Assessing total fungal concentrations on commercial passenger aircraft using mixed-effects modeling

The primary objective of this study was to compare airborne fungal concentrations onboard commercial passenger aircraft at various in-flight times with concentrations measured inside and outside airport terminals. A secondary objective was to investigate the use of mixed-effects modeling of repeat measures from multiple sampling intervals and locations. Sequential triplicate culturable and total spore samples were collected on wide-body commercial passenger aircraft (n = 12) in the front and rear of coach class during six sampling intervals: boarding, midclimb, early cruise, midcruise, late cruise, and deplaning. Comparison samples were collected inside and outside airport terminals at the origin and destination cities. The MIXED procedure in SAS was used to model the mean and the covariance matrix of the natural log transformed fungal concentrations. Five covariance structures were tested to determine the appropriate models for analysis. Fixed effects considered included the sampling interval and, for samples obtained onboard the aircraft, location (front/rear of coach section), occupancy rate, and carbon dioxide concentrations. Overall, both total culturable and total spore fungal concentrations were low while the aircraft were in flight. No statistical difference was observed between measurements made in the front and rear sections of the coach cabin for either culturable or total spore concentrations. Both culturable and total spore concentrations were significantly higher outside the airport terminal compared with inside the airport terminal (p-value < 0.0001) and inside the aircraft (p-value < 0.0001). On the aircraft, the majority of total fungal exposure occurred during the boarding and deplaning processes, when the aircraft utilized ancillary ventilation and passenger activity was at its peak.     

Monitoring microbial populations on wide-body commercial passenger aircraft

Although exposure to bacteria has been assessed in cabin air previously, minimal numbers of samples have been collected in-flight. The purpose of this research was to comprehensively characterize bacterial concentrations in the aircraft cabin. Twelve randomly selected flights were sampled on Boeing-767 aircraft, each with a flight duration between 4.5 and 6.5 h. N-6 impactors were used to collect sequential, triplicate air samples in the front and rear of coach class during six sampling intervals throughout each flight: boarding, mid-climb, early cruise, mid-cruise, late cruise and deplaning. Comparison air samples were also collected inside and outside the airport terminals at the origin and destination cities. The MIXED procedure in SAS was used to model the mean and the covariance matrix of the natural log-transformed bacterial concentrations. A total of 513 airborne culturable bacterial samples were collected. During flight (mid-climb and cruise intervals), a model-adjusted geometric mean (GM) of 136 total colony-forming units per cubic meter of air sampled (CFU x m(-3)) and geometric standard deviation of 2.1 were observed. Bacterial concentrations were highest during the boarding (GM 290 CFU x m(-3)) and deplaning (GM 549 CFU x m(-3)) processes. Total bacterial concentrations observed during flight were significantly lower than GMs for boarding and deplaning (P values <0.0001-0.021) in the modeled results. Our findings highlight the fact that aerobiological concentrations can be dynamic and underscore the importance of appropriate sample size and design. The genera analysis indicates that passenger activity and high occupant density contribute to airborne bacterial generation. Overall, our research demonstrates that the bacteria recovered on observed flights were either common skin-surface organisms (primarily gram-positive cocci) or organisms common in dust and outdoor air.     

Seasonal fine and coarse culturable fungal constituents and concentrations from indoor and outdoor air samples taken from an arid environment

This study was undertaken to determine the normal indoor and outdoor airborne culturable fungal constituents and concentrations of an arid environment. Air samples were taken with two-stage, ambient, culturable sampler systems and analyzed for nine specific fungal genera from 50 homes as a repeated measure during each season of the year. These homes had no previous histories of indoor air quality issues. This study detected seasonal differences for the arid environment between different culturable fungal concentrations across the two size ranges. The highest concentrations were during fall, in the outdoor fine-size range. The lowest concentrations were the indoor coarse concentrations in the spring. From this study it can be concluded that Cladosporium spp. had the highest concentrations during fall in an arid environment. The overall findings suggest that Cladosporium had concentrations greater than the other genera evaluated, specifically, the fall outdoor fine concentrations. Seasonality was found to be a key factor in determining the variability of fungal constituents and concentrations within the arid indoor and outdoor environments. The fine-size range was 12 times and 6 times greater than the coarse-size range for indoor and outdoor samples, respectively, which accounted for the majority of fungal organisms. In addition, the results from this study in an arid climate differ from those conducted in a moister climate.     

