Coronavirus Disease 2019 and Airborne Transmission: Science Rejected, Lives Lost. Can Society Do Better?

This is an account that should be heard of an important struggle: the struggle of a large group of experts who came together at the beginning of the COVID-19 pandemic to warn the world about the risk of airborne transmission and the consequences of ignoring it. We alerted the World Health Organization about the potential significance of the airborne transmission of SARS-CoV-2 and the urgent need to control it, but our concerns were dismissed. Here we describe how this happened and the consequences. We hope that by reporting this story we can raise awareness of the importance of interdisciplinary collaboration and the need to be open to new evidence, and to prevent it from happening again. Acknowledgement of an issue, and the emergence of new evidence related to it, is the first necessary step towards finding effective mitigation solutions.

Characterization of aerosol plumes from singing and playing wind instruments associated with the risk of airborne virus transmission.

The exhalation of aerosols during musical performances or rehearsals posed a risk of airborne virus transmission in the COVID-19 pandemic. Previous research studied aerosol plumes by only focusing on one risk factor, either the source strength or convective transport capability. Furthermore, the source strength was characterized by the aerosol concentration and ignored the airflow rate needed for risk analysis in actual musical performances. This study characterizes aerosol plumes that account for both the source strength and convective transport capability by conducting experiments with 18 human subjects. The source strength was characterized by the source aerosol emission rate, defined as the source aerosol concentration multiplied by the source airflow rate (brass 383 particle/s, singing 408 particle/s, and woodwind 480 particle/s). The convective transport capability was characterized by the plume influence distance, defined as the sum of the horizontal jet length and horizontal instrument length (brass 0.6 m, singing 0.6 m and woodwind 0.8 m). Results indicate that woodwind instruments produced the highest risk with approximately 20% higher source aerosol emission rates and 30% higher plume influence distances compared with the average of the same risk indicators for singing and brass instruments. Interestingly, the clarinet performance produced moderate source aerosol concentrations at the instrument's bell, but had the highest source aerosol emission rates due to high source airflow rates. Flute performance generated plumes with the lowest source aerosol emission rates but the highest plume influence distances due to the highest source airflow rate. Notably, these comprehensive results show that the source airflow is a critical component of the risk of airborne disease transmission. The effectiveness of masking and bell covering in reducing aerosol transmission is due to the mitigation of both source aerosol concentrations and plume influence distances. This study also found a musician who generated approximately five times more source aerosol concentrations than those of the other musicians who played the same instrument. Despite voice and brass instruments producing measurably lower average risk, it is possible to have an individual musician produce aerosol plumes with high source strength, resulting in enhanced transmission risk; however, our sample size was too small to make generalizable conclusions regarding the broad musician population.

Evaluating SARS-CoV-2 airborne quanta transmission and exposure risk in a mechanically ventilated multizone office building.

The world has faced tremendous challenges during the COVID-19 pandemic since 2020, and effective clean air strategies that mitigate infectious risks indoors have become more essential. In this study, a novel approach based on the Wells-Riley model applied to a multizone building was proposed to simulate exposure to infectious doses in terms of "quanta". This modeling approach quantifies the relative benefits of different risk mitigation strategies so that their effectiveness could be compared. A case study for the US Department of Energy large office prototype building was conducted to illustrate the approach. The infectious risk propagation from the infection source throughout the building was evaluated. Different mitigation strategies were implemented, including increasing outdoor air ventilation rates and adding air-cleaning devices such as Minimum Efficiency Reporting Value (MERV) filters and portable air cleaners (PACs) with HEPA filters in-room/in-duct germicidal ultraviolet (GUV) lights, layering with wearing masks. Results showed that to keep the risk of the infection propagating low the best strategy without universal masking was the operation of in-room GUV or a large industrial-sized PAC; whereas with masking all strategies were acceptable. This study contributes to a better understanding of the airborne transmission risks in multizone, mechanically ventilated buildings and how to reduce infection risk from a public health perspective of different mitigation strategies.

Transmission of SARS-CoV-2 by inhalation of respiratory aerosol in the Skagit Valley Chorale superspreading event.

