We aggregate key research papers and use AI tools to summarize them. Get familiar with UV, aerosol transmission, and other topics needed to understand how to build a safer indoor environment.


Aerosol

Written by: Kaiwei Luo, Zhao Lei, Zheng Hai, Shanliang Xiao, Jia Rui, Hao Yang, Xinping Jing, Hui Wang, Zhengshen Xie, Ping Luo, Wanying Li, Qiao Li, Huilu Tan, Zicheng Xu, Yang Yang, Shixiong Hu, Tianmu Chen

A total of 243 individuals, in addition to patient A, were investigated for the cluster of COVID-19 cases who were epidemiologically linked to the bus trips of patient A on January 22, 2020

  • On January 22, 2020, Patient A travelled without wearing face mask from Place I to Place III via public transportation, with a transfer at Place II
  • According to the guidelines of the New Coronavirus Pneumonia Prevention and Control Program (4th edition) published by National Health Commission of China[8], nasopharyngeal swabs were collected from suspected cases, including patient A and contacts with subsequent illness onsets, and all traced close contacts of confirmed cases
  • A total of 243 individuals, in addition to patient A, were investigated for the cluster of COVID-19 cases who were epidemiologically linked to the bus trips of patient A on January 22, 2020
  • Several limitations are inherent in our study: (1) we could not verify transmission via fomites as no environmental samples were collected; (2) the secondary attack rate (SAR) was likely over-estimated as it is solely based on a single large cluster; (3) there might be recalling bias because the information was collected retrospectively; (4) no viral genetic sequence data were available from these cases to prove linkage; and (5) some of the secondary and tertiary cases could have been exposed to unknown infections, especially asymptomatic ones, before or after the bus trips
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Written by: Andrew D. Haddow, Taylor R. Watt, Holly A. Bloomfield, Joshua D. Shamblin, David N. Dyer, and David E. Harbourt

We carried out a pilot study to model the stability of SARS-CoV-2 on apples, tomatoes, and jalapeño peppers at two temperatures following an aerosol exposure designed to simulate a low-dose SARS-CoV-2 airborne transmission event involving droplet nuclei

  • Certified organic produce was obtained from a local grocery store—selections being made at random
  • We carried out a pilot study to model the stability of SARS-CoV-2 on apples, tomatoes, and jalapeño peppers at two temperatures following an aerosol exposure designed to simulate a low-dose SARS-CoV-2 airborne transmission event involving droplet nuclei
  • Three samples were taken from each produce type at each time point with a swab pass of approximately 7 cm in length, after which the swab was flipped over to the clean side, and a second pass was made in a different area, again the length of swab pass being approximately 7 cm
  • We did not swab the plastic identification stickers commonly found on individual pieces of produce, it is possible that infectious virus may be more stable on these impervious surfaces.
  • Infectious virus contained in respiratory droplets, droplet nuclei, and/or mucus during the course of a natural infection might help stabilize the virus for a longer duration
  • We demonstrated there is a low potential for infectious SARS-CoV-2 to be detected on apples, tomatoes, and jalapeño peppers at 1 hour following a low-dose experimental aerosol exposure
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Written by: Li, Y., Qian, et al.

Aerosol transmission of SARS-CoV-2 due to poor ventilation may explain the community spread of COVID-19

  • Introduction: Debate continues on the role of aerosol transmission of SARS-CoV-2, the virus that causes COVID-19, in the rapidly growing COVID-19 pandemic.
  • The COVID-19 outbreak in Guangzhou, China was identified in early 2020 and linked to three seemingly non-associated clusters of unrelated families (A, B, C) (Lu et al, 2020).
  • The role of aerosols in the transmission of SARS-CoV-2 remains debated.
  • The authors analysed an outbreak involving three non-associated families in Restaurant X in Guangzhou, China, and assessed the possibility of aerosol transmission of SARS-CoV-2 and characterize the associated environmental conditions
  • Methods: The authors collected epidemiological data, obtained a video record and a patron seatingarrangement from the restaurant, and measured the dispersion of a warm tracer gas as a surrogate for exhaled droplets from the suspected index patient.
  • The authors obtained the seating arrangement of the three family members and remaining patrons in Restaurant X as well as the dates of COVID-19 symptom onset (Figure 2A), where the symptom onset date is defined as the day when symptoms were first noticed by the patient.
  • The fire door was used approximately every 2 minutes
  • Results: Three families (A, B, C), 10 members of which were subsequently found to have been infected with SARS-CoV-2 at this time, or previously, ate lunch at Restaurant X on Chinese New Year’s Eve (January 24, 2020) at three neighboring tables.
  • Contact tracing identified 193 patrons in the restaurant, 68 of whom were on the third floor at the same time as families A, B, and C, including 57 restaurant workers and 11 workers in the hotel where Family A had stayed.
  • None of these people were infected with the virus.
  • Only the 10 patrons in the restaurant were infected, comprising the index patient and nine others, and at least five of them who the authors suspect became infected at this lunch due to exposure to exhaled droplets from the index patient that contained virus particles
  • Conclusion: Lu et al (2020) suggested that droplet transmission is the most likely primary cause of this outbreak, but pointed out that the outbreak cannot be explained by droplet transmission alone, because the distances between the index patient (A1) and patrons at the other tables are all greater than 1 m.
  • No evidence was identified to support exposure to SARS-Co-V2 occurring via these routes in this instance.Aerosol transmission of SARS-CoV-2 due to poor ventilation may explain the community spread of COVID-19
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Written by: Sung-Han Kim, So Young Chang, Minki Sung, et al.

Methods: We explored the possible contribution of contaminated hospital air and surfaces to Middle East respiratory syndrome transmission by collecting air and swabbing environmental surfaces in 2 hospitals treating MERS-CoV patients

  • Introduction: The largest outbreak of Middle East respiratory syndrome coronavirus (MERS-CoV) outside the Middle East occurred in South Korea in 2015 and resulted in 186 laboratory-confirmed infections, including 36 (19%) deaths.
  • Some hospitals were considered epicenters of infection and voluntarily shut down most of their operations after nearly half of all transmissions occurred in hospital settings.
  • The ways that MERS-CoV is transmitted in healthcare settings are not well defined
  • Methods: The authors explored the possible contribution of contaminated hospital air and surfaces to MERS transmission by collecting air and swabbing environmental surfaces in 2 hospitals treating MERS-CoV patients.
  • The samples were tested by viral culture with reverse transcription polymerase chain reaction (RT-PCR) and immunofluorescence assay (IFA) using MERS-CoV Spike antibody, and electron microscopy (EM)
  • Results: The presence of MERS-CoV was confirmed by RT-PCR of viral cultures of 4 of 7 air samples from 2 patients' rooms, 1 patient's restroom, and 1 common corridor.
  • MERS-CoV was detected in 15 of 68 surface swabs by viral cultures.
  • IFA on the cultures of the air and swab samples revealed the presence of MERS-CoV.
  • EM images revealed intact particles of MERS-CoV in viral cultures of the air and swab samples
  • Conclusion: These data provide experimental evidence for extensive viable MERS-CoV contamination of the air and surrounding materials in MERS outbreak units.
  • The authors' findings call for epidemiologic investigation of the possible scenarios for contact and airborne transmission, and raise concern regarding the adequacy of current infection control procedures
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Written by: Azaibi Tamin, Brandi N. Williamson, James O. Lloyd-Smith, et al.

