Monitoring of viable airborne SARS virus in ambient air

Virus Dynamics and Decay in Evaporating Human Saliva Droplets on Fomites

The transmission of most respiratory pathogens, including SARS-CoV-2, occurs via virus-containing respiratory droplets, and thus, factors that affect virus viability in droplet residues on surfaces are of critical medical and public health importance. Relative humidity (RH) is known to play a role in virus survival, with a U-shaped relationship between RH and virus viability. The mechanisms affecting virus viability in droplet residues, however, are unclear. This study examines the structure and evaporation dynamics of virus-containing saliva droplets on fomites and their impact on virus viability using four model viruses: vesicular stomatitis virus, herpes simplex virus 1, Newcastle disease virus, and coronavirus HCoV-OC43. The results support the hypothesis that the direct contact of antiviral proteins and virions within the "coffee ring" region of the droplet residue gives rise to the observed U-shaped relationship between virus viability and RH. Viruses survive much better at low and high RH, and their viability is substantially reduced at intermediate RH. A phenomenological theory explaining this phenomenon and a quantitative model analyzing and correlating the experimentally measured virus survivability are developed on the basis of the observations. The mechanisms by which RH affects virus viability are explored. At intermediate RH, antiviral proteins have optimal influence on virions because of their largest contact time and overlap area, which leads to the lowest level of virus activity.

High enrichment and near real-time quantification of airborne viruses using a wet-paper-based electrochemical immunosensor under an electrostatic field

Conventional airborne virus measurement usually requires appreciable sampling and detection times. Viral aerosols should also be collected or prepared in a liquid medium whose volume typically ranges from milliliters to tens of milliliters; hence, many sampling and detection steps need to be taken with the unit horizontal or immobile. Moreover, viral aerosols need to be sufficiently enriched, which makes real-time monitoring difficult. Herein, we present a near real-time enrichment and quantification system of airborne viruses that consists of a wet-paper-based electrochemical immunosensor with a gel electrolyte and a modified electrostatic particle concentrator. A small amount of phosphate-buffered saline flowed on the electrode, which resulted in sensor electrodes that are barely wet (covered in a thin buffer film measuring several micrometers) to ensure antigen-antibody interaction and the removal of non-target particles on the electrode surface. This system ensures that airborne viruses are highly enriched on the working electrode of the immunosensor, and it is possible to measure the MS2 virus particle concentrations every 10 min for 60 min stably and selectively against non-target airborne viruses and bacteria at horizontal and tilted measurement configurations. This system thus has the potential to be used in the real-time mobile monitoring of airborne microorganisms.

High Level Bioaerosol Protection against Infective Aerosols: How Medical Face Masks Compare against Respirators

Face masks and respirators are commonly used to prevent the transmission of infectious diseases that spread by respiratory droplets and aerosols. However, there is still uncertainty about the protective effect of the different types of masks against virus containing aerosols. To determine the as-worn bioaerosol protection efficacy of different face coverings and estimate the possible protective function against airborne diseases, we challenged different respirators and medical masks on a standardized dummy head with a bioaerosol containing MS2 bacteriophages as virus surrogates. In our experiments, FFP2 respirators showed the highest filtration efficacy 94 ± 4 (SD) % followed by medical masks 93 ± 3 (SD) % and KN95 respirators 90 ± 7 (SD) %. Nevertheless, we found no statistically significant difference between respirators and medical masks in terms of provided protection against infective aerosols. Our findings indicate that both respirators and medical masks provide a high as-worn bioaerosol protection efficacy against virus containing aerosols, and therefore, a very high protection against airborne diseases. Considering the higher comfort, better availability, and lower price of medical masks in contrast to respirators, it is recommendable to use medical face masks especially in low risk situations and in general public.

