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

Background It is well established that there are different asthma phenotypes, but whereas determinants of atopic asthma are well studied, little is known about 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, pets, family, diet, and air-quality categories. Using mixed effects logistic regression models we assessed risk factors over 4 pathways: Pathway 1: non-atopic non-asthma to NAA; Pathway 2: non-atopic non-asthma to atopy (no asthma); Pathway 3: atopic non-asthma to AA; Pathway 4: non-atopic non-asthma to AA. We compared the log odds of risk factors between pathways using Pearson’s correlation coefficient. Results Our final sample of 32741 children comprised 67% with neither atopy nor asthma, 15% with atopy but without asthma, 8% with AA and 10% with NAA. Risk factors were similar between Pathway 1 and Pathway 3 (Pearson’s correlation = 0.81, 95% confidence interval = [0.68, 0.94]). In contrast, risk factors differed between Pathway 2 and Pathway 3 (-0.06, [-0.29, 0.17]). Discussion These findings indicate that although atopy increases the risk of asthma, the risk factors for subsequently developing asthma are generally the same in those with and without atopy. 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.