Measuring the ways climate change can affect allergy season: methods and challenges

In another article, we discussed 3 Ways that climate change can affect pollen emissions. Here we describe the link to pollen allergies and how we can measure the disease burden.

It’s expected that climate change will lead to an increase in pollen and that this, in turn, will increase pollen allergies. This is for a number of reasons: an extended pollen season; an increase in pollen production and changes in plant distribution, which leads to new plant species. In addition, changes in levels of atmospheric CO2 and air pollution can increase the burden of pollen allergy.

How can we measure the disease burden of pollen allergies? 

There are several ways to measure and study disease burden:

1. Medical records. The disease burden can be measured using the medical records of patients suffering from allergies. However, these records are often not publicly accessible. To investigate allergy burden, patient records have to be linked to environmental factors, requiring the medical records to have a spatial location for the patients. This can be coordinates, postal codes or addresses. This information is often not available or not disclosed. It’s hard to obtain long temporal georeferenced records of pollen allergy patients.

2. Medication sales. Over-the-counter medication sales can be used as a proxy for patient information. Pharmacies and drug stores collect this information. The data is collected at the granularity of the stores, and the density of the stores impacts how well the spatial dimension is covered. The medication type needs to be correctly matched with the allergy under investigation.

Some factors make this type of data difficult to use. Online sales, for example, make the location of the buyer more difficult to track. Other factors lead to a mismatch between the time of the allergy and the selling of medication, such as when the medication is on sale, or when customers buy it ahead of time in preparation for allergy season.

3. Volunteered Geographical Information (VGI). This is mostly data collected via pollen allergy radar websites and apps. The number of people participating in the collection of VGI can vary in space and time. This makes it difficult to compare various years and areas.

Problems with establishing the link between pollen and the disease burden 

When suitable data has been obtained, the correlation between pollen and disease burden has to be established. This can also lead to problems:

1. Multiple causes. Allergy burden isn’t normally caused by a single pollen-producing plant species but results from combinations of allergenic plants producing pollen during various timeframes. It’s often unclear how various plants contribute to the allergy burden.

 2. Comparing years. Comparing years is difficult because species don’t produce pollen in exactly the same week every year. Due to different climate conditions, a plant may flower earlier or later and can, in different years, overlap with different other species.

 3. Environmental factors. Other climate factors may influence the amount of allergy burden. When there are heavy rains during the flowing season, pollen may wash out from the air, causing fewer allergies than expected. Environmental factors can positively impact the allergy burden. Air pollution, for example, can enlarge the allergy burden even when the total pollen load is the same.

4. Non-local pollen. Not all pollen measured at a location are produced locally. For species like Betula, pollen can be carried over large distances, and can impact unexpected areas. When pollen were only produced locally, we could look at a tree species map to determine which pollen to expect and only local climate factors would determine the moment when pollen dissemination starts.  

To learn more about the project, visit our project page and check out these links:

Tree compass

Tree compass helps create a healthy living environment for hayfever patients

Be cautious planting trees that may cause hayfever