Diary-reported symptoms, medication use, and peak expiratory flow (PEF) in an asthma panel in two Swedish cities

In individuals with allergic asthma sensitized to birch (betula), pollen exposure is associated with airway obstruction, irritation symptoms and increased medication use. The aim of this study was to determine if exposure to air pollution interacts with pollen to augment airway symptoms and obstruction. In this study, subjects with physician-diagnosed asthma and allergy to birch kept symptom diaries and recorded morning and evening PEF for 70 days during two pollen seasons (April – June) in two Swedish cities. Daily exposure levels were assigned from central monitoring stations. Logistic and linear mixed models with individual and city as random effects were used. 38 subjects were included, mean age 49±13 years, 50% women. Pollution concentrations were moderate (24-hour mean PM2.5 6.5, NOX 21.6 and O3 65.0µg/m3) and median pollen was 68 pollen grains/m3 in the study period. Pollen levels above median were associated with increased OR of rhinitis, dry cough, and increased allergy, asthma medication usage, and decreased PEF both morning and evening, but not dyspnea or asthma symptoms. No direct associations were found between reports of rhinitis, decreases in PEF, or lower airway symptoms and PM2.5, NOX or O3. However, several pollutants interacted with pollen (Fig. 1) and we observed associations between PM2.5 and O3 and upper airway symptoms and medication usage at pollen levels above median.