Air- and Dustborne Mycoflora in Houses Free of Water Damage and Fungal Growth

Typically, studies on indoor fungal growth in buildings focus on structures with known or suspected water damage, moisture, and/or indoor fungal growth problems. Reference information on types of culturable fungi and total fungal levels are generally not available for buildings without these problems. This study assessed 50 detached single-family homes in metropolitan Atlanta, Ga., to establish a baseline of “normal and typical” types and concentrations of airborne and dustborne fungi in urban homes which were predetermined not to have noteworthy moisture problems or indoor fungal growth. Each home was visually examined, and samples of indoor and outdoor air and of indoor settled dust were taken in winter and summer. The results showed that rankings by prevalence and abundance of the types of airborne and dustborne fungi did not differ from winter to summer, nor did these rankings differ when air samples taken indoors were compared with those taken outdoors. Water indicator fungi were essentially absent from both air and dust samples. The air and dust data sets were also examined specifically for the proportions of colonies from ecological groupings such as leaf surface fungi and soil fungi. In the analysis of dust for culturable fungal colonies, leaf surface fungi constituted a considerable portion (>20%) of the total colonies in at least 85% of the samples. Thus, replicate dust samples with less than 20% of colonies from leaf surface fungi are unlikely to be from buildings free of moisture or mold growth problems.     

Profiles of airborne fungi in buildings and outdoor environments in the United States

We examined 12,026 fungal air samples (9,619 indoor samples and 2,407 outdoor samples) from 1,717 buildings located across the United States; these samples were collected during indoor air quality investigations performed from 1996 to 1998. For all buildings, both indoor and outdoor air samples were collected with an Andersen N6 sampler. The culturable airborne fungal concentrations in indoor air were lower than those in outdoor air. The fungal levels were highest in the fall and summer and lowest in the winter and spring. Geographically, the highest fungal levels were found in the Southwest, Far West, and Southeast. The most common culturable airborne fungi, both indoors and outdoors and in all seasons and regions, were Cladosporium, Penicillium, nonsporulating fungi, and Aspergillus. Stachybotrys chartarum was identified in the indoor air in 6% of the buildings studied and in the outdoor air of 1% of the buildings studied. This study provides industrial hygienists, allergists, and other public health practitioners with comparative information on common culturable airborne fungi in the United States. This is the largest study of airborne indoor and outdoor fungal species and concentrations conducted with a standardized protocol to date.     

Profiles of Airborne Fungi in Buildings and Outdoor Environments in the United States

We examined 12,026 fungal air samples (9,619 indoor samples and 2,407 outdoor samples) from 1,717 buildings located across the United States; these samples were collected during indoor air quality investigations performed from 1996 to 1998. For all buildings, both indoor and outdoor air samples were collected with an Andersen N6 sampler. The culturable airborne fungal concentrations in indoor air were lower than those in outdoor air. The fungal levels were highest in the fall and summer and lowest in the winter and spring. Geographically, the highest fungal levels were found in the Southwest, Far West, and Southeast. The most common culturable airborne fungi, both indoors and outdoors and in all seasons and regions, were Cladosporium, Penicillium, nonsporulating fungi, and Aspergillus. Stachybotrys chartarum was identified in the indoor air in 6% of the buildings studied and in the outdoor air of 1% of the buildings studied. This study provides industrial hygienists, allergists, and other public health practitioners with comparative information on common culturable airborne fungi in the United States. This is the largest study of airborne indoor and outdoor fungal species and concentrations conducted with a standardized protocol to date.     

