Long-term exposure to air pollution and asthma hospitalisations in older adults: a cohort study

Zorana Jovanovic Andersen 27.09.2011 ERS

Conflict of interest disclosure‘I have no, real or perceived, conflicts of interest that relate to this presentation’

Asthma Chronic inflammatory disease of the airways,

characterized by variable and recurring symptoms, reversible airflow obstruction, hyperresponsiveness, bronchospasm.

Background The prevalence of asthma in older adults is 6-

10% in high-income countries, and increasing, including Denmark, where increase in the severity is also documented

The economic burden associated with hospital care, medications, and years of work lost is projected to escalate with increasing numbers of older people with asthma due to enhanced longevity

Background: Asthma & Air Pollution

Short-term exposure to elevated air pollution linked to exacerbation of asthma symptoms (wheezing, coughing, breathlessness) in children and adults, leading to asthma hospitalizations

More studies in children than adults: long-term exposure to air pollution in early life linked to development of asthma

Limited evidence in adults: does long-time/lifetime exposure to air pollution increases risk of asthma development in adult life?

Background: Asthma & Air Pollution

Limitations:- asthma incidence and prevalence based on self-reports of asthma- losely defined onset, recall/info bias- short air pollution exposure windows

Aim of this study

We studied the association between traffic-related air pollution levels for up to 35 years at the residence and the risk for hospital admission for asthma in an elderly Danish cohort

We tested for an effect modification by lifestyle, education, and co-morbid conditions

Methods - Cohort Danish Diet, Cancer and Health cohort 57 053 subjects, Copenhagen and Aarhus Interviewed in 1993-1997 (baseline) Age 50-65 years Linkage to Central Population Registry and Danish

Address Database - residential address history (1971) Linkage to Danish National Patient Register (1979): first-admission for asthma (ICD-10: J45-46), between

baseline (1993-1997) and 27 June 2006 co-morbidities defined as hospitalizations for COPD

(J40-44), ischemic heart disease (I20-25), and stroke (I60-63)

Methods – Air Pollution Exposure AirGIS dispersion model, sum of:

1) regional background, 2) urban background, & 3) street level contribution

Input for AirGIS model Street/building geometry Street network and traffic data Meteorology

Road centre lineAddress point

BuildingRoad centre lineAddress point

Building

GIS Maps building height, street width, open sector

Traffic counts, emission factors, density, speed, types, variation patterns over time

Methods – Air Pollution Exposure AirGIS Model output:

Annual mean NO2 /NOx concentrations at individual address

NOX (Class)

680000 690000 700000 710000 720000 730000

6140000

6150000

6160000

6170000

6180000

6190000

6200000

6210000

6220000

1 2 3 4 5 6 7 8 9 10

a)

Lille Valby

wind

Leeward Windward

Recirculated pollution

Direct emission

Background pollution

Flow and dispersion inside a street canyon

Methods – Statistical Model

Cox proportional hazards model, left truncation at age at baseline, and right censoring at age at hospital admission for asthma, death, emigration, or 27 June 2006

NO2 time-dependent variables, log transformed, mean since 1971 until asthma/censoring, estimates per IQR

Confounders: sex, smoking (status, intensity, duration, ETS), occupational exposures, BMI, educational level, fruit consumption

Effect modification: interaction term, Wald-test Spline (rcs) in R, for dose-repsonse curve

Results: Study Population

Cohort Asthma57 053

- 571 cancer before baseline

- 962 missing address or geocode

- 1 236 missing address - 589 missing info on

covariates

Original Cohort

53 695 Study Population

977 (1.9%)

53 143 Asthma-free 821 (1.5%)

552 Previous Asthma

176 (31.9%)

Outcome: Asthma Hospitalization

Objective measure of asthma onset, nationwide register

Not marker of disease onset, but hallmark of asthma progression to a more severe stage or exacerbation

Traditionally confirmed by objective measurements of lung function and reversible airflow obstruction in Danish hospitals

The specificity of asthma as high as 0.98 Underestimates real asthma burden

Results: Descriptive Statistics

Results: Exposure to Air Pollution

Median NO2 for cohort 15.2 µg/m3

and for asthmatics (n=977) 16.4 µg/m3

Results: Main Analysis

Excluding 452 subjects with prior COPD admissions:1.11 (1.02-1.21)

1.10 (1.01-1.21)

1.29 (1.03-1.60)

Results: Effect Modification

Results: dose-response

Conclusions

The risk for asthma hospitalization in this elderly cohort was significantly positively associated with increasing levels of NO2 assessed over 35 years at their residences

The risk for new asthma hospitalizations about 10% per IQR

The risk was most pronounced for people with a previous asthma 41% per IQR or COPD hospitalization 31% per IQR.

Limitation

No data on atopy, allergy, or familial history of asthma, important risk factors for asthma and potential effect modifiers

Lack of work address, activity pattern, indoor air pollution sources, which could have imporved air pollution exposure assesment

Acknowledgements Thorax