Viral outbreaks detection and surveillance using wastewater-based epidemiology, viral air sampling, and machine learning techniques: A comprehensive review and outlook

A viral outbreak is a global challenge that affects public health and safety. The coronavirus disease 2019 (COVID-19) has been spreading globally, affecting millions of people worldwide, and led to significant loss of lives and deterioration of the global economy. The current adverse effects caused by the COVID-19 pandemic demands finding new detection methods for future viral outbreaks. The environment's transmission pathways include and are not limited to air, surface water, and wastewater environments. The wastewater surveillance, known as wastewater-based epidemiology (WBE), can potentially monitor viral outbreaks and provide a complementary clinical testing method. Another investigated outbreak surveillance technique that has not been yet implemented in a sufficient number of studies is the surveillance of Severe Acute Respiratory Syndrome Coronavirus-2 (SARS-CoV-2) in the air. Artificial intelligence (AI) and its related machine learning (ML) and deep learning (DL) technologies are currently emerging techniques for detecting viral outbreaks using global data. To date, there are no reports that illustrate the potential of using WBE with AI to detect viral outbreaks. This study investigates the transmission pathways of SARS-CoV-2 in the environment and provides current updates on the surveillance of viral outbreaks using WBE, viral air sampling, and AI. It also proposes a novel framework based on an ensemble of ML and DL algorithms to provide a beneficial supportive tool for decision-makers. The framework exploits available data from reliable sources to discover meaningful insights and knowledge that allows researchers and practitioners to build efficient methods and protocols that accurately monitor and detect viral outbreaks. The proposed framework could provide early detection of viruses, forecast risk maps and vulnerable areas, and estimate the number of infected citizens.

Prevention of SARS-CoV-2 (COVID-19) transmission in residential aged care using ultraviolet light (PETRA): a two-arm crossover randomised controlled trial protocol

Background

SARS-CoV-2 poses a considerable threat to those living in residential aged care facilities (RACF). RACF COVID-19 outbreaks have been characterised by the rapid spread of infection and high rates of severe disease and associated mortality. Despite a growing body of evidence supporting airborne transmission of SARS-CoV-2, current infection control measures in RACF including hand hygiene, social distancing, and sterilisation of surfaces, focus on contact and droplet transmission. Germicidal ultraviolet (GUV) light has been used widely to prevent airborne pathogen transmission. Our aim is to investigate the efficacy of GUV technology in reducing the risk of SARS-CoV-2 infection in RACF.

Methods

A multicentre, two-arm double-crossover, randomised controlled trial will be conducted to determine the efficacy of GUV devices to reduce respiratory viral transmission in RACF, as an adjunct to existing infection control measures. The study will be conducted in partnership with three aged care providers in metropolitan and regional South Australia. RACF will be separated into paired within-site zones, then randomised to intervention order (GUV or control). The initial 6-week period will be followed by a 2-week washout before crossover to the second 6-week period. After accounting for estimated within-zone and within-facility correlations of infection, and baseline infection rates (10 per 100 person-days), a sample size of n = 8 zones (n = 40 residents/zone) will provide 89% power to detect a 50% reduction in symptomatic infection rate. The primary outcome will be the incidence rate ratio of combined symptomatic respiratory infections for intervention versus control. Secondary outcomes include incidence rates of hospitalisation for complications associated with respiratory infection; respiratory virus detection in facility air and fomite samples; rates of laboratory confirmed respiratory illnesses and genomic characteristics.

Discussion

Measures that can be deployed rapidly into RACF, that avoid the requirement for changes in resident and staff behaviour, and that are effective in reducing the risk of airborne SARS-CoV-2 transmission, would provide considerable benefit in safeguarding a highly vulnerable population. In addition, such measures might substantially reduce rates of other respiratory viruses, which contribute considerably to resident morbidity and mortality.

Trial registration Australian and New Zealand Clinical Trials Registry ACTRN12621000567820 (registered on 14th May, 2021).

Airborne spread of infectious SARS-CoV-2: Moving forward using lessons from SARS-CoV and MERS-CoV

BACKGROUND

Although an increasing body of data reports the detection of SARS-CoV-2 RNA in air, this does not correlate to the presence of infectious viruses, thus not evaluating the risk for airborne COVID-19. Hence there is a marked knowledge gap that requires urgent attention. Therefore, in this systematic review, viability/stability of airborne SARS-CoV-2, SARS-CoV and MERS-CoV viruses is discussed.

