Bioaerosol Sampling: Classical Approaches, Advances, and Perspectives

Metataxonomics study of dental bioaerosols affected by waterline disinfection

BACKGROUND

Microorganisms in dental unit water (DUW) play a significant role in dental bioaerosols. If the methods used to decontaminate DUW also help improve air quality in dental clinics is worth exploring. In this study, we aim to identify the source of bacteria in dental bioaerosols and investigate the impact of waterline disinfectants on the quantity and composition of bacteria in DUW and bioaerosols.

METHODS

Two dental chair units in a separate treatment room are installed with two different waterline decontamination systems, a plasma or iodine cartridge. The experiment was performed in two phases, before and after installing the decontamination systems. Aerosol is generated via running airotor in the subject's mouth. Before and after the procedure, the air samples were collected with an active air sampling machine onto agar plate and filter paper for genomic DNA extraction. The subject's saliva and DUW samples were also collected. The samples were analyzed further with bacterial counting and metataxonomics analysis.

RESULTS

The bacteria present in the air sample after the aerosol-generating procedure were confirmed to be derived from the air-before, saliva, and DUW in 51.43%, 6.38%, and 18.60%, respectively. The saliva samples demonstrated the highest alpha diversity (within the sample), whereas the air samples had the least. Both waterline disinfectants effectively controlled bacteria in DUW but did not affect the bacterial number and composition in the air.

CONCLUSIONS

Dental bioaerosols are composed of bacteria from saliva and DUW. Plasma and iodine showed a trend in controlling bacterial contamination in DUW but did not alter the bacterial count and composition in dental bioaerosols.

Airborne DNA: State of the art - Established methods and missing pieces in the molecular genetic detection of airborne microorganisms, viruses and plant particles

Bioaerosol is composed of different particles, originating from organisms, or their fragments with different origin, shape, and size. Sampling, analysing, identification and describing this airborne diversity has been carried out for over 100 years, and more recently the use of molecular genetic tools has been implemented. However, up to now there are no established protocols or standards for detecting airborne diversity of bacteria, fungi, viruses, pollen, and plant particles. In this review we evaluated commonalities of methods used in molecular genetic based studies in the last 23 years, to give an overview of applicable methods as well as knowledge gaps in diversity assessment. Various sampling techniques show different levels of effectiveness in detecting airborne particles based on their DNA. The storage and processing of samples, as well as DNA processing, influences the outcome of sampling campaigns. Moreover, the decisions on barcode selection, method of analysis, reference database as well as negative and positive controls may severely impact the results obtained. To date, the chain of decisions, methodological biases and error propagation have hindered DNA based molecular sequencing from offering a holistic picture of the airborne biodiversity. Reviewing the available studies, revealed a great diversity in used methodology and many publications didn't state all used methods in detail, making comparisons with other studies difficult or impossible. To overcome these limitations and ensure genuine comparability across studies, it is crucial to standardize protocols. Publications need to include all necessary information to enable comparison among different studies and to evaluate how methodological choices can impacts the results. Besides standardization, implementing of automatic tools and combining of different analytical techniques, such as real-time evaluation combined with sampling and molecular genetic analysis, could assist in achieving the goal of accurately assessing the actual airborne biodiversity.

Bioaerosols downwind from animal feeding operations: A comprehensive review

Bioaerosols originating from animal feeding operations (AFOs) may carry pathogens, allergens, and other hazardous biocomponents, such as endotoxins, posing a potential risk to community health and the environment when dispersed downwind. This review summarizes and synthesizes existing literature data on bioaerosols downwind from three major types of AFOs (swine, poultry, and cattle), covering their composition, concentration, dispersion patterns, measurement methodologies, potential health effects, and mitigation strategies. While many of these bioaerosols are typically detected only near AFOs, evidence indicates that certain bioaerosols, particularly viruses, can travel up to tens of kilometers downwind and remain infectious. Despite the critical importance of these bioaerosols, a refined modeling framework to simulate their transport and fate in downwind air has not yet been developed, nor have source attribution methods been established to track their origins in complex agricultural environments where multiple bioaerosols could co-exist. Therefore, it is imperative to further research downwind bioaerosols from AFOs, including their assessment, modeling, source attribution, and mitigation, to address the public health and environmental challenges associated with animal agriculture.

Indoor bioaerosols and asthma: Overview, implications, and mitigation strategies

Aerosolized particles with a biological origin are called bioaerosols. Bioaerosols from plants, animals, fungi, bacteria, and viruses are an important class of environmental exposures that are clinically relevant to asthma. However, there are important differences in the pathways by which various bioaerosols affect asthma. Additionally, differences in individual susceptibility to different bioaerosols affect exposure reduction and mitigation strategies. Strategies to reduce exposures to potential triggers of asthma are routinely considered as part of standard clinical care and asthma management guidelines. Ventilation standards in buildings may reduce bioaerosol exposure for everyone, but they are not necessarily designed specifically to protect patients with asthma. Direct measurement of a bioaerosol is not generally necessary for practical applications where the relevant source of the bioaerosol has been identified. Different types of bioaerosols can be controlled with similar strategies that prioritize source control (eg, reducing resuspension, integrated pest management, controlling moisture), and these can be supplemented by enhancing air filtration. The goal of this review is to summarize the latest information on bioaerosols, including allergens, fungi, bacteria, and viruses, that have been associated with adverse asthma outcomes and to discuss mitigation options.

Improved measurement of airborne viruses using a two-stage highly virus-enriching electrostatic particle concentrator with electric-field-enhancing wire electrodes

High enrichment of airborne viruses during sampling is critical for their rapid measurement and requires a high sampling flow rate (or velocity), small collection areas, and high collection efficiency; however, high collection efficiency can rarely be achieved at high flow velocities and in small collection areas in electrostatic sampling. Herein, we present improved measurement of airborne viruses using a two-stage highly virus-enriching electrostatic particle concentrator (HEPC) with wire electrodes and high values of the-inlet-velocity-to-collection-electrode-width ratio. This sampler was evaluated using MS2 viruses and 0.05-2.0 µm diameter polystyrene latex particles at 20 liters/min. Computer simulations and experiments agreed well, showing that the wire electrodes increased collection efficiency (by up to 37 % than the without-wire-electrodes case) without high viability losses through local electric field enhancement for high-flow-velocity regions over the collection electrode and minimization of local corona discharge. The relative infectious virus concentrations of the HEPC were 41-70 times higher than those of the BioSampler. Airborne influenza A viruses at field-level concentrations (1.8 × 105 and 2.6 × 104 copies/m3) were also detected at 10-min sampling due to the high enrichment capability of HEPC. The HEPC has strong potential as a rapid airborne virus monitoring system in the field.

Airborne fungal concentrations around the Modelo Callao Landfill

Non-hazardous waste generated in Metropolitan Lima and Callao is transported to the Modelo Callao landfill for safe disposal. The accumulation of waste constitutes a significant source of fungal particles released into the atmosphere, posing a potential health risk to nearby populations. The aim of this research was to evaluate the concentration of outdoor fungal particles, considering environmental conditions (temperature, relative humidity, wind speed, and direction) during summer and winter seasons in the 18 de octubre settlement and Chillón Avenue, areas located in the vicinity of the Modelo Callao Landfill in Ventanilla during 2022. The gravitational method was used for sampling. The highest concentrations were detected at 150 and 200 m from the landfill, where a kindergarten and a local park are located. Fifteen fungal genera were identified in both seasons. The predominant fungi were Aspergillus spp. (46.09 %), Penicillium spp. (23.29 %) and Alternaria spp. (11.33 %). The average concentrations during summer and winter were 297.21 CFU/m3 and 471.69 CFU/m3, respectively. Based on these findings, we recommend that residential areas be located beyond 200 m from the landfill to minimize exposure to fungal aerosols. Additionally, we propose the implementation of an action plan to improve air quality in the areas surrounding the final disposal infrastructure.

