Risk factors for atopic and non-atopic asthma in school-aged children from high, and low and middle income countries

Background Although it is well established that there are different asthma phenotypes, little is known about risk factors and mechanisms for non-atopic asthma. We compared risk factors for atopy, atopic asthma (AA) in atopics, and non-atopic asthma (NAA) in non-atopics, in children in a wide variety of countries. Methods Using four studies, across 23 countries, we assessed asthma status and atopy (skin prick tests) for children aged 6-17, plus risk factors from housing, heating, animals, family, diet, and air-quality categories. Using mixed effects logistic regression models we assessed 4 pathways to asthma: Pathway 1: comparing NAA with non-atopic non-asthma (risk factors for NAA among non-atopics); Pathway 2: comparing atopic non-asthma with non-atopic non-asthma (risk factors for atopy); Pathway 3: comparing AA with atopic non-asthma (risk factors for AA among atopics); Pathway 4: comparing AA with non-atopic non-asthma (risk factors for AA among non-atopics). Results Our final sample of 32,741 children comprised 67% non-atopic non-asthmatics, 15% atopic non-asthmatics, 8% with AA and 10% with NAA. Risk factors were similar for AA in atopic individuals and NAA in non-atopic individuals (Pearson's correlation r=0.81). In contrast, risk factors for atopy in non-asthmatics differed from those for AA in atopic individuals (r=-0.06). Discussion These findings indicate that although atopy increases the risk of asthma, the risk factors for subsequently developing asthma are generally the same in atopics and non-atopics. This raises important questions about the role of atopy in asthma, particularly whether it is an inherent part of the aetiological process or is coincidental.