SARS-CoV-2 infection and transmission via the skin to oro-nasal route with the production of bioaerosols in the ferret model.

Direct and indirect transmission of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has been attributed to virus survival in droplets, bioaerosols and on fomites including skin and surfaces. Survival of SARS-CoV-2 variants of concern (Alpha, Beta, Gamma, and Delta) on the skin and virus transference following rounds of skin-to-skin contact were assessed on porcine skin as a surrogate for human skin. SARS-CoV-2 variants were detectable on skin by RT-qPCR after 72 h at biologically relevant temperatures (35.2 °C) with viral RNA (vRNA) detected after ten successive skin-to-skin contacts. Skin-to-skin virus transmission to establish infection in ferrets as a model for mild/asymptomatic SARS-CoV-2 infection in mustelids and humans was also investigated and compared to intranasal ferret inoculation. Naïve ferrets exposed to Delta variant SARS-CoV-2 in a 'wet' or 'dry' form on porcine skin resulted in robust infection with shedding detectable for up to 14 days post-exposure, at comparable viral loads to ferrets inoculated intranasally. Transmission of SARS-CoV-2 to naïve ferrets in direct contact with infected ferrets was achieved, with environmental contamination detected from ferret fur swabs and air samples. Genetic substitutions were identified in bioaerosol samples acquired following single contact passage in ferrets, including Spike, ORF1ab, and ORF3a protein sequences, suggesting a utility for monitoring host adaptation and virus evolution via air sampling. The longevity of SARS-CoV-2 variants survival directly on the skin and skin-to-skin transference, enabling subsequent infection via the skin to oro-nasal contact route, could represent a pathway for SARS-CoV-2 infection with implications to public and veterinary health.

Airborne microbes: sampling, detection, and inactivation.

The human living environment serves as a habitat for microorganisms and the presence of ubiquitous airborne microbes significantly impacts the natural material cycle. Through ongoing experimentation with beneficial microorganisms, humans have greatly benefited from airborne microbes. However, airborne pathogens endanger human health and have the potential to induce fatal diseases. Tracking airborne microbes is a critical prerequisite for a better understanding of bioaerosols, harnessing their potential advantages, and mitigating associated risks. Although technological breakthroughs have enabled significant advancements in accurately monitoring airborne pathogens, many puzzles about these microbes remain unanswered due to their high variability and environmental diffusibility. Consequently, advanced techniques and strategies for special identification, early warning, and efficient eradication of microbial contamination are continuously being sought. This review presents a comprehensive overview of the research status of airborne microbes, concentrating on the recent advances and challenges in sampling, detection, and inactivation. Particularly, the fundamental design principles for the collection and timely detection of airborne pathogens are described in detail, as well as critical factors for eliminating microbial contamination and enhancing indoor air quality. In addition, future research directions and perspectives for controlling airborne microbes are also suggested to promote the translation of basic research into real products.

Fungal Spore Richness and Abundance of Allergenic Taxa: Comparing a Portable Impactor and Passive Trap Indoors and Outdoors in an Urban Setting.

Fungal spores are common airborne allergens, and fungal richness has been implicated in allergic disease. Amplicon sequencing of environmental DNA from air samples is a promising method to estimate fungal spore richness with semi-quantification of hundreds of taxa and can be combined with quantitative PCR to derive abundance estimates. However, it remains unclear how the choice of air sampling method influences these estimates. This study compared active sampling with a portable impactor and passive sampling with a passive trap over different durations to estimate fungal spore richness and the abundance of allergenic taxa. Air sampling was conducted indoors and outdoors at 12 residences, including repeated measurements with a portable impactor and passive traps with 1-day and 7-day durations. ITS2 amplicon sequence data were transformed to spore equivalents estimated by quantitative PCR, repeated active samples were combined, and abundance-based rarefaction was performed to standardize sample coverage for estimation of genus-level richness and spore abundance. Rarefied fungal richness was similar between methods indoors but higher for passive traps with a 7-day duration outdoors. Rarefied abundance of allergenic genera was similar between methods but some genera had lower abundance for passive traps with a 1-day duration, which differed indoors and outdoors indicating stochasticity in the collection of spores on collocated samplers. This study found that similar estimates of fungal spore richness and abundance of allergenic taxa can be obtained using a portable impactor or a passive trap within one day and that increased passive sample duration provides limited additional information.

