Birch pollen asthma in The Netherlands.

The occurrence of birch pollen asthma is related to high birch pollen concentrations in the air, and therefore this type of asthma is rather common in Scandinavia. High birch pollen concentrations are rare in The Netherlands, but in the spring of 1984 extremely high levels were reached, whereas the concentrations of alder and hazel pollen were very low. During this period nine pollinosis patients known to the allergist developed asthmatic complaints. The appearance and disappearance of the asthmatic symptoms in these patients showed strong correlation with the course of the birch pollen concentration in the air, which strongly suggests that birch pollen asthma can occur in The Netherlands. The significance of this finding may be that this type of asthma can be observed regularly when the birch pollen concentrations are very high. This may also hold for other western European countries.