The impact of ventilation rate on the fungal and bacterial ecology of home indoor air

Abstract

The following study explores how measured ventilation rates influence bacterial and fungal community structure and concentrations in the indoor air of homes ventilated by leakage-based airflow. The dynamics of bacterial and fungal communities were quantified from homes within the Cherokee Nation in North Eastern, Oklahoma, USA, where seasonal air exchange rates (AERs) were measured, and seasonal outdoor and indoor air, floor dust, and settled dust samples were collected. Quantitative PCR (qPCR) and DNA amplicon sequencing were paired with a mass balance model to determine if high and low ventilation rate regimes impacted bacterial and fungal concentration and community structure, and to estimate the relative contributions of microbiota to indoor air from infiltration of outdoor air (ventilation) versus indoor emissions. For indoor PM10 and settled dusts samples, comparative analyses of microbial communities revealed no significant bacterial or fungal community differences between samples taken from homes dichotomized into high (average high AER = 0.56 hr−1) and low (average low AER = 0.16 hr−1) AER regimes (p > 0.1 for all), suggesting that ventilation was not a significant factor controlling bacterial and fungal concentrations and ecologies in the indoor air of these homes. A comparison between indoor emissions (typically due to occupancy and resuspension) and ventilation (infiltration of outdoor air) as a source of bacteria and fungi indicates that indoor emissions are the dominant source of particulate matter, bacteria, and fungi, accounting for ~94% indoor air PM10, ~97% of indoor air bacteria, and ~91% of indoor air fungi. Thus, indoor emission sources must be controlled to significantly impact human bacterial and fungal (allergen) exposure in the indoor air of these residential environments.