Indoor dust fungi do not pose risk in childhood asthma development

Key takeaways:

  • House dust fungi found in early life did not impact the risk for childhood asthma development.
  • Children living in homes located on farms with greater fungal richness faced a higher risk for asthma.

Dust fungi in homes shortly after a child’s birth did not heighten the risk for childhood asthma development, according to results published in Annals of the American Thoracic Society.

“There are molds and yeasts everywhere in our living environment, and they are a natural part of the microbiota of a normal home,” Anne M. Karvonen, PhD, and Martin Täubel, PhD, chief researchers at the Finnish Institute for Health and Welfare, told Healio in a statement. “In the study, the number of fungal species, the diversity of fungal species or the amount of fungi in house dust were not linked to the risk of developing asthma. It is important to consider also this ‘normal’ role of molds and yeasts being part of everyday human exposure, rather than only associating ‘mold’ with moisture damage and ill health.”

In a birth cohort study, Karvonen, Täubel and colleagues analyzed 382 living room floor dust samples taken 2 months after birth to determine if indoor mycobiota composition —described by DNA amplicon sequencing — has an impact on childhood asthma development.

Researchers used questionnaires completed when the child was 10.5 years old to determine if they had ever or current asthma, and they used serum samples to determine if the child had inhalant atopy. They then assessed asthma through discrete time hazard models and atopy though logistic regression to identify any relations to early indoor mycobiota.

From the total cohort, 68 children had ever asthma and 27 had current asthma. Among the 259 children who provided a serum sample, 45.9% had inhalant atopy.

During evaluation of house dust fungal composition, researchers observed five genera that protected against asthma: BoeremiaCladosporium (both against current asthma), MicrodochiumMycosphaerella and Pyrenochaetopsis (against ever asthma).

However, after mutual adjustment among the five genera, as well as adjustment for various microbial cell wall markers and asthma protective bacterial indices identified in the past, the protective associations lost significance.

“Before starting this research, we thought we’d be likely to find fungal taxa in house dust with both predisposing and protective quality for the development of asthma,” Karvonen and Täubel told Healio. “Risk associations were to be expected due to the often highlighted, potential role of fungal exposures in moisture damage-associated adverse health effects. What we then found in our study was that any fungal genera that were associated with asthma were protective, but the associations were weak and disappeared when adjusting our results for other microbial exposures.

“Our earlier research in the same children and homes has shown a strong protective role of bacterial exposures as part of the home microbiome in asthma development,” Karvonen and Täubel added. “It was surprising to see how few and weak health associations we seem to observe with fungal taxa, compared to bacteria. It appears that bacteria in the living environment have a greater role in protecting against asthma than fungi do.”

Specifically, when evaluating all children, researchers did not find any significant links between asthma and fungal alpha-diversity or load; however, dust with greater fungal load increased the odds for inhalant atopy (middle vs. lowest tertile, aOR = 1.45; 95% CI, 0.76-2.79; highest vs. lowest tertile, aOR = 2.13; 95% CI, 1.01-4.5).

Notably, elevated fungal richness in dust within farm homes increased the odds for childhood asthma (aOR per interquartile range change = 2.32; 95% CI, 1.05-5.09). Researchers did not observe this heightened risk linked to fungal richness in nonfarm homes.

Among farmers, researchers frequently found heightened fungal richness in newly constructed farm homes and homes on larger farms.

“Molds and yeasts in the indoor environment have often been linked to moisture damage buildings and the related health hazards,” Karvonen and Täubel told Healio. “In the future, our aim will be to specifically examine whether those fungi that are associated with moisture damage in the home can explain part of the connection between moisture damage and asthma. In part of these future analyses, we will improve exposure assessment by studying the significance of living and dead microbial cells separately and also quantify the metabolic products of live microbes, which could well be relevant especially in moisture-damaged homes.”


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