Seasonal variability of culturable fungal genera in the house dust of inner-city residences

House dust samples were collected up to six times over a 1-year period to explore seasonal variability of individual fungal genera in inner-city households in Minneapolis, Minnesota. General linear mixed-effects models were used to explore the variability of 13 fungal genera (Cladosporium, yeasts, Aureobasidium, Alternaria, Penicillium, Epicoccum, Mucor, Rhodotorula, Aspergillus, sterile fungi, Phoma, Pithomyces, and Fusarium) found in more than 20% of total dust samples. The five most common fungi (% of samples detected) were Cladosporium (81%), yeasts (63%), Aureobasidium (57%), Alternaria (56%), and Penicillium (55%), with the remaining genera found in 20-50% of the samples. When expressed as frequency of occurrence (%), genus fraction of total fungal concentration (%), or concentration of individual genera (CFU/g), these five genera also varied substantially by season. In contrast, Aureobasidium, Fusarium, and Mucor levels remained relatively constant throughout the year. The observed concentrations of the five most common fungal genera were higher than levels associated with increased respiratory symptoms reported in previous studies. Our results indicate that seasonal variability in common fungal genera is large: within-home to between-home variance ratios of Penicillium (4.1), Alternaria (4.9), Cladosporium (7.1), and yeasts (20.3) were substantially larger than that observed for total fungi (2.5). These results suggest that future studies attempting to link individual fungal genera to health effects need to characterize and control for this seasonal variability.     

Hintergrundkonzentrationen von Schimmelpilzen in Luft

The mold concentration of indoor air and outdoor air in three parts of Germany was investigated in both winter and summer. In total, air samples from 80 dwellings, reportedly free from mold infestations, were analysed with both the cultivation method and the total spore count method. With the cultivation method, 40 mold species and genera were differentiated, while with the total spore count method, 11 spore types were distinguished. The concentration of the genera Alternaria, Cladosporium, Fusarium and yeast increased in summertime. In contrast, the concentrations of Aspergillus and Penicillium measured in summer were nearly equal to those measured in winter. The majority of the various molds were only found in a small number of samples, too small for a reliable comparison of the winter and summer findings. The 95th percentile of the indoor mold concentrations is suggested as the upper limit of the background concentration. The results are discussed comparing the assessment proposals of various authors, and a new assessment proposal is described.     

Fungi carried from farmers' work into farm homes

Airborne fungal spore concentrations and main fungal genera were compared in rural and urban living environments in Finland during the winter. In addition to conventional viable fungal spore counts (based on the six-stage impactor sampling and cultivation), total spore concentrations were obtained by scanning electron microscope (SEM) investigation of filter samples. The viable spore counts were only 0.2%-25% of the number of total spore aggregates. A high correlation between these two methods was noted, however, at the recommended measuring ranges of the methods. In the farm houses, viable and total spore levels were 10(3) to 10(4) colony forming units/m3 (cfu/m3) and 10(4) to 10(5), spores/m3, respectively. These counts were 10-10(3)-fold higher than the concentrations in an urban apartment. The spore levels of farmers' homes, however, were somewhat lower than those observed in their cow barns. Aspergillus, Cladosporium, and Penicillium spores were present in both urban and rural environments. Actinomycetes and some fungal genera--such as Acremonium, Alternaria, Botrytis, and Chrysosporium--which were detected in cow barns and in farm houses, were not present in urban environment. The results indicated that airborne fungal spores may be carried from cow barns to farmers' homes.     

Characteristics of indoor and outdoor bioaerosols at Korean high-rise apartment buildings

This study attempted to evaluate the bioaerosol exposure of apartment residents at high-rise apartment buildings in a Korean city. The characteristics associated with the bioaerosol exposure included the apartment floor, seasonal variation, summer survey period (seasonal rain-front period (SRFP) or no rain-front period (NRFP)), and room location inside an apartment. Four most prevalent fungal genera detected in both the indoor and the outdoor air were Cladosporium, Penicillium, Aspergillus, and Alternaria. The outdoor bacterial concentrations were significantly higher in the low-floor apartments than in the high-floor apartments. However, the bacterial and fungal concentrations in the interior air of the apartments were not significantly different between the low- and the high-floor apartments. The current bioaerosol concentrations were comparable to those in other reports, with geometric mean (GM) bacterial values between 10 and 10(3) CFU m(-3) and fungal aerosol concentrations in homes ranging also from 10 to 10(3) CFU m(-3). The indoor and outdoor fungal concentrations and the outdoor bacterial concentrations were usually higher in the summer than in the winter. The indoor and outdoor bioaerosol concentrations were both higher for the SRFP than for the NRFP. The difference in the total bacterial concentrations was not significant among the surveyed five rooms. The GM total fungal and Cladosporium concentrations, however, were significantly higher for the kitchen than for the other rooms.     