Indoor and outdoor airborne fungal propagule concentrations in Mexico City

Thirty homes of asthmatic adults located in Mexico City were examined to determine the predominant culturable fungi and the changes in their airborne concentrations. Fungi were cultured and identified microscopically from air samples collected in naturally ventilated homes, during both wet (July–August) and cool dry (November–December) seasons, and from settled dust from the same homes. Airborne dust from indoor yielded 99–4950 cfu m⁻³, and settled dust 10²–10⁶ cfu g⁻¹ on DG18 agar. The indoor geometric mean concentration of airborne fungi during the cool dry season was 460 cfu m⁻³ while in the wet season it was 141 cfu m⁻³. Similarly, numbers of airborne fungal propagules out of doors decreased 60% between the dry and wet season. In general, the total fungal concentrations in indoor air were less than 10³ cfu m⁻³ and a large proportion of them was collected in Stage-2 of the Andersen sampler. Moreover, the ratio between indoor and outdoor concentrations was <3:1. Five of the 30 sampled homes yielded >500 cfu m⁻³ of one genus, with up to 1493Cladosporium cfu m⁻³ or 2549Penicillium cfu m⁻³. Also, these two genera were predominant in both airborne and settled dust, and their concentrations were greater indoors than out, indicating a possible indoor source of fungal propagules. The predominant species wereCladosporium herbarum, Penicillium aurantiogriseum andP. chrysogenum. These results suggest that exposure to large concentrations of fungi occurs indoors and is associated with both seasons of the year and with particular home characteristics.     

Dustborne fungi in large office buildings

Fungi are ubiquitous in our daily environments. However, their effects on office workers' health are of great interest to many environmental health researchers. Dust has been considered an important reservoir of indoor fungi from which aerosolization and exposure could occur. We have examined the characteristics of dustborne fungal populations recovered from floors and chairs in office buildings. We investigated twenty-one offices in four office buildings in Boston, MA over a year beginning May 1997. We conducted intensive environmental sampling every six weeks to measure culturable dustborne fungi from floors and chairs, surface dust levels and water activity in carpeting. Carbon dioxide, temperature, and relative humidity were monitored continuously. Concentrations of total dustborne fungi recovered from floors were positively related to carbon dioxide ( = 0.00064; p-value = 0.0002) and temperatures between 20 and 22.5 °C (p-value = 0.0026). Also, total fungal concentrations in floors gradually increased over the year (p-value = 0.0028). Total fungi recovered from chairs varied significantly by season (p-value < 0.0001),highest in September and lowest in March, and were positively correlated with dust loads in floors ( = 0.25; p-value < 0.0001). We used principal component analysis (PCA) to reduce various observed fungal species to fewer factors. Six groups(PCA factors) were obtained for dustborne fungi recovered from both floors and chairs. The models of the first PCA factors for both floors and chairs were similar to those for total fungal concentrations. The results of this study provide essential information to further evaluate the effects of dustborne fungi on office workers' health.This revised version was published online in October 2005 with corrections to the Cover Date.     

Fungi and fungal products in some Canadian houses

Building related illness prompted a study in the winter of 1986 to identify and quantify and fungal products present in c. 50 Canadian homes. Of these, 70% had been reputedly associated with health problems. Building parameters, i.e. air change rate and the internal moisture levels, were measured, and the fungi present were characterized and quantified along with their metabolites. Air and dust samples were analyzed and the fungal biomass in the dust was measured by a procedure which involved determination of ergosterol by a gas chromatograph/mass spectrometer system. Some 42 fungal species were identified in air, samples of which were further analyzed for fungal volatiles. Penicillium was the most common genus in both air and dust, together with Cladosporium and Alternaria. The potentially hazardous fungus Aspergillus fumigatus was found in only two houses, and Strachybotry atra in only one. New criteria are suggested to define the acceptable standards for indoor fungal levels in air during winter.     

The ecology of microscopic life in household dust

We spend the majority of our lives indoors; yet, we currently lack a comprehensive understanding of how the microbial communities found in homes vary across broad geographical regions and what factors are most important in shaping the types of microorganisms found inside homes. Here, we investigated the fungal and bacterial communities found in settled dust collected from inside and outside approximately 1200 homes located across the continental US, homes that represent a broad range of home designs and span many climatic zones. Indoor and outdoor dust samples harboured distinct microbial communities, but these differences were larger for bacteria than for fungi with most indoor fungi originating outside the home. Indoor fungal communities and the distribution of potential allergens varied predictably across climate and geographical regions; where you live determines what fungi live with you inside your home. By contrast, bacterial communities in indoor dust were more strongly influenced by the number and types of occupants living in the homes. In particular, the female : male ratio and whether a house had pets had a significant influence on the types of bacteria found inside our homes highlighting that who you live with determines what bacteria are found inside your home.     

