investigate children’s
exposure to traffic-related air pollution only1. Include human
studies only 2. and
children’s studies only 4. Include studies which investigate exposure to
traffic-related air pollution or traffic-related air
pollutants when road traffic is specified as their source
6. Include studies which specifically
investigate the subsequent risk of
asthma development in childhood
7. Include observational studies only
5. Include studies which
report measures of
association and their
confidence interval precision
Khreis et al. (2014). Exposure to traffic-related air pollution and the development of childhood asthma. PROSPERO 2014:CRD42014015448,
available from: http://www.crd.york.ac.uk/PROSPERO/display_record.asp?ID=CRD42014015448

6. Screening process

7. Research gaps and impact on validity: asthma definitions
• Heterogeneous disease
• No universally accepted definition
• Has many phenotypes
• AND non-specific symptoms….

8. Research gaps and impact on validity: asthma definitions
Self-report of doctor-diagnosis = 12.0%
Hospitalization registry = 6.6%
Prescription registry = 32.2%
Source: Hansen et al. (2012)

9. Research gaps and impact on validity: asthma definitions
Self-report of doctor-diagnosis = 12.0%
Hospitalization registry = 6.6%
Prescription registry = 32.2%
1
12
Source: Hansen et al. (2012)

10. Research gaps and impact on validity: exposure models
0
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17:04:12
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17:06:57
17:07:52
17:08:47
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17:10:37
17:11:32
17:12:27
17:13:22
17:14:17
17:15:12
17:16:07
17:17:02
17:17:57
17:18:52
17:19:47
17:20:42
Background
Site
Background
Site
Intersection
Corner
Bus
Stop
Road
Crossing
Bus
Stop
Intersection
Corner
Road
Crossing
Intersection
Corner
Intersection
Corner
Road
Crossing
Fay D, Tate J, Khreis H (2015): Investigating pedestrians PNC exposures in urban micro-environments near a busy road traffic intersection

11. Research gaps and impact on validity: exposure models
0
50000
100000
150000
200000
250000
300000
16:38:32
16:39:27
16:40:22
16:41:17
16:42:12
16:43:07
16:44:02
16:44:57
16:45:52
16:46:47
16:47:42
16:48:37
16:49:32
16:50:27
16:51:22
16:52:17
16:53:12
16:54:07
16:55:02
16:55:57
16:56:52
16:57:47
16:58:42
16:59:37
17:00:32
17:01:27
17:02:22
17:03:17
17:04:12
17:05:07
17:06:02
17:06:57
17:07:52
17:08:47
17:09:42
17:10:37
17:11:32
17:12:27
17:13:22
17:14:17
17:15:12
17:16:07
17:17:02
17:17:57
17:18:52
17:19:47
17:20:42
Background
Site
Background
Site
Intersection
Corner
Bus
Stop
Road
Crossing
Bus
Stop
Intersection
Corner
Road
Crossing
Intersection
Corner
Intersection
Corner
Road
Crossing
Fay D, Tate J, Khreis H (2015): Investigating pedestrians PNC exposures in urban micro-environments near a busy road traffic intersection

12. Research gaps and impact on validity: exposure models
Proximity to
roadways
Regulatory
monitoring stations
Land-use regression
models
Dispersion models

13. Research gaps and impact on validity: exposure models
10 studies reporting 30
risk estimates, 53%
were positive (31%
significant)
4 studies reporting 28 risk
estimates, 93% were
positive (65% significant)
10 studies reporting 55
risk estimates, 93% were
positive (29% significant)
4 studies reporting 40
risk estimates, 50% were
positive (35% significant)

14. 23 studies, 153 main risk estimates from 4 exposure models,
114 (75%) positive, 45 (39%) statistically significant… and
more from the other exposure models…
3
5
1
1
3
3
1
2
3
1

15. So does traffic-related air pollution cause asthma?
“The results found across the studies
followed a pattern that would be
expected under the plausible
assumption that the pollutants really
are causally associated with asthma
development, if only among a subset
of children…”
(HEI, 2010, p.363)

16. But…
Which pollutant(s)…

17. But…
… and why this heterogeneity?
• Differences in study designs,
populations, exposure models,
outcome definitions and
confounders selection
• Certain susceptibility factors may
be one reason (early life
exposures, sex)
• Only certain phenotypes of
asthma may be affected?

18. • Traffic-related air pollution might have
contributed to the recent asthma epidemic
• Effect estimates are very likely to have been
distorted/ underestimated
• Many effects were detected in areas meeting
the relevant air quality guidelines
• Black Carbon (and ultra-fine particles) are yet
unregulated
Implications

19. • Traffic-related air pollution is a modifiable
environmental factor
• Black Carbon (and ultra-fine particles) are truly
traffic-related pollutants
• -28% / -40% decreases in Black Carbon in the
Milan congestion charging area (Mattioli, 2014)
• A substantial proportion of asthma cases can
be prevented?
Implications

20. Thank you!

21. References
• Anderson, H. R., Gupta, R., Strachan, D. P., & Limb, E. S. (2007). 50 years of asthma: UK trends from 1955 to 2004. Thorax,
62(1), 85-90.
• Brook, J. R. (2012) 'Estimating exposure to traffic-related air pollution', in Health Effects Institute Annual Conference,
Chicago, Illinois, 15-17th April 2012.
• Cookson, W. (2004). The immunogenetics of asthma and eczema: a new focus on the epithelium. Nature Reviews
Immunology, 4(12), 978-988.
• Hansen, S., Strom, M., Maslova, E., Mortensen, E. L., Granstrom, C., & Olsen, S. F. (2012). A comparison of three methods to
measure asthma in epidemiologic studies: results from the Danish National Birth Cohort. PloS one, 7(5), e36328.
• Health Effects Institute, H. E. I. (2010) Traffic-related air pollution: a critical review of the literature on emissions, exposure,
and health effects, Health Effects Institute.
• Khreis H, Kelly C, Tate J, Parslow R (2014). Exposure to traffic-related air pollution and the development of childhood
asthma. PROSPERO :CRD42014015448, available from:
http://www.crd.york.ac.uk/PROSPERO/display_record.asp?ID=CRD42014015448
• Mattioli, G. (2015). Pollution or congestion charging? Air quality measures and road pricing in Milan, Italy, in Institute for
Transport Studies Research Seminar Series, University of Leeds, 05 March 2015.