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

Indoor/Outdoor airborne microbiome characteristics in residential areas across four seasons and its indoor purification

Bioaerosols are more likely to accumulate in the residential environment, and long-term inhalation may lead to a variety of diseases and allergies. Here, we studied the distribution, influencing factors and diffusion characteristics of indoor and outdoor microbiota pollution in six residential buildings in Guangzhou, southern China over a period of one year. The results showed that the particle sizes of bioaerosol were mainly in the range of inhalable particle size (<4.7 μm) with a small difference among four seasons (74.61 % ± 2.17 %). The microbial communities showed obvious seasonal differences with high abundance in summer, but no obvious geographical differences. Among them, the bacteria were more abundant than the fungi. The dominant microbes in indoor and outdoor environments were similar, with Anoxybacillu, Brevibacillus and Acinetobacter as the dominant bacteria, and Cladosporium, Penicillium and Alternaria as the dominant fungi. The airborne microbiomes were more sensitive to temperature and particulate matter (PM2.5, PM10) concentrations. Based on the Sloan neutral model, bacteria were more prone to random diffusion than fungi, and the airborne microbiome can be randomly distributed in indoor and outdoor environments and between the two environments in each season. Bioaerosol in indoor was mainly from outdoor. The health risk evaluation showed that the indoor inhalation risks were higher than those outdoor. The air purifier had a better removal efficiency on 1.1-4.7 μm microorganisms, and the removal efficiency on Gram-negative bacteria was better than that on Gram-positive bacteria. This study is of great significance for the risk assessment and control of residential indoor bioaerosol exposure.

Risk of fungal exposure in the homes of patients with hematologic malignancies

BACKGROUND

Patients with hematological malignancies are at a high risk of developing invasive fungal infections (IFI) because they undergo several cycles of treatment leading to episodes of neutropenia. In addition, they alternate between hospital stays and periods spent at home. Thus, when an IFI is diagnosed during their hospital stays, it is highly challenging to identify the origin of the fungal contamination. The objective of this study was to analyze at home fungal exposure of 20 patients with leukemia by taking air and water samples in their living residence.

METHODS

Air was sampled in 3 rooms of each home with a portable air system impactor. Tap water was collected at 3 water distribution points of each home. For positive samples, fungi were identified by mass spectrometry or on the basis of their morphological features.

RESULTS

85 % of homes revealed the presence in air of Aspergillus spp. and those belonging to the section Fumigati presented the highest concentrations and the greatest frequency of isolation. Concerning mucorales, Rhizopus spp. and Mucor spp. were isolated in air of 20 % and 5 % of dwellings, respectively. In 4 homes, more than 70 % of the fungal species identified in air were potential opportunists; these were mainly Aspergillus spp. with concentrations greater than 20 cfu/m3. The water samples revealed the presence of Fusarium in 3 dwellings, with concentrations up to 80 cfu/L. Finally, for one patient, fungal species isolated during a period of hospitalization were phenotypically similar to those isolated in samples taken at home. For a second patient, a PCR Mucorale was positive on a sample of bronchoalveolar fluid while air samples taken at his home also revealed also the presence of mucorales.

CONCLUSION

The presence of opportunistic fungal species in the air of all the explored homes suggests the need for strengthened preventive measures in the home of immunocompromised patients. It would be interesting to compare the fungi isolated (from patients and from their environment) by genotyping studies aimed at specifying the correspondence existing between fungal species present in the patients' homes and those responsible for IFI in the same patients.