Variabilities in aerosolizing activities and airborne fungal concentrations in a bakery.

Concentrations of airborne culturable fungi were measured in the kitchen of a bakery in Boston, Mass., to evaluate variabilities associated with common worker activities, outdoor aerosol distributions, and season. Activities were categorized as early morning preparation, cornmeal sifting and tossing, flour dumping and mixing, sweeping, and low activity. Sets of measurements were taken over 1 day in spring and 1 day in summer. Fungal concentrations were measured using a one-stage culture plate impactor, and bulk samples were taken from suspected fungal reservoirs within the bakery and subsequently cultured. Compared with the low activity category, elevated levels of total culturable fungi were found during all other activities, with the amount of increase closely related to individual worker activity as well as outdoor concentrations and initial bakery conditions. In the spring, Penicillium was the dominant genus showing activity-related elevations in concentrations, while Cladosporium was the dominant genus during the summer. Clearly, due to variabilities in worker activities and ambient fungal concentrations, a standardized sampling protocol involving a large sample size over multiple days is needed to estimate accurately exposure to either total airborne fungi or specific fungal taxa.     

A method for detecting fungal contaminants in wall cavities

This article describes a practical method for detecting the presence of both fungal spores and culturable fungi in wall cavities. Culturable fungi were collected in 25 mm cassettes containing 0.8 microm mixed cellulose ester filters using aggressive sampling conditions. Both culturable fungi and fungal spores were collected in modified slotted-disk cassettes. The sample volume was 4 L. The filters were examined microscopically and dilution plated onto multiple culture media. Collecting airborne samples in filter cassettes was an effective method for assessing wall cavities for fungal contaminants, especially because this method allowed the sample to be analyzed by both microscopy and culture media. Assessment criteria were developed that allowed the sample results to be used to classify wall cavities as either uncontaminated or contaminated. As a criterion, wall cavities with concentrations of culturable fungi below the limit of detection (LOD) were classified as uncontaminated, whereas those cavities with detectable concentrations of culturable fungi were classified as contaminated. A total of 150 wall cavities was sampled as part of a field project. The concentrations of culturable fungi were below the LOD in 34% of the samples, whereas Aspergillus and/or Penicillium were the only fungal genera detected in 69% of the samples in which culturable fungi were detected. Spore counting resulted in the detection of Stachybotrys-like spores in 25% of the samples that were analyzed, whereas Stachybotrys chartarum colonies were only detected on 2% of malt extract agar plates and on 6% of corn meal agar plates.     

Field evaluation of a personal, bioaerosol cyclone sampler

A personal cyclone sampler (cyclone) was operated continuously alongside a 25-mm filter sampler (filter), a slit impactor (Burkard slide), and a high-volume cyclone sampler (Burkard cyclone) at an outdoor location with abundant naturally occurring fungi (N = 30; sampling time: 12.5 +/- 2.3 hr). Air concentrations (spore m(-3)) of 28 fungal groups were determined for all samplers by microscopy. Cyclone performance was judged using various indices to determine if it agreed with the other samplers in determination of the frequencies with which the fungal groups were observed, as well as their proportions of the total air concentration. Fungal diversity estimates were similar for all samplers and in the range of what has been reported nationally, i.e., observation of 9-11 equal groups per sample, but spore concentration dominated by 2-3 groups. Plots of paired cyclone:comparison sampler ratios against average concentrations identified biases. For example, ratios were correlated with concentration and there was greater uncertainty at lower concentrations. Mean ratios for cyclone:filter comparisons were not significantly different from one for ascospores, Aspergillus-Penicillium spp., basidiospores, Cladosporium spp., or total spore m(-3). However, agreement was less consistent with the Burkard slide (0.74, 1.12, 0.91, 1.09, and 0.92, respectively) and the Burkard cyclone (2.31, 1.62, 1.43, 1.91, and 1.33, respectively). Concentrations of cell equivalent m(-3) also were determined for the filter and two cyclone samples by polymerase chain reaction. Cell equivalents for Aspergillus fumigatus and Penicillium brevicompactum were compared with Aspergillus-Penicillium spp. spores, and Cladosporium cladosporioides and Cladosporium herbarum cell equivalents were compared with Cladosporium spp. spores. Cell equivalent:spore ratios below one for A. fumigatus and P. brevicompactum indicated that these species comprised smaller factions of total spores or were collected less efficiently than the larger C. cladosporioides and C. herbarum spores. The personal cyclone was shown to be suitable for collection of ambient airborne fungal spores and for analysis by microscopy and polymerase chain reaction.     

