Size-resolved emission rates of airborne bacteria and fungi in an occupied classroom

The role of human occupancy as a source of indoor biological aerosols is poorly understood. Size-resolved concentrations of total and biological particles in indoor air were quantified in a classroom under occupied and vacant conditions. Per-occupant emission rates were estimated through a mass-balance modeling approach, and the microbial diversity of indoor and outdoor air during occupancy was determined via rDNA gene sequence analysis. Significant increases of total particle mass and bacterial genome concentrations were observed during the occupied period compared to the vacant case. These increases varied in magnitude with the particle size and ranged from 3 to 68 times for total mass, 12-2700 times for bacterial genomes, and 1.5-5.2 times for fungal genomes. Emission rates per person-hour because of occupancy were 31 mg, 37 × 10(6) genome copies, and 7.3 × 10(6) genome copies for total particle mass, bacteria, and fungi, respectively. Of the bacterial emissions, ～18% are from taxa that are closely associated with the human skin microbiome. This analysis provides size-resolved, per person-hour emission rates for these biological particles and illustrates the extent to which being in an occupied room results in exposure to bacteria that are associated with previous or current human occupants. PRACTICAL IMPLICATIONS: Presented here are the first size-resolved, per person emission rate estimates of bacterial and fungal genomes for a common occupied indoor space. The marked differences observed between total particle and bacterial size distributions suggest that size-dependent aerosol models that use total particles as a surrogate for microbial particles incorrectly assess the fate of and human exposure to airborne bacteria. The strong signal of human microbiota in airborne particulate matter in an occupied setting demonstrates that the aerosol route can be a source of exposure to microorganisms emitted from the skin, hair, nostrils, and mouths of other occupants.     

Assessment of airborne bacteria and fungi in food courts

A study was undertaken to determine the effect of variations in temperature, relative humidity, occupancy density and location (indoor/outdoor) on the concentrations of viable airborne bacterial and fungal spores at an air-conditioned and a non air-conditioned food stall in Singapore. Typically, bioaerosols consisted of 50.5% bacteria and 49.5% fungi in the indoor environment. In contrast, for the outdoor environment, bacteria on an average only accounted for 20.6% of culturable airborne microorganisms whereas fungal concentrations were 79.4%. Results on bioaerosol size distributions revealed that 67% of indoor bacteria and 68% of outdoor bacteria, 85% of indoor fungi and 68% of outdoor fungi were associated with fine mode particulates (<3.3 μm). Occupant density was the key factor that affected indoor airborne bacteria concentrations while concentrations of outdoor airborne bacteria depended strongly on ambient temperature. Indoor fungal concentration was positively correlated to relative humidity whereas outdoor fungal concentration was positively correlated to relative humidity and negatively correlated to temperature. The study also compared the biological air quality between a non air-conditioned food stall (Stall A) and an air-conditioned food stall (Stall B). The dining area of the former had lower bacterial concentrations as compared to the latter, while fungal spore’s concentrations showed a reverse trend. The dominant airborne bacteria genera were Staphylococcus, Pseudomonas, Alcaligens, and Corynebacterium whereas Penicillium, Aspergillus and Cladosporium were the most common fungal genera and groups in both food stalls.     

建筑室内外空气真菌浓度相关性案例测试分析

选取某高校学生办公室进行室内外空气真菌浓度相关性和粒径的研究.结果表明:室内空气真菌浓度变化范围为1 698～4 429 cfu/m3,最大值出现在12:00;室外浓度范围为3 569?29 452 cfu/m3,最大值也出现在12:00.室内外空气真菌浓度比值均小于1,Spearman相关性分析显示室内外空气真菌呈显...     

Identification of airborne bacterial and fungal community structures in an urban area by T-RFLP analysis and quantitative real-time PCR

This study explores the characteristics of bacterial and fungal communities of total suspended particles (TSP) in the atmosphere by using various molecular methods. TSP samples were collected on a glass fiber filter at an urban location in the middle of the Korean Peninsula (Seoul) between middle autumn and early winter in 2007. From the aerosol samples, DNA could be extracted and DNA sequences were determined for bacteria and fungi. Terminal restriction length polymorphism (T-RFLP) analysis was applied to analyze the community structure of them. To estimate the concentration of DNA originating from bacterial and fungal communities, we used the quantitative real-time polymerase chain reaction (Q-PCR). Sequence analyses were also used to determine the identity of biological organisms. The number of bacteria and fungi in the air were between 5.19 × 10¹ and 4.31 × 10³ cells m^− 3 and from 9.56 × 10¹ to 4.22 × 10⁴ cells m^− 3, respectively and bacterium/fungus ratios ranged from 0.09 to 0.76 across the seven sampling dates. Most of the bacterial sequences found in our TSP samples were from Proteobacteria, Actinobacteria, Firmicutes, and Bacteroidetes. The fungal sequences were characteristic for Ascomycota, Basidiomycota, and Glomeromycota which are known to actively discharge spores into the atmosphere. The plant sequences could be also detected. We found that large shifts in the community structure of bacteria and fungi were present in our TSP samples collected on different dates. The results demonstrated that in our TSP samples collected at the urban site; (1) there were very diverse bacterial and fungal groups including potential pathogens and allergens and (2) there were temporal shifts in both bacterial and fungal communities in terms of both diversity and abundances across an inter-seasonal period.     

