The partial contribution of specific airborne pollen to pollen induced allergy

The air that we inhale contains simultaneously a multiple array of allergenic pollen. It is well known that such allergens cause allergic reactions in some 15% of the population of the Western World. However little is known about the quantitative aspect of this phenomenon. What is the lowest concentration of pollen that might trigger allergic responses? As people are exposed to heterogeneous and variable environments, clarification of the partial contribution of each of the major airborne pollen allergens and determination of its role in invoking allergy are of prime importance. Objectives: (1) Assessment of a possible correlation between the concentration of airborne pollen and incidence of allergy. (2) Estimation of the lowest average concentrations for various species of airborne pollen that elicit allergic symptoms when exceeded. (3) Determination of the extent of the variations in manifestation of allergy symptoms that can be explained by fluctuations in the concentration of individual species of airborne pollen. Methods: The study was conducted during 14 months with a rural population in Israel. The participants completed a detailed questionnaire and were skin prick tested with the common airborne allergens. The appearance of clinical symptoms, i.e. nasal, bronchial, ocular or dermal, were reported daily by the patients. Concentrations of the airborne pollen and spores were monitored in the center of activity of the residents during one day every week, using three 'Rotorod' pollen traps. The pollen grains were identified by light microscopy. Results: The pollen spectrum was divided into time-blocks presenting the main pollination periods of the investigated species. The correlation between the concentration of airborne pollen of the relevant species and the clinical symptoms of the patients was determined for each time block. The correlation differed for different clinical symptoms and for different pollen allergens. Highest correlation with airborne pollen counts was found for patients with nasal and bronchial symptoms. The onset of the clinical symptoms by sensitive patients started, in each of the relevant groups, once the weekly average concentration of the airborne pollen crossed a threshold level. Under the limitations of the present study, this level was estimated to be 2-4 pollen m-3 air for olive, 3-5 pollen m-3 air for grasses, 4-5 pollen m-3 air for Artemisia, 10-20 pollen m-3 air for pecan and 50-60 pollen m-3 air for cypress. Conclusions: Fluctuations in specific airborne pollen grains explained up to 2/3 of the variation in clinical allergy responses. Those were: 69% of the variation for cypress (March-April), 66% for the grasses (March-April), 49% for the pecan (May-June) and 62% for Artemisia (Autumn).