Association between dwelling characteristics and concentrations of bacteria, endotoxin and fungi in settling dust

Numerous studies indicate that the presence of fungi, bacteria and endotoxins in the indoor environment is strongly associated with serious health risks such as asthma, allergies and respiratory discomfort (Horick et al. 2005, Denning et al. 2006, Tischer et al. 2011). Hence there is a need to determine potential predictors that influence the presence of these microorganisms in homes.
Fungi can grow on different indoor materials such as humid gypsum-boards. Fungal spores can upon exposure to airflow be aerosolised (Madsen et al. 2006). The size of the fungal spores in indoor air is usually below 5 μm (Chang and Gershwin, 2004). Fungi are naturally present outdoors and levels of outdoor fungi are affected by local climate conditions, such as rainfall and temperature (Chang and Gershwin, 2004). Outdoor fungi contribute to the indoor level of fungi via infiltration through the building envelope (Frankel et al. 2012).
Bacteria and bacterial endotoxins may enter buildings through the same pathways as fungi. However, a study of Madsen et al. (2012) has shown that concentrations of bacteria in indoor settled dust are significantly affected by presence of occupants. Endotoxins are present in the outer cell wall of gram-negative bacteria. When bacteria decease or dry out the cell wall breaks into smaller fragments (Thorne et al. 2008; Gehring et al. 2004; Abraham et al. 2005; Dassoville et al. 2008). Exposed to an airflow created by human activities, the endotoxins can become airborne (Balasubramanian et al. 2012).
Moisture has great influence on fungal growth and viability of bacteria. Likewise the temperature, ventilation rate and construction details reflected in the year of construction influence the moisture level in dwellings (Hägerhed-Engman, 2008; Ren et al. 2001; Bornehag et al. 2004). Studies have showed that the presence of pets also influences the level of bacterial culture and fungi in the indoor environment (Sordillo et al. 2011; Thorne et al. 2008). Furthermore, the levels of fungi and bacteria in the indoor environment are strongly influenced by the season (Frankel et al. 2012).
It has been shown that dust sampling of settled dust by use of the Electrostatic Dust Fall Collector (EDC) is a representative measure of inhalable dust (Frankel et al. 2012), thus this method was used in the present study.
The objective of this study was to investigate possible associations between building characteristics and concentration levels of fungi, bacteria and endotoxins.