We evaluated the stability of SARS-CoV-2 and SARS-CoV-1 in aerosols and on various surfaces and estimated their decay rates using a Bayesian regression model

  • A novel human coronavirus that is named severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) emerged in Wuhan, China, in late 2019 and is causing a pandemic.1 The authors analyzed the aerosol and surface stability of SARS-CoV-2 and compared it with SARS-CoV-1, the most closely related human coronavirus.2.
  • The authors evaluated the stability of SARS-CoV-2 and SARS-CoV-1 in aerosols and on various surfaces and estimated their decay rates using a Bayesian regression model.
  • As shown in Panel A, the titer of aerosolized viable virus is expressed in 50% tissue-culture infectious dose (TCID50) per liter of air.
  • As shown in Panel C, violin plots indicate posterior distribution for the half-life of viable virus based on the estimated exponential decay rates of the virus titer.
  • Experimental conditions are ordered according to the posterior median half-life of SARS-CoV-2.
  • The dashed lines indicate the limit of detection, which was 3.33×100.5 TCID50 per liter of air for aerosols, 100.5 TCID50 per milliliter of medium for plastic, steel, and cardboard, and 101.5 TCID50 per milliliter of medium for copper.
  • SARS-CoV-2 remained viable in aerosols throughout the duration of the experiment (3 hours), with a reduction in infectious titer from 103.5 to 102.7 TCID50 per liter of air.
  • This reduction was similar to that observed with SARS-CoV-1, from 104.3 to 103.5 TCID50 per milliliter (Figure 1A).
  • SARS-CoV-2 was more stable on plastic and stainless steel than on copper and cardboard, and viable virus was detected up to 72 hours after application to these surfaces (Figure 1A), the virus titer was greatly reduced.
  • No viable SARS-CoV-2 was measured after 24 hours and no viable SARS-CoV-1 was measured after 8 hours (Figure 1A).
  • Both viruses had an exponential decay in virus titer across all experimental conditions, as indicated by a linear decrease in the log10TCID50 per liter of air or milliliter of medium over time (Figure 1B).
  • The half-lives of SARS-CoV-2 and SARS-CoV-1 were similar in aerosols, with median estimates of approximately 1.1 to 1.2 hours and 95% credible intervals of 0.64 to 2.64 for SARS-CoV-2 and 0.78 to 2.43 for SARS-CoV-1 (Figure 1C, and Table S1 in the Supplementary Appendix).
  • The longest viability of both viruses was on stainless steel and plastic; the estimated median half-life of SARS-CoV-2 was approximately 5.6 hours on stainless steel and 6.8 hours on plastic (Figure 1C).
  • This indicates that differences in the epidemiologic characteristics of these viruses probably arise from other factors, including high viral loads in the upper respiratory tract and the potential for persons infected with SARS-CoV-2 to shed and transmit the virus while asymptomatic.3,4 The authors' results indicate that aerosol and fomite transmission of SARS-CoV-2 is plausible, since the virus can remain viable and infectious in aerosols for hours and on surfaces up to days.
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Written by: Morgan Soffler MD

Aerosols containing a small concentration of virus in poorly ventilated spaces, combined with low humidity and high temperature,6 might result in an infectious dose over time

  • Data on factors related to this transmission are scarce, the spread of SARS-CoV-2 is thought to mostly be via the transmission of respiratory droplets coming from infected individuals.1 Small droplets, from submicron to approximately 10 μm diameter, produced during speech and coughing, have been shown to contain viral particles,2 which can remain viable and infectious in aerosols for 3 h.3 The droplets can be transmitted either directly by entering the airway through the air,4 or indirectly by contact transfer via contaminated hands.
  • The mode of transmission could affect whether an infection starts in the upper or lower respiratory tract, which is thought to affect the severity of the disease progression.5 Notably, the dose–response relationship of SARS-CoV-2 infection is still unclear, especially with respect to aerosol transmission of the virus.
  • Aerosols containing a small concentration of virus in poorly ventilated spaces, combined with low humidity and high temperature,6 might result in an infectious dose over time.
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Written by: Buonanno, G., Morawska, et al.

This study presents a novel approach for quantitative assessment of the individual infection risk of susceptible subjects exposed in indoor microenvironments in the presence of an asymptomatic infected SARS-CoV-2 subject

  • The airborne transmission of a virus and the consequent contagion risk assessment is a complex issue that requires multidisciplinary knowledge.
  • A distribution of quanta emission rates (ERq), was obtained as a result of application of the Monte Carlo method (Figure 1), i.e. the probability density function of ERq. is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity.
  • In the exposure scenarios tested with the prospective and retrospective approaches, to take the variability of the input parameters into account, the indoor quanta concentration n(t) was determined through eq (2), applying a Monte Carlo method that adopted the probability density functions characteristic of quanta emission rates (ERq).
  • (2) and (3), using the following input data: i) room volume of 810 m3; ii) documented probability of infection, i.e. attack rate, equal to 53%; iii) exposure time of 2.5 h; iv) singing at a light activity level for all people; and v) natural ventilation with an AER = 0.5 h-1.
  • As discussed in section 2.2, the probability density function of the probability of infection is mostly influenced by the probability density function of the quanta emission rate when moving backwards in the four-step approach; once the exposure scenario is defined, all the parameters contributing to the calculation of PI (ventilation, room volume, subject is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity.
  • In the first case, knowing the exposure time of the healthy subject in the environment in question, the corresponding individual infection risk can be evaluated and compared to an is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity.
  • In exposure scenario B, there is no vocalization in the subject's activity, the high inhalation rate produces considerable ERq values, increasing the individual risk; in order to guarantee an acceptable infection risk of [] the maximum exposure times resulted quite short, i.e. 14 min and 29 min for 0.5 h-1 and 10 h-1, respectively.
  • The retrospective analysis applied to the restaurant in Guangzhou (Figure 5a) revealed that, under the boundary conditions considered in the simulation, a probability of infection (PI) after 1 hour of exposure equal to the attack rate (45%) can be reached for a quanta emission rate of
  • The approach and consequent calculation reported here clearly highlights that the explanation of such a high number of infected people does not necessarily require the presence of a superspreader in the environment, but is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity.
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Written by: Miller, S. L., Nazaroff, et al.