Environmental factors and particle size shape the community structure of airborne total and pathogenic bacteria in a university campus

Given the dense population on university campuses, indoor and outdoor airborne bacterial contamination may lead to the rapid spread of diseases in a university environment. However, there are few studies of the characteristics of airborne and pathogenic bacterial communities in different sites on a university campus. In this study, we collected particulate matter samples from indoor and outdoor locations at a university in Bengbu City, Anhui Province, China, and analyzed the community characteristics of airborne and pathogenic bacteria using a high-throughput sequencing technique. The results showed that the composition of the dominant airborne and pathogenic bacterial communities was consistent among sites at the phylum and genus levels, with differences in their relative abundance. There were significant differences in the structure of the airborne and pathogenic bacterial communities between indoor and outdoor sites (p < 0.05). An analysis of similarities (ANOSIM) indicated that the structure of airborne bacterial communities in indoor sites was influenced by the room occupancy rate, ventilation conditions, and the extent of indoor furnishing (p < 0.05), while the structure of pathogenic bacterial communities was influenced by the number of individuals and spatial dimensions (p < 0.05). The impact of particle size on the structure of airborne and pathogenic bacterial communities was relatively minor. A total of 194 suspected pathogenic bacterial species were identified, accounting for 0.0001-1.3923% of the total airborne bacteria, all of which were conditional pathogens. Among them, Saccharopolyspora rectivirgula, Acinetobacter johnsonii, and Moraxella osloensis exhibited relatively high relative abundance, accounting for 24.40, 16.22, and 8.66% of the total pathogenic bacteria, respectively. Moreover, 18 emerging or re-emerging pathogenic bacterial species with significant implications for human health were identified, although their relative abundance was relatively low (0.5098%). The relative abundance of pathogenic bacteria in indoor environments was significantly higher than outdoors, with the laboratory and dormitory having the highest levels. The findings of this study provide valuable guidance for the prevention and control of airborne bacterial contamination and the associated health risks in both a campus environment and other public spaces with high occupancy rates.

Airborne bacterial species in indoor air and association with physical factors

The aim of this study is to obtain knowledge about which cultivable bacterial species are present in indoor air in homes, and whether the concentration and diversity of airborne bacteria are associated with different factors. Measurements have been performed for one whole year inside different rooms in five homes and once in 52 homes. Within homes, a room-to-room variation for concentrations of airborne bacteria was found, but an overlap in bacterial species was found across rooms. Eleven species were found very commonly and included: Acinetobacter lowffii, Bacillus megaterium, B. pumilus, Kocuria carniphila, K. palustris, K. rhizophila, Micrococcus flavus, M. luteus, Moraxella osloensis and Paracoccus yeei. The concentrations of Gram-negative bacteria in general and the species P. yeei were significantly associated with the season with the highest concentrations in spring. The concentrations of P. yeei, K. rhizophila and B. pumilus were associated positively with relative humidity (RH), and concentrations of K. rhizophila were associated negatively with temperature and air change rate (ACR). Micrococcus flavus concentrations were associated negatively with ACR. Overall, this study identified species which are commonly present in indoor air in homes, and that the concentrations of some species were associated with the factors: season, ACR and RH.

Comparison of airborne bacteria and fungi in different built environments in selected cities in five climate zones of China

Bioaerosols in different built environments and climate zones have unique effects on occupant health, which demands comparisons of their characteristics to make targeted control measures. This study investigated bioaerosol distribution in five different climate zones across China with four building types (n = 686 rooms). The results showed significant disparities in bioaerosol concentrations among various buildings and climate zones. The bacterial concentrations in residences (536 ± 647 CFU/m³) were significantly higher than in schools, offices, and hospitals owing to different built environments and human activities. The highest mean value of fungal concentration was found in schools (826 ± 955 CFU/m³) due to their greater landscaping area. The bacterial concentrations in the cold zone (307 ± 506 CFU/m³) and the hot summer and cold winter zone (214 ± 180 CFU/m³) were significantly lower than in the other three climate zones. The fungal concentrations in the severe cold zone (709 ± 900 CFU/m³) and the hot summer and warm winter zone (1094 ± 832 CFU/m³) were significantly higher than in the other three climate zones; the lower the indoor temperature (T) and the higher the air exchange rate, the lower the indoor airborne bacterial concentration; the lower the relative humidity (RH), the lower the indoor airborne fungi. In addition, a higher air exchange rate could also reduce the effect of occupant density on indoor bacterial concentration. The results of this study provide valuable data on bioaerosol profiles in various built environments and climate zones and highlight the significance of T, RH, and air exchange rate on indoor bioaerosol concentrations.