A deployable film method to enable replicable sampling of low-abundance environmental microbiomes

Urbanizing global populations spend over 90% of their time indoors where microbiome abundance and diversity are low. Chronic exposure to microbiomes with low abundance and diversity have demonstrated negative long-term impacts on human health. Sequencing-based analyses of environmental nucleic acids are critical to understanding the impact of the indoor microbiome on human health, however low DNA yields indoors, alongside sample collection and processing inconsistencies, currently challenge study replicability. This study presents a comparative assessment of a novel, passive, easily replicable sampling strategy using polydimethylsiloxane (PDMS) sheets alongside a representative swab-based collection protocol. Deployable, customizable PDMS films designed for whole-sample insertion into standardized extraction kits demonstrated 43% higher DNA yields per sample, and 76% higher yields per cm2 of sampler over swab-based protocols. These results indicate that this accessible, scalable method enables sufficient DNA collection to comprehensively evaluate indoor microbiome exposures and potential human health impacts using smaller, more space efficient samplers, representing an attractive alternative to swab-based collection. In addition, this process reduces the manual steps required for microbiome sampling which could address inter-study variability, transform the current microbiome sampling paradigm, and ultimately benefit the replicability and accessibility of microbiome exposure studies.

Multi-scenario surveillance of respiratory viruses in aerosols with sub-single-copy spatial resolution

Highly sensitive airborne virus monitoring is critical for preventing and containing epidemics. However, the detection of airborne viruses at ultra-low concentrations remains challenging due to the lack of ultra-sensitive methods and easy-to-deployment equipment. Here, we present an integrated microfluidic cartridge that can accurately detect SARS-COV-2, Influenza A, B, and respiratory syncytial virus with a sensitivity of 10 copies/mL. When integrated with a high-flow aerosol sampler, our microdevice can achieve a sub-single-copy spatial resolution of 0.83 copies/m3 for airborne virus surveillance with an air flow rate of 400 L/min and a sampling time of 30 minutes. We then designed a series of virus-in-aerosols monitoring systems (RIAMs), including versions of a multi-site sampling RIAMs (M-RIAMs), a stationary real-time RIAMs (S-RIAMs), and a roaming real-time RIAMs (R-RIAMs) for different application scenarios. Using M-RIAMs, we performed a comprehensive evaluation of 210 environmental samples from COVID-19 patient wards, including 30 aerosol samples. The highest positive detection rate of aerosol samples (60%) proved the aerosol-based SARS-CoV-2 monitoring represents an effective method for spatial risk assessment. The detection of 78 aerosol samples in real-world settings via S-RIAMs confirmed its reliability for ultra-sensitive and continuous airborne virus monitoring. Therefore, RIAMs shows the potential as an effective solution for mitigating the risk of airborne virus transmission.

Filling the knowledge gap: Scoping review regarding sampling methods, assays, and further requirements to assess airborne viruses

Assessment of occupational exposure to viruses is crucial to identify virus reservoirs and sources of dissemination at an early stage and to help prevent spread between employees and to the general population. Measuring workers' exposure can facilitate assessment of the effectiveness of protective and mitigation measures in place. The aim of this scoping review is to give an overview of available methods and those already implemented for airborne virus' exposure assessment in different occupational and indoor environments. The results retrieved from the different studies may contribute to the setting of future standards and guidelines to ensure a reliable risk characterization in the occupational environments crucial for the implementation of effective control measures. The search aimed at selecting studies between January 1st 2010 and June 30th 2023 in the selected databases. Fifty papers on virus exposure assessment fitted the eligibility criteria and were selected for data extraction. Overall, this study identified gaps in knowledge regarding virus assessment and pinpointed the needs for further research. Several discrepancies were found (transport temperatures, elution steps, …), as well as a lack of publication of important data related to the exposure conditions (contextual information). With the available information, it is impossible to compare results between studies employing different methods, and even if the same methods are used, different conclusions/recommendations based on the expert judgment have been reported due to the lack of consensus in the contextual information retrieved and/or data interpretation. Future research on the field targeting sampling methods and in the laboratory regarding the assays to employ should be developed bearing in mind the different goals of the assessment.

Optimal environmental sampling conditions for electrostatic aerosol-to-hydrosol collection of airborne viruses

Due to adverse effects of viral outbreaks on human health, accurate detection of airborne pathogens is essential. Among many methods available for bioaerosol sampling, electrostatic precipitation (ESP) has been used to directly collect bioaerosols as hydrosols. The performance of an ESP sampler depends on its design, operational and environmental parameters such as air relative humidity (RH), air temperature, sampling liquid type and liquid temperature. Thus, it is essential to identify and maintain optimal conditions throughout sampling process to operate the sampler at its highest capacity. This study provides crucial insights into parameters that affect the collection efficiency of the aerosol-to-hydrosol ESP sampler and its virus recovery. The results indicate that air temperature does not affect collection efficiency, meanwhile, air RH, sampling liquid temperature, and salt concentration are the main parameters that significantly affect collection efficiency. Likewise, when deionized water is used as sampling liquid, hydrogen peroxide concentration increases proportionally with increasing air RH, resulting in significant decrease of virus viability. Consequently, for ESP samplers similar to our study, the following conditions are recommended: air RH of 55-65%, air and sampling liquid temperature of 37 °C, and a mixture of 10-20 mM ascorbic acid in PBS as sampling liquid.

Macrobial airborne environmental DNA analysis: A review of progress, challenges, and recommendations for an emerging application

In the context of looming global biodiversity loss, effective species detection represents a critical concern for ecological research and management. Environmental DNA (eDNA) analysis, which refers to the collection and taxonomic identification of genetic fragments that are shed from an organism into its surroundings, emerged approximately 15 years ago as a sensitive tool for species detection. Today, one of the frontiers of eDNA research concerns the collection and analysis of genetic material in dust and other airborne materials, termed airborne eDNA analysis. As the study of airborne eDNA matures, it is an appropriate time to review the foundational and emerging studies that make up the current literature, and use the reviewed literature to summarize, synthesize, and forecast the major challenges and opportunities for this advancing research front. Specifically, we use the "ecology of eDNA" framework to organize our findings across the origin, state, transport, and fate of airborne genetic materials in the environment, and summarize what is so far known of their interactions with surrounding abiotic and biotic factors, including population and community ecologies and ecosystem processes. Within this work we identify key challenges, opportunities, and future directions associated with the application of airborne eDNA development. Lastly, we discuss the development of applications, partnerships, and messaging that promote development and growth of the field. Together, the broad potential of eDNA analysis and the rate at which research is accelerating in this field suggest that the sky's the limit for airborne eDNA science.