METHODS

A systematic literature review was performed on PubMed/MEDLINE, Web of Science and Scopus to assess the stability and viability of SARS-CoV, MERS-CoV and SARS-CoV-2 on air samples.

RESULTS AND DISCUSSION

The initial search identified 27 articles. Following screening of titles and abstracts and removing duplicates, 11 articles were considered relevant. Temperatures ranging from 20 °C to 25 °C and relative humidity ranging from 40% to 50% were reported to have a protective effect on viral viability for airborne SARS-CoV and MERS-CoV. As no data is yet available on the conditions influencing viability for airborne SARS-CoV-2, and given the genetic similarity to SARS-CoV and MERS-CoV, one could extrapolate that the same conditions would apply. Nonetheless, the effect of these conditions seems to be residual considering the increasing number of cases in the south of USA, Brazil and India, where high temperatures and humidities have been observed.

CONCLUSION

Higher temperatures and high relative humidity can have a modest effect on SARS-CoV-2 viability in the environment, as reported in previous studies to this date. However, these studies are experimental, and do not support the fact that the virus has efficiently spread in the tropical regions of the globe, with other transmission routes such as the contact and droplet ones probably being responsible for the majority of cases reported in these regions, along with other factors such as human mobility patterns and contact rates. Further studies are needed to investigate the extent of aerosol transmission of SARS-CoV-2 as this would have important implications for public health and infection-control policies.

Survival of Virus Particles in Water Droplets: Hydrophobic Forces and Landauer's Principle

Many small biological objects, such as viruses, survive in a water environment and cannot remain active in dry air without condensation of water vapor. From a physical point of view, these objects belong to the mesoscale, where small thermal fluctuations with the characteristic kinetic energy of k_BT (where k_B is the Boltzmann’s constant and T is the absolute temperature) play a significant role. The self-assembly of viruses, including protein folding and the formation of a protein capsid and lipid bilayer membrane, is controlled by hydrophobic forces (i.e., the repulsing forces between hydrophobic particles and regions of molecules) in a water environment. Hydrophobic forces are entropic, and they are driven by a system’s tendency to attain the maximum disordered state. On the other hand, in information systems, entropic forces are responsible for erasing information, if the energy barrier between two states of a switch is on the order of k_BT, which is referred to as Landauer’s principle. We treated hydrophobic interactions responsible for the self-assembly of viruses as an information-processing mechanism. We further showed a similarity of these submicron-scale processes with the self-assembly in colloidal crystals, droplet clusters, and liquid marbles.

Sampling and detection of corona viruses in air: A mini review

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is a strain of coronaviruses that causes coronavirus disease 2019 (COVID-19). In these days, the spread of the SARS-CoV-2 virus through the air has become a controversial topic among scientists. Various organizations provide standard methods for monitoring biological agents in the air. Nevertheless, there has been no standard recommended method for sampling and determination of viruses in air. This manuscript aimed at reviewing published papers for sampling and detection of corona viruses, especially SARS-Cov-2 as a global health concern. It was found that SARS-Cov 2 was present in some air samples that were collected from patient's rooms in hospitals. This result warrants its airborne transmission potential. However, due to the fact that in the most reviewed studies, sampling was performed in the patient's room, it seems difficult to discriminate whether it is airborne or is transmitted through respiratory droplets. Moreover, some other disrupting factors such as patient distance from the sampler, using protective or oxygen masks by patients, patient activities, coughing and sneezing during sampling time, air movement, air conditioning, sampler type, sampling conditions, storage and transferring conditions, can affect the results. About the sampling methods, most of the used samplers such as PTFE filters, gelatin filers and cyclones showed suitable performance for trapping SARS-Co and MERS-Cov viruses followed by PCR analysis.