Bioaerosol size as a potential determinant of airborneE. coliviability under ultraviolet germicidal irradiation and ozone disinfection.

Ultraviolet germicidal irradiation (UVGI) and ozone disinfection are crucial methods for mitigating the airborne transmission of pathogenic microorganisms in high-risk settings, particularly with the emergence of respiratory viral pathogens such as SARS-CoV-2 and avian influenza viruses. This study quantitatively investigates the influence of UVGI and ozone on the viability ofE. coliin bioaerosols, with a particular focus on howE. coliviability depends on the size of the bioaerosols, a critical factor that determines deposition patterns within the human respiratory system and the evolution of bioaerosols in indoor environments. This study used a controlled small-scale laboratory chamber whereE. colisuspensions were aerosolized and subjected to varying levels of UVGI and ozone levels throughout the exposure time (2-6 s). The normalized viability ofE. coliwas found to be significantly reduced by UVGI (60-240µW s cm-2) as the exposure time increased from 2 to 6 s, and the most substantial reduction ofE. colinormalized viability was observed when UVGI and ozone (65-131 ppb) were used in combination. We also found that UVGI reduced the normalized viability ofE. coliin bioaerosols more significantly with smaller sizes (0.25-0.5µm) than with larger sizes (0.5-2.5µm). However, when combining UVGI and ozone, the normalized viability was higher for smaller particle sizes than for the larger ones. The findings provide insights into the development of effective UVGI disinfection engineering methods to control the spread of pathogenic microorganisms in high-risk environments. By understanding the influence of the viability of microorganisms in various bioaerosol sizes, we can optimize UVGI and ozone techniques to reduce the potential risk of airborne transmission of pathogens.

Height-Resolved Analysis of Indoor Airborne Microbiome: Comparison with Floor Dust-Borne Microbiome and the Significance of Shoe Sole Dust.

Exposure to the indoor airborne microbiome is closely related to the air that individuals breathe. However, the floor dust-borne microbiome is commonly used as a proxy for indoor airborne microbiome, and the spatial distribution of indoor airborne microbiome is less well understood. This study aimed to characterize indoor airborne microorganisms at varying heights and compare them with those in floor dust. An assembly of three horizontally and three vertically positioned Petri dishes coated with mineral oil was applied for passive air sampling continuously at three heights without interruption. The airborne microbiomes at the three different heights showed slight stratification and differed significantly from those found in the floor dust. Based on the apportionment results from the fast expectation-maximization algorithm (FEAST), shoe sole dust contributed approximately 4% to indoor airborne bacteria and 14% to airborne fungi, a contribution that is comparable to that from the floor dust-borne microbiome. The results indicated that floor dust may not be a reliable proxy for indoor airborne microbiome. Moreover, the study highlights the need for height-resolved studies of indoor airborne microbiomes among humans in different activity modes and life states. Additionally, shoe sole-dust-associated microorganisms could potentially be a source to "re-wild" the indoor microbiota.

Bacterial Emission Factors: A Foundation for the Terrestrial-Atmospheric Modeling of Bacteria Aerosolized by Wildland Fires.

Wildland fire is a major global driver in the exchange of aerosols between terrestrial environments and the atmosphere. This exchange is commonly quantified using emission factors or the mass of a pollutant emitted per mass of fuel burned. However, emission factors for microbes aerosolized by fire have yet to be determined. Using bacterial cell concentrations collected on unmanned aircraft systems over forest fires in Utah, USA, we determine bacterial emission factors (BEFs) for the first time. We estimate that 1.39 × 1010 and 7.68 × 1011 microbes are emitted for each Mg of biomass consumed in fires burning thinning residues and intact forests, respectively. These emissions exceed estimates of background bacterial emissions in other studies by 3-4 orders of magnitude. For the ∼2631 ha of similar forests in the Fishlake National Forest that burn each year on average, an estimated 1.35 × 1017 cells or 8.1 kg of bacterial biomass were emitted. BEFs were then used to parametrize a computationally scalable particle transport model that predicted over 99% of the emitted cells were transported beyond the 17.25 x 17.25 km model domain. BEFs can be used to expand understanding of global wildfire microbial emissions and their potential consequences to ecosystems, the atmosphere, and humans.

