A molecular epidemiological investigation into the contribution of fungal spores to seasonal asthma spikes

Introduction

Nearly every breath we take contains fungal spores that can reach the alveolar regions of the lungs. While some spores are associated with allergy and exacerbation of asthma, relatively little is known about direct associations for different fungal taxa. The objective here was to utilise high-throughput sequencing (HTS) to gain a deeper understanding of the outdoor fungal composition across the UK and use this information in an epidemiological analysis against healthcare seeking behaviour for asthma.

Methods

A systematic review was conducted to explore patterns of fungal seasonality across Europe. HTS was then used to characterise relative abundances of fungi, using outdoor air samples collected throughout 2021 at two regionally distinct sites in the UK. The sampling, molecular, and bioinformatic methodologies were validated prior to use. The composition and seasonal dynamics of the outdoor airspora were explored across the two sites. Finally, a novel time-series design with distributed lag non-linear models was utilised to draw associations between airborne abundances of fungal spores and seasonal syndromic data for asthma. The use of microscopy-based counts as alternative exposure data was compared.

Results

Clear seasonality was established in previous studies, but for a limited range of taxa. Validated HTS methodology revealed similar diversity and compositions of fungi between the two sites, with some influence from meteorological variables. Time-series analyses with syndromic data revealed associations with the genera of Fusarium in multiple clinical settings. Other findings were less consistent, except with use of microscopy exposure data, which revealed associations between spore exposure and emergency department visits related to asthma in children.

Conclusion

Findings suggest that a broader range of fungi, including spores from Fusarium, are likely further associated with asthma than previously known. Quantitative methods could be developed for associated fungal taxa found here to enable continued monitoring, and potential preventive public health actions.