The Air Quality Health Index and Asthma Morbidity: A Population-Based Study

Teresa To,^1,2,3 Shixin Shen,^1,2 Eshetu G. Atenafu,^2,4 Jun Guan,³ Susan McLimont,¹ Brian Stocks,⁵ and Christopher Licskai^6,7

¹Child Health Evaluative Sciences, The Hospital for Sick Children, Toronto, Ontario, Canada; ²Dalla Lana School of Public Health, University of Toronto, Toronto, Ontario, Canada; ³Institute for Clinical Evaluative Sciences, Toronto, Ontario, Canada; ⁴University Health Network, Toronto, Ontario, Canada; ⁵Ontario Lung Association, Toronto, Ontario, Canada; ⁶Department of Medicine, University of Western Ontario, London, Ontario, Canada; ⁷St. Joseph’s Health Care, London, Ontario, Canada


Abstract

Background: Exposure to air pollution has been linked to the exacerbation of respiratory diseases. The Air Quality Health Index (AQHI), developed in Canada, is a new health risk scale for reporting air quality and advising risk reduction actions.


Objective: We used the AQHI to estimate the impact of air quality on asthma morbidity, adjusting for potential confounders.


Methods: Daily air pollutant measures were obtained from 14 regional monitoring stations in Ontario. Daily counts of asthma-attributed hospitalizations, emergency department (ED) visits, and outpatient visits were obtained from a provincial registry of 1.5 million patients with asthma. Poisson regression was used to estimate health services rate ratios (RRs) as a measure of association between the AQHI or individual pollutants and health services use. We adjusted for age, sex, season, year, and region of residence.


Results: The AQHI values were significantly associated with increased use of asthma health services on the same day and on the 2 following days, depending on the specific outcome assessed. A 1-unit increase in the AQHI was associated with a 5.6% increase in asthma outpatient visits (RR = 1.056; 95% CI: 1.053, 1.058) and a 2.1% increase in the rate of hospitalization (RR = 1.021; 95% CI: 1.014, 1.028) on the same day and with a 1.3% increase in the rate of ED visits (RR = 1.013; 95% CI: 1.010, 1.017) after a 2-day lag.


Conclusions: The AQHI values were significantly associated with the use of asthma-related health services. Timely AQHI health risk advisories with integrated risk reduction messages may reduce morbidity associated with air pollution in patients with asthma.


Key words: air pollution, air quality health index, asthma, health services utilization. 


Environ Health Perspect 121:46–52 (2013). http://dx.doi.org/10.1289/ehp.1104816 [Online 10 October 2012]


Address correspondence to T. To, Child Health Evaluative Sciences, The Hospital for Sick Children, 555 University Ave., Toronto, ON M5G 1X8 Canada. Telephone: (416) 813-8498. Fax: (416) 813-5979. Email: teresa.to@sickkids.ca


Supplemental Material is available online (http://dx.doi.org/10.1289/ehp.1104816).


The authors thank the Ministry of the Environment and the Institute for Clinical Evaluative Sciences (Toronto, Ontario, Canada), for providing the provincial data for this study.


This study was funded by the Ontario Lung Association through a grant from the Government of Ontario. T.T. is supported by the University of Toronto, Life Sciences Committee, Dales Award in Medical Research. 


The opinions, results and conclusions reported in this article are those of the authors and do not necessarily represent those of the Ontario Lung Association, the government of Ontario, or the Ministry of the Environment. 


The authors declare they have no actual or potential competing financial interests.


Received 4 December 2011; Accepted 10 Ocotober 2012; Online 10 October 2012.