Evaluating the Performance of UV Disinfection across the 222-365 nm Spectrum against Aerosolized Bacteria and Viruses.

Bioaerosols play a significant role in the transmission of many infectious diseases, especially in enclosed indoor environments. Ultraviolet (UV) disinfection has demonstrated a high efficacy in inactivating microorganisms suspended in the air. To develop more effective and efficient UV disinfection protocols, it is necessary to evaluate and optimize the effectiveness of UV disinfection against aerosolized bacteria and viruses across the entire UV spectrum. In this study, we evaluated the performance of UV disinfection across the UV spectrum, ranging from 222 to 365 nm, against aerosolized bacteria and viruses, including Escherichia coli, Staphylococcus epidermidis, Salmonella enterica, MS2, P22, and Phi6. Six commonly available UV sources, including gas discharge tubes and light-emitting diodes with different emission spectra, were utilized, and their performance in terms of inactivation efficacy, action spectrum, and energy efficiency was determined. Among these UV sources, the krypton chloride excilamp emitting at a peak wavelength of 222 nm was the most efficient in inactivating viral bioaerosols. A low-pressure mercury lamp emitting at 254 nm performed well on both inactivation efficacy and energy efficiency. A UV light-emitting diode emitting at 268 nm demonstrated the highest bacterial inactivation efficacy, but required approximately 10 times more energy to achieve an equivalent inactivation level compared with that of the krypton chloride excilamp and low-pressure mercury lamp. This study provides insights into UV inactivation on bioaerosols, which can guide the development of effective wavelength-targeted UV air disinfection technologies and may significantly help reduce bioaerosol transmission in public areas.

Distribution and survival of pathogens from different waste components and bioaerosol traceability analysis in household garbage room.

Household garbage rooms release abundant bioaerosols and are an important source of pathogens; however, information on the distribution and survival patterns of pathogens in different waste components is limited. In this study, a culture method and 16S rRNA high-throughput sequencing were used to determine bacterial communities, culturable pathogens, and human bacterial pathogens (HBPs). The results showed that abundant culturable bacteria were detected in all waste types, and a large number of S. aureus was detected on the surface of recyclable wastes, whereas S. aureus, total coliforms, Salmonella, Enterococcus, and hemolytic bacteria were detected in food waste and other waste. The activities of these detected pathogenic bacteria decreased after 24 h of storage but re-activated within one week. Factors affecting the emergence of pathogens varied with different waste components. Sequencing results showed that Pseudomonas, Acinetobacter, and Burkholderia were abundant in the waste samples, whereas Achromobacter, Exiguobacteriums, Bordetella, and Corynebacterium were the primary pathogens in the bioaerosol and wall attachment. The results of traceability analysis showed that bioaerosol microbes were mainly derived from raw kitchen waste (5.98%) and plastic and paper contaminated with food waste (19.93%) in garbage rooms. In addition, bioaerosols were the main source of microflora in the wall attachment, which possessed high HBP diversity and required more attention. These findings will help in understanding the microbial hazards in different waste components and provide guidance for the control and risk reduction of bioaerosols during waste management and recycling.

Fungal aerosol and particulate matter in horse stables in Poland.

Horses stay in different types of stables; especially during the cold season, they stay inside for most of the day. A stable is also a place where many people spend quite a lot of time either as employees who care for and train horses or as equine enthusiasts. Keeping horses in stables causes their constant exposure to high concentrations of particulate matter (PM) and molds in the air inside these facilities. The study was conducted in Udórz Stud Farm located in the southern region of Poland. It was carried out in two different types of stables: three runners and two box stables. The study continued for 2 years; samples were collected in each season of the year. The following devices were used: a six-stage Andersen-Graseby cascade impactor, the DustTrak™ II Aerosol Monitor 8530. The obtained results allowed for the conclusion that horses kept in box stables are exposed to lower concentrations of molds and yeasts than those kept in runners. Molds dominated in the stable air during humid periods-spring and autumn-while yeasts were more prominent during summer and winter. It was observed that cleaning stables reduces the morphotic elements of fungi in the air, even though it results in a higher level of particulate matter in the stable air. It should be noted that microclimate conditions were optimal for horses practically throughout the whole year. KEY POINTS: • In stables, there is a high level of air intoxication, both by yeast and by mold fungi • The concentrations of fungi in the air depend on the season and the stable cleaning procedure • The PM concentrations depend on the type of stable.