Modeling Evaporation of Water Droplets as Applied to Survival of Airborne Viruses

Many viruses, such as coronaviruses, tend to spread airborne inside water microdroplets. Evaporation of the microdroplets may result in a reduction of their contagiousness. However, the evaporation of small droplets is a complex process involving mass and heat transfer, diffusion, convection and solar radiation absorption. Virological studies indicate that airborne virus survival is very sensitive to air humidity and temperature. We employ a model of droplet evaporation with the account for the Knudsen layer. This model suggests that evaporation is sensitive to both temperature and the relative humidity (RH) of the ambient air. We also discuss various mechanisms such as the effect of solar irradiation, the dynamic relaxation of moving droplets in ambient air and the gravitational sedimentation of the droplets. The maximum estimate for the spectral radiative flux in the case of cloudless sky showed that the radiation contribution to evaporation of single water droplets is insignificant. We conclude that at small and even at moderately high levels of RH, microdroplets evaporate within dozens of seconds with the convective heat flux from the air being the dominant mechanism in every case. The numerical results obtained in the paper are in good qualitative agreement with both the published laboratory experiments and seasonal nature of many viral infections. Sophisticated experimental techniques may be needed for in situ observation of interaction of viruses with organic particles and living cells within microdroplets. The novel controlled droplet cluster technology is suggested as a promising candidate for such experimental methodology.

Rapid Airborne Influenza Virus Quantification Using an Antibody-Based Electrochemical Paper Sensor and Electrostatic Particle Concentrator

Airborne influenza viruses are responsible for serious respiratory diseases, and most detection methods for airborne viruses are based on extraction of nucleic acids. Herein, vertical-flow-assay-based electrochemical paper immunosensors were fabricated to rapidly quantify the influenza H1N1 viruses in air after sampling with a portable electrostatic particle concentrator (EPC). The effects of antibodies, anti-influenza nucleoprotein antibodies (NP-Abs) and anti-influenza hemagglutinin antibodies (HA-Abs), on the paper sensors as well as nonpulsed high electrostatic fields with and without corona charging on the virus measurement were investigated. The antigenicity losses of the surface (HA) proteins were caused by H₂O₂ via lipid oxidation-derived radicals and ¹O₂ via direct protein peroxidation upon exposure of a high electrostatic field. However, minimal losses in antigenicity of NP of the influenza viruses were observed, and the concentration of the H1N1 viruses was more than 160 times higher in the EPC than the BioSampler upon using NP-Ab based paper sensors after 60 min collection. This NP-Ab-based paper sensors with the EPC provided measurements comparable to quantitative polymerase chain reaction (qPCR) but much quicker, specific to the influenza H1N1 viruses in the presence of other airborne microorganisms and beads, and more cost-effective than enzyme-linked immunosorbent assay and qPCR.

Covid-19 Airborne Transmission and Its Prevention: Waiting for Evidence or Applying the Precautionary Principle?

Besides the predominant ways of transmission of SARS-CoV-2 (namely, contacts and large droplets) the airborne one is increasingly taken into consideration as a result of latest research findings. Nevertheless, this possibility has been already suggested by previous studies on other coronaviruses including SARS-CoV and MERS-CoV. To describe the state of the art of coronaviruses and airborne transmission, a systematic review was carried out using the PRISMA methodology. Overall, 64 papers were selected and classified into three main groups: laboratory experiments (12 papers), air monitoring (22) and epidemiological and airflow model studies (30). The airborne transmission of SARS-CoV-2 is suggested by the studies of the three groups, but none has yet obtained complete evidence. The sampling and detection methods have not been validated, therefore monitoring results are affected by a possible underestimation. Then, epidemiological investigations only hypothesize the airborne transmission as a possible explanation for some illness cases, but without estimating its attributable risk. Nevertheless, while waiting for more evidence, it is urgent to base advice on preventive measures, such as the use of masks, safe distancing and air ventilation, on the precautionary principle.

Survival of aerosolized coronavirus in the ambient air

An inactivation of airborne pathogenic Middle East Respiratory Syndrome (MERS-CoV) virus was investigated under controlled laboratory conditions. Two sets of climatic conditions were used in the experiments; (1) representing common office environment (25 °C and 79% RH) and (2) climatic conditions of the Middle Eastern region where the virus was originated from (38 °C and 24% RH). At the lower temperature, the virus demonstrated high robustness and strong capability to survive with about 63.5% of microorganisms remaining infectious 60 min after aerosolisation. Fortunately, virus decay was much stronger for hot and dry air scenario with only 4.7% survival over 60 min procedure.