The risk of widespread transmission owing to close contact would seem to be low in this event, considering that there is believed to have been only one index case who would have been seated in proximity to only a small proportion of the other chorale members

  • Introduction: SARS-CoV-2 was first reported in China at the end of 2019 and rapidly spread to the rest of the world over the subsequent months.
  • Airborne transmission is strongly suspected to play a significant role in superspreading events (SSEs) under certain conditions.[13] SSEs occur when a large number of secondary transmissions are produced early in an outbreak and transmission is sustained in later stages.[14] Some people release respiratory aerosol at an order of magnitude greater rate than their peers and might contribute to superspreading events.[15] The very broad range of viral loads in respiratory fluids may be an important factor influencing SSE.
  • An infectious respiratory aerosol is a collection of pathogen-laden particles in air emitted during respiring activities of an infected individual. 16
  • Results: The mean (± standard deviation) inferred emission rate was E = 970 (± 390) quanta per h.
  • It is plausible that more than one person attending the rehearsal was infectious, given that the disease was diagnosed in some of the singers soon after the March 10 rehearsal
  • If this was the case the emission rate would be the sum of emission rates from each infectious individual.
  • The average incubation time for this case was ~3-4 days, which is comparable to literature reports, making the presence of additional index cases less likely
  • Conclusion: Growing evidence supports a view that inhaling respiratory aerosol is an important route for transmission of SARS-CoV-2 under certain conditions.
  • Given the circumstances of the rehearsal, such a high secondary attack rate by the close-contact route would have necessitated effective transmission based largely on brief proximate encounters.
  • That interpretation of the high attack rate in this event seems much less probable than the alternative explanation, i.e. that inhalation of infectious respiratory aerosol from “shared air” was the leading mode of transmission
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Written by: T.G. Matthews, C.V. Thompson, D.L. Wilson, et al.

Very low air velocities were measured in six occupied homes and one unoccupied house when forced-air air-conditioning systems were turned off

  • Very low air velocities were measured in six occupied homes and one unoccupied house when forced-air air-conditioning systems (i.e., HVAC) were turned off.
  • Segregating the velocity data by monitoring site, median velocities of 4.2, 4.3, 10.2, and 12.4 cm/s were found in the master bedroom, basement, and kitchen of the six occupied homes and the dining/living room of the unoccupied house, respectively.
  • The comparatively high velocities in the kitchens correlated with increased occupant activities and the use of ceiling and/or exhaust fans.
  • Segregating the data by use of forced-air HVAC systems, the median velocities increased from 5.8 to 6.2, 3.2 to 5.7, 1.5 to 8.1, and 4.4 to 15.5.
  • Cm/s with HVAC operation in three occupied houses and one unoccupied house, respectively.
  • The lowest median velocity of 1.1 cm/s was found in a parent's bedroom, where occupant activities were purposely limited and the HVAC was off.
  • These low air velocities raise concern that air movement may sometimes be inadequate for quantitative passive monitoring of pollutant vapors.
  • Ten and 50% reductions in sampling rates are reported in the literature for passive monitors at air velocities ranging from <0.7 to 25 cm/s and from <0.7 to 2 cm/s, respectively.
  • Low velocities may limit off-gassing from evaporatively controlled emitters and decrease the thermal comfort of inhabitants under warm and humid conditions.
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Written by: Ignatius T.S. Yu, Yuguo Li, Tze Wai Wong, et al.

Residents of the floors at the middle and upper levels in building E were at a significantly higher risk than residents on lower floors; this finding is consistent with a rising plume of contaminated warm air in the air shaft generated from a middle-level apartment unit

  • Introduction: Hong Kong was the hardest-hit area during the worldwide epidemic of infection with the severe acute respiratory syndrome (SARS) virus in 2003, with the highest incidence rate (1755 cases in a population of 6.7 million) and a high case fatality rate of 17 percent (299 deaths).[1].
  • The large community outbreak in the Amoy Gardens housing complex affected more than 300 residents of this private housing estate.
  • Subsequent cases of SARS were located in clusters in four buildings and at certain floor levels.[6] Previously available reports have not provided a satisfactory explanation of the features of the outbreak in the Amoy Gardens housing complex.[7-9].
  • The authors analyzed the temporal and spatial distributions of cases in a large community outbreak of SARS in Hong Kong and examined the correlation of these data with the three-dimensional spread of a virus-laden aerosol plume that was modeled using studies of airflow dynamics
  • Methods: The authors determined the distribution of the initial 187 cases of SARS in the Amoy Gardens housing complex in 2003 according to the date of onset and location of residence.
  • The spread of the airborne, virus-laden aerosols generated by the index patient was modeled with the use of airflow-dynamics studies, including studies performed with the use of computational fluid-dynamics and multizone modeling
  • Results: The curves of the epidemic suggested a common source of the outbreak. All but 5 patients lived in seven buildings (A to G), and the index patient and more than half the other patients with SARS (99 patients) lived in building E.
  • Residents of the floors at the middle and upper levels in building E were at a significantly higher risk than residents on lower floors; this finding is consistent with a rising plume of contaminated warm air in the air shaft generated from a middle-level apartment unit.
  • The risks for the different units matched the virus concentrations predicted with the use of multizone modeling.
  • The distribution of risk in buildings B, C, and D corresponded well with the three-dimensional spread of virus-laden aerosols predicted with the use of computational fluid-dynamics modeling
  • Conclusion: Various hypotheses have been proposed to explain the spread of the SARS virus in the Amoy Gardens outbreak.
  • The investigation by the government of the Hong Kong Special Administrative Region suggested that the index patient infected a small group of residents in building E and that the infection subsequently spread to the other residents in that building through the sewage-disposal system, person-to-person contact, and the use of communal facilities such as elevators and staircases.
  • The WHO report did not provide an explanation for the spread of the infection from building E to the other buildings.Airborne spread of the virus appears to explain this large community outbreak of SARS, and future efforts at prevention and control must take into consideration the potential for airborne spread of this virus
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Written by: L. Morawska, G.R. Johnson, Z.D. Ristovski, et al.