Characteristics and health impacts of bioaerosols in animal barns: A comprehensive study.

Bioaerosols produced during animal production have potential adverse effects on the health of workers and animals. Our objective was to investigate characteristics, antibiotic-resistance genes (ARGs), and health risks of bioaerosols in various animal barns. Poultry and swine barns had high concentrations of airborne bacteria (11156 and 10917 CFU/m3, respectively). Acinetobacter, Clostridium sensu stricto, Corynebacterium, Pseudomonas, Psychrobacter, Streptococcus, and Staphylococcus were dominant pathogenic bacteria in animal barns, with Firmicutes being the most abundant bacterial phylum. Based on linear discriminant analysis effect size (LEfSe), there were more discriminative biomarkers in cattle barns than in poultry or swine barns, although the latter had the highest abundance of bacterial pathogens and high abundances of ARGs (including tetM, tetO, tetQ, tetW sul1, sul2, ermA, ermB) and intI1). Based on network analyses, there were higher co-occurrence patterns between bacteria and ARGs in bioaerosol from swine barns. Furthermore, in these barns, relative abundance of bacteria in bioaerosol samples was greatly affected by environmental factors, mainly temperature, relative humidity, and concentrations of CO2, NH3, and PM2.5. This study provided novel data regarding airborne bio-contaminants in animal enclosures and an impetus to improve management to reduce potential health impacts on humans and animals.

Research advances in microfluidic collection and detection of virus, bacterial, and fungal bioaerosols.

Bioaerosols are airborne suspensions of fine solid or liquid particles containing biological substances such as viruses, bacteria, cellular debris, fungal spores, mycelium, and byproducts of microbial metabolism. The global Coronavirus disease 2019 (COVID-19) pandemic and the previous emergence of severe acute respiratory syndrome (SARS), Middle East respiratory syndrome (MERS), and influenza have increased the need for reliable and effective monitoring tools for bioaerosols. Bioaerosol collection and detection have aroused considerable attention. Current bioaerosol sampling and detection techniques suffer from long response time, low sensitivity, and high costs, and these drawbacks have forced the development of novel monitoring strategies. Microfluidic technique is considered a breakthrough for high performance analysis of bioaerosols. In recent years, several emerging methods based on microfluidics have been developed and reported for collection and detection of bioaerosols. The unique advantages of microfluidic technique have enabled the integration of bioaerosol collection and detection, which has a higher efficiency over conventional methods. This review focused on the research progress of bioaerosol collection and detection methods based on microfluidic techniques, with special attention on virus aerosols and bacterial aerosols. Different from the existing reviews, this work took a unique perspective of the targets to be collected and detected in bioaerosols, which would provide a direct index of bioaerosol categories readers may be interested in. We also discussed integrated microfluidic monitoring system for bioaerosols. Additionally, the application of bioaerosol detection in biomedicine was presented. Finally, the current challenges in the field of bioaerosol monitoring are presented and an outlook given of future developments.

Concern about the risk of aerosol contamination from ultrasonic scaler: a systematic review and meta-analysis.

