An investigation of the environmental determinants of asthma hospitalizations: An applied spatial approach Diogo Ayres-Sampaio a, * , Ana C. Teodoro a , Neftalí Sillero a , Cristina Santos b , João Fonseca b , Alberto Freitas b a Geo-Space Sciences Research Center, Faculty of Sciences, University of Porto, Astronomical Observatory, Alameda do Monte da Virgem, 4430-146 Vila Nova de Gaia, Portugal b Center for Research in Health Technologies and Information Systems, Faculty of Medicine, University of Porto, Rua Dr. Plácido da Costa, 4200-450 Porto, Portugal Keywords: Air pollution Asthma Satellite data Spatial epidemiology Urbanization abstract Several previous studies have connected asthma exacerbations with environmental factors such as pollutants. However, the majority do not analyze the information spatially. The objective of this study was to evaluate the relationship between asthma hospital admissions and several environmental vari- ables in mainland Portugal using spatial data from remote sensing and spatial modeling. A set of five environmental variables were considered: near-surface air temperature (T a ) from the temperature profile of the Moderate Resolution Imaging Spectroradiometer (MODIS); relative humidity (RH) from meteo- rological station data interpolated by kriging; vegetation density from MODIS Normalized Difference Vegetation Index (NDVI); and space-time estimates of nitrogen dioxide (NO 2 ) and particulate matter less than 10 mm (PM 10 ), both from Land-Use Regression (LUR) models based on data from air quality stations. Districts were aggregated into three groups based on their percent urban cover, and the municipality was chosen as the sampling unit to assess the relationship between asthma hospital admission rates and environmental variables by season for the years 2003e2008. In the most urban group, T a , NDVI, and NO 2 had consistent relationships with asthma in all seasons (Pearson correlation coefficients ranging from 0.351 to 0.600, 0.376 to 0.498, and 0.405 to 0.513, respectively). The associations in the other groups were very weak or non-existent. The percentage of urban cover influences the relationship between the environment and asthma. The results suggest that asthmatic people living in highly urbanized and sparsely vegetated areas are at a greater risk of suffering severe asthma attacks that lead to hospital admissions. Ó 2013 Elsevier Ltd. All rights reserved. Introduction Asthma is a chronic inflammatory disorder of the airways that affects people of all ages throughout the world. The chronic inflammation is associated with a hyper-responsiveness of the airways that leads to recurrent episodes of wheezing, breathless- ness, chest tightness, and coughing, particularly at night or in the early morning. The disease is prevalent in all age groups (GINA, 2011; Sa-Sousa et al., 2012) and affects approximately 300 million people worldwide, causing 250 thousand deaths per year (GINA, 2011). The disease can be exacerbated by environmental factors such as allergens, air pollution or weather changes (Portnov, Reiser, Karkabi, Cohen-Kastel, & Dubnov, 2012) and infectious factors such as viruses and bacteria (GINA, 2011). When uncontrolled, asthma can place severe limits on daily life and is sometimes fatal. In recent years, several studies have analyzed how asthma is exacerbated by pollutants (Wilhelm et al., 2008) such as ozone (O 3 ), particulate matter (PM) with aerodynamic diameters less than 10 mm or 2.5 mm (PM 10 or PM 2.5 , respectively), nitrogen dioxide (NO 2 ), carbon monoxide (CO), and sulfur dioxide (SO 2 ). However, the results of these studies do not agree (Akinbami, Lynch, Parker, & Woodruff, 2010; Delamater, Finley, & Banerjee, 2012), and thus, the role of pollutants in asthma exacerbations remains controversial (GINA, 2011). The discrepancies among studies could be explained by variations in study design and the modeling methods adopted (Akinbami et al., 2010). In addition, the choice of outcome (e.g., prevalence, emergency department visits, hospitalizations, and * Corresponding author. Tel.: þ351 227 861 290; fax: þ351 227 861 299. E-mail addresses: dsampaio@fc.up.pt, diogo.ayres@gmail.com (D. Ayres- Sampaio), amteodor@fc.up.pt (A.C. Teodoro), neftali.pablos@fc.up.pt (N. Sillero), csantos@med.up.pt (C. Santos), jfonseca@med.up.pt (J. Fonseca), alberto@med.up. pt (A. Freitas). Contents lists available at ScienceDirect Applied Geography journal homepage: www.elsevier.com/locate/apgeog 0143-6228/$ e see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.apgeog.2013.11.011 Applied Geography 47 (2014) 10e19