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

BACKGROUND

It is well established that there are different asthma phenotypes, but whereas determinants of atopic asthma (AA) are well studied, little is known about non-atopic asthma (NAA). We compared risk factors for atopy, AA in atopics and 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 four 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 the Pearson correlation coefficient (PCC).

RESULTS

Our final sample of 32 741 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 (PCC=0.81, 95% CI 0.68 to 0.94). In contrast, risk factors differed between pathway 2 and pathway 3 (PCC=-0.06, 95% CI -0.29 to 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.