Asthma exacerbations are linked to variations in air allergens, respiratory infections, and weather. A study evaluated 2,637 young adult asthma patients. Skin prick test was used to identify sensitizations and asthma attacks were assessed by questionnaire. Patients report more frequent asthma attacks during certain times of the year, ranging from 47% in Sweden to 87% in Spain. These variations were unrelated to sensitization to house dust mite or cat.
Southern European patients with grass sensitization were more likely to report asthma attacks in spring or summer versus winter: odds ratio (OR) 2.60 in March/April versus 4.43 in May/June. In contrast, for Northern European patients, the peaks were smaller and appeared later in the year: OR 1.25 in May/June and 1.66 in July/August. Asthma patients with self-reported hay fever but without grass sensitization did not have seasonal variations.