Comparisons of seasonal fungal prevalence in indoor and outdoor air and in house dusts of dwellings in one Northeast American county

Fungi cause allergies and many other adverse health effects. In this study, we characterized the nature and seasonal variation of fungi inside and outside homes in the Greater New Haven, Connecticut area. Three indoor air samples (in the living room, bedroom, and basement) and one outdoor sample were collected by the Burkard portable air sampler. House dust samples were collected in the living room by a vacuum cleaner. The mold concentrations varied widely from house to house in both indoor and outdoor air. No significant difference (p>0.05) in concentration and type of fungi between living room and bedroom or by season was observed. Both concentration and type of fungi were significantly higher (p<0.05) in the basement than other indoor areas and outdoor air in winter. The type of fungi in living room, bedroom, and outdoor air were found to have significant changes among seasons, but there was no significant difference for the basement among seasons. Cladosporium spp. was dominant in both indoor and outdoor air in summer. Penicillium and Aspergillus were dominant in indoor air in winter, but neither was dominant in any season in outdoor air. The type of fungi and their concentrations in house dust samples were not representative of those isolated in indoor air. In dust samples, more Mucor, Wallemia, and Alternaria species, but less Aspergillus, Cladosporium, and Penicillium species were found in all seasons. Air sampling in spring or fall in every suspected house is suggested for year-round fungal exposure assessment.     

Exposure level and distribution characteristics of airborne bacteria and fungi in Seoul metropolitan subway stations

The exposure level and distribution characteristics of airborne bacteria and fungi were assessed in the workers' activity areas (station office, bedroom, ticket office and driver's seat) and passengers' activity areas (station precinct, inside the passenger carriage, and platform) of the Seoul metropolitan subway. Among investigated areas, the levels of airborne bacteria and fungi in the workers' bedroom and station precincts were relatively high. No significant difference was found in the concentration of airborne bacteria and fungi between the underground and above ground activity areas of the subway. The genera identified in all subway activity areas with a 5% or greater detection rate were Staphylococcus, Micrococcus, Bacillus and Corynebacterium for airborne bacteria and Penicillium, Cladosporium, Chrysosporium, Aspergillus for airborne fungi. Staphylococcus and Micrococcus comprised over 50% of the total airborne bacteria and Penicillium and Cladosporium comprised over 60% of the total airborne fungi, thus these four genera are the predominant genera in the subway station.     

室内常见气传真菌的分布及其培养提取物的免疫抑制作用研究

目的 了解室内常见气传真菌的分布及其影响因素,并分析其代谢提取物对呼吸道免疫功能的影响。方法 以平皿沉降法进行室内环境气传真菌的采样,并进行菌株鉴定及其分布影响因素的分析;同时以改良的混合淋巴细胞反应研究了室内常见气传真菌代谢提取物的非特异性免疫抑制作用。结果 室内环境中的主要真菌污染源为芽枝菌属、曲霉属、交链孢属、镰刀霉属、青霉属等,影响室内真菌分布的主要因素为温度、湿度及室外菌落数;青霉属、曲霉属的代谢提取物在无明显的细胞毒性浓度下,可抑制异型小鼠淋巴细胞混合刺激而产生的增生。结论 长期暴露于室内气传真菌对人体呼吸道防御功能构成了潜在的威胁。     

Exposure levels of airborne bacteria and fungi in Korean swine and poultry sheds

There is a limited amount of information available on stock farmers' exposure to airborne bacteria and fungi. In this study, the authors measured the airborne bacteria and fungi concentrations 46 times inside two swine sheds and four poultry sheds. Aspergillus, Cladosporium, and Penicillium were the most prevalent fungal genera, as most of the fungi belonged to these groups. Many microbial concentrations exceeded the Korean indoor bioaerosol guideline 800 CFU m(-3) (i.e., colony-forming units per cubic meter of air). This finding suggests the need for a strategy to reduce stock farmers' occupational exposure to the microorganisms in swine and poultry sheds, and the necessity of performing a longitudinal survey to better examine farmer exposure levels and their variability. Another finding was that the use of a sanitary mask may reduce stock farmers' exposure to bioaerosols.     