During the 2020 COVID-19 pandemic, an outbreak occurred following attendance of a symptomatic index case at a weekly rehearsal on 10 March of the Skagit Valley Chorale (SVC). After that rehearsal, 53 members of the SVC among 61 in attendance were confirmed or strongly suspected to have contracted COVID-19 and two died. Transmission by the aerosol route is likely; it appears unlikely that either fomite or ballistic droplet transmission could explain a substantial fraction of the cases. It is vital to identify features of cases such as this to better understand the factors that promote superspreading events. Based on a conditional assumption that transmission during this outbreak was dominated by inhalation of respiratory aerosol generated by one index case, we use the available evidence to infer the emission rate of aerosol infectious quanta. We explore how the risk of infection would vary with several influential factors: ventilation rate, duration of event, and deposition onto surfaces. The results indicate a best-estimate emission rate of 970 ± 390 quanta/h. Infection risk would be reduced by a factor of two by increasing the aerosol loss rate to 5 h-1 and shortening the event duration from 2.5 to 1 h.

Modeling the impacts of physical distancing and other exposure determinants on aerosol transmission.

Minimization of airborne virus transmission has become increasingly important due to pandemic and endemic infectious respiratory diseases. Physical distancing is a frequently advocated control measure, but the proximity-based transmission it is intended to control is challenging to incorporate into generalized, ventilation-based models. We utilize a size-dependent aerosol release model with turbulent dispersion to assess the impact of direct, near-field transport in conjunction with changes in ventilation, exposure duration, exhalation/inhalation rates, and masks. We demonstrate this model on indoor and outdoor scenarios to estimate the relative impacts on infection risk. The model can be expressed as a product of six multiplicative factors that may be used to identify opportunities for risk reduction. The additive nature of the short-range (proximity) and long-range (background) transmission components of the aerosol transport factor implies that they must be minimized simultaneously. Indoor simulations showed that close physical distances attenuated the impact of most other risk reduction factors. Increasing ventilation resulted in a 17-fold risk decrease at further physical distances but only a 6-fold decrease at shorter distances. Distance, emission rate, and duration also had large impacts on risk (11-65-fold), while air direction and inhalation rate had lower risk impacts (3-4-fold range). Surgical mask and respirator models predicted higher maximum risk impacts (33- and 280-fold, respectively) than cloth masks (4-fold). Most simulations showed decreasing risk at distances > 1-2 m (3-6 ft). The risk benefit of maintaining 2-m distance vs. 1 m depended substantially on the environmental turbulence and ventilation rate. Outdoors, long-range transmission was negligible and short-range transmission was the primary determinant of risk. Temporary passing events increased risk by up to 50 times at very slow walking speeds and close passing distances, but the relative risks outdoors were still much lower than indoors. The current model assumes turbulent dispersion typical of a given room size and ventilation rate. However, calm environments or confined airflows may increase transmission risks beyond levels predicted with this turbulent model.

Review and comparison of HVAC operation guidelines in different countries during the COVID-19 pandemic.

Various organizations and societies around the globe have issued guidelines in response to the coronavirus disease (COVID-19) and virus (SARS-CoV-2). In this paper, heating, ventilating, and air-conditioning-related guidelines or documents in several major countries and regions have been reviewed and compared, including those issued by the American Society of Heating Refrigerating and Air-Conditioning Engineers, the Federation of European Heating, Ventilation, and Air Conditioning Associations, the Society of Heating, Air-Conditioning and Sanitary Engineers of Japan, Architectural Society of China, and the Chinese Institute of Refrigeration. Most terms and suggestions in these guidelines are consistent with each other, although there are some conflicting details, reflecting the underlying uncertainty surrounding the transmission mechanism and characteristics of COVID-19 in buildings. All guidelines emphasize the importance of ventilation, but the specific ventilation rate that can eliminate the risk of transmission of airborne particulate matter has not been established. The most important countermeasure, commonly agreed countermeasures, the conflicting content from different guidelines, and further work have been summarized in this paper.

Time-Resolved Measurements of Indoor Chemical Emissions, Deposition, and Reactions in a University Art Museum.

A 6-week study was conducted at the University of Colorado Art Museum, during which volatile organic compounds (VOCs), carbon dioxide (CO2), ozone (O3), nitric oxide (NO), nitrogen dioxide (NO2), other trace gases, and submicron aerosol were measured continuously. These measurements were then analyzed using a box model to quantify the rates of major processes that transformed the composition of the air. VOC emission factors were quantified for museum occupants and their activities. The deposition of VOCs to surfaces was quantified across a range of VOC saturation vapor concentrations ( C*) and Henry's Law constants ( H) and determined to be a major sink for VOCs with C* < 108 µg m-3 and H > 102 M atm-1. The reaction rates of VOCs with O3, OH radicals, and nitrate (NO3) radicals were quantified, with unsaturated and saturated VOCs having oxidation lifetimes of >5 and >15 h, making deposition to surfaces and ventilation the dominant VOC sinks in the museum. O3 loss rates were quantified inside a museum gallery, where reactions with surfaces, NO, occupants, and NO2 accounted for 62%, 31%, 5%, and 2% of the O3 sink. The measured concentrations of acetic acid, formic acid, NO2, O3, particulate matter, sulfur dioxide, and total VOCs were below the guidelines for museums.