Integrated environmental and clinical surveillance for the prevention of acute respiratory infections (ARIs) in indoor environments and vulnerable communities (Stell-ARI): Protocol

The epidemiological relevance of viral acute respiratory infections (ARIs) has been dramatically highlighted by COVID-19. However, other viruses cannot be neglected, such as influenza virus, respiratory syncytial virus, human adenovirus. These viruses thrive in closed spaces, influenced by human and environmental factors. High-risk closed communities are the most vulnerable settings, where the real extent of viral ARIs is often difficult to evaluate, due to the natural disease progression and case identification complexities. During the COVID-19 pandemic, wastewater-based epidemiology has demonstrated its great potential for monitoring the circulation and evolution of the virus in the environment. The "Prevention of ARIs in indoor environments and vulnerable communities" study (Stell-ARI) addresses the urgent need for integrated surveillance and early detection of ARIs within enclosed and vulnerable communities such as long-term care facilities, prisons and primary schools. The rapid transmission of ARIs in such environments underscores the importance of comprehensive surveillance strategies to minimise the risk of outbreaks and safeguard community health, enabling proactive prevention and control strategies to protect the health of vulnerable populations. This study consists of designing and validating tools for integrated clinical and environmental-based surveillance for each setting, coupled with analytical methods for environmental matrices. The clinical surveillance involves specialized questionnaires and nasopharyngeal swabs for virus identification, while the environmental surveillance includes air and surface microbiological and chemical monitoring, and virological analysis of wastewater. Integrating this information and the collection of behavioural and environmental risk factors into predictive and risk assessment models will provide a useful tool for early warning, risk assessment and informed decision-making. The study aims to integrate clinical, behavioural, and environmental data to establish and validate a predictive model and risk assessment tool for the early warning and risk management of viral ARIs in closed and vulnerable communities prior to the onset of an outbreak.

Sampling and analysis methods of air-borne microorganisms in hospital air: a review

Pathogenic microorganisms can spread in the air as bioaerosols. When the human body is exposed to different bioaerosols, various infectious diseases may occur. As indoor diagnosis and treatment environments, hospitals are relatively closed and have a large flow rate of people. This indoor environment contains complex aerosol components; therefore, effective sampling and detection of microbial elements are essential in airborne pathogen monitoring. This article reviews the sampling and detection of different kinds of microorganisms in bioaerosols from indoor diagnostic and therapeutic settings, with a particular focus on microbial activity. This provides deeper insights into bioaerosols in diagnostic and therapeutic settings.

Airborne concentrations of bacteria and mold in Korean public-use facilities: measurement, systematic review, meta-analysis, and probabilistic human inhalation risk assessment

Bioaerosols adversely affect human health posing risk to users of public facilities in Korea. Between October 2021 and May 2022, airborne bacteria and mold were measured in 1,243 public-use facilities across 23 categories. A systematic review and meta-analysis were performed on these and other studies from June 2004 to May 2021, and the non-carcinogenic risks to humans were assessed using Monte Carlo simulations. For bacteria, the maximum 95th percentile concentration was 584.4 cfu/m3 and 1384.8 cfu/m3 for mold. The heterogeneity statistic I2 was over 50% in all facilities, and for subway station bacteria, there was a significant difference according to the measurement method. The 95th percentile of hazard by population group was 8.83 × 10-2 to 3.42 × 10-1 for bacteria, and 1.31 × 10-1 to 3.55 × 10-1 for mold. The probability of a hazard quotient exceeding 1 for some population groups was derived from exposure to bacteria and mold in the air resulting from the use of all public facilities. The most powerful explanatory factor for risk was exposure time to the facility, both within (up to 0.922 for bacteria and up to 0.960 for mold) and between populations (up to 0.543 for bacteria and 0.483 for mold). This study identified populations at risk of bioaerosol exposure in Korean public-use facilities and estimated the influencing factors, highlighting the need for comprehensive improvement in bioaerosol control in public-use facilities.

Evaluation of germicidal ultraviolet-C disinfection in a real-world outpatient health care environment

BACKGROUND

The coronavirus disease 2019 pandemic has highlighted the need for effective infection control in outpatient health care settings. Germicidal ultraviolet-C (GUV) light, known for inactivating microorganisms by damaging their deoxyribonucleic acid or ribonucleic acid, offers a potential solution. This study examines the efficacy of GUV air disinfection systems in real-world outpatient environments.

METHODS

We deployed upper-room and far-UV GUV fixtures in 3 outpatient facilities, assessing their impact on bacterial loads through air and surface sampling and bioindicator tests. Occupancy was also monitored.

RESULTS

While manual air and surface sampling did not show a significant difference in bacterial loads between control and Ultraviolet C-treated groups, bioindicator tests demonstrated a high level of spore inactivation (up to 99.7% for upper-room GUV and 96.26% for far-UV). Occupancy levels did not significantly influence these outcomes.

DISCUSSION

The discrepancy between bioindicator efficacy and environmental sampling results suggests limitations in the latter's ability to accurately capture environmental bioburden. Bioindicators proved to be reliable for in-situ validation of Ultraviolet C surface disinfection.

CONCLUSIONS

Bioindicators are effective for validating GUV surface disinfection efficacy in health care settings, though further research is needed to optimize environmental sampling methods for assessing GUV's impact on real-world bacterial loads.

Towards tailored guidelines for microbial air quality in the food industry

Airborne microorganisms in food processing environments pose a potential risk for food product contamination. Yet, the absence of established standards or guidelines setting quantitative limits on airborne microorganisms underscores a critical gap in current regulatory frameworks. This review seeks to explore the feasibility of establishing quantitative limits for airborne microorganisms in food processing facilities, aiming to provide evidence-based guidance to enhance food safety practices in the industry. The review begins by addressing the complexities of microbial air quality in the food industry through a general literature search covering sources of airborne microorganisms, factors affecting particle deposition, air sampling methods and preventive measures. Subsequently, it employs a structured approach to assess the significance of air quality and its impact on product quality. Utilizing the PRISMA method, relevant scientific literature from May 2002 to May 2022 was examined, resulting in 26 articles meeting inclusion criteria from a pool of 11,737 original research papers. Additionally, the review investigates existing probability models for assessing airborne contamination to enhance air quality risk assessment in food safety management systems. The literature reveals a lack of substantial evidence supporting a direct correlation between airborne microorganisms and food contamination. The absence of standardized air sampling methodologies in previous studies hinders the comparability and reliability of research findings. Additionally, the literature fails to establish a conclusive relationship between influencing factors such as total particle counts, temperature, relative humidity and airborne contamination. Contradictory probability models for quantifying airborne contamination, and the absence of tailored preventive measures, hinder effective control and undermine microbial contamination control in diverse food processing contexts. In conclusion, the development of numeric guidelines for airborne contamination necessitates a tailored approach, considering factors such as product characteristics and production context. By integrating risk assessment models into this process, a more thorough comprehension of contamination risks can be achieved, providing tailored guidance based on the identified risk levels for each product. Ongoing collaborative efforts are essential to develop evidence-based guidelines that effectively mitigate risks without incurring unnecessary costs.

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.

Concentrating viable airborne pathogens using a virtual impactor with a compact water-based condensation air sampler

Pathogens can be collected from air and detected in samples by many methods. However, merely detecting pathogens does not answer whether they can spread disease. To fully assess health risks from exposure to airborne pathogens, the infectivity of those agents must be assessed. Air samplers which operate by growing particles through water vapor condensation and subsequently collecting them into a liquid medium have proven effective at conserving the viability of microorganisms. We present a study that assessed performance improvement of one such sampler, BioSpot-GEM™, gained by augmenting it with an upstream virtual impactor (VI) designed to concentrate particles in aerosols. We demonstrate that such an integrated unit improved the collection of live Escherichia coli by a median Concentration Factor (C F ) of 1.59 and increased the recovery of viable human coronavirus OC43 (OC43) by a median C F of 12.7 as compared to the sampler without the VI. Our results also show that OC43 can be concentrated in this way without significant loss of infectivity. We further present that the small BioSpot-GEM™ bioaerosol sampler can collect live E. coli at an efficiency comparable to the larger BioSpot-VIVAS™ bioaerosol sampler. Our analyses show potential benefits toward improving the collection of viable pathogens from the air using a more portable water-based condensation air sampler while also highlighting challenges associated with using a VI with concentrated bioaerosols. This work can aid further investigation of VI usage to improve the collection of pathogens from air ultimately to better characterize health risks associated with airborne pathogen exposures.