Correlation between the prevalence of certain fungi and sick building syndrome

OBJECTIVE: To examine the role of fungi in the production of sick building syndrome. METHODS: A 22 month study in the United States of 48 schools (in which there had been concerns about health and indoor air quality (IAQ). Building indoor air and surface samples, as well as outdoor air samples were taken at all sites to look for the presence of fungi or their viable propagules. RESULTS: Five fungal genera were consistently found in the outdoor air and comprised over 95% of the outdoor fungi. These genera were Cladosporium (81.5%), Penicillium (5.2%), Chrysosporium (4.9%), Alternaria (2.8%), and Aspergillus (1.1%). At 20 schools, there were significantly more colony forming units per cubic metre (CFU/m3) (p < 0.0001) of propagules of Penicillium species in the air samples from complaint areas when compared with the outdoor air samples and the indoor air samples from noncomplaint areas. At five schools, there were more, although not significant (p = 0.10), Penicillium propagules in the air samples from complaint areas when compared with the outdoor air samples and the indoor air samples from noncomplaint areas. In 11 schools, the indoor air (complaint areas) fungal ratios were similar to that in the outdoor air. In these 11 schools Stachybotrys atra was isolated from swab samples of visible growth under wetted carpets, on wetted walls, or behind vinyl wall coverings. In the remaining 11 schools, the fungal ratios and CFU/m3 of air were not significantly different in different areas. Many of the schools took remedial action that resulted in an indoor air fungal profile that was similar to that outdoors. CONCLUSIONS: Propagules of Penicillium and Stachybotrys species may be associated with sick building syndrome.

 

     

Firefighting efforts may lead to massive fungal growth and exposure within one week. A case report

A case study on extensive fungal growth that occurred in an apartment building after firefighting efforts is described in this paper. Exposure to airborne microorganisms (both viable and total) was investigated by filter sampling in three periods before and during remedial actions after the fire. Material samples were also analyzed. Extensive mold growth was observed on the building materials as soon as eight days after the fire. High concentrations of fungal spores, 10(7) cfu/g, were found when material samples were analyzed. Concentrations of airborne fungal spores (10(4) spores/m3) were also high and increased by two orders of magnitude during the demolition of moldy building materials and during the clean-up after the demolition. The proportions of airborne viable fungi in comparison with the total spore concentrations were 28-83% immediately after the fire, but they had decreased to <1% two months after the fire during the reconstruction phase. Paecilomyces was the main fungal genus in the indoor air before and during the demolition, while Penicillium dominated during the reconstruction. Paecilomyces was not detected in the outdoor air. Paecilomyces and Penicillium were also found in the material samples. The results show that fast and extensive mold growth in a building may take place also in subarctic climates, at least during summer. High concentrations of fungal spores are released to the air during the demolition of moldy building materials and the following clean-up. Therefore, personal protection is necessary during such work.     

Airborne mold and endotoxin concentrations in New Orleans, Louisiana, after flooding, October through November 2005

BACKGROUND: The hurricanes and flooding in New Orleans, Louisiana, in October and November 2005 resulted in damp conditions favorable to the dispersion of bioaerosols such as mold spores and endotoxin. OBJECTIVE: Our objective in this study was to assess potential human exposure to bioaerosols in New Orleans after the flooding of the city. METHODS: A team of investigators performed continuous airborne sampling for mold spores and endotoxin outdoors in flooded and nonflooded areas, and inside homes that had undergone various levels of remediation, for periods of 5-24 hr during the 2 months after the flooding. RESULTS: The estimated 24-hr mold concentrations ranged from 21,000 to 102,000 spores/m3 in outdoor air and from 11,000 to 645,000 spores/m3 in indoor air. The mean outdoor spore concentration in flooded areas was roughly double the concentration in nonflooded areas (66,167 vs. 33,179 spores/m3 ; p < 0.05) . The highest concentrations were inside homes. The most common mold species were from the genera of Cladosporium and Aspergillus/Penicillium ; Stachybotrys was detected in some indoor samples. The airborne endotoxin concentrations ranged from 0.6 to 8.3 EU (endotoxin units) /m3 but did not vary with flooded status or between indoor and outdoor environments. CONCLUSIONS: The high concentration of mold measured indoors and outdoors in the New Orleans area is likely to be a significant respiratory hazard that should be monitored over time. Workers and returning residents should use appropriate personal protective equipment and exposure mitigation techniques to prevent respiratory morbidity and long-term health effects.     