Microbial Growth Inside Insulated External Walls as an Indoor Air Biocontamination Source

The association between moisture-related microbial growth (mesophilic fungi and bacteria) within insulated exterior walls and microbial concentrations in the indoor air was studied. The studied apartment buildings with precast concrete external walls were situated in a subarctic zone. Actinomycetes in the insulation layer were found to have increased concentrations in the indoor air. The moisture content of the indoor air significantly affected all measurable airborne concentrations.     

Microbial growth inside insulated external walls as an indoor air biocontamination source

The association between moisture-related microbial growth (mesophilic fungi and bacteria) within insulated exterior walls and microbial concentrations in the indoor air was studied. The studied apartment buildings with precast concrete external walls were situated in a subarctic zone. Actinomycetes in the insulation layer were found to have increased concentrations in the indoor air. The moisture content of the indoor air significantly affected all measurable airborne concentrations.     

Domestic exposure to fungi and total serum IgE levels in asthmatic children

We measured the number of airborne, viable fungi and house dust mite (HDM) allergen levels in the homes of a group of asthmatic children. Blood samples were drawn and the amounts of total and specific serum IgE were determined. The association between the number of fungal colonies, dust mite allergen exposure, and specific and total IgE was evaluated. The number of viable airborne fungi was high (20,543 CFU/m(3)) in those investigated houses. Der p1 concentrations on child's mattress exceeding 2 microg/g were found in 78.6% of the houses. A quantitative dose-response relationship was demonstrated between the exposure to viable, airborne molds and the amount of total IgE (r = 0.4399 and P = .0249) and the level was further increased in children with coexposure to viable fungi and HDM.     

Concentration and distribution characteristics of airborne fungi in indoor and outdoor air of Tehran subway stations

The concentration and distribution characteristics of airborne fungi were investigated in indoor and outdoor air of two metro stations (Imam Khomeini and Sadeghiyeh stations) in Tehran subway. Samples were taken from indoor air at each station from platform and ticket office area also from adjacent outdoor air of each station. Indoor sampling was conducted for two types of trains, old and new. The concentration of airborne fungi ranged from 21 CFU/m³ at the outdoor air of Imam Khomeini station to 1,402 CFU/m³ in the air samples collected from the platform of this station. Results showed that airborne fungi concentrations at indoor air were higher than the outdoor air (p < 0.05), and fungal levels significantly correlated with the number of passengers (p < 0.05; r = 0.68) and RH % (p < 0.05; r = 0.43). Sixteen genera of fungi were isolated in all sampled environments. The predominant genera identified in indoor and outdoor air were Penicillium spp. (34.88 % of total airborne fungi) and Alternaria spp. (29.33 % of total airborne fungi), respectively. The results of this study showed that the indoor air quality in subway is worse than the outdoor air.     

The Diversity and Distribution of Fungi on Residential Surfaces

The predominant hypothesis regarding the composition of microbial assemblages in indoor environments is that fungal assemblages are structured by outdoor air with a moderate contribution by surface growth, whereas indoor bacterial assemblages represent a mixture of bacteria entered from outdoor air, shed by building inhabitants, and grown on surfaces. To test the fungal aspect of this hypothesis, we sampled fungi from three surface types likely to support growth and therefore possible contributors of fungi to indoor air: drains in kitchens and bathrooms, sills beneath condensation-prone windows, and skin of human inhabitants. Sampling was done in replicated units of a university-housing complex without reported mold problems, and sequences were analyzed using both QIIME and the new UPARSE approach to OTU-binning, to the same result. Surfaces demonstrated a mycological profile similar to that of outdoor air from the same locality, and assemblages clustered by surface type. “Weedy” genera typical of indoor air, such as Cladosporium and Cryptococcus, were abundant on sills, as were a diverse set of fungi of likely outdoor origin. Drains supported more depauperate assemblages than the other surfaces and contained thermotolerant genera such as Exophiala, Candida, and Fusarium. Most surprising was the composition detected on residents’ foreheads. In addition to harboring Malassezia, a known human commensal, skin also possessed a surprising richness of non-resident fungi, including plant pathogens such as ergot (Claviceps purperea). Overall, fungal richness across indoor surfaces was high, but based on known autecologies, most of these fungi were unlikely to be growing on surfaces. We conclude that while some endogenous fungal growth on typical household surfaces does occur, particularly on drains and skin, all residential surfaces appear – to varying degrees – to be passive collectors of airborne fungi of putative outdoor origin, a view of the origins of the indoor microbiome quite different from bacteria.     

