Sneezing, nasal congestion, and ocular irritation are just a few symptoms patients with seasonal allergic rhinitis (SAR) are faced with over the course of a year. As the name suggests, SAR symptoms present during allergic seasons, with the term ‘hay fever’ often being associated with spring and summer months. However, moving into the autumn months the pollen season is just starting its second peak. In fact, studies have shown SAR symptom severity to be worse in the cooler months (Chen et al., 2012).
Attempting to understand how SAR trends change over the course of a year, one study in Taiwan has revealed two distinct peaks in SAR activity. In this cross-sectional population-based study, 4,221 school students completed a self-reporting questionnaire covering respiratory conditions including SAR and potential exposure risk such as mould and maternal smoking during pregnancy.
Participants retrospectively reported the months were affected by allergic rhinitis symptoms over the previous 12 months. Based on the month participants reported to be symptomatic, subgroups of SAR (winter, spring, summer/fall) and perennial (symptomatic all year round) were formed.
Interestingly, the number of SAR cases increases as the average monthly temperature reduces, resulting in two peaks over the course of the year; the first peak during winter (December–February), and a second less severe peak in autumn (August–October) (figure 1) (Chen et al., 2012).
This peak in autumn allergic rhinitis activity has also been observed in other studies; a 2017 study carried out in China found pollen counts in autumn (August 9.9% and September 10.5%) to be higher than summer and winter but less severe than spring (March 29.7% and April 34.8%) (Wang et al., 2017). In addition, 45% of patients with SAR in a USA study reported their allergic rhinitis symptoms to be worse during autumn (Blaiss et al., 2007).
However, the results from Taiwan (Chen et al., 2012) contrast typical reports of SAR, as disease severity has often been reported to be highest during spring (Blaiss et al., 2007; Teng et al., 2016; Wang et al., 2017). Although patients with spring SAR did have a peak during March, the overall number of cases declined during the spring months. This demonstrates how variable SAR can be depending on country-specific pollen and varying seasons.
This global variation questions the use of generalised approaches to the classification of AR. A recent study from Korea analysed the relationship between confirmed allergen sensitisation and occurrence of allergic symptoms. To understand if allergy symptoms appear outside of the typical allergy seasons, 226 patients with suspected allergic rhinitis were tested for common allergens with a skin prick test. The results of the skin prick tests allowed patients to be grouped into subgroups of SAR dependent on which allergen(s) the patients were sensitised to (e.g. tree pollen is typically a spring allergy, grass allergy tends to peak in summer, and weed pollen is highest in autumn and winter).
Alongside the skin prick test, a questionnaire was also completed by the patients where they identified which seasons they typically experience allergic rhinitis symptoms. Interestingly, patients sensitised to specific allergens experienced symptoms outside of the pollen seasons: patients with grass pollen sensitisation experienced symptoms throughout the year (n=7/16) or in spring or winter (n=4/16), as well as patients sensitised to weed pollen experiencing symptoms during spring months (n=6/12). In contrast 5 out of 12 patients with weed pollen sensitisation didn’t experience symptoms during autumn when weed pollen is at its highest.
The mismatch of allergens and symptoms in seasonal peaks has been theorised to be due to multiple influencing factors such as environmental changes, psychological factors and sensitisation to multiple allergens (Chung et al., 2013).
This is an interesting theory, given the ongoing challenge of climate change and increased pollution from increasing industrialisation of many countries globally. Hoping to test this theory, one study carried out in North China investigated the impact air pollution has on allergic rhinitis severity. Air pollution was monitored between 2013–2015 and compared with the number of hospital visits due to allergic rhinitis. As suggested by Chung et al. environmental factors did have an impact; the results identified an increase in hospital visits with increasing air pollution, particularly during autumn as straw burning in North China causes an increased concentration of air pollution during this time. This study offers a glimpse into the future of growing industrialisation and raises questions about other respiratory conditions and the link to seasonal air pollution (Teng et al., 2017).
Incidence of asthma has also been seen to increase during the peak of autumn allergic rhinitis in North China. In a study of 1,013 patients with a positive serum specific IgE (sIgE) for Artemisia and/or Humulus (two of the most prevalent autumn pollens in North China), 55.6% had developed asthma with or after the development of allergic rhinitis. Risk of developing asthma increased with increasing sIgE levels to both Artemisia and Humulus (p<0.05) (Cui et al., 2018).
Along with weed pollen, autumn allergic rhinitis is typically related to house dust mite (HDM) allergy. A European study carried out across Italy, France and Spain looked at allergy trends between 2012–2013 in patients with severe HDM allergy-induced allergic rhinitis or asthma. After completing an initial online questionnaire, 313 patients (n=114 in Italy, n=92 in France, n=107 in Spain) took part in fortnightly telephone questionnaires reporting their allergic symptoms.
Similar to the study in Taiwan (Chen et al., 2012), a peak in symptom intensity and physician consultation rate was observed over the autumn months (figure 2). The consultation rate included consultations with any physician including general practitioners and specialists. Many patients had additional allergies such as grass and birch pollen, explaining the higher peaks in the spring months for the combined results (figure 2a) (Demoly et al., 2016).
As the weather transitions into the autumn months, we’re faced with cooler temperatures, falling leaves and an increase in damp areas within our homes or working environments; all of these factors result in the perfect conditions for mould to thrive. Autumn allergic rhinitis is often linked to mould allergies, in fact a literature review of meta-analyses and systematic reviews published between 2006–2017 found indoor mould exposure to be linked with allergic rhinitis, with a general odds ratio of >1.35 (Caillaud et al., 2018).
Outdoor mould is also a risk for allergic rhinitis exacerbations. One study in France compared the number of prescribed reimbursable allergic medication sales between 2010–2015 to daily spore concentrations. Unsurprisingly, increase in the most prevalent fungi detected, Cladosporium (70.7%), was associated with an increase in antihistamine and topical treatments sales (RR 1.08 [95 CI 1.02–1.14]). Interestingly, an increase in the rarer fungi Aspergillus and Penicillium (0.8%) was also associated with increased medication sales (RR 1.05 [95% CI 1.02–1.08]). When comparing the moulds for influencing factors such as age and gender, Cladosporium had a significant relationship with males between 0–49 years of age, and Aspergillus-Penicillium was significant in males older than 13 years of age. Risk ratios were also elevated in females within the 13–49 age group for both moulds, however these were not significant (table 1) (Caillaud et al., 2018).
Table 1. Relative risk (95% CI) of allergic medication sales estimated for single mould association (Caillaud et al., 2018).
The studies have demonstrated how varied and complexed SAR can be, particularly autumn allergic rhinitis. With seasonal changes differing between countries, disease activity occurring outside of expected allergic seasons, and many patients being sensitised to multiple allergens, SAR has become increasingly difficult to define.
These factors along with the growing pollution challenge are making SAR exacerbations less predictable and disease management even more complex. It’s unknown how far the growth in air pollution will affect respiratory conditions such as SAR, and only time will tell the true burden of this environmental change.
As we approach the autumn and the winter months and temperatures begin to decline, it is important to consider the multiple factors that may be affecting your patient’s allergic rhinitis symptoms and consider SAR when treating other associated respiratory conditions such as asthma.
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The EAACI 2018 Congress focussed on innovation in allergy, with numerous advances in allergic rhinitis discussed; including the burden of AR, the benefits of the Allergic Rhinitis and its impact on Asthma guidelines, and the diagnosis of local allergic rhinitis.
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Seasonal allergic rhinitis (SAR) is often associated with spring and summer months. However in Autumn months the SAR symptoms can be worse.