Samuel Hemmings, Diana Varaden, Jessica Barnes, M Elmi, Adam Skillern, Benjamin Barratt, Ian Mudway, David C Green, Frank J Kelly, Matthew C Fisher (17773886)
Background Long-term exposure to indoor fungal bioaerosols is a recognised risk factor for respiratory illness, particularly in damp and poorly ventilated housing. However, the diversity and seasonal variability of these fungal communities are poorly understood. As part of the West London Healthy Home and Environment Study (WellHome), this study aimed to characterise the composition, diversity, and temporal dynamics of indoor fungal bioaerosols in urban UK homes, as compared with outdoor air, to inform future exposure baselines and policy development. Methods In this prospective, community-based observational study, 118 households were recruited across West London, UK, via community networks and partner organisations, prioritising families with children aged 5–17 years with asthma or allergies, from diverse socioeconomic backgrounds. Sampling occurred between Oct 3, 2022, and June 14, 2024. Participant data were collected via questionnaires completed by household members, capturing demographics, building characteristics, and respiratory health. Passive-air samplers were used in living rooms for 28 days during two seasonal campaigns, with concurrent outdoor sampling at four fixed community sites. Fungal bioaerosols were identified by ITS2 amplicon sequencing and quantified using broad-range quantitative PCR targeting the 18S rRNA gene. Diversity indexes and temporal dynamics were analysed using ecological statistics and generalised additive models. Findings 118 households were enrolled, comprising 504 residents (263 women, 237 men, and four not reported). Among 504 participants who self-identified, the largest groups comprised individuals identifying as Black African (n=47), Somali (n=46), White British (n=42), and African (n=38), with additional representation from mixed race ethnic backgrounds (n=29), Black British (n=27), White (n=22), and Black Caribbean (n=18), alongside several other ethnicities each represented at lower frequencies. Of 118 households, 104 completed both seasonal campaigns and 14 completed one, yielding 262 air samples (222 indoor and 40 outdoor). DNA was successfully recovered from all samples, identifying 2027 fungal genera. Indoor environments showed significantly higher richness (mean 646 vs 495 amplicon sequence variants; p<0·0001) and Shannon diversity (4·21 vs 3·53; p<0·0001) than outdoors. Community composition differed markedly (permutational multivariate ANOVA p<0·0001), with Penicillium , Aspergillus , and Wallemia enriched indoors. Indoor fungal communities presented stronger seasonal cycling (R 2 =0·203) than outdoor communities (R 2 =0·012). Fungal burden across all homes had a median 11 043 genomic equivalence (GE); IQR 4598–20 579 GE. The highest levels were observed in homes with visible mould; one household showed elevated Aspergillus exposure linked to repeated asthma hospitalisations in a sensitised resident. Interpretation Indoor fungal bioaerosols are more diverse and dynamic than outdoor communities in urban UK homes. These findings establish foundational exposure data and highlight the need for incorporating fungal bioaerosol monitoring into public health policy to mitigate mould-related health risks. Funding UK Research and Innovation (UKRI) Strategic Priorities Fund (SPF) Clean Air Programme.