Association of birch pollen and air pollution with asthma-control questionnaire scores among individuals with allergic asthma in Sweden

Abstract

Introduction: Asthma is a chronic respiratory disease that affect both adult and children. The disease is as part of the most reported emergency cases to the hospital globally. Over the years asthma prevalence has increased in many countries. In 2016, the disease affected 339 million people globally. To fight asthma, we need to understand the risk factors and triggers that lead to asthma attack and symptoms exacerbation. Investigating the interplay between the risk factors and triggers of asthma is one of the ways to ensure effective asthma management and control. Aim: This study investigated the association between birch pollen and air pollution with Asthma Control Questionnaire score (aggregate score of reported symptoms) among people with allergic asthma. The study also investigated the association of pollen and ACQ, air pollutants and ACQ and the effect of pollen and air pollutant on ACQ score of participants. Methods: Mixed effect linear regression analyses were performed with independent variables to establish which variables showed an association with the ACQ score. Asthma Control Questionnaires (ACQ) was used as a composite measure, an instrument that aggregate the reported asthmatic symptoms after exposure to pollen and air pollution to investigate this association. The study is panel study that collected data in three waves. Both the outcome and explanatory variable were log transformed for statistical analysis. Results: In an unadjusted mixed linear model regression with ACQ as the dependent variable and 24 hours of pollen exposure as the explanatory variable, pollen was statistically significantly (P=0.03). When other variables like temperature, relative humidity and air pollutants were added to the model air pollutants were not significant. Though air pollutants did not have a directly association on patients ACQ score, when air pollutant meets pollen, pollen become a strong agent to induce symptoms of asthma. In addition, average ACQ was 0.59(SD=0.40) which signifies that, generally most of the participants had well controlled or managed asthma. Conclusion: Birch pollen is investigated to have some impact on asthma, even though this association was moderate. Association of air pollutant and ACQ score was insignificant, this notwithstanding pollutant like PM10 could influenced the association between asthma and ACQ (reported symptoms).