BACKGROUND: Many instruments used in dentistry are rotary, such as handpieces, water syringes, and ultrasonic scalers that produce aerosols. The spray created by these instruments can carry, in addition to water, droplets of saliva, blood, and microorganisms, which can pose a risk of infections for healthcare professionals and patients. Due to the COVID-19 pandemic, this gained attention. OBJECTIVE: The aim was to carry out a systematic review of the evidence of the scope of the aerosol produced by ultrasonic scaler in environmental contamination and the influence of the use of intraoral suction reduction devices. DESIGN: Scientific literature was searched until June 19, 2021 in 6 databases: Pubmed, EMBASE, Web of science, Scopus, Virtual Health Library and Cochrane Library, without restrictions on language or publication date. Studies that evaluated the range of the aerosol produced by ultrasonic scaler during scaling/prophylaxis and the control of environmental contamination generated by it with the use of low (LVE) and high (HVE) volume evacuation systems were included. RESULTS: Of the 1893 potentially relevant articles, 5 of which were randomized controlled trials (RCTs). The meta-analysis of 3 RCTs showed that, even at different distances from the patient's oral cavity, there was a significant increase in airborne bacteria in the dental environment with the use of ultrasonic scaler. In contrast, when meta-analysis compared the use of HVE with LVE, there was no significant difference (P = 0.40/CI -0.71[-2.37, 0.95]) for aerosol produced in the environment. CONCLUSIONS: There is an increase in the concentration of bioaerosol in the dental environment during the use of ultrasonic scaler in scaling/prophylaxis, reaching up to 2 m away from the patient's mouth and the use of LVE, HVE or a combination of different devices, can be effective in reducing air contamination in the dental environment, with no important difference between different types of suction devices.

Sampling efficiency and nucleic acid stability during long-term sampling with different bioaerosol samplers.

Aerosol microbiome studies have received increased attention as technological advancements have made it possible to dive deeper into the microbial diversity. To enhance biomass collection for metagenomic sequencing, long-term sampling is a common strategy. While the impact of prolonged sampling times on microorganisms' culturability and viability is well-established, its effect on nucleic acid stability remains less understood but is essential to ensure representative sample collection. This study evaluated four air samplers (SKC BioSampler, SASS3100, Coriolis µ, BioSpot-VIVAS 300-P) against a reference sampler (isopore membrane filters) to identify nucleic acid stability during long-term sampling. Physical sampling efficiencies determined with a fluorescent tracer for three particle sizes (0.8, 1, and 3 µm), revealed high efficiencies (> 80% relative to reference) for BioSampler, SASS3100, and BioSpot-VIVAS for all particle sizes, and for Coriolis with 3 µm particles. Coriolis exhibited lower efficiency for 0.8 µm (7%) and 1 µm (50%) particles. During 2-h sampling with MS2 and Pantoea agglomerans, liquid-based collection with Coriolis and BioSampler showed a decrease in nucleic acid yields for all test conditions. BioSpot-VIVAS displayed reduced sampling efficiency for P. agglomerans compared to MS2 and the other air samplers, while filter-based collection with SASS3100 and isopore membrane filters, showed indications of DNA degradation for 1 µm particles of P. agglomerans after long-term sampling. These findings show that long-term air sampling affects nucleic acid stability in both liquid- and filter-based collection methods. These results highlight bias produced by bioaerosol collection and should be considered when selecting an air sampler and interpreting aerosol microbiome data.

A super sandstorm altered the abundance and composition of airborne bacteria in Beijing.

Sandstorm, which injects generous newly emerging microbes into the atmosphere covering cities, adversely affects the air quality in built environments. However, few studies have examined the change of airborne bacteria during severe sandstorm events. In this work, we analyzed the airborne bacteria during one of the strongest sandstorms in East Asia on March 15th, 2021, which affected large areas of China and Mongolia. The characteristics of the sandstorm were compared with those of the subsequent clean and haze days. The composition of the bacterial community of air samples was investigated using quantitative polymerase chain reaction (qPCR) and high-throughput sequencing technology. During the sandstorm, the particulate matter (PM) concentration and bacterial richness were extremely high (PM2.5: 207 µg/m3; PM10: 1630 µg/m3; 5700 amplicon sequence variants/m3). In addition, the sandstorm brought 10 pathogenic bacterial genera to the atmosphere, posing a grave hazard to human health. As the sandstorm subsided, small bioaerosols (0.65-1.1 µm) with a similar bacterial community remained suspended in the atmosphere, bringing possible long-lasting health risks.

Lessons from Dairy Farmers for Occupational Allergy and Respiratory Disease.