Highly Enriched, Controllable, Continuous Aerosol Sampling Using Inertial Microfluidics and Its Application to Real-Time Detection of Airborne Bacteria

We report a novel microfluidic technique for sampling of aerosols into liquids. The two-phase fluid, sampling air and collecting liquid, forms a stratified flow in the curved microchannel. By passing fluids through the curved region, the particles are transferred from air into the liquid phase by the particle centrifugal and drag forces. This microfluidic-based aerosol-into-liquid sampling system, called the MicroSampler, is driven by particle inertial differences. To evaluate the physical particle collection efficiency of the MicroSampler, we used standard polystyrene-latex (PSL) particles ranging in size from 0.6 to 2.1 μm and measured particle concentrations upstream and downstream of the MicroSampler with an aerodynamic particle sizer. The cutoff diameter of particle collection was selected controlling the air flow velocity (microfluidic air flow of 0.6 L/min showed a particle collection efficiency of ∼98% at a particle diameter of 1 μm), and continuous enriched particle sampling was possible for real-time postprocessing application. With regard to biological collection efficiency, the MicroSampler showed superior microbial recovery (Staphylococcus epidermidis) compared to the conventional BioSampler technique. These results indicate that our MicroSampler can be used as a portable, cost-effective, simple, and continuous airborne microorganism collector for applications in real-time bioaerosol detection.

Miniature PCR based portable bioaerosol monitor development

AIMS

A portable bioaerosol monitor is greatly demanded technology in many areas including air quality control, occupational exposure assessment and health risk evaluation, environmental studies and, especially, in defence and bio-terrorism applications. Our recent groundwork allowed us to formulate the concept of a portable bioaerosol monitor, which needs to be light, user friendly, reliable and capable of detecting airborne pathogens within 1-1·5 h on the spot.

METHODS AND RESULTS

Conceptually, the event of a bioaerosol concentration burst is determined by triggers to commence the representative air sampling with sequential real-time polymerase chain reaction (PCR) confirmation of the targeted micro-organism present in the air. To minimize reagent consumption and idle running of the technology, an event of a bioaerosol burst is confirmed by three parameters: aerosol particle size, concentration and composition. Only particle sizes above 200 nm attract interest in the bioaerosol. Only an elevated aerosol concentration above the threshold (background aerosol concentration) is a signal to commence the analytical procedure. The combination of our previously developed personal bioaerosol sampler, aerosol particle counter based trigger and portable real-time PCR device formed the basis of the bioaerosol monitoring technology. The portable real-time PCR device was advanced to provide internally controlled detection, significantly reducing false-positive alarms.

CONCLUSIONS

The technique is capable of detecting selected airborne micro-organisms on the spot within 30-80 min, depending on the genome organization of the particular strain.

SIGNIFICANCE AND IMPACT OF THE STUDY

Due to recent outbreaks of infectious airborne diseases and the continuing threat of intentionally released bioaerosol attacks, investigations into the possibility of the early and reliable detection of pathogenic micro-organisms in the air is becoming increasingly important. The proposed technology consisting of a bioaerosol sampler, technology trigger and PCR device is capable of detecting selected airborne micro-organisms on the spot within a short time period.

Integrated micro-optofluidic platform for real-time detection of airborne microorganisms

We demonstrate an integrated micro-optofluidic platform for real-time, continuous detection and quantification of airborne microorganisms. Measurements of the fluorescence and light scattering from single particles in a microfluidic channel are used to determine the total particle number concentration and the microorganism number concentration in real-time. The system performance is examined by evaluating standard particle measurements with various sample flow rates and the ratios of fluorescent to non-fluorescent particles. To apply this method to real-time detection of airborne microorganisms, airborne Escherichia coli, Bacillus subtilis, and Staphylococcus epidermidis cells were introduced into the micro-optofluidic platform via bioaerosol generation, and a liquid-type particle collection setup was used. We demonstrate successful discrimination of SYTO82-dyed fluorescent bacterial cells from other residue particles in a continuous and real-time manner. In comparison with traditional microscopy cell counting and colony culture methods, this micro-optofluidic platform is not only more accurate in terms of the detection efficiency for airborne microorganisms but it also provides additional information on the total particle number concentration.