Masks and respirators for prevention of respiratory infections: a state of the science review

SUMMARYThis narrative review and meta-analysis summarizes a broad evidence base on the benefits-and also the practicalities, disbenefits, harms and personal, sociocultural and environmental impacts-of masks and masking. Our synthesis of evidence from over 100 published reviews and selected primary studies, including re-analyzing contested meta-analyses of key clinical trials, produced seven key findings. First, there is strong and consistent evidence for airborne transmission of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and other respiratory pathogens. Second, masks are, if correctly and consistently worn, effective in reducing transmission of respiratory diseases and show a dose-response effect. Third, respirators are significantly more effective than medical or cloth masks. Fourth, mask mandates are, overall, effective in reducing community transmission of respiratory pathogens. Fifth, masks are important sociocultural symbols; non-adherence to masking is sometimes linked to political and ideological beliefs and to widely circulated mis- or disinformation. Sixth, while there is much evidence that masks are not generally harmful to the general population, masking may be relatively contraindicated in individuals with certain medical conditions, who may require exemption. Furthermore, certain groups (notably D/deaf people) are disadvantaged when others are masked. Finally, there are risks to the environment from single-use masks and respirators. We propose an agenda for future research, including improved characterization of the situations in which masking should be recommended or mandated; attention to comfort and acceptability; generalized and disability-focused communication support in settings where masks are worn; and development and testing of novel materials and designs for improved filtration, breathability, and environmental impact.

VLP-based model for the study of airborne viral pathogens

The recent COVID-19 pandemic has underscored the danger of airborne viral pathogens. The lack of model systems to study airborne pathogens limits the understanding of airborne pathogen distribution as well as potential surveillance and mitigation strategies. In this work, we develop a novel model system to study airborne pathogens using virus-like particles (VLPs). Specifically, we demonstrate the ability to aerosolize VLP and detect and quantify aerosolized VLP RNA by reverse transcription-loop-mediated isothermal amplification in real-time fluorescent and colorimetric assays. Importantly, the VLP model presents many advantages for the study of airborne viral pathogens: (i) similarity in size and surface components; (ii) ease of generation and noninfectious nature enabling the study of biosafety level 3 and biosafety level 4 viruses; (iii) facile characterization of aerosolization parameters; (iv) ability to adapt the system to other viral envelope proteins, including those of newly discovered pathogens and mutant variants; and (v) the ability to introduce viral sequences to develop nucleic acid amplification assays.

IMPORTANCE

The study and detection of airborne pathogens are hampered by the lack of appropriate model systems. In this work, we demonstrate that noninfectious virus-like particles (VLPs) represent attractive models to study airborne viral pathogens. Specifically, VLPs are readily prepared, are similar in size and composition to infectious viruses, and are amenable to highly sensitive nucleic acid amplification techniques.

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.

Laboratory studies on the infectivity of human respiratory viruses: Experimental conditions, detections, and resistance to the atmospheric environment

The environmental stability of infectious viruses in the laboratory setting is crucial to the transmission potential of human respiratory viruses. Different experimental techniques or conditions used in studies over the past decades have led to diverse understandings and predictions for the stability of viral infectivity in the atmospheric environment. In this paper, we review the current knowledge on the effect of simulated atmospheric conditions on the infectivity of respiratory viruses, mainly focusing on influenza viruses and coronaviruses, including severe acute respiratory syndrome coronavirus 2 and Middle East respiratory syndrome coronavirus. First, we summarize the impact of the experimental conditions on viral stability; these involve the methods of viral aerosol generation, storage during aging and collection, the virus types and strains, the suspension matrixes, the initial inoculum volumes and concentrations, and the drying process. Second, we summarize and discuss the detection methods of viral infectivity and their disadvantages. Finally, we integrate the results from the reviewed studies to obtain an overall understanding of the effects of atmospheric environmental conditions on the decay of infectious viruses, especially aerosolized viruses. Overall, this review highlights the knowledge gaps in predicting the ability of viruses to maintain infectivity during airborne transmission.

On-Site Bioaerosol Sampling and Airborne Microorganism Detection Technologies

Bioaerosols are small airborne particles composed of microbiological fragments, including bacteria, viruses, fungi, pollens, and/or by-products of cells, which may be viable or non-viable wherever applicable. Exposure to these agents can cause a variety of health issues, such as allergic and infectious diseases, neurological disorders, and cancer. Therefore, detecting and identifying bioaerosols is crucial, and bioaerosol sampling is a key step in any bioaerosol investigation. This review provides an overview of the current bioaerosol sampling methods, both passive and active, as well as their applications and limitations for rapid on-site monitoring. The challenges and trends for detecting airborne microorganisms using molecular and immunological methods are also discussed, along with a summary and outlook for the development of prompt monitoring technologies.

Aeromicrobiology: A global review of the cycling and relationships of bioaerosols with the atmosphere

Airborne microorganisms and biological matter (bioaerosols) play a key role in global biogeochemical cycling, human and crop health trends, and climate patterns. Their presence in the atmosphere is controlled by three main stages: emission, transport, and deposition. Aerial survival rates of bioaerosols are increased through adaptations such as ultra-violet radiation and desiccation resistance or association with particulate matter. Current research into modern concerns such as climate change, global gene transfer, and pathogenicity often neglects to consider atmospheric involvement. This comprehensive review outlines the transpiring of bioaerosols across taxa in the atmosphere, with significant focus on their interactions with environmental elements including abiotic factors (e.g., atmospheric composition, water cycle, and pollution) and events (e.g., dust storms, hurricanes, and wildfires). The aim of this review is to increase understanding and shed light on needed research regarding the interplay between global atmospheric phenomena and the aeromicrobiome. The abundantly documented bacteria and fungi are discussed in context of their cycling and human health impacts. Gaps in knowledge regarding airborne viral community, the challenges and importance of studying their composition, concentrations and survival in the air are addressed, along with understudied plant pathogenic oomycetes, and archaea cycling. Key methodologies in sampling, collection, and processing are described to provide an up-to-date picture of ameliorations in the field. We propose optimization to microbiological methods, commonly used in soil and water analysis, that adjust them to the context of aerobiology, along with other directions towards novel and necessary advancements. This review offers new perspectives into aeromicrobiology and calls for advancements in global-scale bioremediation, insights into ecology, climate change impacts, and pathogenicity transmittance.

Assessment of personal deposited dose and particle size distribution of bacterial aerosol in kindergarten located in southern Poland

The study's primary focus lies in examining the relationship between respiratory and deposition doses of bacterial aerosols in urban kindergarten, providing valuable insights into the specific doses absorbed by individuals in different sections of their respiratory systems based on the aerodynamic diameter of bacterial particles. Samples were collected twice a week, using by an Andersen cascade impactor during autumn and winter seasons 2018/2019 resulting in a total of 1152 Petri dishes analyzed. The highest average concentration of bacterial aerosol was observed during autumn (1698 ± 663 CFU/m3) in comparison to winter months (723 ± 134 CFU/m3). Respirable doses for children and staff were 2945 and 2441 CFU/day during winter and 5988 and 4964 CFU/day during autumn, respectively. Deposition doses incorporated from empirical models for regional deposition in the respiratory tract showed that children in kindergarten absorb 33% less of bacteria into alveolar region if breath by nose instead of mouth. Additionally, risk assessment results indicate that the hazard indices for children attending kindergartens for 3 years and for staff working 25 years are below 1, suggesting minor risks associated with the inhalation of bioaerosols during autumn and winter. HI was <1, so the non-carcinogenic effects are on an acceptable level, but the indoor/outdoor ratio were 3.5 and 2.4 for autumn and winter, respectively, indicating children's and adult's exposure to bacterial aerosol should be reduced.

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.