Microfiber-loaded bacterial community in indoor fallout and air-conditioner filter dust

Microfibers (MFs) are widely existed in indoor air; however, characteristic of microbiota on MFs is largely unknown. In this study, air-borne MFs were collected from fallout or air-conditioner (AC) filter dust in three types of indoor space including living room, dormitory and office. Both plastic and natural MFs were identified by Fourier transform infrared spectroscopy. Ultramicroscopic observation showed dense biofilms adhering on surfaces of MFs. Fallout MFs contained more bacteria but fewer fungi than MFs from AC filter dust. MFs-loaded bacteria were of highest abundance in living rooms, following dormitories and offices. Bacterial community and its diversity were further analyzed by 16S rRNA High-throughput sequencing. Up to 4540 of bacterium OTUs were shared in these MFs samples, unique OTUs in fallout and AC filter samples accounting for 26.3 % and 25.7 % of the total. Compared to MFs fallout, AC filter MFs contained more species of pathogenic bacteria, such as Betaproteobacteriales and Ralstonia, with obviously different β-diversity between two groups. Phenotypic analysis showed that fallout and AC filter MFs bacteria presented high index values of film formation, oxidative stress tolerance and potential pathogenicity. Overall, these results suggest that abundant bacteria including pathogen can be loaded on MFs, and would pose health risks through delivery of indoor MFs.

Opportunistic Mycobiota of Dust in Cities of Different Climate Zones: Murmansk and Moscow

For the first time, mycological analysis of dust, including assessment of opportunistic fungal species, was carried out for the urban ecosystems of air, vegetation, and paved surfaces in different climate areas (the cities of Murmansk and Moscow). The combined effect of environmental factors (climate, functional zone, and substrate type) on qualitative and quantitative parameters of micromycete communities was assessed using MANOVA and cluster analysis. It was found that the abundance of culturable mycobiota in the air, on tree leaves, and on paved surfaces was lower in Murmansk than in Moscow. In both cities, approximately a half of fungal species were opportunistic pathogens. The relative abundance of opportunistic fungi of the BSL-2 group was higher in the air of the traffic zone in both cities and of the residential zone in Moscow. In the residential and traffic zones of Moscow, the most abundant species in the air in on the road dust were Aspergillus fumigatus and A. niger, while in Murmansk communities were dominated by members of the genera Cephalosporium, Scopulariopsis, and Trichoderma, which are less pathogenic for humans. The most significant factors affecting the abundance and species diversity of micromycetes, including opportunistic fungi, were the substrate type (air, leaves, or paved surfaces) and the climate, while the effect of the functional zone was not significant. The recreation zones of cities located in different climate regions are the most favorable for humans due to lower abundance of opportunistic fungi in the air and to lack of micromycetes of the BSL-2 and BSL-3 groups. However, the abundance of potentially pathogenic species on the surfaces of leaves and roads in this zone was higher than in the air. Therefore, it can be recommended that city residents minimize their contact with the leaves surface and road pavements, which is especially relevant for toddlers, so as to diminish the probability of encountering opportunistic mycobiota that potentially represents a health hazard.

Exposure Assessment of Airborne Bacteria and Fungi in the Aircraft

Objective

The exposure levels of disease-causing bacteria and germs were assessed on aircraft cleaning workers on multiple different aircrafts.

Method

Five measuring points were selected depending on the aircraft types. Four aircraft cleaning agencies were selected for the test. Aircraft cleaning work was classified as intensive cleaning and general cleaning work. Ventilation in aircraft when sampling during the cleaning operation was categorized into forced ventilation and natural ventilation. The collection of airborne microorganisms was made through inertial impactors which were installed 1.5 meters above the bottom of the aircraft. The airborne bacteria and fungus growth badges were selected by Trytpic Soy Agar and Sabouraud Dextrose Agar.