Characteristics of airborne Staphylococcus aureus (including MRSA) in Chinese public buildings

The aim of this study was to evaluate the concentration and size distribution of airborne culturable Staphylococcus aureus (S. aureus) (including MRSA) in Chinese public buildings. Air samples were collected, using six-stage Andersen sampler from five different public buildings in one large Chinese community. The mean indoor concentrations of the total and respirable airborne S. aureus were 72 and 50 CFU/m3 in the general hospital, 72 and 49 CFU/m3 in the kindergarten, 76 and 52 CFU/m3 in the hotel, 84 and 57 CFU/m3 in the movie theater, and 55 and 40 CFU/m3 in the university classroom. Respirable S. aureus amounted to approximately 57-73 % of the total S. aureus concentrations. Mean total and respirable concentrations of airborne MRSA were 32 and 20 CFU/m3 in the general hospital, 20 and 13 CFU/m3 in the kindergarten, 23 and 16 CFU/m3 in the hotel, 33 and 20 CFU/m3 in the movie theater, and 24 and 17 CFU/m3 in the university classroom. Respirable MRSA amounted to approximately 61-72 % of the total MRSA concentrations. The ratios of indoor and outdoor concentration for airborne S. aureus and MRSA were more than 1.0 in all the investigated public buildings. The size distribution results showed relatively high collection rates on stage 4 (2.1-3.3 μm) for both airborne culturable S. aureus and MRSA regardless of the type of public buildings.

Surface plasmon resonance-based real-time bioaerosol detection

AIMS

Rapid and precise bioaerosol detection in different environments has become an important research and technological issue over last decades. Previously, we employed a real-time PCR protocol in conjunction with personal bioaerosol sampler for rapid detection of airborne viruses. The approach has been proved to be specific and sensitive. However, a period of time required for entire procedure was in manner of hours. Some new developments are required to decrease the detection time down to real-time protocols.

METHODS AND RESULTS

Presently, a surface plasmon resonance (SPR)-based immunosensor that coupled with a specific antigen-antibody reaction could offer sensitive, specific, rapid and label-free detection. This study describes the possibility of combining the personal sampler with SPR technology for qualitative and extremely rapid detection of airborne micro-organisms. Common viral surrogate MS2 bacteriophage, frequently used in bioaerosol studies, was employed as a model organism. The results of the sensor functionalizing procedure with monoclonal anti-MS2 antibody and optimization of the chip performance are presented. The SPR-based detection of the airborne virus was found to be very fast; the viral presence was detected in less than 2 min, and the entire procedure (sampling and analysis) was undertaken in 6 min, which could be considered as real-time detection for this type of measurements.

CONCLUSIONS

The combination of SPR with the personal sampler targeted towards bioaerosol detection was proven to be feasible. The SPR sensor was found to be highly stable and suitable for multiple utilizations without significant decrease in response. The suggested approach opens new possibilities for the development of portable and rapid (almost real time) bioaerosol monitors.

SIGNIFICANCE AND IMPACT OF THE STUDY

This technology is the first in the world real-time bioaerosol monitor. This outcome would be of strong interest to individuals representing public health, biosecurity, defence forces, environmental sciences and many others.

Degenerate primers based RT-PCR for rapid detection and differentiation of airborne chicken Newcastle disease virus in chicken houses

Airborne Newcastle disease (ND) viruses in the air of five chicken houses were detected and differentiated by reverse transcriptase polymerase chain reaction (RT-PCR) using degenerate primers. Fifteen air samples were collected with All Glass Impinger-30 (AGI-30) air samplers in each house. Airborne ND viruses were also isolated and virulence identified by in vivo tests. Avirulent viruses were detected both in air samples and swab samples in four houses by degenerate primers based RT-PCR. Virulent viruses were detected only in the air samples by degenerate primers based RT-PCR in two houses. Seven strains viruses were isolated from the RT-PCR positive air samples. Of the seven strains, three strains were virulent viruses and four strains were avirulent viruses identified by in vivo tests. The results showed that it was feasible to detect and differentiate NDV in the air samples using degenerate primers based RT-PCR. This technique could decrease the time it required identify NDV infected flocks while distinguishing between virulent and avirulent viruses. It will help effectively to control Newcastle disease.

