Pollen and health effects:: Synthesis of epidemiological studies

Allergic rhinitis grew up by threefold in French population in the last 25 years. In this context, we conduced a review on the relationships between pollens and health effects. Three fields are discussed: assessment of exposure in epidemiological studies, relationships between pollens and health effects, finally the results of the retained studies are presented. In epidemiological studies, population exposure to pollens is always done by outdoor stationary measurement. Relationships between aeroallergen concentrations and clinical effects are difficult to study because some factors as individual susceptibility, differences in the potential noxious effect of each allergen; lag between pollen and clinical effects, concentration limit that start up clinical effects and concentration limit for maximal effect; the successive productions and emissions of the different kinds of pollens; and multi-sensibility. Studying these relationship needs also to take into account several confounding factors such as: meteorological parameters, fungal aeroallergens concentrations; chemical air pollutants concentrations. Most of the epidemiological studies analyse the relationship between daily variations in pollen counts and daily variations in health effects quantified at individual levels in specific populations (panel study) or quantified at population levels (time-series). A review was already realised on studies published between 1978 and 1995 that examined the relationship between pollens and allergic rhinoconjunctivitis. Only 16 of the published studies had been retained (15 panels and one time-series). The conclusion of this work was that these studies showed associations between pollen counts and allergic rhinoconjunctivitis. But these associations could not be quantified and the dose-response curves could not be characterised because of inappropriate statistical methods and not taking into account confounding factors. In our review, nine studies that examined the short-term effect of pollen were retained for their good methodology (two of them are panels). Their results confirm associations between pollen counts and health effects and some of them succeed in quantifying the short-term effect of pollens on allergic rhinitis, allergic conjunctivitis and also asthma. (C) 2007 Elsevier Masson SAS. Tous droits reserves.