Ragweed pollen in France: origin, diffusion, exposure

To detect the origin of ragweed pollen and to measure the impact of this pollen exposure on allergic patients, so their sensitivity can be noted (using specific IgE production: sIgEw1) in order to inform the population about an "allergy" against those ragweed pollen grains.

To measure population exposure to ragweed pollen, the R.N.S.A (National Aerobiological Monitoring Network, a French association) has a pollen trap network located in urban areas. These traps allow continuous recording of airborne pollen, the light microscope analysis (with a bi-hourly time step) allows one to know the daily concentrations of ragweed grains and the circadian rhythm of grains impaction. It is thus possible to follow the evolution of pollination during each day ofeach season and to compare seasons and years at each station. Biomnis is a biological laboratory which performs more than 85% of ragweed specific IgE assay in France. It seems to be clear that when allergists ask ragweed IgE for a patient, it is because they think that this patient seems to be allergic to this specific pollen. The statistical analysis of results about specific IgE (for ragweed) from the Allergology laboratories Biomnis (located in Lyon and Paris) can determine the number ofpatients sensitized to ragweed in French departments.

The distribution ofsensitized patients to ragweed is compared to ragweed pollen distribution studied by the R.N.S.A from the year 2005 to 2008 in France, whatever the ragweed plant' origin: local (closed topollen trap) or imported (by wind).

The biological database (Health impact) allows a correlation between the geographical distribution ofragweed pollen and the number ofpatients with specific IgE against ragweed (sIgEw1), i.e., whose sensitization is due to local plants. That also permits one to estimate the expected number of allergy cases in the next years, because the sensitivity precedes the allergy.