Grass pollen allergen may be better indicator of symptom risk than grass pollen count
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Key takeaways:
- Pollen counts and Phl p 5 levels had positive associations with symptom and medication scores.
- Associations pertaining to pollen counts were attenuated in mutually adjusted models.
Allergic respiratory symptoms consistently had stronger associations with Phl p 5 grass allergen than with grass pollen counts in a study published in The Journal of Allergy and Clinical Immunology.
These findings indicate that allergen levels may be a more appropriate metric than pollen counts for measuring allergic potential in the air, Elaine Fuertes, PhD, research fellow, National Heart and Lung Institute, Imperial College, and colleagues wrote.
The Pollen Low dose Intradermal Therapy Evaluation, or PollenLITE, comprised 93 adults (mean age, 33.5 years; 66% men; 80% white) with moderate to severe allergic rhinitis induced by grass pollen.
Patients recorded daily symptoms and medication use on diary cards, in addition to providing blood samples for analyzing IgE levels specific to grass pollen group 5. Hospital admissions and ED visits for asthma were recorded as well.
The researchers collected daily airborne pollen counts with a standardized Hirst-type volumetric air sampler on the southwestern corner of the Strand Building at King’s College London during grass pollen season between May 17 and Aug. 31, 2013.
Also, the researchers used a ChemVol High Volume Cascade Impactor located within 5 meters of the pollen trap during the same period. Overall, the researchers said, there was a high correlation between daily Phl p 5 levels and grass pollen counts (rho = 0.769).
Analysis yielded positive associations between daily pollen counts and scores in the top quarter of each participant’s symptom score (OR = 1.1; 95% CI, 1.05-1.16), medication score (OR = 1.09; 95% CI, 1.02-1.15) and total symptom and medication score (OR = 1.11; 95% CI, 1.05-1.17).
Similarly, there were elevated associations observed with Phl p 5 levels and symptom score (OR = 1.17; 95% CI, 1.13-1.22), medication score (OR = 1.16; 95% CI, 1.11-1.21) and total symptom and medication score (OR = 1.18; 95% CI, 1.14-1.22).
However, mutually adjusted models that included terms for pollen count and Phl p 5 levels found effect estimates for pollen counts to be attenuated to the null, but those for Phl p 5 levels remained stable.
When the researchers adjusted for participant blood IgE levels specific to Phl p 5, daily mean particulate matter at the 2.5 µg (PM2.5) and 10 µg (PM10) scales and ozone (O3), in addition to restricting analysis to the height of the grass pollen season, results remained consistent.
The differences in the size of the effect estimates between pollen counts and Phl p 5 levels were smaller after adjusting models for pollen counts and Phl p 5 levels the day before, the researchers continued, although they advised caution in interpreting these results because of the high number of correlated exposure variables.
Further, the researchers said there was statistical significance for some of the interaction terms between the pollen variables and daily mean PM2.5 and PM10 concentrations (P < .05), but there were no consistent patterns when they stratified the models into tertiles of pollution.
The effect estimates for pollen counts continued to be null in mutually adjusted models when the researchers considered symptom scores individually, the researchers continued, but the effect estimates for eye, nose and mouth/throat symptoms were elevated for Phl p 5.
Additionally, the researchers said there were positive associations between daily pollen counts and percentage change in asthma admissions in the overall population (percent change = 6.7%; 95% CI, 3.4%-10.2%).
These associations persisted for patients aged younger than 15 years (percent change = 13.2%; 95% CI, 7.6% to 19.2%) and for those aged 15 to 44 years (percent change = 7.5%; 95% CI, 3%-12.3%). Patients aged older than 44 years had null associations (percent change = –1.7%; 95% CI, –6.1% to 2.9%).
Associations between daily Phl p 5 levels and percentage change in asthma additions were similar, including 4.5% (95% CI, 1.5%-7.5%) for the overall cohort, 9.9% (95% CI, 4.8%-15.2%) for patients aged younger than 15 years, 4% (95% CI, 0%-8.1%) for those age 15 to 44 years and –0.8% (95% CI, –4.5% to 3.1%) for those aged older than 44 years.
All the sensitivity analyses yielded null associations with Phl p 5 levels. Also, adjustments for PM2.5, PM10 and O3 did not change findings for pollen counts. Limiting analysis to the height of grass pollen season attenuated associations for all ages as well.
The main findings did not change when the researchers included 1-day lag terms for pollen counts and Phl p 5 levels. Additionally, there was no consistent pattern in models stratified by tertiles of pollutant concentrations, although a few interaction terms between pollutant and pollen variables were statistically significant.
Based on these findings, the researchers called this study the first to demonstrate that Phl p 5 levels are more consistently associated with occurrence of allergic and respiratory symptoms than pollen counts.
Current risk assessments, pollen forecasts and public health tools use pollen counts, the researchers noted, although they may not be the best measure for patients with allergies and asthma to self-manage their symptoms.
For example, the year, location, plant growth and other meteorological and environmental factors influence the mismatch between pollen counts and allergen levels. The external exposome also affects how patients experience allergic exacerbations, the researchers added.
Using multiyear data, the researchers said, future studies should assess whether studies should model airborne allergen content and if allergen levels should be added to or replace pollen counts as the standard for measuring allergic potential.
Reference:
- Measuring grass pollen allergens instead of grass pollen count will help hay fever sufferers. https://www.kcl.ac.uk/news/measuring-grass-pollen-allergens-will-help-hay-fever-sufferers. Published Jan. 8, 2024. Accessed Jan. 12, 2024.
Perspective
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This is an important study because it showed that grass pollen allergens are more consistently associated with allergic symptoms than grass pollen counts in adults with moderate to severe allergic rhinitis. The results suggest that it may be better to use allergen levels instead of pollen counts to predict risk for adverse events in those with moderate to severe grass pollen-induced allergic rhinitis.
The findings also are as expected, given that the study sample consists of people who are highly sensitive to grass pollen allergens. They are also consistent with previous research. However, it is quite surprising that the authors did not find similar results when investigating asthma admissions as an outcome, but they have provided some explanations for this.
Pollen allergen may be a better predictor for symptom risk in those who are pollen sensitized. But pollen counts are still important, especially in those who are non-sensitized, because pollen has been shown to possess nonallergenic properties that could trigger the immune response regardless of pollen sensitization status. The authors somewhat supported this, indicating that the results for hospital admissions for asthma might have been more consistent had serological data been available to restrict the analysis to those sensitized to grass pollen.
This study is novel, as it was the first to compare grass pollen counts and Phl p 5 levels with respiratory health outcomes in models adjusted for both meteorological factors and air pollutants. The authors also mutually adjusted for the effects of allergen levels and pollen counts.
Nevertheless, more research is needed to investigate the associations between pollen allergen levels and symptoms in the general population to better understand whether pollen allergen would be a better allergy symptom risk indicator than pollen counts at a population level. As the authors mentioned, it would also be good to consider other components of grass pollen such as Phl p 1 and allergens of other types of pollen and molds.
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