Blazing the trail for innovative tuberculosis diagnostics

The COVID-19 pandemic brought diagnostics into the spotlight in an unprecedented way not only for case management but also for population health, surveillance, and monitoring. The industry saw notable levels of investment and accelerated research which sparked a wave of innovation. Simple non-invasive sampling methods such as nasal swabs have become widely used in settings ranging from tertiary hospitals to the community. Self-testing has also been adopted as standard practice using not only conventional lateral flow tests but novel and affordable point-of-care molecular diagnostics. The use of new technologies, including artificial intelligence-based diagnostics, have rapidly expanded in the clinical setting. The capacity for next-generation sequencing and acceptance of digital health has significantly increased. However, 4 years after the pandemic started, the market for SARS-CoV-2 tests is saturated, and developers may benefit from leveraging their innovations for other diseases; tuberculosis (TB) is a worthwhile portfolio expansion for diagnostics developers given the extremely high disease burden, supportive environment from not-for-profit initiatives and governments, and the urgent need to overcome the long-standing dearth of innovation in the TB diagnostics field. In exchange, the current challenges in TB detection may be resolved by adopting enhanced swab-based molecular methods, instrument-based, higher sensitivity antigen detection technologies, and/or artificial intelligence-based digital health technologies developed for COVID-19. The aim of this article is to review how such innovative approaches for COVID-19 diagnosis can be applied to TB to have a comparable impact.

The atmosphere: a transport medium or an active microbial ecosystem?

The atmosphere may be Earth's largest microbial ecosystem. It is connected to all of Earth's surface ecosystems and plays an important role in microbial dispersal on local to global scales. Despite this grand scale, surprisingly little is understood about the atmosphere itself as a habitat. A key question remains unresolved: does the atmosphere simply transport microorganisms from one location to another, or does it harbour adapted, resident, and active microbial communities that overcome the physiological stressors and selection pressures the atmosphere poses to life? Advances in extreme microbiology and astrobiology continue to push our understanding of the limits of life towards ever greater extremes of temperature, pressure, salinity, irradiance, pH, and water availability. Earth's atmosphere stands as a challenging, but potentially surmountable, extreme environment to harbour living, active, resident microorganisms. Here, we confront the current understanding of the atmosphere as a microbial habitat, highlighting key advances and limitations. We pose major ecological and mechanistic questions about microbial life in the atmosphere that remain unresolved and frame the problems and technical pitfalls that have largely hindered recent developments in this space, providing evidence-based insights to drive future research in this field. New innovations supported by rigorous technical standards are needed to enable progress in understanding atmospheric microorganisms and their influence on global processes of weather, climate, nutrient cycling, biodiversity, and microbial connectivity, especially in the context of rapid global change.

VLP-Based Model for Study of Airborne Viral Pathogens

The recent COVID-19 pandemic has underscored the danger of airborne viral pathogens. The lack of model systems to study airborne pathogens limits the understanding of airborne pathogen distribution, as well as potential surveillance and mitigation strategies. In this work, we develop a novel model system to study airborne pathogens using virus like particles (VLP). Specifically, we demonstrate the ability to aerosolize VLP and detect and quantify aerosolized VLP RNA by Reverse Transcription-Loop-Mediated Isothermal Amplification (RT-LAMP) in real-time fluorescent and colorimetric assays. Importantly, the VLP model presents many advantages for the study of airborne viral pathogens: (i) similarity in size and surface components; (ii) ease of generation and noninfectious nature enabling study of BSL3 and BSL4 viruses; (iii) facile characterization of aerosolization parameters; (iv) ability to adapt the system to other viral envelope proteins including those of newly discovered pathogens and mutant variants; (v) the ability to introduce viral sequences to develop nucleic acid amplification assays.

Comprehensive performance evaluation of six bioaerosol samplers based on an aerosol wind tunnel

Choosing a suitable bioaerosol sampler for atmospheric microbial monitoring has been a challenge to researchers interested in environmental microbiology, especially during a pandemic. However, a comprehensive and integrated evaluation method to fully assess bioaerosol sampler performance is still lacking. Herein, we constructed a customized wind tunnel operated at 2-20 km/h wind speed to systematically and efficiently evaluate the performance of six frequently used samplers, where various aerosols, including Arizona test dust, bacterial spores, gram-positive and gram-negative bacteria, phages, and viruses, were generated. After 10 or 60 min of sampling, the physical and biological sampling efficiency and short or long-term sampling capabilities were determined by performing aerodynamic particle size analysis, live microbial culturing, and a qPCR assay. The results showed that AGI-30 and BioSampler impingers have good physical and biological sampling efficiencies for short-term sampling. However, their ability to capture aerosols at low concentrations is restricted. SASS 2300 and BSA-350 wet-wall cyclones had excellent enrichment ratios and high microbial cultivability in both short-term and long-term sampling; however, they were not suitable for quantitative studies of aerosols. Polycarbonate filter samplers showed outstanding performance in physical and long-term sampling but lacked the ability to maintain microbial activity, which can be improved by gelatin filter samplers. However, limitations remain for some fragile microorganisms, such as E. coli phage PhiX174 and coronavirus GX_P2V. In addition, the effects of wind speed and direction should be considered when sampling particles larger than 4 µm. This study provides an improved strategy and guidance for the characterization and selection of a bioaerosol sampler for better measurement and interpretation of collected ambient bioaerosols.

Resistomes in freshwater bioaerosols and their impact on drinking and recreational water safety: A perspective

Antibiotic resistance genes (ARGs) are widespread environmental pollutants of biological origin that pose a significant threat to human, animal, and plant health, as well as to ecosystems. ARGs are found in soil, water, air, and waste, and several pathways for global dissemination in the environment have been described. However, studies on airborne ARG transport through atmospheric particles are limited. The ARGs in microorganisms inhabiting an environment are referred to as the "resistome". A global search was conducted of air-resistome studies by retrieving bioaerosol ARG-related papers published in the last 30 years from PubMed. We found that there is no dedicated methodology for isolating ARGs in bioaerosols; instead, conventional methods for microbial culture and metagenomic analysis are used in combination with standard aerosol sampling techniques. There is a dearth of information on the bioaerosol resistomes of freshwater environments and their impact on freshwater sources used for drinking and recreational activities. More studies of aerobiome freshwater environments are needed to ensure the safe use of water and sanitation. In this review we outline and synthesize the few studies that address the freshwater air microbiome (from tap water, bathroom showers, rivers, lakes, and swimming pools) and their resistomes, as well as the likely impacts on drinking and recreational waters. We also discuss current knowledge gaps for the freshwater airborne resistome. This review will stimulate new investigations of the atmospheric microbiome, particularly in areas where both air and water quality are of public health concern.

Control technologies to prevent aerosol-based disease transmission in animal agriculture production settings: a review of established and emerging approaches

Transmission of infectious agents via aerosols is an ever-present concern in animal agriculture production settings, as the aerosol route to disease transmission can lead to difficult-to-control and costly diseases, such as porcine respiratory and reproductive syndrome virus and influenza A virus. It is increasingly necessary to implement control technologies to mitigate aerosol-based disease transmission. Here, we review currently utilized and prospective future aerosol control technologies to collect and potentially inactivate pathogens in aerosols, with an emphasis on technologies that can be incorporated into mechanically driven (forced air) ventilation systems to prevent aerosol-based disease spread from facility to facility. Broadly, we find that control technologies can be grouped into three categories: (1) currently implemented technologies; (2) scaled technologies used in industrial and medical settings; and (3) emerging technologies. Category (1) solely consists of fibrous filter media, which have been demonstrated to reduce the spread of PRRSV between swine production facilities. We review the mechanisms by which filters function and are rated (minimum efficiency reporting values). Category (2) consists of electrostatic precipitators (ESPs), used industrially to collect aerosol particles in higher flow rate systems, and ultraviolet C (UV-C) systems, used in medical settings to inactivate pathogens. Finally, category (3) consists of a variety of technologies, including ionization-based systems, microwaves, and those generating reactive oxygen species, often with the goal of pathogen inactivation in aerosols. As such technologies are typically first tested through varied means at the laboratory scale, we additionally review control technology testing techniques at various stages of development, from laboratory studies to field demonstration, and in doing so, suggest uniform testing and report standards are needed. Testing standards should consider the cost-benefit of implementing the technologies applicable to the livestock species of interest. Finally, we examine economic models for implementing aerosol control technologies, defining the collected infectious particles per unit energy demand.

