Profiles of airborne fungi in buildings and outdoor environments in the
Kirkland KH, Flanders WD, Morris GK. . Applied and Environmental
Microbiology. April, 2002; 68(4):1743-1753.
Purpose: This comprehensive analysis compared the relative
frequencies of indoor and outdoor airborne fungi in samples taken at
different seasons and regional locations around the United States.
Design: Standardized survey quantifying fungal concentrations from
air samples and interviews with a subgroup of building occupants. Over
twelve thousand fungal air samples (9,619 indoor samples and 2,407
outdoor samples) from 1,717 buildings across the US were collected using
Anderson N6 samplers. Actual fungal counts were measured as colony
forming units per cubic meter of air. A follow-up telephone
questionnaire of 100 random building owners determined the type of
building, reason for performing air quality investigation, and whether
there were any health complaints among the building occupants.
Outcome: Both the indoor and outdoor fungal concentrations were
highest in the fall and summer and lowest in the spring and winter.
Overall, the ratio of indoor and outdoor concentrations was one to one
or lower for the majority of the buildings throughout the year,
indicating that the amount of mold indoors was equal to or less than the
amount of mold detected outdoors. The ratios indicated that the indoor
concentrations were greater than the outdoor concentrations for 15% of
the buildings studied. The indoor to outdoor fungal concentration ratios
did not vary significantly by season, whereas the regional variation was
substantial with concentrations highest in the Southwest, Far West, and
Southeast. The outdoor levels were lowest in the Northwest and the
indoor levels were lowest in the Northeast. Cladosporium, Penicillium,
Aspergillus, and nonsporulating fungi were the most common fungi found
indoors and outdoors in each season and in each region. The results
suggested that the presence of Stachybotrys is not unusual and occurred
at similar frequencies across the country. There was no association
between fungal counts and any reported respiratory, dermatologic or eye
problems amongst the building occupants that were interviewed. There was
a relationship between elevated indoor fungal counts and complaints of
Significant Quotes: "This is the largest study of airborne indoor
and outdoor fungal species and concentrations conducted with a
standardized protocol to date." (p. 1743).
"[R]egion may be more important than season in determining ratios of
indoor [fungal] population size to outdoor [fungal] population size."
"Although the purpose of this study was not to measure any potential
health association and the number of questionnaires was small, we found
no association between reported health complains and the presence of any
common fungal type or potentially toxigenic fungus." (p.1752).
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