Occurrence and transmission of Newcastle disease virus aerosol originating from infected chickens under experimental conditions

In order to better understand airborne transmission of Newcastle disease, a model system was established and two trials were conducted. Twenty-five principal specific pathogen free (SPF) chickens were inoculated with NDV and were housed in one isolator. 6 days after the chickens were challenged, 15 chickens were placed into another isolator which received its air supply from the first isolator. The NDV aerosol originating from inoculated chickens was collected with All Glass Impinger-30 (AGI-30) to study the occurrence and concentration of NDV aerosol. The antibody response to infection was assessed by the hemagglutination inhibition (HI) test and viral shedding was detected by RT-PCR and Dot-ELISA. NDV aerosol was initially detectable by RT-PCR and cell culture at day 2 or 3 post-inoculation (dpi). The aerosol concentration peaked at 1.69x10(4)PFU/m(3) air at 13dpi in trial 1, 9.14x10(3)PFU/m(3) air at 11dpi in trial 2 and was consistently detectable up to 40dpi. NDV shedding was detectable from 2 to 40dpi of inoculated chickens and from 6 days post-aerosol exposed infection (dpi) to 33dpi of aerosol exposed chickens. The viral strain induced high antibody level, both in inoculated and in aerosol exposed chickens. Airborne transmission did occur, as shown by NDV shedding and seroconversion to NDV in aerosol exposed chickens. The results indicated that viruses shed from infected chickens readily aerosolized and airborne transmission of NDV was possible.

Removal of bioaerosols by the combination of a photocatalytic filter and negative air ions

This study focused on the investigation of the effectiveness of negative air ionization (NAI), photocatalytic oxidation (PCO), and the combination of NAI and PCO on the removal of aerosolized Escherichia coli, Candida famata, and λ vir phage under different relative humidity. The experiments were conducted with a stainless steel reactor equipped with a negative air ion generator, a photocatalytic filter, and two ultraviolet lamps with 365 nm wavelength. The removal efficiency ( η ) , defined as one minus the ratio of the outlet concentration to the inlet concentration of the appropriate bioaerosol, was used to evaluate the effectiveness of the removal methods. The combination of NAI and PCO was the most efficient removal method for aerosolized E. coli ( η = 0.304 ± 0.06 - 0.364 ± 0.008 ) , C. famata ( η = 0.433 ± 0.08 - 0.598 ± 0.047 ) , and λ vir phage ( η = 0.689 ± 0.02 - 0.903 ± 0.06 ) . In this removal method, the contributions of NAI were higher than those of PCO for the removal of E. coli and C. famata; for the removal of λ virus phage the contributions of NAI and PCO were comparable NAI was the least efficient removal method for bioaerosols, and the removal efficiencies are: η = 0.175 ± 0.04 - 0.245 ± 0.03 for E. coli; η = 0.216 ± 0.007 - 0.297 ± 0.044 for C. famata; and η = 0.299 ± 0.12 - 0.384 ± 0.02 for λ vir phage.

Effects of humidity and other factors on the generation and sampling of a coronavirus aerosol

Suspensions of transmissible gastroenteritis virus (TGEV), a porcine coronavirus, were nebulized at rates of 0.1-0.2 ml/min into moving air using a Collison nebulizer or a plastic medical nebulizer operating at pressures ranging from 7 to 15 psi. The airborne viruses were collected on heating, ventilating, and air conditioning (HVAC) filters in an experimental apparatus and also sampled upstream of these test filters using AGI-30 and BioSampler impinger samplers. To study the effects of relative humidity (RH) on TGEV collection by the filters and samplers, the virus was nebulized into air at 30, 50, 70, and 90% RH. There were no significant changes in virus titer in the nebulizer suspension before and after nebulization for either nebulizer at any of the pressures utilized. Aerosolization efficiency - the ratio of viable virus sampled with impingers to the quantity of viable virus nebulized - decreased with increasing humidity. BioSamplers detected more airborne virus than AGI-30 samplers at all RH levels. This difference was statistically significant at 30 and 50% RH. Nebulizer type and pressure did not significantly affect the viability of the airborne virus. Virus recovery from test filters relative to the concentration of virus in the nebulizer suspension was less than 10%. The most and the least virus were recovered from filter media at 30% and 90% RH, respectively. The results suggest that TGEV, and perhaps other coronaviruses, remain viable longer in an airborne state and are sampled more effectively at low RH than at high humidity.

