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Background: Questionnaires are commonly used in epidemiologic studies to obtain information about house characteristics in order to predict the household aeroallergen exposure levels. However, the reliability of the predictions made with the questionnaires has not been evaluated. To address this issue, we compared objectively measured fungal propagules including the most frequently isolated mold genera (i.e., Alternaria, Aspergillus, Cladosporium, Penicillium, etc.) in a large sample of homes and compared these measured values to the questionnaire-determined household characteristics.
Methods: As part of a prospective cohort study on the relation between residential allergen exposure and development of asthma in neonates, fungal air samples were collected from infant bedrooms and main living areas in 1000 homes in the Northeast USA, from December 1996 to January 1999. A Burkard portable air sampler was used in combination with DG-18 and MEA agars. A questionnaire was used to obtain information on host and house characteristics that may have an impact on the presence of fungal propagules in the air. This included information on observation of moisture problems (e.g., water leakage or damage, and mold or mildew growth), ventilation and heating facilities, building age and type, number of occupants, annual household income, presence of pets and pests, cleaning regimens, etc.
Results: The number of CFU/m3 air collected on MEA was significantly higher than on DG-18 (means, respectively, 1033.5 and 846.0 CFU/m3) (P<0.0005). However, there was no significant difference between the numbers of CFU/m3 air collected from the main living area and from the infant bedroom. There was only a very weak relationship between the house characteristics, as described by questionnaire, and the presence of fungal propagules in indoor air. Only the temperature, relative humidity, season, and cats inside homes had a statistically significant impact on the presence of fungal propagules in indoor air.
Conclusions: The presence of fungal propagules in indoor air cannot be reliably predicted by home characteristics. Actual measurements are required for fungal exposure assessment, and the use of only one medium to collect samples in one location in a home might be adequate to represent residential levels of fungi in indoor air.
There has been considerable concern about possible adverse health effects related to exposure to airborne materials of biologic origin. Molds are ubiquitous indoors as well as outdoors. The role of fungi in producing respiratory allergy and asthma has long been established (1–4). A number of recent epidemiologic studies have indicated a relation between home dampness/molds and respiratory symptoms (5–8). In most of these studies, information on home dampness, mold growth, and respiratory symptoms was obtained from the occupants of the homes by means of questionnaires or observation, without objective exposure measurements of fungi levels. Therefore, the validity of this association has been questioned.
Fungi, which survive in favorable conditions in damp houses, are assumed to be validly assessed by subjective indicators such as damp spots, water leakage or damage report, and observation of mold growth. However, few studies have evaluated how well those surrogate indicators actually predict exposure to fungi in indoor environments.
As part of a prospective cohort study on the relation between residential allergen exposure and development of asthma in neonates, the presence of fungal propagules in indoor air was objectively assessed. The aims of the study were to investigate the applicability of this assessment as a measure of potential exposure to fungi, and to investigate the relation between the presence of fungi in indoor air and house characteristics. Additional objectives were to explore the representative sampling location in a home and to assess the performance of malt extract agar (MEA) and dichloran-18% glycerol agar (DG-18) in sampling and culturing target mold genera, and determining the concentrations of total culturable airborne fungal propagules.
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Health effects caused by exposure to fungi in nonindustrial indoor environments, including allergic reactions and the role of fungal metabolites, have been the focus of increased attention recently. Several ongoing epidemiologic studies are investigating the nature of the relationship between exposure to fungi and health effects. As part of a prospective epidemiologic study on the relation between residential allergen exposure and the development of asthma in neonates, we assessed indoor residential aeroallergen concentrations in 1000 homes. The exposure assessment protocol employed in the study permitted an evaluation of sampling methods for fungal propagules, the spatial distribution of concentrations within homes, and the utility of using questionnaire data to predict indoor concentration. The results provide new information that should be considered in designing new studies aimed at assessing residential fungi levels.
Although significantly higher numbers of total culturable fungi were measured for samples collected on the MEA medium than the DG-18 medium, some specific genera, such as Aspergillus, Cladosporium, and Alternaria, had a significantly higher number of CFU/m3 on the DG-18 than the MEA medium. However, no difference for Penicillium between these two media was observed. These results indicated that DG-18 had superior performance on the counts of Aspergillus, Cladosporium, and Alternaria. DG-18, however, collected more diverse fungi than MEA. This finding generally agrees with the report by Russell et al. (10), suggesting that the use of only DG-18 to collect indoor air samples of fungi might be adequate to represent residential levels of those fungi which might be more directly related to health concerns. The advantages of using one medium for sampling are that it can save time, and be economical and practical.
No significant differences were found for the total number of culturable fungi as well as the numbers of the genera Alternaria, Aspergillus, and Penicillium, and yeast between the infant bedroom and the main living area. Only Cladosporium had a significantly higher concentration in the main living area than in the infant bedroom (P<0.0001). The threshold concentration for evoking allergic symptoms for Cladosporium is 3000 spores per cubic meter air, which is much higher than the thresholds for Alternaria, Aspergillus, and Penicillium (11). More Cladosporium and Alternaria are fungi that grow mainly outdoors; Aspergillus and Penicillium mainly grow indoors. However, Alternaria is the most important outdoor mold and Aspergillus is the most important indoor mold (12). Therefore, our result suggests that it may be necessary to sample only in one location in a home in order to assess the household concentration of fungi if the allergenic species of fungi are of more concern. This apparently holds for measurements of both total and specific genera.
In this investigation, we documented an association between questionnaire reports of regular housing conditions and the concentrations of total culturable/viable fungal propagules and some common genera in indoor air by larger sample size (up to 3998 indoor air samples) than ever. Little information on the associations between home characteristics and fungal concentrations in indoor air is available in the published literature. In our study, strong and significant associations were found between the number of total culturable fungi in indoor air and season of the year, temperature, and relative humidity, as well as the presence of a cat in the home. However, the power was low to predict the dependent variable (airborne fungal concentrations) from the values of the independent variables (season of the year, temperature, relative humidity, and the presence of a cat in the home). Damp spots, water leakage or report of water damage, observation of mold or mildew growth, etc. from questionnaires have often been used as surrogate measures for the number of fungi in several published epidemiologic studies (5–8). However, these characteristics were not consistently and significantly related to the measured culturable fungal propagules in indoor air in our study. Other questionnaire-obtained measures of house characteristics, such as the year of construction, use of air conditioner and humidifier, and heating system, were also not found to be predictors of fungal propagules. These results suggested that the presence of fungal propagules in indoor air cannot be reliably predicted by home characteristics. A similar conclusion was drawn by Verhoeff et al. (13), who found that the presence of fungal propagules in house dust could not be reliably predicted by house characteristics, as surveyed by a checklist and questionnaire. These results suggest that an actual measurement of fungal concentration in a home is more reliable than questionnaires for assessing residential exposure in epidemiologic studies. This finding may apply only to the Northeast USA, as this relationship may be different for different parts of country or world.
In this large sample, we further confirm that fungal concentrations show substantial variations or trends among seasons, as is consistent with our previous study (14). Summer and autumn were more likely to have higher concentrations of fungal propagules in indoor air than spring/winter. In addition, the seasons are associated with indoor temperature and relative humidity. Summer and autumn tend to have higher temperature and be more humid than spring/winter, which favor fungal growth. However, the question of how many samples in a year or in which season samples should be taken to best represent household fungal concentration is not clear. In our ongoing epidemiologic study on the relation between residential allergen exposure and the development and severity of asthma in childhood, we will assess how household fungal concentrations vary by season within and between homes.