Results

The average concentrations of bacteria in the air were higher in the order of small, medium, and large airplanes. Rainy days had higher concentrations inside and outside the aircraft as compared to those in sunny days. Regarding ventilation, concentrations in natural ventilation were higher than concentrations in forced ventilation. According to the type of work, the concentrations in the intensive cleaning groups (cleaning one plane a day) were lower than those of the ordinary cleaning groups (cleaning several planes per day).

Conclusion

The concentration levels of airborne bacteria and fungi in the aircraft surveyed were lower than the indoor environmental standards of Korea (800 cfu/m³ and 500 cfu/m³). The average concentrations of bacteria in the air and fungi in the air were highest in small aircraft owned by Company D.

Indoor formaldehyde levels in residences, schools, and offices in China in the past 30 years: A systematic review

Exposure to formaldehyde causes a variety of adverse health outcomes, while the distributions of indoor formaldehyde in different building types are still not clear in China. In this study, based on the systematic review of previously published data and Monte Carlo simulation, we assessed geographical and temporal distributions of indoor formaldehyde concentrations in residences, schools, and offices across China. A total of 397 studies covered 34 provincial-level regions since 1986 were collected. The results showed that indoor formaldehyde concentrations in residences, schools, and offices in nationwide were decreasing over years due to the publishment of indoor air quality standards since 2002. During 2011 to 2015, the median concentrations of indoor formaldehyde in newly renovated residences, schools, and offices were 153 μg/m³ , 163 μg/m³ , and 94 μg/m³ , with an exceeding rate of 82%, 46%, and 91% considering a standard threshold of 100 μg/m³ at that time, while the exceeding rate was less than 5% for buildings that were renovated beyond one year. Our findings release the temporal trends and geographic distributions of indoor formaldehyde concentrations in residences, schools, and offices in China in the past 30 years, and provide basic data for the comprehensive evaluation of disease burden attributable to indoor formaldehyde exposure.

Survey of Airborne Microorganisms in an Arcade-Type Traditional Market in Anseong, South Korea

We aimed to analyze airborne microorganisms and assess air quality, temperature, and relative humidity at “J” Market, an arcade-type traditional market in Anseong (South Korea). Measurements were taken 16 times, twice per quarter (January, April, July, and October), at both the entrance and intersection of the market in 2020. The concentrations of airborne bacteria and fungi at the entrance and intersection were highest in October and lowest in April; however, they were below the recommended indoor levels (airborne bacteria: <800 CFU/m3, airborne fungi: <500 CFU/m3) in January (second measurement) and April (first and second measurements). The concentrations of microbes during the first measurement in January and both measurements in July and October exceeded the allowed limits. The concentration of microorganisms exceeded the acceptable levels at relative humidity ≥60%. At all time points, except during the eighth survey, when the microorganisms were too numerous to count, microbial concentrations were higher at the intersection than at the entrance. It was confirmed that the microorganisms detected in this experiment were 26 species of bacteria and 21 species of fungi. Three of the four species of bacteria and fungi detected in more than 50% of the 16 experimental results were pathogenic. Our findings suggest that air purification systems must be installed in the market to improve sanitary conditions.

Seasonal variation of aerosol fungal community structure in reed constructed wetlands

In recent years, the impact of biological aerosols produced by sewage treatment plants on air quality and human health has become a hot spot of concern. Airborne fungi were characterized via KC-1000 large-flow air sampler and Anderson-type six-stage sampler, at free surface flowing reed constructed wetland located in Qingdao City, Shandong Province. The high-throughput sequencing technology and fungal culture-dependent method were selected to analyze the composition and dynamic changes of the fungal community attached to the atmospheric particulate matter in the free surface flow constructed wetland. The results showed that the aerosol concentration of fungi in the constructed wetlands varied from 587 to approximately 3382 CFU m^-3, with a peak at the range of 1.10 to 2.10 μm particle size, and the particles (< 4.70 μm) that easily entered the lungs accounted for 57.03 ~ 96.03%. Significant seasonal differences in fungal richness and community diversity were found. The particle size distribution of fungi in atmospheric particles was not obvious. Fungal genera in the atmospheric particulate matter were mainly driven by humidity. However, other factors, i.e., temperature, NO₂, SO₂, and PM₁₀ contents, also contributed.

