title: Effects of airborne birch pollen levels on clinical symptoms of seasonal allergic rhinoconjunctivitis.
abstract: BACKGROUND
  Most panel studies focusing on rhinitis and conjunctivitis symptoms and birch pollen have been performed on a linear basis and have not included air pollution and meteorological variables as potential confounders. The objective of this panel study was to assess the relationship between symptoms of seasonal allergic rhinoconjunctivitis and daily airborne birch pollen concentrations, checking with adequate statistical tools the shapes of concentration-response curves and controlling for confounders.
  
  
  METHODS
  The severity of rhinitis, conjunctivitis, and bronchial symptoms was recorded daily in March and April 2010 (3,311 person-days) in 61 seasonal allergic rhinoconjunctivitis patients sensitized to birch. Data were analyzed with generalized additive and generalized estimating equation models to quantify the effects of birch pollens.
  
  
  RESULTS
  The relationship between birch pollen and the percentage of patients with nasal, ocular and bronchial symptoms was linear until birch daily average concentrations of, respectively, 110, 70, and 70 grains/m(3); it reached a plateau thereafter. For an increase of 10 grains/m(3), the OR (95% CI) for nasal, ocular, and bronchial symptoms were, respectively, 1.07 (1.03-1.12), 1.17 (1.08-1.27), and 1.12 (1.03-1.21). At the beginning of the season, no nasal or ocular symptoms were observed below a threshold of 30 grains/m(3).
  
  
  CONCLUSIONS
  Adequate modeling regression shows that the clinical response to natural exposure to birch pollen in sensitized patients varies during Betula pollen season, with a threshold at the beginning of the season, while over the whole season the relationship is linear for nasal, ocular, and bronchial symptoms up to a saturation point, followed by a plateau.
authors.affiliation: Service de Pneumologie, Hôpital Gabriel Montpied, Clermont-Ferrand, France.
authors.forename: Denis
authors.initials: D
authors.lastname: Caillaud
authors.forename: Sylvie
authors.initials: S
authors.lastname: Martin
authors.forename: Claire
authors.initials: C
authors.lastname: Segala
authors.forename: Jean-Pierre
authors.initials: JP
authors.lastname: Besancenot
authors.forename: Bernard
authors.initials: B
authors.lastname: Clot
authors.forename: Michel
authors.initials: M
authors.lastname: Thibaudon
mesh_terms: D000328:Adult; D000393:Air Pollutants / Q000276:immunology*; D000485:Allergens / Q000276:immunology*; D029662:Betula / Q000276:immunology*; D003233:Conjunctivitis, Allergic / Q000150:complications / Q000276:immunology / Q000503:physiopathology*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D011058:Pollen / Q000276:immunology*; D012044:Regression Analysis; D006255:Rhinitis, Allergic, Seasonal / Q000150:complications / Q000276:immunology / Q000503:physiopathology*; D012621:Seasons; D012720:Severity of Illness Index
chemical_list: D000393:Air Pollutants; D000485:Allergens