Airborne fungal spores in a cross-sectional study of office buildings

Airborne fungal spores were measured in 44 office buildings in the summer and winter throughout the continental United States, as part of the Building Assessment, Survey and Evaluation (BASE) program. Six indoor air and two outdoor air samples were collected on a single day from each building. The cross-sectional and repeated measure design afforded evaluation of between-building and within-building variability of fungal spore levels in buildings. Total fungal spore concentrations in indoor air ranged from < 24 to 1000 spores/m3, except for one building with natural ventilation where indoor levels were approximately 9000 spores/m3. Indoor air concentrations of total spores did not vary significantly between winter and summer or morning and afternoon monitoring periods or among climate zones or locations within a test area. Indoor-outdoor ratios of total spore concentrations typically ranged between 0.01 and 0.1 and were approximately seven times greater in winter than summer because of relatively low outdoor levels in the winter. The indoor-outdoor ratio of total spore concentrations for a building was consistent (reliability coefficient = 0.91) among repeated measures. Distributions of rank correlation coefficients for spore types in pairs of individual indoor-outdoor and indoor-indoor samples were weakly correlated (Spearman correlation = 0.2 on average). When spore type data were aggregated among samples from the same building, the central tendency of the rank correlation coefficients increased to 0.45. Rank correlation coefficients were also proportional to the number of spore types present in the samples that were compared. The BASE study provides normative data on concentrations of fungal spores that can aid in identification of problematic levels of mold in buildings.     

Gastrointestinal illness associated with a long-haul flight

An in-flight incident of vomiting in the cabin and toilet on a trans-Pacific aircraft flight resulted in an outbreak of gastrointestinal (GI) illness among passengers, some of whom subsequently joined a 14-day cruise in New Zealand and Australia. A retrospective cohort analysis of illness occurring in aircraft passengers was undertaken using routine GI illness surveillance data collected by medical staff on a cruise vessel. This was supplemented with data collected from some other passengers and crew on the aircraft. Information was gathered on 224 of the 413 (54.2%) people on the flight (222 passengers and 2 crew members). GI illness within 60 h of arrival in Auckland was reported by 41 of the 122 (33.6%, Fisher's 95% confidence interval 25.3-42.7) passengers seated in the two zones adjacent to the vomiting incident. The pattern of illness suggests a viral infection and highlights the potential of aerosol transmission as well as surface contamination in a closed environment. The spread of infection may have been enhanced by cross-contamination in the toilet cubicle. The significance of the vomiting event was not recognized by the aircraft cabin crew and no pre-arrival information about on-board illness was given to airport health authorities. Isolation of vomiting passengers, where possible, and promotion of appropriate hand hygiene on aircraft has the potential to reduce the spread of infection in passengers on long-haul flights.     

Fungal types and concentrations from settled dust in normal residences

Analysis of settled dust collected from carpeting and furnishings is occasionally used by investigators to determine whether an environment contains unusual fungi. Little information is available concerning the types and concentrations of culturable fungi present on textile surfaces in normal residential settings not affected by unusual mold reservoirs, such as from fungal growth sites within the built environment. This study presents the results of the collection and analysis of surface dust from 26 residential environments that were prescreened by interview, physical inspection, and air sampling to limit the surface dust collection to structures in which there was no history of water intrusion, flooding, plumbing leaks, signs of mold growth, or evidence of unusual airborne fungal spore types or concentrations. In those structures found to have no history or indications of water events or unusual fungi, surface dust was vacuumed from prescribed horizontal areas on carpet and textile-covered furnishings. These samples were then subjected to fungal culture, from which viable colonies were enumerated and identified. Based on the study results, it does not appear reasonable that the frequently quoted total fungi concentration exceeding 10(5) CFU/g is definitive evidence that a residential surface is contaminated with unusual amounts of culturable fungi. Collocated samples collected from eight side-by-side carpets sections revealed poor reproducibility. While settled dust sampling may be appropriate for determining the fungal status of a localized area, or as a gross screening tool, using settled dust results alone to establish the presence of unusual fungal types or concentrations within a structure appears to be inappropriate, and using settled dust results with other investigative methods, such as visual observations and air sampling, requires cautious interpretation.