Objectives: To generate baseline data for indoor airborne fungal spores in noncomplaint residential properties (with no moisture/moldrelated problems) and to identify home characteristics indicative of elevated fungal levels.

Methods: Air samples were collected onto petroleum jelly–coated slides from living rooms of 100 residential properties in Leicestershire, United Kingdom, using a Burkard continuous recording air sampler. The slides were examined by microscopy to determine fungal spore concentrations (spores/m3 air/day).

Results: Total indoor fungal spore concentrations were approximately 16% of outdoor concentrations. Abundant indoor fungal genera include Cladosporium, Sporobolomyces, Tilletiopsis, and Didymella, all of which followed seasonal patterns of release and detection. No clear association was shown between outdoor-predominant fungi and home characteristics. In contrast, Aspergillus/Penicillium-type (Asp/Pen-type) spores were common indoors and exceeded outdoor levels, with the highest concentrations detected in properties over 90 years old (P=.006) and terraced properties (P=.003).

Conclusion: Asp/Pen-type spores are found in noncomplaint UK residential properties and mostly in old terraced houses. This study provides guidelines on acceptable levels of Asp/Pen-type spores and other abundant indoor fungal taxa that can be comparatively used in clinical evaluations of fungal exposure–related disease.

Key words: Mold/mould. Fungal spores. Environmental exposure. Reference values. Aerobiology