Air- and dustborne mycoflora in houses free of water damage and fungal growth

Abstract

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.

FIG. 1.

Frequency distribution of air samples by colony loading per plate.

FIG. 2.

Box plots showing median concentrations (in CFU per cubic meter) and distribution of total airborne fungi by location and season in 180-liter air samples. The horizontal line in each box is the median value; the bottom and top of the box are the 25th and 75th percentiles, respectively; and the line extending above the box marks 1.5 times the median value. Circles, values greater than 3 times the median value; asterisks, values greater than 1.5 times the median value.

FIG. 3.

Box plots showing median concentrations (in CFU per gram) and distribution of total culturable fungi detected by direct plating by medium and season. The horizontal line in each box is the median value; the bottom and top of the box are the 25th and 75th percentiles, respectively; and the line extending above the box marks 1.5 times the median value. Circles, values greater than 3 times the median value; asterisks, values greater than 1.5 times the median value.

FIG. 4.

Frequencies of dust samples (direct plated) with various proportions of leaf surface fungi (LSF). Fewer than one in five samples had very low proportions (<20%) of LSF.