The Most Challenging Places to Live with Allergies

ISeasonal allergies caused by pollen allergens are a major global public health concern,1 particularly as climate change increases the geographical spread and length of exposure to allergenic pollen.2 It has been estimated that 40% of Europeans are sensitized to pollen allergens.3 Pollen allergies lead to an IgE-mediated systemic inflammatory response to seasonal allergens like birch tree or grass pollen, typically causing allergic rhinitis (or “hay fever”), which is characterized by nasal congestion, rhinorrhea, itching of the nose, and sneezing.4 These symptoms have a significant impact on quality of life, as they often impair social life, sleep quality, and school or workplace productivity.4, 5, 6 Pollen allergies are also associated with other common diseases such as asthma, chronic hyperplastic eosinophilic sinusitis, nasal polyposis, and atopic dermatitis based on their shared type-2 immune responses.4
Antihistamines are the main symptomatic treatment for mild to moderate disease, with intranasal corticosteroids being used for more severe cases.4 Evidence suggests that causal treatment of symptomatic allergic rhinitis with allergen-specific immunotherapy can prevent exacerbations and progression to other diseases such as asthma.7 Effective diagnosis and treatment are crucial for adequately managing symptoms, improving quality of life, and reducing the socioeconomic costs of the disease. However, allergies are often underdiagnosed or trivialized and therefore not treated adequately, with many affected individuals lacking an official diagnosis from a health-care practitioner or appropriate medication.8, 9, 10 This indicates a gap between the provided healthcare and medical needs of a population. To combat the public health issues inflicted by pollen allergies, new methods for monitoring airborne pollen and disease activity as well as for gaining an understanding of health-seeking behavior in a population are needed. A promising approach is the referral to crowdsourced data such as web search data as a tool for epidemiological surveillance.11,12 Previous studies using web search data on diseases have demonstrated the potential and value of search patterns for quantifying disease burden and have also given insight into health-seeking behaviors.13, 14, 15, 16
The aim of this study was to examine the value of pollen allergy-related web search data for public health applications by conducting an in-depth analysis of absolute regional search volumes and contents, seasonal trends, and correlations with environmental factors and disease activity as mirrored by antihistamine prescription rates.
In this study on pollen allergy-related search behavior in Germany and Sweden, a north-south axis regarding seasonality of search interest was observed and strong correlations of search volume with pollen concentration and antihistamine prescription rates were demonstrated. Additionally, differences in search volume and keyword topics were discovered in comparisons of the two countries, indicating potential unmet medical needs. The notably higher relative search volume in Sweden compared to in Germany may reflect a greater medical need regarding pollen allergies in Sweden. Prior studies showed that the prevalence of allergic rhinitis was between 26.9 and 30.9% in Sweden,21,22 while in Germany a prevalence between 14.8 and 20.6% was reported.23,24 Although a direct comparison between the countries is difficult due to different definitions and methods in epidemiological studies, the substantially different levels of interest in this study support the observation that the disease has a higher prevalence in Sweden. The significantly higher relative search volume in the German city-states of Bremen and Hamburg may be attributed to the fact that allergies have a higher prevalence in urban areas than in rural areas.25
A further aspect to consider when comparing the 2 countries is the ambitious objective of the Swedish government regarding digitalization and e-health,26 which lead to telemedical services like digital appointments becoming increasingly common.27 Thus, the high number of search queries could also be linked to the higher relevance of the internet and digitalization in Swedish healthcare.
A continuous increase in search volume observed during a 4-year time period has also been reported in similar studies on web search data related to sarcoidosis, abdominal pain, and skin cancer,28, 29, 30 suggesting an overall increase in the importance of the internet for health information. However, the relative increase in search volume related to pollen allergy or hay fever observed in this study was higher than the relative increase in search volume for these other diseases, demonstrating an additional increased interest in the disease independent from general changes in search behavior. This may be explained by a growing burden of hay fever and pollen allergies, contrasting with epidemiological findings stating that their prevalence appears to have reached a plateau in recent years.31 Additionally, the COVID-19 outbreak in 2020 occurring simultaneously with the onset of the pollen season is likely to have caused another peak in interest in pollen allergies and their symptoms, as allergy symptoms can resemble those of COVID-19 infection.32,33
Variation over the course of the year Among the various pollen allergens in Europe, birch and grass pollen are the most relevant to consider in Germany and Sweden due to the high prevalence of sensitization against them as well as their potency.3,34 The flowering period of birch, which is the most dominant tree pollen allergen, typically starts at the beginning of April in central Europe and then progresses northwards, starting in May in Northern Europe.3 Grass pollen season starts in May and peaks in June.3
This flowering pattern was mirrored by search behavior in our study: April was the month with the highest search volume in Germany, coinciding with the peak of birch pollen season. Interestingly, in southern Swedish counties the average number of searches was also highest in April, while it was highest in May in northern counties, reflecting the northward progression and subsequent delay in pollen exposure. In both countries, search frequency remained high in June, which can be linked to the peak of the grass pollen season.
The relationship between pollen seasonality and frequency of related searches was confirmed by the strong correlation between regional search volume and corresponding pollen concentrations, which supports similar findings from other studies on internet search volume and allergies.35,36 The consideration of climactic factors like temperature and precipitation, and the correlations with search activity that were demonstrated in this study contribute to an understanding of the role that web search data can play in predicting and assessing the pollen season across a larger spatial and temporal dimension.
The high correlation between antihistamine prescription rates and internet search volume emphasizes the clinical relevance of these findings. Furthermore, these findings are consistent with those of a study examining the relationship between internet search behavior and real-world epidemiological data of pollen allergies in the United States. The study analyzed airborne pollen concentration and antihistamine sales data, which detected similarly high correlations as those in our study.37 The validity of our findings is further supported by a study from the United Kingdom that has found correlations between web search data on asthma and allergic rhinitis and classical epidemiologic surveillance data.38 Disease surveillance using crowdsourced information like web search data may present a cost-efficient approach to “patient-centered” care in medicine. As this data can alert to seasonal or regional medical needs in real time, it can contribute to an efficient and timely allocation of medical resources and improve adequate and purposeful public health interventions.
It is likely that the internet acts as a source of information on the possibilities for self-medication or usage of complementary medicine. These findings demonstrate the ability of internet search data to reflect different healthcare behaviors and cultural perspectives. An analysis of such data can be used to develop targeted public health campaigns and disease prediction models. These findings also underline the importance of trustworthy and high-quality online resources and digital services in healthcare, particularly as the internet becomes an increasingly important source of health information.
In the four-year study period, the interest in pollen allergies has increased in the 2 countries, reflecting the increasing relevance of the internet for health information and a growing interest in pollen allergies. Based on our findings, internet search data appears to be an excellent proxy for disease activity of allergic rhinitis. As this cost-efficient data is available in real-time compared to data from conventional medical settings, it can provide valuable insight into current developments in disease activity. Combined with other influential factors like climate or geography, web search data can serve as a tool to identify and predict spatial and regional dimensions of the pollen season. Specific medical needs of a population can therefore be identified, and the timely allocation of medical resources and public health interventions can be optimized accordingly.