Characterization of airborne molds, endotoxins, and glucans in homes in New Orleans after Hurricanes Katrina and Rita

In August and September 2005, Hurricanes Katrina and Rita caused breeches in the New Orleans, LA, levee system, resulting in catastrophic flooding. The city remained flooded for several weeks, leading to extraordinary mold growth in homes. To characterize the potential risks of mold exposures, we measured airborne molds and markers of molds and bacteria in New Orleans area homes. In October 2005, we collected air samples from 5 mildly water-damaged houses, 15 moderately to heavily water-damaged houses, and 11 outdoor locations. The air filters were analyzed for culturable fungi, spores, (1-->3,1-->6)-beta-D-glucans, and endotoxins. Culturable fungi were significantly higher in the moderately/heavily water-damaged houses (geometric mean=67,000 CFU/m3) than in the mildly water-damaged houses (geometric mean=3,700 CFU/m3) (P=0.02). The predominant molds found were Aspergillus niger, Penicillium spp., Trichoderma, and Paecilomyces. The indoor and outdoor geometric means for endotoxins were 22.3 endotoxin units (EU)/m3 and 10.5 EU/m3, respectively, and for (1-->3,1-->6)-beta-D-glucans were 1.7 microg/m3 and 0.9 microg/m3, respectively. In the moderately/heavily water-damaged houses, the geometric means were 31.3 EU/m3 for endotoxins and 1.8 microg/m3 for (1-->3,1-->6)-beta-D-glucans. Molds, endotoxins, and fungal glucans were detected in the environment after Hurricanes Katrina and Rita in New Orleans at concentrations that have been associated with health effects. The species and concentrations were different from those previously reported for non-water-damaged buildings in the southeastern United States.     

Removal of Viable Airborne Fungi from Indoor Environments by Benzalkonium Chloride-Based Aerosol Disinfectants

Fungi are ubiquitous in indoor environments, and some taxa can cause clinical symptoms in humans. Thus, from the viewpoint of public health, methods to reduce indoor airborne fungi are needed. The goal of this study was to examine the efficacies of benzalkonium chloride (BAC)–based aerosol disinfectants to remove airborne viable fungi from indoor environments. The laboratory- and field-based experiments were conducted to compare airborne culturable fungal concentrations before and after the disinfectant aerosol applications. The laboratory-based experiments showed the greater efficacies by the BAC-based disinfectant aerosol than by pure-water control aerosol (p <.05, t-test). In the field study using the BAC-based disinfectant aerosols, on average a 58% reduction of total airborne culturable fungal concentrations were observed. Additionally, the significant reduction was found for a group of airborne yeasts or yeast-like organisms (p <.05, Wilcoxon signed rank test). The BAC-based aerosol disinfectants are effective when used to reduce the numbers of airborne culturable fungi, in particular yeasts or yeast-like organisms, from indoor environments.     

