Does urban extent from satellite images relate to symptoms of asthma, rhinoconjunctivitis and eczema in children? A cross-sectional study from ISAAC Phase Three

<i>Objective</i>: The relationship between urbanisation and the symptom prevalence of asthma, rhinoconjunctivitis and eczema is not clear, and varying definitions of urban extent have been used. Furthermore, a global analysis has not been undertaken. This study aimed to determine whether the symptom prevalence of asthma, rhinoconjunctivitis and eczema in centres involved in the International Study of Asthma and Allergies in Childhood (ISAAC) were higher in urban than rural centres, using a definition of urban extent as land cover from satellite data. <i>Methods</i>: A global map of urban extent from satellite images (MOD500 map) was used to define the urban extent criterion. Maps from the ISAAC centres were digitised and merged with the MOD500 map to describe the urban percentage of each centre. We investigated the association between the symptom prevalence of asthma, rhinoconjunctivitis and eczema and the percentage of urban extent by centre. <i>Results</i>: A weak negative relationship was found between the percentage of urban extent of each ISAAC centre and current wheeze in the 13–14-year age group. This association was not statistically significant after adjusting for region of the world and gross national income. No other relationship was found between urban extent and symptoms of asthma, rhinoconjunctivitis and eczema. <i>Conclusions</i>: In this study, the prevalence of symptoms of asthma, rhinoconjunctivitis and eczema in children were not associated with urbanisation, according to the land cover definition of urban extent from satellite data. Comparable standardised definitions of urbanisation need to be developed so that global comparisons can be made.

研究目标：城市化与哮喘、鼻结膜炎及湿疹的症状患病率之间的关联尚不明确，且当前学界对城市范围的定义并不统一。此外，目前尚未开展相关全球尺度分析。本研究旨在以卫星数据获取的土地覆被作为城市范围的定义标准，探究国际儿童哮喘与过敏研究（International Study of Asthma and Allergies in Childhood）各参与中心中，儿童哮喘、鼻结膜炎及湿疹的症状患病率是否在城市中心高于乡村中心。
研究方法：本研究采用卫星影像获取的全球城市范围地图（MOD500 map）作为城市范围判定标准。将国际儿童哮喘与过敏研究各参与中心的地图进行数字化处理，并与MOD500地图进行融合，以计算各中心的城市用地占比。随后分析各中心的哮喘、鼻结膜炎及湿疹症状患病率与城市用地占比之间的关联。
研究结果：在13~14岁年龄组中，各国际儿童哮喘与过敏研究参与中心的城市用地占比与当前喘息症状患病率之间仅存在微弱的负相关关系。在对全球区域及国民总收入进行校正后，该关联不再具有统计学显著性。未发现城市范围与哮喘、鼻结膜炎及湿疹症状患病率之间存在其他关联。
研究结论：本研究基于卫星数据获取的土地覆被城市范围定义，未发现儿童哮喘、鼻结膜炎及湿疹的症状患病率与城市化水平存在关联。未来需制定统一标准化的城市化定义，以便开展全球范围的对比研究。