Emerging investigator series: Phthalate losses in floor dust are due to abiotic chemical degradation as well as microbial degradation of phthalates under elevated relative humidity conditions.

Shortages of personal protective equipment, including N95 respirators, during the coronavirus (CoV) disease 2019 (COVID-19) pandemic have highlighted the need to develop effective decontamination strategies for their reuse. This is particularly important in health care settings for reducing exposure to respiratory viruses, like severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the virus that causes COVID-19. Although several treatment methods are available, a widely accessible strategy will be necessary to combat shortages on a global scale. We demonstrate that the combination of heat and humidity inactivates a range of RNA viruses, including both viral pathogens and common viral pathogen surrogates, after deposition on N95 respirators and achieves the necessary virus inactivation detailed by the U.S. Food and Drug Administration guidelines to validate N95 respirator decontamination technologies. We further demonstrate that depositing viruses onto surfaces when suspended in culture media can greatly enhance observed inactivation, adding caution to how heat and humidity treatment methods are validated.

Dampness and visible mold growth in homes are associated with negative human health outcomes, but causal relationships between fungal exposure and health are not well established. The purpose of this study was to determine whether dampness in buildings impacts fungal community gene expression and how, in turn, gene expression may modulate human health impacts. A metatranscriptomic study was performed on house dust fungal communities to investigate the expression of genes and metabolic processes in chamber experiments at water activity levels of 0.5, 0.85, and 1.0. Fungi at water activities as low as 0.5 were metabolically active, focusing their transcriptional resources on primary processes essential for cell maintenance. Metabolic complexity increased with water activity where communities at 1.0 displayed more diverse secondary metabolic processes. Greater gene expression at increasing water activity has important implications for human health: Fungal communities at 1.0 a upregulated a greater number of allergen-, mycotoxin-, and pathogenicity-encoding genes versus communities at 0.85 and 0.5 a . In damp buildings, fungi may display increases in secondary metabolic processes with the potential for greater per-cell production of allergens, toxins, and pathogenicity. Assessments in wet versus dry buildings that do not account for this elevated health impact may not accurately reflect exposure.

Carpet and rugs currently represent about half of the United States flooring market and offer many benefits as a flooring type. How carpets influence our exposure to both microorganisms and chemicals in indoor environments has important health implications but is not well understood. The goal of this manuscript is to consolidate what is known about how carpet impacts indoor chemistry and microbiology, as well as to identify the important research gaps that remain. After describing the current use of carpet indoors, questions focus on five specific areas: 1) indoor chemistry, 2) indoor microbiology, 3) resuspension and exposure, 4) current practices and future needs, and 5) sustainability. Overall, it is clear that carpet can influence our exposures to particles and volatile compounds in the indoor environment by acting as a direct source, as a reservoir of environmental contaminants, and as a surface supporting chemical and biological transformations. However, the health implications of these processes are not well known, nor how cleaning practices could be optimized to minimize potential negative impacts. Current standards and recommendations focus largely on carpets as a primary source of chemicals and on limiting moisture that would support microbial growth. Future research should consider enhancing knowledge related to the impact of carpet in the indoor environment and how we might improve the design and maintenance of this common material to reduce our exposure to harmful contaminants while retaining the benefits to consumers.

Multiple students often share desks in schools. Results on the removal and reestablishment of microbial communities on these surfaces are critical for setting cleaning schedules and practices that effectively interrupt exposure to surface-associated pathogens and allergens.