Occurrence of mites and fungi in the homes of patients with allergic manifestations

This survey was carried out to evaluate mites and moulds concentrations in the homes of patients with allergic manifestations and positive skin-test for mites and/or fungi. The home environments of 277 patients were evaluated by questionnaire, by sampling of airborne fungal spores and by determining the occurrence of mites and moulds in dust samples. Among the 277 patients examined, 83% reacted positively to house dust mites. The fungal allergen most frequently responsible for skin positivity was Alternaria tenuis. The prevalent airborne fungi were Cladosporium, Penicillium and Alternaria, followed by Aspergillus and Aureobasidium. The other genera were found in less than 50% of the homes. The presence of domestic mites in dust was documented in more than 85% of the homes sampled. The occurrence of fungi in dust was generally higher than in the air. The most common genera recovered were Penicillium, Candida, Aspergillus, Aureobasidium, Alternaria and Cladosporium. The homes investigated were divided into two groups, damp and dry, on the basis of the reported presence of wet or damp spots on inside surfaces and moulds growing inside the home. Our results showed that the concentration of mites and moulds in dust was significantly higher (p < 0.01) in damp homes as compared to dry ones.In general, a good agreement between skin positivity and presence of the same allergens in patients' home environment was observed for mites and, among fungi, for Alternaria, Cladosporium and Aspergillus. Our results seem to confirm that the study of mycoaeroflora and the quantification of mites and moulds in dust samples of allergic patients' homes could lead to more precise diagnoses and therefore to better prophylactic and therapeutic programs for each individual patient.     

Dispersal of fungal spores from three types of air handling system duct material

Exposure to airborne microorganisms in indoor environments may result in infectious disease or elicit an allergic or irritant response. Air handling system components contaminated by fungi have been implicated in the dispersal of spores into the indoor environment, thereby serving as a route of exposure to occupants. This study was conducted to provide quantitative data on the dispersal of spores from fungal colonies growing on three types of duct material. Galvanized metal, rigid fibrous glass ductboard, and fiberglass duct liner were soiled and contaminated with a known concentration of Penicillium chrysogenum spores. The duct materials were incubated in humidity chambers to provide a matrix of growing, sporulating fungal colonies at a contamination level of 109 colony forming units (CFU) per duct section, consistent for all materials. For each experiment a contaminated duct section was inserted into the air handling system of an experimental room, and the air handling system was operated for three 5-minute cycles with an air flow of 4.2 m3 min–1. The duct air velocity was approximately 2.8 m sec–1. The airborne concentration of culturable P. chrysogenum spores (CFU m–3), total P. chrysogenum spores (spores m–3), and total P. chrysogenum-sized particles (particles m–3) were measured in the room using Andersen single-stage impactor samplers, Burkard slide impactor samplers, and an aerodynamic particle sizer, respectively. The highest airborne concentrations (104 CFU m–3; 105 spores m–3; 104 particles m–3) were measured during the first operating cycle of the air handling system for all duct materials with decreasing airborne concentrations measured during the second and third cycles. There was no significant difference in spore dispersal from the three contaminated duct materials. These data demonstrate the potential exposure for building occupants to high concentrations of spores dispersed from fungal colonies on air handling system duct materials during normal operation of the system.     

Indoor and outdoor atmospheric fungal spores in the São Paulo metropolitan area (Brazil): species and numeric concentrations

The aim of this study was to estimate the indoor and outdoor concentrations of fungal spores in the Metropolitan Area of Sao Paulo (MASP), collected at different sites in winter/spring and summer seasons. The techniques adopted included cultivation (samples collected with impactors) and microscopic enumeration (samples collected with impingers). The overall results showed total concentrations of fungal spores as high as 36,000 per cubic meter, with a large proportion of non culturable spores (around 91% of the total). Penicillium sp. and Aspergillus sp. were the dominant species both indoors and outdoors, in all seasons tested, occurring in more than 30% of homes at very high concentrations of culturable airborne fungi [colony forming units(CFU) m⁻³]. There was no significant difference between indoor and outdoor concentrations. The total fungal spore concentration found in winter was 19% higher than that in summer. Heat and humidity were the main factors affecting fungal growth; however, a non-linear response to these factors was found. Thus, temperatures below 16°C and above 25°C caused a reduction in the concentration (CFU m⁻³) of airborne fungi, which fits with MASP climatalogy. The same pattern was observed for humidity, although not as clearly as with temperature given the usual high relative humidity (above 70%) in the study area. These results are relevant for public health interventions that aim to reduce respiratory morbidity among susceptible populations.     