A new expiratory droplet investigation system was used to conduct the most comprehensive program of study to date, of the dilution corrected droplet size distributions produced during different respiratory activities

  • Distinct physiological processes were responsible for specific size distribution modes.
  • A new expiratory droplet investigation system (EDIS) was used to conduct the most comprehensive program of study to date, of the dilution corrected droplet size distributions produced during different respiratory activities.
  • The majority of particles for all activities were produced in one or more modes, with diameters below 0.8 μm at average concentrations up to 0.75 cm−3.
  • These particles occurred at varying concentrations, during all respiratory activities, including normal breathing.
  • A second mode at 1.8 μm was produced during all activities, but at lower concentrations of up to 0.14 cm−3.
  • Speech produced additional particles in modes near 3.5 and 5 μm.
  • These two modes became most pronounced during sustained vocalization, producing average concentrations of 0.04 and 0.16 cm−3, respectively, suggesting that the aerosolization of secretions lubricating the vocal chords is a major source of droplets in terms of number.
  • For the entire size range examined of 0.3–20 μm, average particle number concentrations produced during exhalation ranged from 0.1 cm−3 for breathing to 1.1 cm−3 for sustained vocalization.
  • Non-equilibrium droplet evaporation was not detectable for particles between 0.5 and 20 μm, implying that evaporation to the equilibrium droplet size occurred within 0.8 s.
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Written by: M. Khalid Ijaz, Bahram Zargar, Kathryn E. Wright, et al.

Indoor air can be an important vehicle for a variety of human pathogens

  • Review of airborne transmission of infectious agents from experimental and field studies, predisposing to establish air-surface-air nexus and possible ways of transmission to susceptible hosts.
  • An overview of the methods for experimentally generating and recovering airborne human pathogens and environmental factors affecting their survival in air.
  • Current and emerging technologies for decontamination of indoor air for human pathogens.
  • Establishment, and validation of a room-size aerobiology chamber meeting the U.S Environmental Protection Agency guidelines (2012) that can be used for assessment of air-decontamination technologies.
  • Indoor air can be an important vehicle for a variety of human pathogens.
  • This review provides examples of airborne transmission of infectious agents from experimental and field studies and discusses how airborne pathogens can contaminate other parts of the environment to give rise to secondary vehicles leading air-surface-air nexus with possible transmission to susceptible hosts.
  • The following groups of human pathogens are covered because of their known or potential airborne spread: vegetative bacteria, fungi (Aspergillus, Penicillium, and Cladosporium spp and Stachybotrys chartarum), enteric viruses, respiratory viruses, mycobacteria, and bacterial spore formers (Clostridium difficile and Bacillus anthracis).
  • An overview of methods for experimentally generating and recovering airborne human pathogens is included, along with a discussion of factors that influence microbial survival in indoor air.
  • Available guidelines from the U.S Environmental Protection Agency and other global regulatory bodies for the study of airborne pathogens are critically reviewed with particular reference to microbial surrogates that are recommended.
  • Recent developments in experimental facilities to contaminate indoor air with microbial aerosols are presented, along with emerging technologies to decontaminate indoor air under field-relevant conditions.
  • The role that air decontamination may play in reducing the contamination of environmental surfaces and its combined impact on interrupting the risk of pathogen spread in both domestic and institutional settings is discussed.
  • Indoor air microbiome
  • Air-surface-air nexus
  • Aerobiologic testing chamber
  • Air decontamination technologies
  • Funding/Support: This paper was presented at a workshop organized under the auspices of ASTM International's biannual meeting held in April 2016.
  • Publication of this supplement is primarily supported by RB, Montvale, New Jersey, with additional support from MicroBioTest, a division of Microbac Laboratories, Inc., Sterling, Virginia.
  • The City University of New York (CUNY) and the University of Ottawa, Ottawa, Canada, are academic sponsors.
  • Editorial support was provided by Ashely O'Dunne, PhD; Shannon O'Sullivan, ELS; and Alanna Franchetti, ELS of Medergy (Yardley, PA), and funded by RB.
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Written by: Leslie Dietz, Patrick F. Horve, David A. Coil, et al.

This work has revealed common pathogen exchange pathways and mechanisms that could lend insights into potential methods to mediate the spread of severe acute respiratory virus-CoV-2 through built environment-mediated pathways

  • With the rapid spread of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) that results in coronavirus disease 2019 (COVID-19), corporate entities, federal, state, county, and city governments, universities, school districts, places of worship, prisons, health care facilities, assisted living organizations, daycares, homeowners, and other building owners and occupants have an opportunity to reduce the potential for transmission through built environment (BE)-mediated pathways.
  • While transmission of COVID-19 has been documented only through respiratory droplet spread and not through deposition on fomites, steps should still be taken to clean and disinfect all potential sources of SARS-CoV-2 under the assumption that active virus may be transmitted by contact with these abiotic surfaces [34, 39].
  • SARS-CoV-2 has been observed in aerosolized particles in a spectrum of sizes, including 0.25 to 0.5 ␮m [96], necessitating high efficiency filtration techniques to reduce the transmission potential of pathogens such as SARSCoV-2.
  • These community-level measures act to prevent disease transmission through the same mechanisms as the worldwide travel restrictions by reducing typical person-to-person contact, decreasing the possibility of fomite contamination by those that are shedding viral particles, and decreasing the possibility of airborne, particle transmission between individuals in the same room or close proximity.
  • Within the BE, environmental precautions that can be taken to potentially prevent the spread of SARS-CoV-2 include chemical deactivation of viral particles on surfaces [39].
  • Even though some of these particles have been identified in sizes that could potentially penetrate high efficiency filters, ventilation and filtration remain important in reducing the transmission potential of SARS-CoV-2.
  • Based upon studies of other viruses, including CoVs, higher RH decreases airborne dispersal by maintaining larger droplets that contain viral particles, causing them to deposit onto room surfaces more quickly [63, 68, 69].
  • The current ventilation standard adopted by health care and residential care facilities, ASHRAE 170-2017, permits a wider range of RH from 20% to 60%, maintaining a RH between 40% and 60% indoors may help to limit the spread and survival of SARS-CoV-2 within the BE, while minimizing the risk of mold growth and maintaining hydrated and intact mucosal barriers of human occupants [50, 67].
  • While PE rooms typically function as intended for the occupant, if an immunocompromised patient is under treatment for an airborne infectious disease, the process of limiting pathogen ingress into the room could potentially create involuntary exposure to health care workers, other patients, and visitors via the corridor space.
  • The authors hope this information can help to inform the decisions and infection control mechanisms that are implemented by corporate entities, federal, state, county, and city governments, universities, school districts, places of worship, prisons, health care facilities, assisted living organizations, daycares, homeowners, and other building owners and occupants to reduce the potential for transmission through BE mediated pathways.
  • This information is useful to corporate and public administrators and individuals responsible for building design and operation in their decision-making process about the degree and duration of social-distancing measures during viral epidemics and pandemics
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Far UVC

Written by: Manuela Buonanno, David Welch, Igor Shuryak & David J. Brenner

In this work we have used an aerosol irradiation chamber to test the efficacy of 222-nm far-UVC light to inactivate two aerosolized human coronaviruses, beta HCoV-OC43 and alpha HCoV-229E