Supply shortages of N95 respirators during the coronavirus disease 2019 (COVID-19) pandemic have motivated institutions to develop feasible and effective N95 respirator reuse strategies. In particular, heat decontamination is a treatment method that scales well and can be implemented in settings with variable or limited resources. Prior studies using multiple inactivation methods, however, have often focused on a single virus under narrowly defined conditions, making it difficult to develop guiding principles for inactivating emerging or difficult-to-culture viruses. We systematically explored how temperature, humidity, and virus deposition solutions impact the inactivation of viruses deposited and dried on N95 respirator coupons. We exposed four virus surrogates across a range of structures and phylogenies, including two bacteriophages (MS2 and phi6), a mouse coronavirus (murine hepatitis virus, MHV), and a recombinant human influenza A virus subtype H3N2 (IAV), to heat treatment for 30 minutes in multiple deposition solutions across several temperatures and relative humidities (RH). We observed that elevated RH was essential for effective heat inactivation of all four viruses tested. For heat treatments between 72°C and 82°C, RH greater than 50% resulted in > 6-log10 inactivation of bacteriophages and RH greater than 25% resulted in > 3.5-log10 inactivation of MHV and IAV. Furthermore, deposition of viruses in host cell culture media greatly enhanced virus inactivation by heat and humidity compared to other deposition solutions such as phosphate buffered saline, phosphate buffered saline with bovine serum albumin, and human saliva. Past and future heat treatment methods or technologies must therefore explicitly account for deposition solutions as a factor that will strongly influence observed virus inactivation rates. Overall, our data set can inform the design and validation of effective heat-based decontamination strategies for N95 respirators and other porous surfaces, especially for emerging or low-titer viruses that may be of immediate public health concern such as SARS-CoV-2.

Dampness and fungal (mold) growth in buildings are persistent environmental health problems. This study sought to determine the extent to which fungi grown on damp materials are distributed throughout a single-family home. Samples were collected from fungi growing directly on building materials in the basement (direct mold), and as a proxy for indoor and outdoor air, settled dust was collected from the top of door frames (basement, first and second floor, and exterior). Direct mold in the basement influenced both the fungal richness and ecology of air throughout the building. Fungal communities clustered by sample type (ANOSIM R = 0.62; p = 0.001) and floor (indoor samples; ANOSIM R = 0.58; p = 0.001) with the direct mold ecologies dominated by taxa (i.e., Sterigmatomyces, Stachybotrys, and Aspergillus) associated with mold growth on building materials and not present in outdoor samples. The relative abundances of these highly enriched direct mold taxa were also found to be inversely correlated to the distance to mold growth, decreasing by >70% between the basement and second floor. Through intense spatial characterization of the fungal community of one home, this study illustrates that fungal growth in a single location can significantly influence the fungal communities and human fungal exposure throughout the building.

Dampness or water damage in buildings and human exposure to the resultant mold growth is an ever-present public health concern. This study provides quantitative evidence that the airborne fungal ecology of homes with known mold growth (“moldy”) differs from the normal airborne fungal ecology of homes with no history of dampness, water damage, or visible mold (“no mold”). Settled dust from indoor air and outdoor air and direct samples from building materials with mold growth were examined in homes from 11 cities across dry, temperate, and continental climate regions within the United States. Community analysis based on the sequence of the internal transcribed spacer region of fungal ribosomal RNA encoding genes demonstrated consistent and quantifiable differences between the fungal ecology of settled dust in homes with inspector-verified water damage and visible mold versus the settled dust of homes with no history of dampness, water damage, or visible mold. These differences include lower community richness (p adj = 0.01) in the settled dust of moldy homes versus no mold homes, as well as distinct community taxonomic structures between moldy and no mold homes (ANOSIM, R = 0.15, p = 0.001). We identified 11 Ascomycota taxa that were more highly enriched in moldy homes and 14 taxa from Ascomycota, Basidiomycota, and Zygomycota that were more highly enriched in no mold homes. The indoor air differences between moldy versus no mold homes were significant for all three climate regions considered. These distinct but complex differences between settled dust samples from moldy and no homes were used to train a machine learning-based model to classify the mold status of a home. The model was able to accurately classify 100% of moldy homes and 90% of no mold homes. The integration of DNA-based fungal ecology with advanced computational approaches can be used to accurately classify the presence of mold growth in homes, assist with inspection and remediation decisions, and potentially lead to reduced exposure to hazardous microbes indoors.