The incidence of fungal spores in the ambient air and inside homes: Evidence from London

Little research has been carried out in London concerning fungal spore prevalence yet this information may help to elucidate geographical patterns of asthma and hay fever. Although many types of spore reach peak concentrations outdoors in late-summer, the incidences in the indoor environment may be more important through the winter because of heating and poor ventilation. Daily average concentrations of fungal spores in the ambient atmosphere were monitored with a Burkard volumetric spore trap on an exposed roof in North London from autumn 1991 until the summer of 1992. Indoor spore measurements were taken in 19 homes in the vicinity through the winter months, both by direct air sampling using a portable Burkard sampler and by dust culture. Trends in the occurrence and concentrations of fungal spores indoors and outdoors were examined. Relationships between the abundance of selected allergenic fungi and features of the houses were analysed including age of dwelling, dampness, cleanliness and presence of pets.Aspergillus andPenicillium were the most frequently occurring spore types in the homes. Overall, high spore incidence was associated with dampness and dust accumulation. The outdoor spore samples revealed generally low concentrations through the winter until March when concentrations of many types includingCladosporium, Epicoccum andAlternaria increased in abundance in response to the warmer weather. Even during the late-spring and early-summer, concentrations of most fungal spores were notably below those reported for rural sites.     

A survey of the aeromycota of Sydney and its correspondence with environmental conditions: grass as a component of urban forestry could be a major determinant

A comprehensive survey of airborne fungi has been lacking for the Sydney region. This study determined the diversity and abundance of outdoor airborne fungal concentrations in urban Sydney. Monthly air samples were taken from 11 sites in central Sydney, and culturable fungi identified and quantified. The genus Cladosporium was the most frequently isolated fungal genus, with a frequency of 78 % and a mean density of 335 CFU m^?3. The next most frequently encountered genus was Alternaria, occurring in 53 % of samples with a mean of 124 CFU m^?3. Other frequently identified fungi, in decreasing occurrence, were as follows: Penicillium, Fusarium, Epicoccum, Phoma, Acremonium and Aureobasidium. Additionally, seasonal and spatial trends of airborne fungi were assessed, with increases in total culturable fungal concentrations experienced in the summer months. The correspondence between a range of key environmental variables and the phenology of airborne fungal propagules was also examined, with temperature, wind speed and proximal greenspace having the largest influence on fungal propagule density. If the greenspace was comprised of grass, stronger associations with fungal behaviour were observed.     

Fungal and Bacterial Communities in Indoor Dust Follow Different Environmental Determinants

People spend most of their time inside buildings and the indoor microbiome is a major part of our everyday environment. It affects humans’ wellbeing and therefore its composition is important for use in inferring human health impacts. It is still not well understood how environmental conditions affect indoor microbial communities. Existing studies have mostly focussed on the local (e.g., building units) or continental scale and rarely on the regional scale, e.g. a specific metropolitan area. Therefore, we wanted to identify key environmental determinants for the house dust microbiome from an existing collection of spatially (area of Munich, Germany) and temporally (301 days) distributed samples and to determine changes in the community as a function of time. To that end, dust samples that had been collected once from the living room floors of 286 individual households, were profiled for fungal and bacterial community variation and diversity using microbial fingerprinting techniques. The profiles were tested for their association with occupant behaviour, building characteristics, outdoor pollution, vegetation, and urbanization. Our results showed that more environmental and particularly outdoor factors (vegetation, urbanization, airborne particulate matter) affected the community composition of indoor fungi than of bacteria. The passage of time affected fungi and, surprisingly, also strongly affected bacteria. We inferred that fungal communities in indoor dust changed semi-annually, whereas bacterial communities paralleled outdoor plant phenological periods. These differences in temporal dynamics cannot be fully explained and should be further investigated in future studies on indoor microbiomes.