Comprehensive insights into advances in ambient bioaerosols sampling, analysis and factors influencing bioaerosols composition

While the study of bioaerosols has a long history, it has garnered heightened interest in the past few years, focusing on both culture-dependent and independent sampling and analysis approaches. Observations have been made regarding the seasonal fluctuations in microbial communities and their connection to particular ambient atmospheric factors. The study of airborne microbial communities is important in public health and atmospheric processes. Nevertheless, the establishment of standardized protocols for evaluating airborne microbial communities and utilizing microbial taxonomy as a means to identify distinct bioaerosols sources and seasonal patterns remains relatively unexplored. This article discusses the challenges and limitations of ambient bioaerosols sampling and analysis, including the lack of standardized methods and the heterogeneity of sources. Future prospects in the field of bioaerosols, including the use of high-throughput sequencing technologies, omics studies, spectroscopy and fluorescence-based monitoring to provide comprehensive incite on metabolic capacity, and activity are also presented. Furthermore, the review highlights the factors that affect bioaerosols composition, including seasonality, atmospheric conditions, and pollution levels. Overall, this review provides a valuable resource for researchers, policymakers, and stakeholders interested in understanding and managing bioaerosols in various environments.

Droplet digital PCR application for the detection of SARS-CoV-2 in air sample

Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) may transmit through airborne route particularly when the aerosol particles remain in enclosed spaces with inadequate ventilation. There has been no standard recommended method of determining the virus in air due to limitations in pre-analytical and technical aspects. Furthermore, the presence of low virus loads in air samples could result in false negatives. Our study aims to explore the feasibility of detecting SARS-CoV-2 ribonucleic acid (RNA) in air samples using droplet digital polymerase chain reaction (ddPCR). Active and passive air sampling was conducted between December 2021 and February 2022 with the presence of COVID-19 confirmed cases in two hospitals and a quarantine center in Klang Valley, Malaysia. SARS-CoV-2 RNA in air was detected and quantified using ddPCR and real-time reverse transcriptase-polymerase chain reaction (RT-PCR). The comparability of two different digital PCR platforms (QX200 and QIAcuity) to RT-PCR were also investigated. Additionally negative staining transmission electron microscopy was performed to visualize virus ultrastructure. Detection rates of SARS-CoV-2 in air samples using ddPCR were higher compared to RT-PCR, which were 15.2% (22/145) and 3.4% (5/145), respectively. The sensitivity and specificity of ddPCR was 100 and 87%, respectively. After excluding 17 negative samples (50%) by both QX200 and QIAcuity, 15% samples (5/34) were found to be positive both ddPCR and dPCR. There were 23.5% (8/34) samples that were detected positive by ddPCR but negative by dPCR. In contrast, there were 11.7% (4/34) samples that were detected positive by dPCR but negative by ddPCR. The SARS-CoV-2 detection method by ddPCR is precise and has a high sensitivity for viral RNA detection. It could provide advances in determining low viral titter in air samples to reduce false negative reports, which could complement detection by RT-PCR.

A Survey of Airborne Fungi and Their Sensitization Profile in Wuhan, China

INTRODUCTION

Airborne fungi induce allergic symptoms in 3-10% of the population worldwide. To better prevent and manage fungi-related allergic diseases, it is essential to identify the genus and the distribution profile of airborne fungi.

METHODS

With this purpose in mind, we carried out a 12-month volumetric sampling study to monitor the airborne fungi and retrospectively analyzed the sensitization profile of four dominant fungi (Cladosporium, Alternaria, Aspergillus, and Penicillium) among respiratory allergies during the same study period in Wuhan, China.

RESULTS

A total of 29 different fungal genuses were identified, and the peak fungal concentration period was found to be in September and October, followed by May and June. The most prevalent fungi in this area were Cladosporium (36.36%), Ustilago (20.12%), and Alternaria (13.87%). In addition, the skin prick test data from 1,365 respiratory allergies patients showed that 202 (14.80%) of them were sensitized to fungi. The sensitization rates to Cladosporium, Alternaria, Aspergillus, and Penicillium were 11.72%, 4.69%, 1.98%, and 4.76%, respectively. The seasonal fluctuation of Alternaria and Aspergillus correlated with their sensitization rates. Among the fungal sensitized patients, 76 (37.62%) were sensitized to two or more kinds of fungi. The serum-specific IgE tests suggested low to high correlations existed between these fungi; however, these correlations were not found between fungi and other allergens.

CONCLUSION

Our study provides the distribution profile and reveals the clinical significance of the airborne fungi in Wuhan, which will facilitate the precise management of fungal allergy.

Postharvest Diseases of Pomegranate: Alternative Control Means and a Spiderweb Effect

The pomegranate is a fruit known since ancient times for its beneficial properties. It has recently aroused great interest in the industry and among consumers, leading to a significant increase in demand. Consequently, its cultivation has been boosted all over the world. The pomegranate crop suffers considerable yield losses, especially at the postharvest stage, because it is a "minor crop" with few permitted control means. To control latent (Alternaria spp., Botrytis spp., Coniella spp., Colletotrichum spp., and Cytospora spp.) and wound (Aspergillus spp., Penicillium spp., and Talaromyces spp.) fungal pathogens, different alternative compounds, previously evaluated in vitro, were tested in the field on pomegranate cv. Wonderful. A chitosan solution, a plant protein hydrolysate, and a red seaweed extract were compared with a chemical control treatment, all as preharvest (field application) and postharvest treatments and their combinations. At the end of the storage period, the incidence of stamen infections and external and internal rots, and the severity of internal decay were evaluated. Obtained data revealed that pre- and postharvest application of all substances reduced the epiphytic population on stamens. Preharvest applications of seaweed extract and plant hydrolysate were the most effective treatments to reduce the severity of internal pomegranate decays. Furthermore, the influence of spider (Cheiracanthium mildei) cocoons on the fruit calyx as a possible barrier against postharvest fungal pathogens was assessed in a 'Mollar de Elche' pomegranate organic orchard. Compared to no-cocoon fruit (control), the incidence of infected stamens and internal molds in those with spiderwebs was reduced by about 30%, and the mean severity of internal rots was halved. Spiderwebs analyzed via Scanning Electron Microscopy (SEM) disclosed a layered, unordered structure that did not allow for the passage of fungal spores due to its mean mesh size (1 to 20 µm ca). The aims of this research were (i) to evaluate alternative compounds useful to control postharvest pomegranate decays and (ii) to evaluate the effectiveness of spiders in reducing postharvest fungal infections by analyzing related mechanisms of action. Alternative control means proposed in the present work and calyx spider colonization may be helpful to reduce postharvest pomegranate diseases, yield losses, and waste production in an integrated control strategy, satisfying organic agriculture and the planned goals of Zero Hunger Challenge launched by the United Nations.