Using a bioaerosol personal sampler in combination with real-time PCR analysis for rapid detection of airborne viruses

We have recently developed a new personal sampler and demonstrated its feasibility for detection of viable airborne microorganisms including bacteria, fungi and viruses. To accelerate the time-consuming analytical procedure involving 2-5 days of biological testing, we employed a real-time PCR protocol in conjunction with the personal sampler for collection of airborne viruses. The advantage of this approach is that if the presence of a particular pathogen in the air is detected by the PCR, the remaining collecting liquid can be further analysed by more time-consuming biological methods to estimate the number of airborne infectious/live microorganisms. As sampling of bioaerosols in natural environments is likely to be associated with substantial contamination by a range of microorganisms commonly existing in an ambient air, an investigation of the specificity of detection by targeted PCR analysis is required. Here we present the results of the study on the detection of Influenza virus in the ambient air contaminated with high concentrations of bacteria and fungi using real-time PCR protocol. The combined sampling PCR detection method was found to be fully feasible for the rapid ( approximately 2.5 h) and highly specific (no cross-reactivity) identification of the labile airborne virus in the air containing elevated concentrations of other microorganisms.

Personal sampler for monitoring of viable viruses; modelling of outdoor sampling conditions

A new personal bioaerosol sampler has recently been developed and verified to be very efficient for monitoring of viable airborne bacteria, fungi and viruses. The device is capable of providing high recovery rates even for microorganisms which are rather sensitive to physical and biological stresses. However, some mathematical procedure is required for realistic calculation of an actual concentration of viable bioaerosols in the air taking into account a rate of inactivation of targeted microorganisms, sampling parameters, and results of microbial analysis of collecting liquid from the sampler. In this paper, we develop such procedure along with the model of aerosol propagation for outdoor conditions. Combining these procedures allows one to determine the optimal sampling locations for the best possible coverage of the area to be monitored. A hypothetical episode concerned with terrorists' attack during music concert in the central square of Novosibirsk, Russia was considered to evaluate possible coverage of the area by sampling equipment to detect bioaerosols at various locations within the square. It was found that, for chosen bioaerosol generation parameters and weather conditions, the new personal sampler would be capable to reliably detect pathogens at all locations occupied by crowd, even at distances of up to 600 m from the source.

Sampling methodologies and dosage assessment techniques for submicrometre and ultrafine virus aerosol particles

AIMS

The aerosolization and collection of submicrometre and ultrafine virus particles were studied with the objective of developing robust and accurate methodologies to study airborne viruses.

METHODS AND RESULTS

The collection efficiencies of three sampling devices used to sample airborne biological particles - the All Glass Impinger 30, the SKC BioSampler and a frit bubbler - were evaluated for submicrometre and ultrafine virus particles. Test virus aerosol particles were produced by atomizing suspensions of single-stranded RNA and double-stranded DNA bacteriophages. Size distribution results show that the fraction of viruses present in typical aqueous virus suspensions is extremely low such that the presence of viruses has little effect on the particle size distribution of atomized suspensions. It has been found that none of the tested samplers are adequate in collecting submicrometre and ultrafine virus particles, with collection efficiencies for all samplers below 10% in the 30-100 nm size range. Plaque assays and particle counting measurements showed that all tested samplers have time-varying virus particle collection efficiencies. A method to determine the size distribution function of viable virus containing particles utilizing differential mobility selection was also developed.

CONCLUSIONS

A combination of differential mobility analysis and traditional plaque assay techniques can be used to fully characterize airborne viruses.

SIGNIFICANCE AND IMPACT OF THE STUDY

The data and methods presented here provide a fundamental basis for future studies of submicrometre and ultrafine airborne virus particles.