Dampness and visible mold in homes are associated with asthma development, but causal mechanisms remain unclear. The goal of this research was to explore associations among measured dampness, fungal exposure, and childhood asthma development without the bias of culture-based microbial analysis. In the low-income, Latino CHAMACOS birth cohort, house dust was collected at age 12 months, and asthma status was determined at age 7 years. The current analysis included 13 asthma cases and 28 controls. Next-generation DNA sequencing methods quantified fungal taxa and diversity. Lower fungal diversity (number of fungal operational taxonomic units) was significantly associated with increased risk of asthma development: unadjusted odds ratio (OR) 4.80 (95% confidence interval (CI) 1.04–22.1). Control for potential confounders strengthened this relationship. Decreased diversity within the genus Cryptococcus was significantly associated with increased asthma risk (OR 21.0, 95% CI 2.16–204). No fungal taxon (species, genus, class) was significantly positively associated with asthma development, and one was significantly negatively associated. Elevated moisture was associated with increased fungal diversity, and moisture/mold indicators were associated with four fungal taxa. Next-generation DNA sequencing provided comprehensive estimates of fungal identity and diversity, demonstrating significant associations between low fungal diversity and childhood asthma development in this community.
Variations in home characteristics, such as moisture and occupancy, affect indoor microbial ecology as well as human exposure to microorganisms. Our objective was to determine how indoor bacterial and fungal community structure and diversity are associated with the broader home environment and its occupants. Next-generation DNA sequencing was used to describe fungal and bacterial communities in house dust sampled from 198 homes of asthmatic children in southern New England. Housing characteristics included number of people/children, level of urbanization, single/multifamily home, reported mold, reported water leaks, air conditioning (AC) use, and presence of pets. Both fungal and bacterial community structure were non-random and demonstrated species segregation (C-score, p<0.00001). Increased microbial richness was associated with the presence of pets, water leaks, longer AC use, suburban (vs. urban) homes, and dust composition measures (p<0.05). The most significant differences in community composition were observed for AC use and occupancy (people, children, and pets) characteristics. Occupant density measures were associated with beneficial bacterial taxa, including Lactobacillus johnsonii as measured by qPCR. A more complete knowledge of indoor microbial communities is useful for linking housing characteristics to human health outcomes. Microbial assemblies in house dust result, in part, from the building’s physical and occupant characteristics.
Under sustained, elevated building moisture conditions, bacterial and fungal growth occurs. The goal of this study was to characterize microbial growth in floor dust at variable equilibrium relative humidity (ERH) levels. Floor dust from one home was embedded in coupons cut from a worn medium-pile nylon carpet and incubated at 50%, 80%, 85%, 90%, 95%, and 100% ERH levels. Quantitative PCR and DNA sequencing of ribosomal DNA for bacteria and fungi were used to quantify growth and community shifts. Over a 1-wk period, fungal growth occurred above 80% ERH. Growth rates at 85% and 100% ERH were 1.1 × 10 4 and 1.5 × 10 5 spore equivalents d ). Growth resulted in significant changes in fungal (P<.00001) and bacterial community structure (P<.00001) at varying ERH levels. Comparisons between fungal taxa incubated at different ERH levels revealed more than 100 fungal and bacterial species that were attributable to elevated ERH. Resuspension modeling indicated that more than 50% of airborne microbes could originate from the resuspension of fungi grown at ERH levels of 85% and above. K E Y W O R D Sbacteria, DNA sequencing, exposure, fungi, indoor microbiome, moisture, resuspension
Background Allergic and non-allergic asthma severity in children can be affected by microbial exposures. Objective Examine associations between exposures to household microbes and childhood asthma severity stratified by atopic status. Methods Participants (n=196) were selected from a cohort of asthmatic children in Connecticut and Massachusetts, USA. Children were grouped according to asthma severity (mild with no or minimal symptoms and medication, or moderate to severe persistent) and atopic status (determined by serum IgE). Microbial community structure and concentrations in house dust were determined using next-generation DNA sequencing and quantitative Polymerase Chain Reaction. Logistic regression was used to explore associations between asthma severity and exposure metrics, including richness, taxa identification and quantification, community composition, and concentration of total fungi and bacteria. Results Among all children, increased asthma severity was significantly associated with elevated concentration of summed allergenic fungal species, high total fungal concentration, and high bacterial richness by logistic regression, in addition to microbial community composition by distance comparison t-test. Asthma severity in atopic children was associated with fungal community composition (p=0.001). By logistic regression, asthma severity in non-atopic children was associated with total fungal concentration: odds ratio 2.40, 95% confidence interval 1.06–5.44. The fungal genus Volutella was associated with increased asthma severity in atopic children (p=0.0001, q=0.04). Yeast genera Kondoa may be protective; Cryptococcus may also impact asthma severity. Conclusion Asthma severity among this cohort of children was associated with microbial exposure, and associations differed based on atopic status.
TitleIndoor emissions as a primary source of airborne allergenic fungal particles in classrooms This study quantifies the influence of ventilation and indoor emissions on concentrations 2 and particle sizes of airborne indoor allergenic fungal taxa and further examines 3 geographical variability, each of which may affect personal exposures to allergenic fungi. 4Quantitative PCR and multiplexed DNA sequencing were employed to count and identify 5 allergenic fungal aerosol particles indoors and outdoors in seven school classrooms in 6 four different countries. Quantitative diversity analysis was combined with building 7 characterization and mass balance modeling to apportion source contributions of indoor 8 allergenic airborne fungal particles. Mass balance calculations indicate that 70% of 9 indoor fungal aerosol particles and 80% of airborne allergenic fungal taxa were 10
Outdoor traffic-related airborne particles can infiltrate a building and adversely affect the indoor air quality. Limited information is available on the effectiveness of high efficiency particulate air (HEPA) filtration of traffic-related particles. Here, we investigated the effectiveness of portable HEPA air cleaners in reducing indoor concentrations of traffic-related and other aerosols, including black carbon (BC), PM , ultraviolet absorbing particulate matter (UVPM) (a marker of tobacco smoke), and fungal spores. This intervention study consisted of a placebo-controlled cross-over design, in which a HEPA cleaner and a placebo "dummy" were placed in homes for 4-weeks each, with 48-hour air sampling conducted prior to and during the end of each treatment period. The concentrations measured for BC, PM , UVPM, and fungal spores were significantly reduced following HEPA filtration, but not following the dummy period. The indoor fraction of BC/PM was significantly reduced due to the HEPA cleaner, indicating that black carbon was particularly impacted by HEPA filtration. This study demonstrates that HEPA air purification can result in a significant reduction of traffic-related and other aerosols in diverse residential settings.
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