Real-time 4D tracking of airborne virus-laden droplets and aerosols

There is currently no real-time airborne virus tracking method, hindering the understanding of rapid virus changes and associated health impacts. Nano-digital in-line holographic microscopy (Nano-DIHM) is a lensless technology that can directly obtain the interference patterns of objects by recording the scattered light information originating from the objects. Here, we provide evidence for real-time physicochemical tracking of virus-laden droplets and aerosols in the air using desktop label-free Nano-DIHM. The virus interference patterns, as single and ensemble particles, were imaged by the Nano-DIHM with 32.5 ms resolution. The next-generation Stingray and Octopus software was used to automate object detection, characterization and classification from the recorded holograms. The detection system was demonstrated to detect active MS2 bacteriophages, inactivated SARS-CoV-2 and RNA fragments, and an MS2 mixture with metallic and organic compounds. This work demonstrates the feasibility of using Nano-DIHM to provide rapid virus detection to improve transmission management in real time.

Devendra Pal and coworkers report an imaging system using Nano-Digital in-line Holographic Microscopy (NanoDIHM) to detect airborne viruses in droplets and aerosols in real time. This system is able to detect various viruses in air, water and heterogeneous matrices within one minute, enabling real-time tracking of pollutant particles for efficient epidemic management.

Environmental sampling for disease surveillance: Recent advances and recommendations for best practice

The study of infectious diseases includes both the progression of the disease in its host and how it transmits between hosts. Understanding disease transmission is important for recommending effective interventions, protecting healthcare workers, and informing an effective public health response. Sampling the environment for infectious diseases is critical to public health since it can provide an understanding of the mechanisms of transmission, characterization of contamination in hospitals and other public areas, and the spread of a disease within a community. Measurements of biological aerosols, particularly those that may cause disease, have been an ongoing topic of research for decades, and so a wide variety of technological solutions exist. This wide field of possibilities can create confusion, particularly when different approaches yield different answers. Therefore, guidelines for best practice in this area are important to allow more effective use of this data in public health decisions. This review examines air, surface and water/wastewater sampling methods, with a focus on aerosol sampling, and a goal of recommending approaches to designing and implementing sampling systems that may incorporate multiple strategies. This is accomplished by developing a framework for designing and evaluating a sampling strategy, reviewing current practices and emerging technologies for sampling and analysis, and recommending guidelines for best practice in the area of aerosol sampling for infectious disease.

Perspectives on Sampling and New Generation Sequencing Methods for Low-Biomass Bioaerosols in Atmospheric Environments

Bioaerosols play essential roles in the atmospheric environment and can affect human health. With a few exceptions (e.g., farm or rainforest environments), bioaerosol samples from wide-ranging environments typically have a low biomass, including bioaerosols from indoor environments (e.g., residential homes, offices, or hospitals), outdoor environments (e.g., urban or rural air). Some specialized environments (e.g., clean rooms, the Earth's upper atmosphere, or the international space station) have an ultra-low-biomass. This review discusses the primary sources of bioaerosols and influencing factors, the recent advances in air sampling techniques and the new generation sequencing (NGS) methods used for the characterization of low-biomass bioaerosol communities, and challenges in terms of the bias introduced by different air samplers when samples are subjected to NGS analysis with a focus on ultra-low biomass. High-volume filter-based or liquid-based air samplers compatible with NGS analysis are required to improve the bioaerosol detection limits for microorganisms. A thorough understanding of the performance and outcomes of bioaerosol sampling using NGS methods and a robust protocol for aerosol sample treatment for NGS analysis are needed. Advances in NGS techniques and bioinformatic tools will contribute toward the precise high-throughput identification of the taxonomic profiles of bioaerosol communities and the determination of their functional and ecological attributes in the atmospheric environment. In particular, long-read amplicon sequencing, viability PCR, and meta-transcriptomics are promising techniques for discriminating and detecting pathogenic microorganisms that may be active and infectious in bioaerosols and, therefore, pose a threat to human health.

Supplementary Information

The online version contains supplementary material available at 10.1007/s41745-023-00380-x.

Performance evaluation of an electrostatic precipitator with a copper plate using an aerosolized SARS-CoV-2 surrogate (bacteriophage phi 6)

The global spread of severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) has reminded us of the importance of developing technologies to reduce and control bioaerosols in built environments. For bioaerosol control, the interaction between researchers and biomaterials is essential, and considering the characteristics of target pathogens is strongly required. Herein, we used enveloped viral aerosols, bacteriophage phi 6, for evaluating the performance of an electrostatic precipitator (ESP) with a copper-collecting plate (Cu-plate). In particular, bacteriophage phi 6 is an accessible enveloped virus that can be operated in biosafety level (BSL)-1 as a promising surrogate for SARS-CoV-2 with structural and morphological similarities. ESP with Cu-plate showed >91% of particle removal efficiency for viral aerosols at 77 cm/s of airflow face velocity. Moreover, the Cu-plate presented a potent antiviral performance of 5.4-relative log reduction within <15 min of contact. We believe that the evaluation of ESP performance using an aerosolized enveloped virus and plaque assay is invaluable. Our results provide essential information for the development of bioaerosol control technologies that will lead the post-corona era.

Aircraft surveys for air eDNA: probing biodiversity in the sky

Air is a medium for dispersal of environmental DNA (eDNA) carried in bioaerosols, yet the atmosphere is mostly unexplored as a source of genetic material encompassing all domains of life. In this study, we designed and deployed a robust, sterilizable hardware system for airborne nucleic acid capture featuring active filtration of a quantifiable, controllable volume of air and a high-integrity chamber to protect the sample from loss or contamination. We used our hardware system on an aircraft across multiple height transects over major aerosolization sources to collect air eDNA, coupled with high-throughput amplicon sequencing using multiple DNA metabarcoding markers targeting bacteria, plants, and vertebrates to test the hypothesis of large-scale genetic presence of these bioaerosols throughout the planetary boundary layer in the lower troposphere. Here, we demonstrate that the multi-taxa DNA assemblages inventoried up to 2,500 m using our airplane-mounted hardware system are reflective of major aerosolization sources in the survey area and show previously unreported airborne species detections (i.e., Allium sativum L). We also pioneer an aerial survey flight grid standardized for atmospheric sampling of genetic material and aeroallergens using a light aircraft and limited resources. Our results show that air eDNA from terrestrial bacteria, plants, and vertebrates is detectable up to high altitude using our airborne air sampler and demonstrate the usefulness of light aircraft in monitoring campaigns. However, our work also underscores the need for improved marker choices and reference databases for species in the air column, particularly eukaryotes. Taken together, our findings reveal strong connectivity or mixing of terrestrial-associated eDNA from ground level aerosolization sources and the atmosphere, and we recommend that parameters and indices considering lifting action, atmospheric instability, and potential for convection be incorporated in future surveys for air eDNA. Overall, this work establishes a foundation for light aircraft campaigns to comprehensively and economically inventory bioaerosol emissions and impacts at scale, enabling transformative future opportunities in airborne DNA technology.

Research progress of severe acute respiratory syndrome coronavirus 2 on aerosol collection and detection

The outbreak of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) in late 2019 has negatively affected people's lives and productivity. Because the mode of transmission of SARS-CoV-2 is of great concern, this review discusses the sources of virus aerosols and possible transmission routes. First, we discuss virus aerosol collection methods, including natural sedimentation, solid impact, liquid impact, centrifugal, cyclone and electrostatic adsorption methods. Then, we review common virus aerosol detection methods, including virus culture, metabolic detection, nucleic acid-based detection and immunology-based detection methods. Finally, possible solutions for the detection of SARS-CoV-2 aerosols are introduced. Point-of-care testing has long been a focus of attention. In the near future, the development of an instrument that integrates sampling and output results will enable the real-time, automatic monitoring of patients.