  • Introduction: A direct approach to limit airborne viral transmissions is to inactivate them within a short time of their production.
  • The most commonly employed type of UV light for germicidal applications is a low pressure mercury-vapor arc lamp, emitting around 254 nm; more recently xenon lamp technology has been used, which emits broad UV spectrum[6]
  • While these lamps can be used to disinfect unoccupied spaces, direct exposure to conventional germicidal UV lamps in occupied public spaces is not possible since direct exposure to these germicidal lamp wavelengths can be a health hazard, both to the skin and eye[7,8,9,10].
  • Far-UVC light cannot reach or damage living cells in the human skin or the human eye, in contrast to the conventional germicidal UV light which can reach these sensitive cells[7,8,9,10]
  • Methods: MRC-5 fibroblasts (CCL-171) and WI-38 (CCL-75), respectively
  • Both human cell lines were grown in MEM supplemented with 10% Fetal Bovine Serum (FBS), 2 mM L-alanyl-L-glutamine, 100 U/ml penicillin and 100 μg/ml streptomycin (Sigma-Aldrich Corp.
  • The virus infection medium consisted of MEM or RPMI-1640 plus 2% heat inactivated FBS for HCoV-229E and HCoV-OC43, respectively.
  • The viral strains were propagated by inoculation of flasks containing 24-hours old host cells, which were 80–90% confluent.
  • The virus titer was determined by 50% tissue culture infective dose TCID50 by assessing cytopathic effects (CPE), which were scored at a bright field microscope (10×) as vacuolization of cytoplasm, cell rounding and sloughing
  • Results: Inactivation of human coronaviruses after exposure to 222 nm light in aerosols infectivity assay.
  • The authors used a standard approach to measure viral inactivation, assaying coronavirus infectivity in human host cells, in this case after exposure in aerosols to different doses of far-UVC light.
  • Inactivation of human coronaviruses after exposure to 222 nm light in aerosols infectivity assay.
  • The authors used a standard approach to measure viral inactivation, assaying coronavirus infectivity in human host cells, in this case after exposure in aerosols to different doses of far-UVC light.
  • The susceptibility rate for the beta coronavirus HCoV-OC43 was k = 5.9 cm2/mJ (95% C.The author .s3.8–7.1) which corresponds to an inactivation cross section of D90 = 0.39 mJ/cm[2]
  • Conclusion: The severity of the 2020 COVID-19 pandemic warrants the rapid development and deployment of effective countermeasures to reduce indoor person-to-person transmission.
  • As shown in Fig. 1, inactivation of the two human coronavirus by 222-nm light follows a typical exponential disinfection model, with an inactivation constant for HCoV-229E of k = 4.1 cm2/mJ (95% C.The author .s2.5–4.8), and k = 5.9 cm2/mJ (95% C.The author .s3.8–7.1) for HCoV-OC43.
  • Because the assays differ in methods and principles, some variance is expected between these two techniques
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Hydrogen Peroxide

Written by: William A. Rutala, Hajime Kanamori, Maria F. Gergen, et al.

We acknowledge that the device we tested may not be the device currently marketed by Synexis Biodefense Systems

  • The authors acknowledge that the device the authors tested may not be the device currently marketed by Synexis Biodefense Systems.
  • When the authors conducted the study, the authors were told that the authors were studying the device that would be marketed.
  • The authors take exception with Mr Schlote’s claim that the dilute hydrogen peroxide system marketed by Synexis Biodefense Systems has been validated.
  • A single abstract has been published,[2] and no-peer reviewed, published studies have validated that use of this device can effectively provide continuous decontamination of the environment.
  • The one abstract that has been published has substantial limitations: (1) the study used a before–after study design, a relatively weak epidemiologic method; (2) the study assessed the device for only 7 days after installation; (3) the researchers did not measure the concentration of the hydrogen peroxide in the test rooms; and (4) no statistical evaluation was provided.
  • The authors of this abstract recommended further study.
  • Even if a statistical reduction of surface contamination is demonstrated, this method of continuous room disinfection needs to be validated (1) to decrease healthcareassociated infections (HAIs), (2) to be safe for patients and healthcare personnel, and (3) to be cost-effective.
  • The authors were unable to perform additional studies due to the lack of laboratory capabilities, the authors have been in contact with colleagues interested in further studies of this methodology.
  • The authors made several recommendations to them: (1) install the test device consistent with the manufacturer’s recommendations; (2) monitor the concentration of hydrogen peroxide at a low concentration produced both at the unit exhaust and at room surfaces; (3) assess relevant healthcare-associated pathogens; (4) use appropriate controls; (5) monitor microbial reduction quantitatively; (6) monitor compliance with room disinfection using a method such as fluorescent dye; (7) perform room cleaning and disinfection per CDC recommendations; and (8) assess the impact of HAI rates.
  • The authors agree that further studies of self-disinfecting and continuous room disinfection methods are highly important to public health.
  • Financial support.
  • No financial support was provided relevant to this article.
  • Conflicts of interest.
  • Drs Rutala and Weber are consultants for Professional Disposables International.
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Written by: S. Nseir, C. Blazejewski, R. Lubret, et al.

One hydrogen peroxide vapor generator was more effective than 2 aerosolized hydrogen peroxide machines for the inactivation of G. stearothermophilus biological indicators, and cycle times were faster for the HPV system

  • The authors conducted a head-to-head in vitro comparison of a hydrogen peroxide vapor (HPV) system (Bioquell) and an aerosolized hydrogen peroxide system (Sterinis).
  • The tests were conducted in a purpose-built 136-m3 test room.
  • One HPV generator and 2 aHP machines were used, following recommendations of the manufacturers.
  • Three repeated tests were performed for each system.
  • The microbiological efficacy of the 2 systems was tested using 6-log Tyvek-pouched Geobacillus stearo-thermophilus biological indicators (BIs).
  • The indicators were placed at 20 locations in the first test and 14 locations in the subsequent 2 tests for each system.
  • All BIs were inactivated for the 3 HPV tests, compared with only 10% in the first aHP test and 79% in the other 2 aHP tests.
  • The peak hydrogen peroxide concentration was 338 ppm for HPV and 160 ppm for aHP.
  • The total cycle time was 3 and 3.5 hours for the 3 HPV tests and the 3 aHP tests, respectively.
  • Monitoring around the perimeter of the enclosure with a handheld sensor during tests of both systems did not identify leakage.
  • One HPV generator was more effective than 2 aHP machines for the inactivation of G
  • Stearothermophilus BIs, and cycle times were faster for the HPV system.
  • One HPV generator was more effective than 2 aHP machines for the inactivation of G. stearothermophilus BIs, and cycle times were faster for the HPV system
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Written by: S. Nseir, C. Blazejewski, R. Lubret, et al.