PURPOSE OF REVIEW: Exposure to bioaerosols at dairies has long been associated with allergy, respiratory disease, and decreases in lung function. Recent advancements in exposure assessments have aided our understanding on the size distribution and composition of these bioaerosols, but investigations focusing solely on exposures may overlook important intrinsic factors impacting worker's susceptibility to disease. RECENT FINDINGS: In our review, we discuss the most recent studies examining the exposures and genetic factors that contribute to occupational disease in dairy work. We also review more recent concerns in livestock work associated with zoonotic pathogens, antimicrobial resistant genes, and the role of the human microbiome. The studies highlighted in this review demonstrate the need for further research to better understand bioaerosol exposure-response relationships in the context of extrinsic and intrinsic factors, antibiotic-resistant genes, viral pathogens, and the human microbiome to help inform effective interventions that improve respiratory health among dairy farmers.

Pathogenic Bacteria Are the Primary Determinants Shaping PM2.5-Borne Resistomes in the Municipal Food Waste Treatment System.

Bioaerosol pollution poses a substantial threat to human health during municipal food waste (FW) recycling. However, bioaerosol-borne antibiotic-resistant genes (ARGs) have received little attention. Herein, 48 metagenomic data were applied to study the prevalence of PM2.5-borne ARGs in and around full-scale food waste treatment plants (FWTPs). Overall, FWTP PM2.5 (2.82 ± 1.47 copies/16S rRNA gene) harbored comparable total abundance of ARGs to that of municipal wastewater treatment plant PM2.5 (WWTP), but was significantly enriched with the multidrug type (e.g., AdeC/I/J; p < 0.05), especially the abundant multidrug ARGs could serve as effective indicators to define resistome profiles of FWTPs (Random Forest accuracy >92%). FWTP PM2.5 exhibited a decreasing enrichment of total ARGs along the FWTP-downwind-boundary gradient, eventually reaching levels comparable to urban PM2.5 (1.46 ± 0.21 copies/16S rRNA gene, N = 12). The combined analysis of source-tracking, metagenome-assembled genomes (MAGs), and culture-based testing provides strong evidence that Acinetobacter johnsonii-dominated pathogens contributed significantly to shaping and disseminating multidrug ARGs, while abiotic factors (i.e., SO42-) indirectly participated in these processes, which deserves more attention in developing strategies to mitigate airborne ARGs. In addition, the exposure level of FWTP PM2.5-borne resistant pathogens was about 5-11 times higher than those in urban PM2.5, and could be more severe than hospital PM2.5 in certain scenarios (<41.53%). This work highlights the importance of FWTP in disseminating airborne multidrug ARGs and the need for re-evaluating the air pollution induced by municipal FWTP in public health terms.

Behaviour of aerosols and their role in the transmission of SARS-CoV-2; a scoping review.

Covid-19 has triggered an unprecedented global health crisis. The highly contagious nature and airborne transmission route of SARS-CoV-2 virus requires extraordinary measures for its containment. It is necessary to know the behaviour of aerosols carrying the virus to avoid this contagion. This paper describes the behaviour of aerosols and their role in the transmission of SARS-CoV-2 according to published models using a scoping review based on the PubMed, Scopus, and WOS databases. From an initial 530 references, 9 papers were selected after applying defined inclusion criteria. The results reinforce the airborne transmission route as a means of contagion of the virus and recommend the use of face masks, extending social distance to more than 2 metres, and natural ventilation of enclosed spaces as preventive measures. These results contribute to a better understanding of SARS-CoV-2 and help design effective strategies to prevent its spread.

Immunomagnetic separation coupled with flow cytometry for the analysis of Legionella pneumophila in aerosols.

Legionella pneumophila are pathogenic bacteria that can be found in high concentrations in artificial water systems like evaporative cooling towers, which have been the source of frequent outbreaks in recent years. Since inhaled L. pneumophila can lead to Legionnaires' disease, the development of suitable sampling and rapid analysis strategies for these bacteria in aerosols is therefore of great relevance. In this work, different concentrations of viable L. pneumophila Sg 1 were nebulized and sampled by the cyclone sampler Coriolis® µ under defined conditions in a bioaerosol chamber. To quantify intact Legionella cells, the collected bioaerosols were subsequently analyzed by immunomagnetic separation coupled with flow cytometry (IMS-FCM) on the platform rqmicro.COUNT. For analytical comparison, measurements with qPCR and cultivation were performed. Limits of detection (LOD) of 2.9 × 103 intact cells m-3 for IMS-FCM and 7.8 × 102 intact cells m-3 for qPCR indicating a comparable sensitivity as in culture (LOD = 1.5 × 103 culturable cells m-3). Over a working range of 103 - 106 cells mL-1, the analysis of nebulized and collected aerosol samples with IMS-FCM and qPCR provides higher recovery rates and more consistent results than by cultivation. Overall, IMS-FCM is a suitable culture-independent method for quantification of L. pneumophila in bioaerosols and is promising for field application due to its simplicity in sample preparation.

