Indoor exposure levels of bacteria and fungi in residences, schools, and offices in China: A systematic review

Abstract

Microbes in buildings have attracted extensive attention from both the research community and the general public due to their close relationship with human health. However, there still lacks comprehensive information on the indoor exposure level of microbes in China. This study systematically reviews exposure levels, the community structures, and the impact factors of airborne bacteria and fungi in residences, schools, and offices in China. We reviewed the major literature databases between 1980 and 2019 and selected 55 original studies based on a set of criteria. Results show that the concentration of indoor bacteria varies from 72.5 to 7500 CFU/m 3 , with a median value of 1000 CFU/m 3 , and the concentration of fungi varies from 12 to 9730 CFU/m 3 , with a median value of 526 CFU/m 3. The concentration level of microbes varies in different climate zones, with higher bacterial concentrations in the severe cold zone, and higher fungal concentrations in the hot summer and warm winter zone. Among different buildings, classrooms have the highest average bacteria and fungi levels. This review reveals that a unified assessment system based on health effects is needed for evaluating the exposure levels of bacteria and fungi.

Combining culturing and 16S rDNA sequencing to reveal seasonal and room variations of household airborne bacteria and correlative environmental factors in nanjing, southeast china

“…Nanjing has a typical humid subtropical climate and is greatly influenced by the East Asian monsoon, creating four distinct seasons with damp conditions throughout the year, which may particularly favor bioaerosols indoors. In a recent study, Guo et al reviewed exposure levels, community structures, and impact factors of airborne bacteria in residences, schools, and offices in China, suggesting that the concentration level of microbes varies in different climate zones, with higher bacteria concentrations in the severe cold zone 50 . Hao et al have measured household culturable bioaerosols in Hangzhou, a nearby city of Nanjing with similar climate, and reported the highest and lowest concentrations of airborne bacteria, respectively, appeared in spring and in winter, 51 which agrees well with that in Beijing 17 .…”

Aerosols and Bacteria From Hand Washing and Drying in Indoor Air

“…There are no international standards that specify limits for bacteria in indoor air, but national or regional guidelines stipulate levels that should not be exceeded, which vary from 5.00 x 10 2 to 1.00 x 10 4 CFU m −3 (24). The results in this study show that walking and washing hands increased the number of bacteria in indoor air compared to just walking.…”

“…The exception was for drying hands with paper towels (after rinsing) compared to walking, and for drying hands with jet air dryer model D (after rinsing and washing) compared to walking or walking and washing hands, which were statistical significant at location 2, possibly because this sampling location was the nearest to the hand drying location. The highest increase in the number of bacteria was for model D, an expected result since this device was placed on the sink, which was wet and may have contained bacteria; however the number of bacteria in air were below acceptable levels, according to regional guidelines for bacteria in indoor air reported by Guo et al (24). For all jet air dryer models tested, the increase of bacteria in air was not statistically different compared to drying hands with paper towels and to washing without drying up hands.…”

Quantitative distribution of human exhaled particles in a ventilation room

“…Considering the spatial distribution of indoor particles is thus helpful in providing a basis for reducing indoor particle concentration and improving indoor air quality, which is of great significance for the accurate design of a healthy indoor environment. To date, the distribution and propagation of aerosols and other apparent properties have been studied in many indoor places, such as public hospitals (Chow and Wang 2012;Sadrizadeh et al 2014;Wang et al 2018), workplaces (Kalogerakis et al 2005;He et al 2011;Zhang et al 2017), houses (Lis and Pastuszka 1997;Jo and Seo 2005;Guo et al 2020), and public restrooms (Lee et al 2012;Kim et al 2014;Sassi et al 2018). At the same time, more in-depth and rigorous researches on aerosols have been carried out.…”