One hydrogen peroxide vapor generator was more effective than 2 aerosolized hydrogen peroxide machines for the inactivation of G. stearothermophilus biological indicators, and cycle times were faster for the HPV system

  • The authors conducted a head-to-head in vitro comparison of a hydrogen peroxide vapor (HPV) system (Bioquell) and an aerosolized hydrogen peroxide system (Sterinis).
  • The tests were conducted in a purpose-built 136-m3 test room.
  • One HPV generator and 2 aHP machines were used, following recommendations of the manufacturers.
  • Three repeated tests were performed for each system.
  • The microbiological efficacy of the 2 systems was tested using 6-log Tyvek-pouched Geobacillus stearo-thermophilus biological indicators (BIs).
  • The indicators were placed at 20 locations in the first test and 14 locations in the subsequent 2 tests for each system.
  • All BIs were inactivated for the 3 HPV tests, compared with only 10% in the first aHP test and 79% in the other 2 aHP tests.
  • The peak hydrogen peroxide concentration was 338 ppm for HPV and 160 ppm for aHP.
  • The total cycle time was 3 and 3.5 hours for the 3 HPV tests and the 3 aHP tests, respectively.
  • Monitoring around the perimeter of the enclosure with a handheld sensor during tests of both systems did not identify leakage.
  • One HPV generator was more effective than 2 aHP machines for the inactivation of G.
  • Stearothermophilus BIs, and cycle times were faster for the HPV system.
  • One HPV generator was more effective than 2 aHP machines for the inactivation of G. stearothermophilus BIs, and cycle times were faster for the HPV system
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Written by: T. Pottage, C. Richardson, S. Parks, et al.

This study demonstrates that the effectiveness of gaseous disinfectants against bacteriophage is a function of the viral concentration as well as the degree of soiling

  • This study assessed the efficacy of two commonly used gaseous disinfection systems against high concentrations of a resistant viral surrogate in the presence and absence of soiling.
  • MS2 bacteriophage suspensions were dried on to stainless steel carriers and exposed to hydrogen peroxide vapour (HPV) and vapour hydrogen peroxide (VHP) gaseous disinfection systems.
  • The bacteriophages were suspended and dried in 10% and 50% of horse blood to simulate the virus being present in a spill of blood/bodily fluids in a hospital ward environment.
  • Carriers were removed from the gaseous disinfectant at regular intervals into phosphate-buffered saline, vortexed and assayed using a standard plaque assay.
  • The effectiveness of both the HPV and VHP systems varied with the concentration of the bacteriophage with HPV resulting in a 6 log10 reduction in 10 min at the lowest viral concentration [107 plaque-forming units/carrier] and requiring 45 min at the highest concentration (109 pfu/carrier).
  • For the VHP system a 30 min exposure period was required to achieve a 6 log10 reduction at the lowest concentration and 60–90 min for the highest concentration.
  • The addition of blood to the suspension greatly reduced the effectiveness of both disinfectants.
  • This study demonstrates that the effectiveness of gaseous disinfectants against bacteriophage is a function of the viral concentration as well as the degree of soiling.
  • It highlights the importance of effective cleaning prior to gaseous disinfection especially where high concentration agents are suspended in body fluids to ensure effective decontamination in hospitals.
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Written by: R A Heckert, M Best, L T Jordan, G C Dulac, D L Eddington, W G Sterritt

The efficacy of vapor-phase hydrogen peroxide in a pass-through box for the decontamination of equipment and inanimate materials potentially contaminated with exotic animal viruses was evaluated

  • Introduction: The efficacy of vapor-phase hydrogen peroxide in a pass-through box for the decontamination of equipment and inanimate materials potentially contaminated with exotic animal viruses was evaluated.
  • Vaporphase hydrogen peroxide decontamination can be recommended as a safe and efficacious way of removing potentially virus-contaminated objects from biocontainment level III laboratories in which exotic animal disease virus agents are handled.
  • This study was initiated to validate the efficacy of VPHP in a pass-through box for the decontamination of equipment and inanimate materials potentially contaminated with exotic animal viruses.
  • These included representatives of several virus families, from both avian and mammalian species
  • Methods: VPHP was generated by a biodecontamination system (VHP 1000; Steris Corporation, Mentor, Ohio) which controlled all phases of the decontamination process.
  • This machine was connected to an 18-ft3 stainless-steel pass-through box via 1.5-in.
  • The pass-through box was equipped with two internal circulation fans to ensure even distribution of VPHP within the box.
  • The pressure within the box was monitored by a manometer during each decontamination run.
  • The pass box was leak tested by pressurizing the enclosure to an equivalent of a 2.0-in. water column, and a decay rate of 0.08 in./h was calculated over an observation period of 18 h
  • Results: During all phases of each run, the pressure inside the enclosure remained at 2 to 3 in. of water.
  • During all phases of each run, the pressure inside the enclosure remained at 2 to 3 in.
  • Any deviation from this range would have been an indication of a mechanical failure and reason to abort the cycle.
  • Titer of virusa in: Dried state Virus No VPHP Out of box Glass Steel In box, glass.
  • VPHP, in box, glass In box
  • Conclusion: The results of this study show that VPHP gas can be safely generated to high concentrations within an enclosure.
  • It is possible that blood, being a protein-rich substance, protected the virus in some way from the oxidizing properties of the gas, the other viruses were either in 5% fetal calf serum or in egg fluid
  • It is possible, since cells naturally contain peroxidase and catalase, that these endogenous enzymes in the erythrocytes neutralized some or all of the hydrogen peroxide, rendering the decontamination process ineffective
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Written by: Stephen N.Rudnick ScD

After 2.5 minutes, exposure to 10-ppm hydrogen peroxide vapor resulted in 99% inactivation

  • Introduction: Surfaces in congregate settings, such as vehicles used for mass transportation, can become contaminated with infectious microorganisms and facilitate disease transmission.
  • The authors disinfected surfaces contaminated with H1N1 influenza viruses using hydrogen peroxide (HP) vapor at concentrations below 100 ppm and triethylene glycol (TEG)-saturated air containing 2 ppm of TEG at 25°C
  • Methods: Influenza viruses in aqueous suspensions were deposited on stainless-steel coupons, allowed to dry at ambient conditions, and exposed for up to 15 minutes to 10 to 90 ppm of HP vapor or TEG-saturated air.
  • Virus assays were done on the solution used to wash the viruses from these coupons and from coupons treated but without exposure to HP or TEG vapor
  • Results: After 2.5 minutes, exposure to 10-ppm HP vapor resulted in 99% inactivation. For air saturated with TEG at 25 to 29°C, the disinfection rate was about 1.3 log10 reductions per hour, about 16 times faster than the measured natural inactivation rate under ambient conditions.
  • Conclusion: Vapor concentrations of 10 ppm HP or 2 ppm TEG can provide effective surface disinfection.
  • At these low concentrations, the potential for damage to even the avionics of an airplane would be expected to be minimal.
  • At a TEG vapor concentration of 2 ppm, there are essentially no health risks to people
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Written by: Torsten Holmdahl

