Dermatophagoides pteronyssinus in ambient air bioaerosols

House dust mite (HDM) sensitization is a leading cause of allergic rhinitis and asthma worldwide, with Dermatophagoides pteronyssinus, Dermatophagoides farinae, and Blomia tropicalis being the primary allergenic species typically associated with indoor environments. Even effective multicomponent interventions creating an HDM-free indoor environment are often insufficient to prevent allergy, as HDM exposure may also occur outdoors.

To assess the potential for outdoor HDM exposure, we applied air biomass sequencing and metagenomic techniques to detect HDM DNA in both indoor and outdoor bioaerosols, offering an alternative to conventional dust sampling methods.

We used 2 data sets in this study: (1) a global data set comprising 1,171 outdoor air samples collected across 33 countries in open air environments and (2) a data set of indoor (n = 161) and outdoor (n = 156) air samples collected across 156 apartments from 106 locations in Singapore. All air samples were collected by drawing 24,000 to 36,000 L of air using SASS3100 air samplers; all samples were processed identically. Species-level taxonomic classification was performed using Kaiju software aligned to the National Center for Biotechnology Information nonredundant database, with a minimum threshold of 40 reads per taxon.

Analysis of 1,171 global outdoor air samples revealed D pteronyssinus as the most prevalent HDM species; it was detected in 208 samples, with abundance increasing from temperate toward equatorial regions. In Singaporean households, D pteronyssinus was found in 58.4% of indoor samples and 21.2% of nearby outdoor samples, with high median DNA read counts outdoors suggesting that exposure to HDM is not limited to domestic environments. B tropicalis and D farinae were also detected in Singapore, albeit at lower frequencies.

Our findings highlight the need to expand environmental allergen surveillance beyond household dust to include ambient and outdoor air, particularly in tropical climates.