Understanding the influence of the bioaerosol source on the distribution of airborne bacteria in hospital indoor air.

The composition and concentration of airborne microorganisms in hospital indoor air has been reported to contain airborne bacteria and fungi concentrations ranged 101-103 CFU/m3 in inpatients facilities which mostly exceed recommendations from the World Health Organization (WHO). In this work, a deeper knowledge of the performance of airborne microorganisms would allow improving the designs of the air-conditioning installations to restrict hospital-acquired infections (HAIs). A solution containing Escherichia coli (E. coli) as a model of airborne bacteria was nebulized using the Collison nebulizer to simulate bioaerosols in various hospital areas such as patients' rooms or bathrooms. Results showed that the bioaerosol source had a significant influence on the airborne bacteria concentrations since 4.00 102, 6.84 103 and 1.39 104 CFU mL-1 were monitored during the aerosolization for 10 min of urine, saliva and urban wastewater, respectively. These results may be explained considering the quite narrow distribution profile of drop sizes around 1.10-1.29 µm obtained for urban wastewater, with much vaster distribution profiles during the aerosolization of urine or saliva. The airborne bacteria concentration may increase up to 107 CFU mL-1 for longer sampling times and higher aerosolization pressures, causing several cell damages. The cell membrane damage index (ID) can vary from 0 to 1, depending on the genomic DNA releases from bacteria. In fact, the ID of E. coli was more than two times higher (0.33 vs. 0.72) when increasing the pressure of air flow was applied from 1 to 2 bar. Finally, the ventilation air flow also affected the distribution of bioaerosols due to its direct relationship with the relative humidity of indoor air. Specifically, the airborne bacteria concentration diminished almost below 3-logs by applying more than 10 L min-1 during the aerosolization of urine due to their inactivation by an increase in their osmotic pressure.

A new filterless indoor air purifier for particulate matter and bioaerosol based on heterogeneous condensation.

Using an indoor air purifier is an important solution for improving indoor air quality and protecting people from the harmful effects of air pollution on their health. The filter air purifiers can remove particulate matter including bioaerosols, but their filter media can cause secondary pollution. To fulfill this need, a new filterless indoor air purifier, the Cloud-Air-Purifying (CAP) air purifier, is presented in this study. Using heterogeneous condensation and supergravity technology, the CAP air purifier grows and collects fine particles, while rapidly disinfecting bioaerosols with chemical disinfection and ultraviolet (UV) disinfection. Furthermore, the purifying performance of the CAP air purifier was tested in a simulated cabin. The results showed the clean air delivery rate (CADR) of the CAP air purifier was approximately 150 m3/h, and the effective coefficient was 0.93. The CAP air purifier was highly efficient in purifying fine particulate matter, 93% for PM10 and 91% for particle size of 0.5-1 µm in 60 min, which was 13-58 times more than natural decay. The reason for the efficient removal of fine particles is that they can condense and grow in water vapor supersaturated environment and be collected in a supergravity field. Moreover, the CAP air purifier has significant bactericidal effects on bioaerosols. It achieved a disinfection efficiency of 99.99997% by decreasing bioaerosols from 108 CFU/m3 to less than 30 CFU/m3 in only 20 min when particle purification in combination with UV disinfection and disinfectant (ClO2). Furthermore, ClO2 release concentrations, noise, and power consumption were investigated for application purposes, with results showing that they were within acceptable limits. The study presents an innovative idea and design for preventing airborne microorganisms and particulate matter through heterogeneous condensation technology.