Inactivation of murine norovirus viability by hydrogen peroxide vapour was not reflected in quantitative Polymerase Chain Reaction levels

  • Introduction: Human noroviruses are among the most common viral causes of gastroenteritis in the community as well as in hospitals [1].
  • Human norovirus and murine norovirus are structurally similar and share tissue tropism for enterocytes in the gut of the respective species [11].
  • Another calicivirus, not classified as a norovirus, which is often used for research is the feline calicivirus [12], a respiratory virus, which causes significant morbidity in cats [13].
  • Its activity against murine norovirus, a surrogate viability marker for human norovirus, indicates that it is active against human norovirus
  • Objectives: One arising question when hydrogen peroxide vapour treatment becomes more widely used, is: Do post-hydrogen peroxide vapour treatment human norovirus RNA levels indicate a remaining infectivity? The aim of this study is to assess how this effect on viability is reflected in measurements of RNA by quantitative PCR
  • Methods: Faeces suspensions of two human norovirus field strains, genogroup the author ands II and one cultured murine norovirus strain, were dried on plastic plates, and underwent hydrogen peroxide vapour treatment or were mock treated.
  • The influence of hydrogen peroxide on RNA was measured on genogroups I, II and V by qPCRs and for the cultivable murine norovirus for viability by cell culture.
  • Cut-off threshold (Ct) was set at 0.1 at less than 40 cycles, combined with a typical amplification curve
  • Results: The mean impact on the human norovirus qPCRs was 0.4 log10. The murine norovirus qPCR changed by 1.7 log10 but by an alternative qPCR only by 0.4 log10.
  • Noroviral RNA levels determined by qPCRs with and without hydrogen peroxide vapour treatment
  • Both these human norovirus qPCRs are based on hydrolysis probe chemistry.
  • For murine norovirus in culture medium, hydrogen peroxide vapour treatment induced an about 1.7 log10 reduction (6 Ct steps) versus the control with the same murine norovirus Taqman qPCR.
  • When aliquots of the same murine norovirus medium derived material instead were assessed by the plus-strand specific murine norovirus SYBR green qPCR, the reduction upon hydrogen peroxide vapour treatment was only 0.3 log10 (1 Ct step above untreated samples).
  • The impact of a high concentration of hydrogen peroxide vapour on the noroviruses RNA measured with qPCR was mild. (Table 2)
  • Conclusion: The authors demonstrated inactivation by hydrogen peroxide vapour of two caliciviruses, murine norovirus and feline calicivirus in an authentic, full-size hospital patient room [12].
  • The authors have in additional experiments seen that diluting faecal human norovirus in culture medium has an impact on the probe based qPCR beyond that of the dilution effect [28] adding 2–3 Ct steps beyond that caused by dilution as such.Inactivation of murine norovirus viability by hydrogen peroxide vapour was not reflected in qPCR levels
  • This finding might be extrapolated to the related human norovirus genogroups.
  • The authors further found that cellular minus strand murine norovirus PCR was an observer-independent marker to study reduction of murine norovirus viability
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UVC

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Written by: Lisa Eisenlöffel, Tobias Reutter, Matthias Horn, et al.

Combining UVC irradiation to recirculating air filtration proved to be successful in reducing airborne bacteria and dust in a small animal facility

  • Introduction: Pathogens can be transmitted over the airborne route. This has been impressively demonstrated e.g. for porcine reproductive and respiratory syndrome virus (PRRSV), Foot-andMouth-Disease virus, Coxiella burnetii and Mycoplasma hyopneumoniae which can be transported over several kilometers by wind [1,2,3,4,5].
  • In another study on a commercial pig farm mean airborne dust concentration was lowest in a barn with recirculating air filtration resulting in enhanced lung health in animals [14].
  • These findings were not affirmed by a significant reduction of airborne bacteria [14].
  • The objectives of this study were: 1) To determine the efficiency of UVC irradiation combined to air filtration in an air filter test chamber at laboratory scale using selected pathogens with high relevance in pig production, and 2) to determine the impact of UVC-combined air filtration on the total amount of airborne bacteria and dust in an animal housing at experimental scale
  • Objectives: The objectives of this study were: 1) To determine the efficiency of UVC irradiation combined to air filtration in an air filter test chamber at laboratory scale using selected pathogens with high relevance in pig production, and 2) to determine the impact of UVC-combined air filtration on the total amount of airborne bacteria and dust in an animal housing at experimental scale.
  • Methods: Pathogens chosen for air filter tests
  • Staphylococcus aureus was chosen because Gram-positive bacteria account for the majority of airborne bacteria inside animal housings.
  • Pathogens chosen for air filter tests.
  • Actinobacillus pleuropneumoniae (APP) causes acute, sub-acute and chronic respiratory infections in pigs.
  • Culture conditions and preparation of test suspensions for the bacteria and PRRSV has been previously described in detail [6].
  • Bacterial test suspensions in tryptic soy broth (Carl Roth GmbH + Co. KG, Karlsruhe, Germany) were adjusted to 108−109 colony-forming units/ml and PRRSV suspensions grown in MARC145 cells revealed a titer of 105.6–106.1 tissue culture infectious dose (TCID)50/ml.
  • The culture medium was composed of equal parts of MEM Hank‘s salts (Life Technologies
  • Results: The results of the different test runs are summarized in Table 1.
  • Using UVC irradiation alone or in combination to the air filter resulted in a more than 99% reduction for bacteria and viruses.
  • Higher RH resulted in higher reduction rates for all pathogens in air filter tests without UVC irradiation.
  • The effectiveness of the latter was not affected by higher RH.
  • Bacteria and dust in barn 1 could be reduced to an average of 68.4% (95% CI [40.6%,115%]) and 86.5%
  • Conclusion: Air filters are highly efficient in reducing pathogens at laboratory scale [6]. According to the manufacturer, the efficiency of the coarse dust filter used in this study was less than 50% at removing particles of <10 μm in diameter.
  • Using UVC irradiation in addition to the air filter resulted in a >99% to 100% reduction of viruses and bacteria.
  • This is accordant to others UVC intensity varied distinctly between the experiments and these studies [17,23,35].
  • The colored graphs display the UVC intensity within the filter test chamber. (PDF)
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Written by: James J. McDevitt, Stephen N. Rudnick, Lewis J. Radonovich