An Optimized Active Sampling Procedure for Aerobiological DNA Studies

The Earth's atmosphere plays a critical role in transporting and dispersing biological aerosols. Nevertheless, the amount of microbial biomass in suspension in the air is so low that it is extremely difficult to monitor the changes over time in these communities. Real-time genomic studies can provide a sensitive and rapid method for monitoring changes in the composition of bioaerosols. However, the low abundance of deoxyribose nucleic acid (DNA) and proteins in the atmosphere, which is of the order of the contamination produced by operators and instruments, poses a challenge for the sampling process and the analyte extraction. In this study, we designed an optimized, portable, closed bioaerosol sampler based on membrane filters using commercial off-the-shelf components, demonstrating its end-to-end operation. This sampler can operate autonomously outdoors for a prolonged time, capturing ambient bioaerosols and avoiding user contamination. We first performed a comparative analysis in a controlled environment to select the optimal active membrane filter based on its ability to capture and extract DNA. We have designed a bioaerosol chamber for this purpose and tested three commercial DNA extraction kits. The bioaerosol sampler was tested outdoors in a representative environment and run for 24 h at 150 L/min. Our methodology suggests that a 0.22-µm polyether sulfone (PES) membrane filter can recover up to 4 ng of DNA in this period, sufficient for genomic applications. This system, along with the robust extraction protocol, can be automated for continuous environmental monitoring to gain insights into the time evolution of microbial communities within the air.

Three Experimental Common High-Risk Procedures: Emission Characteristics Identification and Source Intensity Estimation in Biosafety Laboratory

Biosafety laboratory is an important place to study high-risk microbes. In biosafety laboratories, with the outbreak of infectious diseases such as COVID-19, experimental activities have become increasingly frequent, and the risk of exposure to bioaerosols has increased. To explore the exposure risk of biosafety laboratories, the intensity and emission characteristics of laboratory risk factors were investigated. In this study, high-risk microbe samples were substituted with Serratia marcescens as the model bacteria. The resulting concentration and particle size segregation of the bioaerosol produced by three experimental procedures (spill, injection, and sample drop) were monitored, and the emission sources' intensity were quantitatively analyzed. The results showed that the aerosol concentration produced by injection and sample drop was 103 CFU/m3, and that by sample spill was 102 CFU/m3. The particle size of bioaerosol is mainly segregated in the range of 3.3-4.7 μm. There are significant differences in the influence of risk factors on source intensity. The intensity of sample spill, injection, and sample drop source is 3.6 CFU/s, 78.2 CFU/s, and 664 CFU/s. This study could provide suggestions for risk assessment of experimental operation procedures and experimental personnel protection.

Mind the gap between non-activated (non-aggressive) and activated (aggressive) indoor fungal testing: impact of pre-sampling environmental settings on indoor air readings

Indoor fungal testing has been within the researchers' scope of interest for more than a century. Various sampling and analysis techniques have been developed over the years, but no testing protocol has been yet standardised and widely accepted by the research and practitioner communities. The diversity in fungal taxa within buildings with varied biological properties and implications on the health and wellbeing of the occupants and the building fabric complicates the decision-making process for selecting an appropriate testing protocol. This study aims to present a critical review of non-activated and activated approaches to indoor testing, with an emphasis on the preparation of the indoor environment prior to sampling. The study demonstrates the differences in the outcomes of non-activated and activated testing through a set of laboratory experiments in idealised conditions and a case study. The findings suggest that larger particles are particularly sensitive to the sampling height and activation, and that non-activated protocols, despite dominating the current literature, can significantly underestimate the fungal biomass and species richness. Therefore, this paper calls for better-defined and activated protocols that can enhance robustness and reproducibility across the research domain focused on indoor fungal testing.

Transmission of SARS-CoV-2 in the workplace: Key findings from a rapid review of the literature

At the beginning of the COVID-19 pandemic, the primary route of transmission of the SARS-CoV-2 virus was not well understood. Research gathered from other respiratory infectious diseases, including other coronaviruses, was the basis for the initial perceptions for transmission of SARS-CoV-2. To better understand transmission of SARS-CoV-2, a rapid literature review was conducted from literature generated March 19, 2020, through September 23, 2021. 18,616 unique results were identified from literature databases and screened. Of these, 279 key articles were reviewed and abstracted covering critical topics such as environmental/workplace monitoring, sampling and analytical method evaluation, and the ability of the virus to remain intact and infectious during sampling. This paper describes the results of the rapid literature review, which evaluated pathways that contribute to transmission as well as the strengths and limitations of current sampling approaches. This review also evaluates how different factors, including environmental conditions and surface characteristics, could impact the transmission potential of SARS-CoV-2. A continual rapid review in the midst of a pandemic proved particularly useful for quickly understanding the transmission parameters of the virus and enabled us to comprehensively assess literature, respond to workplace questions, and evaluate our understanding as the science evolved. Air and surface sampling with the accompanying analytical methods were not generally effective in recovering SARS-CoV-2 viable virus or RNA in many likely contaminated environments. In light of these findings, the development of validated sampling and analysis methods is critical for determining worker exposure to SARS-CoV-2 and to assess the impact of mitigation efforts.

On-site bioaerosol sampling and detection in microfluidic platforms

As the recent coronavirus disease (COVID-19) pandemic and several severe illnesses such as Middle East respiratory syndrome coronavirus (MERS-CoV), Influenza A virus (IAV) flu, and severe acute respiratory syndrome (SARS) have been found to be airborne, the importance of monitoring bioaerosols for the control and prevention of airborne epidemic diseases outbreaks is increasing. However, current aerosol collection and detection technologies may be limited to on-field use for real-time monitoring because of the relatively low concentrations of targeted bioaerosols in air samples. Microfluidic devices have been used as lab-on-a-chip platforms and exhibit outstanding capabilities in airborne particulate collection, sample processing, and target molecule analysis, thereby highlighting their potential for on-site bioaerosol monitoring. This review discusses the measurement of airborne microorganisms from air samples, including sources and transmission of bioaerosols, sampling strategies, and analytical methodologies. Recent advancements in microfluidic platforms have focused on bioaerosol sample preparation strategies, such as sorting, concentrating, and extracting, as well as rapid and field-deployable detection methods for analytes on microfluidic chips. Furthermore, we discuss an integrated platform for on-site bioaerosol analyses. We believe that our review significantly contributes to the literature as it assists in bridging the knowledge gaps in bioaerosol monitoring using microfluidic platforms.

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 (I_D) can vary from 0 to 1, depending on the genomic DNA releases from bacteria. In fact, the I_D 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.

Catching Spores: Linking Epidemiology, Pathogen Biology, and Physics to Ground-Based Airborne Inoculum Monitoring

Monitoring airborne inoculum is gaining interest as a potential means of giving growers an earlier warning of disease risk in a management unit or region. This information is sought by growers to aid in adapting to changes in the management tools at their disposal and the market-driven need to reduce the use of fungicides and cost of production. To effectively use inoculum monitoring as a decision aid, there is an increasing need to understand the physics of particle transport in managed and natural plant canopies to effectively deploy and use near-ground aerial inoculum data. This understanding, combined with the nuances of pathogen-specific biology and disease epidemiology, can serve as a guide to designing improved monitoring approaches. The complexity of any pathosystem and local environment are such that there is not a generalized approach to near-ground air sampler placement, but there is a conceptual framework to arrive at a "semi-optimal" solution based on available resources. This review is intended as a brief synopsis of the linkages among pathogen biology, disease epidemiology, and the physics of the aerial dispersion of pathogen inoculum and what to consider when deciding where to locate ground-based air samplers. We leverage prior work in developing airborne monitoring tools for hops, grapes, spinach, and turf, and research into the fluid mechanics governing particle transport in sparse canopies and urban and forest environments. We present simulation studies to demonstrate how particles move in the complex environments of agricultural fields and to illustrate the limited sampling area of common air samplers.