Aerosols and Bacteria From Hand Washing and Drying in Indoor Air

Effective hand drying is an important part of hand hygiene that can reduce the risk of infectious disease transmission through cross-contamination of surfaces by wet hands. However, hand drying methods may also cause aerosolisation of pathogenic microorganisms if they are present in washed hands. This study investigated experimentally the impact of washing hands and different hand drying methods on the concentration and size distribution of aerosols and bacteria in indoor air. In this experiment, aerosol and bacteria concentrations were measured in indoor air while volunteers rinsed their hands with water or washed with soap and water prior to drying them with paper towels or jet air dryers. Results showed that the concentration of aerosols and bacteria in air increased with people walking in the room and washing hands, with a further increase during the hand drying process. The concentration of aerosols decreased with particle size, with maximum concentrations after drying hands of 6.63 × 10⁶ ± 6.49 × 10⁵ and 2.28 × 10⁴ ± 9.72 × 10³ particles m⁻³ for sizes 0.3 to <0.5 and ≥5.0 μm, respectively. The concentration of bacteria in indoor air after drying hands increased to a maximum of 3.81 × 10² ± 1.48 × 10² CFU m⁻³ (jet air dryers) and 4.50 × 10² ± 4.35 × 10¹ CFU m⁻³ (paper towels). This study indicates that the increase of aerosols and bacteria in air after drying hands with jet air dryers or paper towels are comparable and not statistically different from concentrations associated with walking and washing hands in the same environment. This work can support the development of hand hygiene practices and guidelines for public washrooms.

Quantitative distribution of human exhaled particles in a ventilation room

Respiratory viruses can be attached to human exhaled particles and spread from person to person through respiratory activities. The purpose of this study is to obtain the quantitative description formula of human exhaled particles in the ventilated room through amount number of numerical simulation calculations and regression statistical analysis of the simulated data. In this study, a combination of numerical simulation and laboratory experiments was used, and the results were tallied preferably. Bacillus subtilis was released as a release source to investigate the migration and distribution of bioaerosol. The results show that under the condition of high air supply velocity, due to the disturbance of human respiration and airflow, the diffusion velocity of exhaled particles was faster and the diffusion range is larger than that of low air supply velocity within the same time frame. No matter where the location of the manikin was in the room, the exhaled particles would spread to the whole room in at least 900 s. The method used in this study could be used to predict the distribution of human exhaled particles concentration in different indoor spaces, such as public transport and hospitals. These findings could provide valuable reference for the location of indoor air purifiers, which plays a guiding role in the construction of a healthy indoor environment.

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

Exposure to bioaerosols poses important health effects on occupants. To elucidate seasonal and room variations of household airborne bacteria, this study investigated 30 residential homes during summer and winter throughout Nanjing, Southeast China, with a humid subtropical climate. Culturing and 16S rDNA sequencing methods were combined in this study. Results showed that the community structure and composition in the same season but different homes show similarity, however, they in the same home but in different seasons show a huge difference, with Sphingomonas (25.3%), Clostridium (14.8%), and Pseudomonas (7.6%) being the dominant bacteria in summer, and Pseudomonas (57.1%) was dominant bacteria in winter. Culturable concentrations of bacteria were also significantly higher in summer (854 ± 425 CFU/m³ ) than in winter (231 ± 175 CFU/m³ ), but difference by home or room was relatively minor. More than 80% of culturable bacteria (<4.7 μm) could penetrate into lower respiratory tract. The seasonal variations of bacterial community and concentrations were closely associated with seasonal variations of temperature, humidity, and PM_2.5 . Higher concentrations and larger sizes were observed in the bathroom and kitchen, typically with higher humidity than other rooms.