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

Abstract

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.

FIG. 1.

Regions of the United States in which air samples were collected. n, number of buildings studied.

FIG. 2.

Distribution of airborne fungal concentrations by region and season for indoor and outdoor samples. The dotted bars indicate the inner quartiles ranging from the 25th percentile to the 75th percentile, and the horizontal lines indicate themedian fungal concentrations. The top of the vertical line represents the maximum observed value. The maximum value is shown at the top of the figure when it exceeds the scale.

FIG. 3.

Distribution of the indoor/outdoor fungal ratio for buildings by region and season. The dotted bars indicate the inner quartiles ranging from the 25th percentile to the 75th percentile, and the horizontal lines indicate the median fungal concentrations. The top of the vertical line represents the maximum observed value. The maximum value is shown at the top of the figure when it exceeds the scale.