Budgets of Organic Carbon Composition and Oxidation in Indoor Air.

The chemical composition of indoor air at the University of Colorado, Boulder art museum was measured by a suite of gas- and particle-phase instruments. Over 80% of the total observed organic carbon (TOOC) mass (100 µg m-3) consisted of reduced compounds (carbon oxidation state, OSC < -0.5) with high volatility (log10 C* > 7) and low carbon number (nC < 6). The museum TOOC was compared to other indoor and outdoor locations, which increased according to the following trend: remote < rural ≤ urban < indoor ≤ megacity. The museum TOOC was comparable to a university classroom and 3× less than residential environments. Trends in the total reactive flux were remote < indoor < rural < urban < megacity. High volatile organic compound (VOC) concentrations compensated low oxidant concentrations indoors to result in an appreciable reactive flux. Total hydroxyl radical (OH), ozone (O3), nitrate radical (NO3), and chlorine atom (Cl) reactivities for each location followed a similar trend to TOOC. High human occupancy events increased all oxidant reactivities in the museum by 65-125%. The lifetimes of O3, NO3, OH, and Cl reactivities were 13 h, 15 h, 23 days, and 189 days, respectively, corresponding to over 88% of indoor VOC oxidant reactivity being consumed outdoors after ventilation.

Relationships between home ventilation rates and respiratory health in the Colorado Home Energy Efficiency and Respiratory Health (CHEER) study.

BACKGROUND: As societies adopt green building practices to reduce energy expenditures and emissions that contribute to climate change, it is important to consider how such building design changes influence health. These practices typically focus on reducing air exchange rates between the building interior and the outdoor environment to minimize energy loss, the health effects of which are not well characterized. This study aims to evaluate the relationship between air exchange rates and respiratory health in a multi-ethnic population living in low-income, urban homes. METHODS: The Colorado Home Energy Efficiency and Respiratory Health (CHEER) study is a cross-sectional study that enrolled 302 people in 216 non-smoking, low-income single-family homes, duplexes and town-homes from Colorado's Northern Front Range. A blower door test was conducted and the annual average air exchange rate (AAER) was estimated for each home. Respiratory health was assessed using a structured questionnaire based on standard instruments. We estimated the association between AAER and respiratory symptoms, adjusting for relevant confounders. RESULTS: Air exchange rates in many homes were high compared to prior studies (median 0.54 air changes per hour, range 0.10, 2.17). Residents in homes with higher AAER were more likely to report chronic cough, asthma and asthma-like symptoms, including taking medication for wheeze, wheeze that limited activities and dry cough at night. Allergic symptoms were not associated with AAER in any models. The association between AAER and asthma-like symptoms was stronger for households located in areas with high potential exposure to traffic related pollutants, but this was not consistent across all health outcomes. CONCLUSIONS: While prior studies have highlighted the potential hazards of low ventilation rates in residences, this study suggests high ventilation rates in single-family homes, duplexes and town-homes in urban areas may also have negative impacts on respiratory health, possibly due to the infiltration of outdoor pollutants.

A Four Marker Digital PCR Toolkit for Detecting Heavy Alcohol Consumption and the Effectiveness of Its Treatment.

Background.-Heavy alcohol consumption (HAC) is a shared concern of the forensic, medical and insurance underwriting communities. Unfortunately, there is a relative lack of clinically employable tools for detecting HAC and monitoring treatment response. Building on the results of 3 genome wide methylation studies, we have previously shown in a small group of samples that methylation sensitive digital PCR assays (MSdPCR) have the potential to accurately classify individuals with respect to HAC in a small set of individuals. Objective.-We now expand on those earlier findings using data and biomaterials from 143 participants with current HAC and 200 abstinent controls. Results.-We show that a set of 4 digital PCR assays that have a receiver operating characteristic (ROC) area under the curve (AUC) of 0.96 for detecting those with HAC. After a mean of 21 days of inpatient enforced abstinence, methylation status at one of these markers, cg04987734, began to revert to baseline values. Re-examination of methylation data from our smaller 2014 study with respect to this locus demonstrated a similarly significant reversion pattern at cg04987734 in association with treatment enforced abstinence. Conclusions.-We conclude that clinically implementable dPCR tools can sensitively detect the presence of HAC and that they show promise for monitoring alcohol treatment results. These dPCR tools could be useful to clinicians and researchers in monitoring those enrolled in substance use disorder treatment, employee wellness programs and insurance underwriting.