Ultrafine particle concentrations and exposures in six elementary school classrooms in northern California

Potential health risks may result from environmental exposure to ultrafine particles (UFP), i.e., those smaller than 0.1 μm in diameter. One important exposure setting that has received relatively little attention is school classrooms. We made time-resolved, continuous measurements of particle number (PN) concentrations for 2-4 school days per site (18 days total) inside and outside of six classrooms in northern California during normal occupancy and use. Additional time-resolved information was gathered on ventilation conditions, occupancy, and classroom activity. Across the six classrooms, average indoor PN concentrations when students were present were 5200-16,500/cm(3) (overall average 10,800/cm(3)); corresponding outdoor concentrations were 9000-26,000/cm(3) (overall average 18,100/cm(3)). Average indoor levels were higher when classrooms were occupied than when they were unoccupied because of higher outdoor concentrations and higher ventilation rates during occupancy. In these classrooms, PN exposures appear to be primarily attributable to outdoor sources. Indoor emission sources (candle use, cooking on an electric griddle, use of a heater, use of terpene-containing cleaning products) were seen to affect indoor PN concentrations only in a few instances. The daily-integrated exposure of students in these six classrooms averaged 52,000/cm(3) h/day for the 18 days monitored. PRACTICAL IMPLICATIONS: This study provides data and insight concerning the UFP exposure levels children may encounter within classrooms and the factors that most significantly affect these levels in an urban area in northern California. This information can serve as a basis to guide further study of children's UFP exposure and the potential associated health risks.     

Influence of housing characteristics on bacterial and fungal communities in homes of asthmatic children

Variations in home characteristics, such as moisture and occupancy, affect indoor microbial ecology as well as human exposure to microorganisms. Our objective was to determine how indoor bacterial and fungal community structure and diversity are associated with the broader home environment and its occupants. Next‐generation DNA sequencing was used to describe fungal and bacterial communities in house dust sampled from 198 homes of asthmatic children in southern New England. Housing characteristics included number of people/children, level of urbanization, single/multifamily home, reported mold, reported water leaks, air conditioning (AC) use, and presence of pets. Both fungal and bacterial community structures were non‐random and demonstrated species segregation (C‐score, P < 0.00001). Increased microbial richness was associated with the presence of pets, water leaks, longer AC use, suburban (vs. urban) homes, and dust composition measures (P < 0.05). The most significant differences in community composition were observed for AC use and occupancy (people, children, and pets) characteristics. Occupant density measures were associated with beneficial bacterial taxa, including Lactobacillus johnsonii as measured by qPCR. A more complete knowledge of indoor microbial communities is useful for linking housing characteristics to human health outcomes. Microbial assemblies in house dust result, in part, from the building's physical and occupant characteristics.     

Particle size distributions and concentrations of airborne endotoxin using novel collection methods in homes during the winter and summer seasons

A comparison study of novel collection methods for airborne bacteria and endotoxin was performed in an environmentally controlled chamber and in pilot-field studies. Airborne particulate matter was collected in swirling liquid impingers, air-monitoring filter cassettes, and with a micro-orifice uniform deposit impactor (MOUDI) to evaluate aerodynamic particle size distributions. Environmentally controlled chamber studies showed that impingers and MOUDI recovered significantly more airborne bacteria than filter cassettes, whereas collection methods for airborne endotoxin were not significantly different. In addition, total airborne bacteria and endotoxin concentrations were measured indoors and outdoors at three homes in Boulder, CO during winter and summer seasons. Indoor concentrations collected with the three different samplers were significantly different for airborne endotoxin, but not for airborne bacteria. Total airborne bacteria indoors and outdoors significantly varied with seasons. Outdoor airborne endotoxin significantly varied with season; no seasonal variation was seen for indoor airborne endotoxin. Indoor and outdoor levels were not significantly different for both airborne bacteria and endotoxin. The largest proportion of endotoxin was associated with airborne particulate matter <1 microm. PRACTICAL IMPLICATIONS: This study compared sampling methods for airborne endotoxin, a potent and nonspecific immune system stimulant which can induce negative health responses. The data from this study showed that swirling liquid impingers and the micro-orifice uniform deposit impactor (MOUDI) recovered significantly more airborne endotoxin than the more widely adapted method of collecting airborne endotoxin on membrane filters, when collection methods were applied in realistic settings (homes). The MOUDI measured the particle size distribution of airborne endotoxin, which can be useful for determining endotoxin respiratory toxicity and its health effects.     

A study of local electrostatic filtration and main pre-filtration on airborne and surface dust levels in air-conditioned office premises

The impact of electrostatic precipitation as a useful form of particulate filtration in the breathing zone is investigated in an intervention study in an air-conditioned commercial office in central London. Surface dust deposition and airborne dust levels are measured in the open plan zones of two floors--a control floor and a floor where the intervention is effected. The intervention consists of a sequence of weekly scenarios where the main pre-filters of the air-handling unit are switched between new and old filters, and where the electrostatic filters, located as uniformly as practicable on the open plan areas, are switched on or off. This 2 x 2 set of interventions is repeated over 4 cycles. It was found that the breathing zone filtration (BZF) by electrostatic precipitators reduces airborne dust significantly and appears to be more efficient in reducing smaller sized particles. No significant effect of BZF filters in reducing surface dust deposition was detected.