Environmental Research 106 (2008) 203–211 Associations between grass and weed pollen and emergency department visits for asthma among children in Montreal Le´a He´guy a,b,Ã , Michelle Garneau a,b , Mark S. Goldberg c,d , Marie Raphoz a,b , Fre´de´ric Guay b , Marie-France Valois c,d a Geography Department, Universite´du Que´bec a` Montre´al, Montre´al, Que., Canada b Consortium Ouranos sur la Climatologie Re´gionale et l’Adaptation aux Changements Climatiques, Montre´al, Que., Canada c Department of Medicine, McGill University, Montre´al, Que., Canada d Division of Clinical Epidemiology, McGill University Health Centre, Montre´al, Que., Canada Received 9 March 2007; received in revised form 4 October 2007; accepted 10 October 2007 Abstract Context and objective: Asthma among children is a major public health problem worldwide. There are increasing number of studies suggesting a possible association between allergenic pollen and exacerbations of asthma. In the context of global climate change, a number of future climate and air pollution scenarios predict increases in concentrations of pollen, an extension of the pollen season, and an increase in the allergenicity of pollen. The goal of the present study is to evaluate the short-term effects of exposure to grass and weed pollen on emergency department visits and readmissions for asthma among children aged 0–9 years living in Montreal between April and October, 1994–2004. Methodology and results: Time-series analyses were carried out using parametric log-linear overdispersed Poisson models that were adjusted for temporal variations, daily weather conditions (temperature, atmospheric pressure), and gaseous air pollutants (ozone and nitrogen dioxide). We have found positive associations between emergency department visits and concentrations of grass pollen 3 days after exposure. The effect of grass pollen was higher on emergency department readmissions as compared to initial visits. Weak negative associations were found between weed pollen (including ragweed pollen) and emergency department visits 2 days after exposure. Conclusion: The data indicate that among children, emergency department visits increased with increasing concentrations of grass pollen. r 2007 Elsevier Inc. All rights reserved. Keywords: Pediatric asthma; Pollen; Epidemiology; Time-series studies; Climate change 1. Introduction Climatic conditions have a large influence on the environment and on vegetation, and it appears likely that climate change will affect growth and the reproduction cycle of vegetation and the production of pollen (D’Amato et al., 2005; Beggs and Bambrick, 2005). Particularly sensitive to temperature, duration of sunshine, and ambient CO 2 , the production of pollen has increased with the 0.6 1C increase in the global average temperature at the surface of the earth over the past 100 years (Root et al., 2003). Additionally, studies have shown an earlier start to the pollen season, an increase in the number of growing days, and greater pollen production (Ziska and Caulfield, 2000; Breton et al., 2006; Thibaudon et al., 2005). With the anticipated longer growing seasons and higher concentrations of pollen, attention has now turned to understanding the effects of pollen on respiratory health problems, such as asthma and allergic rhinitis (Breton et al., 2006). There is mounting evidence that asthma has a multifactorial pathology, and may include interactions ARTICLE IN PRESS www.elsevier.com/locate/envres 0013-9351/$ - see front matter r 2007 Elsevier Inc. All rights reserved. doi:10.1016/j.envres.2007.10.005 Abbreviations: AIC, Akaike Information Criterion; CI, confidence interval; df, degrees of freedom; MPC, mean percent change; NO 2 , nitrogen dioxide; O 3 , tropospheric ozone; QHIP, Que´bec Health Insurance Plan. Ã Corresponding author. Geography Department, Universite´ du Que´bec a` Montre´al, Montre´al, Que., Canada. E-mail address: lea.heguy@mcgill.ca (L. He´guy).