Morphology and quantification of fungal growth in residential dust and carpets

Abstract

Mold growth indoors is associated with negative human health effects, and this growth is limited by moisture availability. Dust deposited in carpet is an important source of human exposure due to potential elevated resuspension compared to hard floors. However, we need an improved understanding of fungal growth in dust and carpet to better estimate human exposure. The goal of this study was to compare fungal growth quantity and morphology in residential carpet under different environmental conditions, including equilibrium relative humidity (ERH) (50%, 85%, 90%, 95%, 100%), carpet fiber material (nylon, olefin, wool) and presence/absence of dust. We analyzed incubated carpet and dust samples from three Ohio homes for total fungal DNA, fungal allergen Alt a 1, and fungal morphology. Dust presence and elevated ERH (≥85%) were the most important variables that increased fungal growth. Elevated ERH increased mean fungal DNA concentration (P < 0.0001), for instance by approximately 1000 times at 100% compared to 50% ERH after two weeks. Microscopy also revealed more fungal growth at higher ERH. Fungal concentrations were up to 100 times higher in samples containing house dust compared to no dust. For fiber type, olefin had the least total fungal growth, and nylon had the most total fungi and A. alternata growth in unaltered dust. Increased ERH conditions were associated with increased Alt a 1 allergen concentration. The results of this study demonstrate that ERH, presence/absence of house dust, and carpet fiber type influence fungal growth and allergen production in residential carpet, which has implications for human exposure.

Ten questions concerning the implications of carpet on indoor chemistry and microbiology

“…Generally, studies have focused on fungal growth from carpets exposed to high moisture [ 113 ], but research exploring the slow growth processes by fungi (including yeasts) and bacteria tolerating lower water activities may offer further insights [ 149 ]. Additionally, we need to understand how different carpet types and dust loadings influence microbial communities [ 150 ]. We need to build upon existing knowledge of how carpet influences health [ 6 ] by studying how carpet, compared to other flooring types, affects human health through immunomodulatory stimulation, allergenic, toxicological and other combined synergistic and antagonistic effects.…”

Modeling microbial growth in carpet dust exposed to diurnal variations in relative humidity using the “Time‐of‐Wetness” framework

“…Microbes grow in house dust at increased relative humidity conditions, 15 with fungi able to grow at lower relative humidity levels than bacteria 16 . Increased equilibrium relative humidity (ERH) is associated with increased microbial growth rates, 16 and moisture availability also influences fungal morphology in carpet under these conditions 17 . Fungal growth typically occurs above about 80% ERH 18 .…”

Loading Rates of Dust and Bioburden in Dwellings in an Inland City of Southern Europe

“…Noteworthy, the observed correlation between higher fungal counts in POS and higher number of floors suggests that these housing typologies may favor the development indoors of fungal resistance. Dust and moisture are strongly associated with fungal concentration [57]. However, there are other important determinants, such as type of building material [58], air temperature and moisture levels [59] and also some type of carpet fiber that can affect fungal growth [57].…”

“…Dust and moisture are strongly associated with fungal concentration [57]. However, there are other important determinants, such as type of building material [58], air temperature and moisture levels [59] and also some type of carpet fiber that can affect fungal growth [57]. Additionally, occupants' behavior can also influence the indoor microbiome through the different frequency of window opening, the use of exhaust fans [60] or of humidifiers [60,61].…”