Seasonal variation of asthma and allergic rhinitis. Consultation pattern in general practice related to pollen and spore counts and to five indicators of air pollution.

The seasonal variation of consultations on account of asthma and allergic rhinitis, and the relationship with air concentrations of pollen, spores, and lead, cadmium, dust, soot and sulfur dioxide was investigated in Danish general practice during a 1-year period 1977-78. A population of about 500,000 was studied. Among about 3000 asthmatics there were less consultations during spring than the rest of the year, but the seasonal variation of consultations with symptoms was rather small. The highest rate of consultations was in week 24, which is close to the peak of the grass pollen period. No relationship was found between asthma symptoms and concentrations of pollution indicators. Among about 5000 patients with allergic rhinitis the rate of consultations with symptoms increased at the start of the tree pollen season, still more at the start of the birch pollen season, and was very high during weeks 21-26 in the grass pollen season. Two thirds of all consultations for symptomatic allergic rhinitis took place within 10 weeks (Nos. 18-27). During the grass pollen season there was a relative preponderance of young patients, while during the birch pollen season older patients dominated. No connection was seen between rhinitis symptoms and pollution indicators. The different seasonal variation of asthma and allergic rhinitis indicates that the two patient categories differ as regards symptom-provoking factors. Allergic rhinitis is mainly precipitated by grass and birch pollen. The precipitating factors of asthma were not disclosed in this study, with the exception perhaps of some influence from pollen, and - among 0-4-year-old children - respiratory infections.