Transmission of Airborne Bacteria across Built Environments and Its Measurement Standards: A Review

Abstract

Human health is influenced by various factors including microorganisms present in built environments where people spend most of their lives (approximately 90%). It is therefore necessary to monitor and control indoor airborne microbes for occupational safety and public health. Most studies concerning airborne microorganisms have focused on fungi, with scant data available concerning bacteria. The present review considers papers published from 2010 to 2017 approximately and factors affecting properties of indoor airborne bacteria (communities and concentration) with respect to temporal perspective and to multiscale interaction viewpoint. From a temporal perspective, bacterial concentrations in built environments change depending on numbers of human occupancy, while properties of bacterial communities tend to remain stable. Similarly, the bacteria found in social and community spaces such as offices, classrooms and hospitals are mainly associated with human occupancy. Other major sources of indoor airborne bacteria are (i) outdoor environments, and (ii) the building materials themselves. Indoor bacterial communities and concentrations are varied with varying interferences by outdoor environment. Airborne bacteria from the outdoor environment enter an indoor space through open doors and windows, while indoor bacteria are simultaneously released to the outer environment. Outdoor bacterial communities and their concentrations are also affected by geographical factors such as types of land use and their spatial distribution. The bacteria found in built environments therefore originate from any of the natural and man-made surroundings around humans. Therefore, to better understand the factors influencing bacterial concentrations and communities in built environments, we should study all the environments that humans contact as a single ecosystem. In this review, we propose the establishment of a standard procedure for assessing properties of indoor airborne bacteria using four factors: temperature, relative humidity (RH), air exchange rate, and occupant density, as a minimum requirement. We also summarize the relevant legislation by country. Choice of factors to measure remain controversial are discussed.

Viruses in the Built Environment (VIBE) meeting report

“…While recent studies have shed light on the microbiome of "traditional" built environments, including homes, offices, schools, medical facilities, and farms [55,78] [79,80], other types of built environments have received less attention. For example, very little is known about the virome of aquatic and outdoor built environments, such as aquatic engineered systems and water-based amusement parks created for recreation or food production.…”

Size resolved characteristics of urban and suburban bacterial bioaerosols in Japan as assessed by 16S rRNA amplicon sequencing

“…As shown in Fig. 4 , LEfSe analysis showed that the high abundance of human skin-associated bacteria, such as Propionibacterium, Staphylococcus , and Corynebacterium , may be a feature of urban site 23 , 24 . This situation could indicate that outdoor bacterial communities were influenced by bacteria in the built environment.…”

“…Whereas, the high abundance of bacteria associated with soil and plants, such as Methylobacterium and Sphingomonas , may be a feature of suburban site 24 . These five bacterial genera have been frequently detected in outdoor and indoor air 23 – 25 . The genus Propionibacterium is a Gram-positive, anaerobic, rod-shaped bacteria that produces propionic acid as its end product of fermentation.…”

Skin Microbiome Analysis for Forensic Human Identification: What Do We Know So Far?

“…The particular composition of human microbial communities is influenced by many factors, such as environment [19,20], development, presence, or absence of diseases [21], habits [22], relationships [12], nutrition [23], and health status in general. Additionally, a bidirectional influence was shown; while environmental bacteria can alter the microbiomes of people who spend their time in there, humans shed bacteria from their body surface into the surrounding environment, changing its bacterial composition [24,25]. Many studies demonstrated how human microbial signatures can be recovered in several indoor or outdoor settings, such as houses [19,26], offices [27], healthcare facilities [28], classrooms [29], dormitory rooms [30,31], restrooms [32], and subways [33].…”