By characterizing the susceptibility of influenza virus to UV-C exposure, this work provides an essential scientific basis for designing effective upper-room UV-C installations for the prevention of influenza virus infection transmitted from person to person via an airborne route

  • Introduction: The person-to-person transmission of influenza virus, especially in the event of a pandemic caused by a highly virulent strain of influenza, such as H5N1 avian influenza, is of great concern due to widespread mortality and morbidity.
  • Microorganism susceptibility to UV-C light is traditionally thought to follow first-order kinetics according to the equation FR ϭ CUV/CNo UV ϭ eϪZD, where FR is the fraction remaining, CUV is microorganism concentration with UV exposure, CNo UV is microorganism concentration without UV exposure, Z is the susceptibility parameter expressed in m2/J, and D is the dose of UV-C in J/m2 [4, 8, 18]
  • These susceptibility parameters, or Z values, do not appear to be static but vary with environmental conditions, such as relative humidity (RH) [12, 13, 18].
  • The aim of the investigation was to determine Z values for influenza virus aerosols at low, medium, and high relative humidity
  • Methods: Virus infectivity assay.
  • A fluorescent focus reduction assay was used to enumerate numbers of infective viruses and has been described previously [9, 28].
  • Infected Madin-Darby canine kidney (MDCK) cells (ATTC CCL-34) containing influenza A nucleoproteins were labeled with influenza A virus nucleoprotein antibody (Abcam, Cambridge, MA) and subsequently labeled with rhodamine-labeled goat anti-mouse IgG (Jackson ImmunoResearch Laboratories, West Grove, PA).
  • The number of cells having resulting fluorescent foci was counted using an Olympus CKX-41 inverted fluorescence microscope (200ϫ total power; Olympus, Center Valley, PA).
  • The number of FFU per sample was computed based on dilution factors and the fraction of the well counted
  • Results: The average airborne concentration of influenza virus in the chamber as measured by the focus assay was 5.62 ϫ 103 FFU per liter of air, which corresponded to 2,636 FFU per well on the 96-well plate.
  • The fractional survival of influenza aerosols was measured in triplicate for combinations of three ranges of relative humidity and 6 UV doses ranging from 4.9 to 15.0 J/m2 (Fig. 1).
  • The fractional survival of influenza aerosolized at low (25 to 27%), medium (50 to 54%), or high (81 to 84%) RH is shown in Fig. 1.
  • The authors calculated Z values of 0.29, 0.27, and 0.22 m2/J for low, medium, and high relative humidity levels, respectively (Table 1).
  • Bootstrap results of the 1,000 samples show that all Z values are significantly different from each other (P Ͻ 0.0001)
  • Conclusion: The Z values determined for influenza aerosols in the study suggest that influenza will be effectively inactivated during exposure to upper-room UV-C.
  • The Z values reported all are higher than those reported previously for influenza virus aerosols in a review by Kowalski et al [14], which was based on research by Jensen [10], and suggest an increased efficacy of UV-C for deactivating influenza virus.
  • The Z values determined for influenza virus were higher than those previously reported.
  • UV-C effectiveness was shown to decrease with increasing relative humidity
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Written by: James J. McDevitt, Donald K. Milton, Stephen N. Rudnick, et al.

We demonstrate through aerosol decay experiments that upper-room UVC fixtures used with mixing provided by a conventional ceiling fan and minimal general ventilation produced decreases in airborne virus concentrations that would require additional ventilation of more than 87 air changes per hour

  • Introduction: Hospitals limit aerosol disease transmission in indoor spaces by reducing the concentration of airborne microorganisms through dilution ventilation.
  • These measures are largely impractical beyond a limited number of respiratory isolation rooms due to the large amounts of air exchange needed to significantly reduce the threat of infection and are costly in terms of heating and cooling these large amounts of air.
  • Some hospitals currently employ upper-room UVC for this purpose in their emergency departments (e.g. Brigham and Women’s Hospital, Boston, MA), but its effectiveness against viral aerosols is not well established
  • Methods: Experimental Chamber The testing chamber, ante room, aerosol generation, and sampling arrangements have been described previously and are shown in Figure 3.[9] Briefly, virus aerosols were delivered at 1.5 meters above the floor in the center of a climate controlled 4.60 m62.97 m63.05 m high room equipped with a ceiling fan and two black boxes containing 100-watt light bulbs.
  • Vaccinia virus aerosols were generated using a 6-jet Collison nebulizer (BGI Inc., Waltham, MA) operating at 138 kPa. The nebulizer was located in a class II biological safety cabinet (BSC) in the ante room and attached to a permanently installed pipe leading to the center of the test chamber.
  • Results: Decay The environmental conditions within the chamber during decay experiment were maintained at 2063uC and 50610% RH.
  • The results of chamber decay experiments performed with background decay, without heat boxes, and with heat boxes are shown either without the ceiling fan operating (Figure 1a) or with the ceiling fan operating (Figure 1b).
  • Based on a model for a chamber in which the air is perfectly mixed, the effective air exchange rate is equal to the amount of virus-free dilution air that would be needed to provide the same reduction of virus concentration that was measured.
  • The background decay rate reflects the decrease in infective viruses due to the exhaust airflow required to maintain negative pressure within the chamber, as well as any physical and non-UVC-related biological decay of the virus aerosol
  • Conclusion: These data show that in a ‘real world’ test setup, upper-room UVC is highly effective for reducing the concentration of vaccinia virus aerosols.
  • The authors demonstrate through aerosol decay experiments that upper-room UVC fixtures used with mixing provided by a conventional ceiling fan and minimal general ventilation produced decreases in airborne virus concentrations that would require additional ventilation of more than 87 ACH.
  • During steady-state experiments the combined effect of upper-room UVC and ventilation had a nonlinear impact on the fraction of remaining virus aerosol.[9] As a result, under winter conditions when vaccinia is most susceptible to UVC inactivation, the effective ACH due to upper-room UVC (ACHUVC) increased approximately five fold with increasing air exchange from ventilation.
  • The equivalent ventilation achieved by UVC ranged from a low of 18 to 1000 ACHUVC, with winter equivalent ventilation rates consistently .100 ACHUVC
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Written by: Jun Han, Xiao-Ping Dong, et al.

Some of the authors of this publication are working on these related projects: National Natural Science Foundation in China View project Genetic Dissection of Yield-related Traits in wheat View project. All content following this page was uploaded by Xiao-Ping Dong on 28 January 2020

  • Some of the authors of this publication are working on these related projects: National Natural Science Foundation in China View project Genetic Dissection of Yield-related Traits in wheat View project.
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