Diversity of DNA and RNA Viruses in Indoor Air As Assessed via Metagenomic Sequencing.

Diverse bacterial and fungal communities inhabit human-occupied buildings and circulate in indoor air; however, viral diversity in these man-made environments remains largely unknown. Here we investigated DNA and RNA viruses circulating in the air of 12 university dormitory rooms by analyzing dust accumulated over a one-year period on heating, ventilation, and air conditioning (HVAC) filters. A metagenomic sequencing approach was used to determine the identity and diversity of viral particles extracted from the HVAC filters. We detected a broad diversity of viruses associated with a range of hosts, including animals, arthropods, bacteria, fungi, humans, plants, and protists, suggesting that disparate organisms can contribute to indoor airborne viral communities. Viral community composition and the distribution of human-infecting papillomaviruses and polyomaviruses were distinct in the different dormitory rooms, indicating that airborne viral communities are variable in human-occupied spaces and appear to reflect differential rates of viral shedding from room occupants. This work significantly expands the known airborne viral diversity found indoors, enabling the design of sensitive and quantitative assays to further investigate specific viruses of interest and providing new insight into the likely sources of viruses found in indoor air.

Genome-wide and digital polymerase chain reaction epigenetic assessments of alcohol consumption.

The lack of readily employable biomarkers of alcohol consumption is a problem for clinicians and researchers. In 2014, we published a preliminary DNA methylation signature of heavy alcohol consumption that remits as a function of abstinence. Herein, we present new genome-wide methylation findings from a cohort of additional subjects and a meta-analysis of the data. Using DNA from 47 consecutive heavy drinkers admitted for alcohol detoxification in the context of alcohol treatment and 47 abstinent controls, we replicate the 2014 results and show that 21,221 CpG residues are differentially methylated in active heavy drinkers. Meta-analysis of all data from the 448,058 probes common to the two methylation platforms shows a similarly profound signature with confirmation of findings from other groups. Principal components analyses show that genome-wide methylation changes in response to alcohol consumption load on two major factors with one component accounting at least 50% of the total variance in both smokers and nonsmoking alcoholics. Using data from the arrays, we derive a panel of five methylation probes that classifies use status with a receiver operator characteristic area under the curve (AUC) of 0.97. Finally, using droplet digital polymerase chain reaction (PCR), we convert these array-based findings to two marker assays with an AUC of 0.95 and a four marker set AUC of 0.98. We conclude that DNA methylation assessments are capable of quantifying alcohol use status and suggest that readily employable digital PCR approaches for substance consumption may find widespread use in alcohol-related research and patient care.

Potential airborne pathogen transmission in a hospital with and without surge control ventilation system modifications.

To better understand the transport of airborne particulate matter (PM) in hospital environments when surge control strategies are implemented, tests were conducted in a recently decommissioned hospital during a one-week period. An aerosol was released within a patient room and concentrations measured in the room and hallway with and without surge control ventilation system modifications. The average hallway protection efficiencies were high (>98%) both for the baseline ventilation configuration and when the ventilation system was modified for whole floor negative pressure, indicating very little PM reached the hallway. During entry/exit events through the patient room door into the hallway, the average minimum hallway protection efficiencies were lower during the modified ventilation operation (93-94%) than for the baseline operation (98-99%). These lower hallway protection efficiencies may be explained by the 52% reduction in the outdoor air ventilation being supplied to the hallway during the modified operation mode. This suggests that patient room doors should remain closed to control PM movement into the hallway. In addition, if there is concern about airborne infection transmission, an anteroom may be used to further reduce the transport of particles from the patient rooms to the hallways of the ward.

The ecology of microscopic life in household dust.

We spend the majority of our lives indoors; yet, we currently lack a comprehensive understanding of how the microbial communities found in homes vary across broad geographical regions and what factors are most important in shaping the types of microorganisms found inside homes. Here, we investigated the fungal and bacterial communities found in settled dust collected from inside and outside approximately 1200 homes located across the continental US, homes that represent a broad range of home designs and span many climatic zones. Indoor and outdoor dust samples harboured distinct microbial communities, but these differences were larger for bacteria than for fungi with most indoor fungi originating outside the home. Indoor fungal communities and the distribution of potential allergens varied predictably across climate and geographical regions; where you live determines what fungi live with you inside your home. By contrast, bacterial communities in indoor dust were more strongly influenced by the number and types of occupants living in the homes. In particular, the female : male ratio and whether a house had pets had a significant influence on the types of bacteria found inside our homes highlighting that who you live with determines what bacteria are found inside your home.