Microbes are ubiquitous in the environment, both indoors and outdoors. They can cause disease, trigger allergies and allergenic asthma, degrade/discolor building materials, reduce the efficiency of heating/cooling systems, and produce odors, but they often have unknown or unnoticeable effects (even positive effects) on our homes and quality of life.
The purpose of this study was to learn about the seasonal and environmental factors that contribute to the diversity of microbes living in people’s homes. The study spanned one year with sampling at each home at least two times each season for a 24-hour measurement period. Our study population was 15 single-family detached homes on the front range in or near Boulder County. Home volunteers were identified based on their willingness to participate and location within the county. We enrolled a diverse set of housing types and ages located throughout the study area. We limited the sample population to volunteers with homes they have lived in for at least two years, with 2-5 occupants, a living space between 1,400 – 3,000 square feet, and are non-smoking. We had roughly equal numbers of homes with and without centralized HVAC systems, children, pets, plants, and types of heating/cooking fuel sources.
Twice each season the research team visited the homes to collect detailed 24-h measurements of indoor and outdoor environmental quality, and collect air and surface samples for microbial sequencing using the Illumina HiSeq platform. Environmental data included temperature, humidity, carbon dioxide, carbon monoxide, and particulate matter (PM10/PM2.5). Surface swab samples were taken from six locations: top of exterior and interior door sills, kitchen surface where food is prepared, used pillow case, floor near the indoor air sampling station, and face of a HVAC air filter. Investigators documented the building infrastructure with a walk-through inspection. Volunteer participants completed a questionnaire and activity diary for the sample period. The two paper summarizing this work can be found here: Clements at al. 2018 and Emerson et al., 2017.
This detailed study is an adjunct to a large nationwide study by PIs Noah Fierer, University of Colorado Boulder, and Rob Dunn, North Carolina State University. The nationwide study aimed to determine how and why house-associated microbial communities vary across >1,500 homes throughout the United States. They compared bacterial and fungal communities found in homes that represented a wide range of characteristics from urban, suburban, and rural locations in the U.S. Home volunteers filled out a web-based questionnaire and submitted four sample swabs from pre-identified locations in the home: outside doorsill, interior doorsill, kitchen surface where food is prepared, and a used pillow case. The swabs were analyzed for bacteria and fungi using the high-throughput DNA sequencing on the Illumina HiSeq platform. A summary of some of the results of this work can be found here: Barberan et al., 2015.
These studies of microbial diversity in homes, with detailed characterization, across locations or seasons increases our fundamental understanding of the microbial ecology of the indoor environment, the factors that shape the biogeographic patterns exhibited by the microbes, and the likely sources of microbes with whom we share our home.