Allergen Update

About Allergen Forecasting

The pollen forecast is designed with the primary considerations of allergenicity and the allergy sufferer. The system is designed around a combination of the plants present in any given area and their probable affects in terms of the degree of discomfort they cause people suffering with allergies.

Forecasts combine weather, current pollen levels, historical data, and advanced statistical modelling to project what the concentrations of certain major allergens will be on any one day.

The general categories of weeds, grasses, and trees were used as a starting point. Ragweed was selected for primary consideration since this group is composed of a few species which are quite similar in allergenicity. Cross reactivity is high, so an allergic reaction to ragweed is almost universal regardless of what species is present. There is also a high level of cross allergenicity, and biologically the species are also similar. The ragweed group is both easily predictable and highly significant.

The grasses form an intermediate group both in terms of allergenicity and predictability. The number of species in this group is much higher than the ragweed group and the reactions are more diverse. There is less cross reactivity than ragweed, hence a person with allergies to one species of grass may not be allergic to other species. A high grass may not be universally associated with an allergic reaction. Despite the fact that different species flower at different times within the grass season they are biologically similar enough that weather conditions affecting one species usually affect other species similarly. We have found the grasses, as a group, realistic to predict and utilize.

Trees and shrubs are totally different since the number of species found is usually more diverse. Of all the species present at any one site their role in causing allergic reactions is diverse. Allergenicity is a level of allergic reaction elicited by the pollen of a particular species. For trees with a high level of allergenicity the amount of pollen in the air may not need to be high to elicit an allergic response in sensitized individuals. Conversely a species of tree with a relatively low level of allergenicity may pollinate in large amounts but may elicit a low allergic response. A total pollen count, which includes many genera and species, can be confusing especially if what is included in that count is not clearly defined. We believe that a total pollen count should not be indicative of potential allergenicity and needs to be qualified as to what is included or predominant in that count.

It is important to keep in mind that an individual's sensitivity is specific to that individual, therefore, the level of outdoor allergens may not reflect the potential of allergic reactions. This is due to the predominance of one or more specific species of pollen or spore, the possibility of multiple allergies, cross-reactivity between allergens or any combination of these. Allergies are very individual and reports on outdoor allergens have to be used in conjunction with a person's reaction and a medical professional.

The complexity and individualism of trees is also prominent biologically. The trees studied react differently and independently to all weather conditions making it necessary to study each group individually. A cold or wet spring may delay pollinosis in one genus by several weeks but won't necessarily have as much of an effect on other tree species.

Because trees display highly individualistic characteristics, both in terms of allergenicity and predictability, predicting on a genus basis is most appropriate both from the standpoint of achieving a realistic prediction and from the actual utility of this information by allergy sufferers.

To achieve a realistic starting point we have selected six groups believed to be most common, potentially allergenic and by extension most likely to create a reaction depending on which species may be present. The genus selected include alder (Alnus), maple (Acer), birch (Betula), poplar (Populus), oak (Quercus) and elm (Ulmus).

These were also selected on the basis of number of pollen grains that would be collected and in accordance with their distribution across the country.

The selection, however, eliminates many of the types of pollen that are highly or moderately allergenic but have limited distribution. This means that even though the pollen report, as broadcast, is useful and valuable information it unfortunately does not cover all of the allergenic species.

Another aspect of outdoor allergens, about which a great deal is not known, is related to the fungi and the role they play in allergies and asthma. There are thousands of genera and species of fungal spores seen in air samples, thus differentiating and understanding what they mean or what role they play in allergies needs a lot more work and research. We attempt to identify all of the major fungal spores that we know are capable of causing allergic reactions. The problem is that we cannot identify the spores to the lowest level (the species) in air samples. Many of the species in one genera do not necessarily cause disease. Interpreting spores and what they mean has a long way to go before we can begin to produce forecasts. What we attempt to do is to identify the most prominent spores found at a particular site and report the level or concentration in our samples. We also identify the ones we know are important in causing disease.

The future of forecasting will involve more information on spores and more detail on the individual sites and other allergens specific to them. The various websites on the internet, including our own, should attempt to give more information that is up to date and relevant to allergenicity.

Predicting Methodology for Canada

Samples are collected daily on rotation impacting samplers at stations across Canada. Specimens are delivered to Aerobiology Research Laboratories and analyzed by highly trained technicians via optical microscopy and computer aided calculations. Standardization of sampling methodology and analysis ensures data comparability. The latest available analysis, which is always between one and seven days old, is used to support the generation of reports and forecast products. All data is warehoused to support statistics and research activities to continually improve forecasting products.

Objectives of Predicting

Our operational objectives are to provide prompt and detailed information on the status of outdoor aeroallergen levels to professionals in the field, and concurrently via broadcasting, useful summaries to individuals who suffer from allergies. To this end we have designed a system to predict and broadcast pollen forecasts, as well as some fungal spore information, where the primary consideration is the allergy sufferer. The system is designed around a combination of the plants present in any given area and the probable affects of these plants in terms of the degree of discomfort they cause to persons suffering from allergies.

Parameters Used in Predicting

Production and dispersal of pollen: the main parameter is a minimum of five years of accurate daily pollen counts at the collection site together with daily parameters for weather factors on a year-round basis. Pollination is a reaction not only to current but also to prior weather conditions. In temperate areas the type of winter and spring immediately prior to and the type of growing season from the previous year are especially important for pollen production. Distribution is influenced by current weather factors and any pollen prediction is tied to the accuracy of the weather forecast parameters in the computer model. Due to biological and weather differences each location must have a separate statistical analysis and model for each pollen type predicted. Hence, separate statistical analyses and computer models are necessary for each location.

Dealing with predicting large sites with diversification in distribution of trees.

One of the big problems that we are constantly faced with is predicting for certain diverse sites with only one sampling location. Cities such as Halifax and Edmonton, where the distribution of elm populations varies a great deal from one location to another, are excellent examples. Another city is Calgary, where we presently have two locations. The maple tree distributions at each of the Calgary sites are very different, with one site having many and the other site having very few. The pollen levels we forecast for cities such as these are not necessarily representative of the entire city, although the forecasts should provide a good relative indicator: pollen levels will usually increase and decrease at roughly the same time throughout the region.


An example of a generic next-day forecast would be as follows:

1 2 3 4 5 6 7 8 9 10
Low Moderate High


The third column indicates the forecasted pollen index level for your area. The legend on the right (column 4) shows whether these levels are low, moderate or high. It is important to note that persons extremely allergic to pollen can be affected even at a low index reading.

Management of allergies to pollen and spores is not easy but can be minimized by staying indoors when pollen counts for outdoor allergens are high. Spores, however, are much harder to minimize since they are found in abundance both in the indoor and outdoor environments. The same fungal spores that are found outdoors also exist indoors, however, there are also some differences. Air conditioning, staying indoors when aeroallergens are high, avoiding carpets, vacuuming and air filtration can all help in limiting the amount of allergen one is exposed to. Immunotherapy has also shown to benefit patients with inhalant allergies.

We have observed that seasons can vary drastically from year to year, especially with the trees. Forecasting is not an exact science and our aim is to try and inform interested individuals as to what is going to happen with the pollen and spores so they are better prepared to deal with their allergies.

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