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

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Long-term exposure to air pollution and asthmahospitalisationsin 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

  • Chronicinflammatorydisease 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:

- asthmaincidence and prevalencebased on self-reports of asthma

- loselydefinedonset, recall/info bias

- short air pollution exposurewindows


Aim of thisstudy

  • 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) regionalbackground, 2) urbanbackground, & 3) streetlevelcontribution

  • Input for AirGIS model

    • Street/building geometry

    • Street network and traffic data

    • Meteorology

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

GIS Mapsbuildingheight,

streetwidth, opensector


Methods – Air Pollution Exposure

  • AirGIS Model output:

    • Annual mean NO2 /NOx

      concentrations at individual address

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


Outcome: AsthmaHospitalization

  • 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: DescriptiveStatistics


Results: Exposure to Air Pollution

Median NO2 for cohort15.2 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: EffectModification


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 familialhistory of asthma, importantrisk factors for asthma and potential effectmodifiers

  • Lack of workaddress, activity pattern, indoor air pollution sources, whichcould have imporved air pollution exposureassesment


Acknowledgements

  • Thorax


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