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2.
Interface Focus ; 12(2): 20210079, 2022 Apr 06.
Article in English | MEDLINE | ID: covidwho-1713825

ABSTRACT

Responses to the early (February-July 2020) COVID-19 pandemic varied widely, globally. Reasons for this are multiple but likely relate to the healthcare and financial resources then available, and the degree of trust in, and economic support provided by, national governments. Cultural factors also affected how different populations reacted to the various pandemic restrictions, like masking, social distancing and self-isolation or self-quarantine. The degree of compliance with these measures depended on how much individuals valued their needs and liberties over those of their society. Thus, several themes may be relevant when comparing pandemic responses across different regions. East and Southeast Asian populations tended to be more collectivist and self-sacrificing, responding quickly to early signs of the pandemic and readily complied with most restrictions to control its spread. Australasian, Eastern European, Scandinavian, some Middle Eastern, African and South American countries also responded promptly by imposing restrictions of varying severity, due to concerns for their wider society, including for some, the fragility of their healthcare systems. Western European and North American countries, with well-resourced healthcare systems, initially reacted more slowly, partly in an effort to maintain their economies but also to delay imposing pandemic restrictions that limited the personal freedoms of their citizens.

3.
Proc Natl Acad Sci U S A ; 119(4)2022 01 25.
Article in English | MEDLINE | ID: covidwho-1642082

ABSTRACT

The phase state of respiratory aerosols and droplets has been linked to the humidity-dependent survival of pathogens such as SARS-CoV-2. To inform strategies to mitigate the spread of infectious disease, it is thus necessary to understand the humidity-dependent phase changes associated with the particles in which pathogens are suspended. Here, we study phase changes of levitated aerosols and droplets composed of model respiratory compounds (salt and protein) and growth media (organic-inorganic mixtures commonly used in studies of pathogen survival) with decreasing relative humidity (RH). Efflorescence was suppressed in many particle compositions and thus unlikely to fully account for the humidity-dependent survival of viruses. Rather, we identify organic-based, semisolid phase states that form under equilibrium conditions at intermediate RH (45 to 80%). A higher-protein content causes particles to exist in a semisolid state under a wider range of RH conditions. Diffusion and, thus, disinfection kinetics are expected to be inhibited in these semisolid states. These observations suggest that organic-based, semisolid states are an important consideration to account for the recovery of virus viability at low RH observed in previous studies. We propose a mechanism in which the semisolid phase shields pathogens from inactivation by hindering the diffusion of solutes. This suggests that the exogenous lifetime of pathogens will depend, in part, on the organic composition of the carrier respiratory particle and thus its origin in the respiratory tract. Furthermore, this work highlights the importance of accounting for spatial heterogeneities and time-dependent changes in the properties of aerosols and droplets undergoing evaporation in studies of pathogen viability.


Subject(s)
Calcium Chloride/chemistry , Models, Chemical , SARS-CoV-2/chemistry , Serum Albumin/chemistry , Sodium Chloride/chemistry , COVID-19/virology , Diffusion , Disinfection/methods , Humans , Humidity , Kinetics , Microbial Viability , Phase Transition , Surface Properties
4.
Clin Infect Dis ; 73(10): 1924-1926, 2021 11 16.
Article in English | MEDLINE | ID: covidwho-1522131

ABSTRACT

We examine airborne transmission of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) potential using a source-to-dose framework beginning with generation of virus-containing droplets and aerosols and ending with virus deposition in the respiratory tract of susceptible individuals. By addressing 4 critical questions, we identify both gaps in addressing 4 critical questions with answers having policy implications.


Subject(s)
COVID-19 , Viruses , Aerosols , Humans , Respiratory System , SARS-CoV-2
6.
mBio ; 12(5): e0252721, 2021 10 26.
Article in English | MEDLINE | ID: covidwho-1476394

ABSTRACT

Respiratory viruses such as SARS-CoV-2 are transmitted in respiratory droplets and aerosol particles, which are released during talking, breathing, coughing, and sneezing. Noncontact transmission of SARS-CoV-2 has been demonstrated, suggesting transmission via virus carried through the air. Here, we demonstrate that golden Syrian hamsters produce infectious SARS-CoV-2 in aerosol particles prior to and concurrent with the onset of mild clinical signs of disease. The average emission rate in this study was 25 infectious virions/hour on days 1 and 2 postinoculation, with average viral RNA levels 200-fold higher than infectious virus in aerosol particles. The majority of virus was contained within particles <5 µm in size. Thus, we provide direct evidence that, in hamsters, SARS-CoV-2 is an airborne virus. IMPORTANCE SARS-CoV-2 is a respiratory virus and has been isolated from the air near COVID-19 patients. Here, using a hamster model of infection, we demonstrate that SARS-CoV-2 is emitted in aerosol particles prior to and concurrent with the onset of mild disease. Virus is contained primarily within aerosol particles <5 µm in size, which can remain airborne and be inhaled. These findings indicate that SARS-CoV-2 is an airborne virus and support the use of ventilation to reduce SARS-CoV-2 transmission.


Subject(s)
Aerosols , COVID-19/transmission , SARS-CoV-2/pathogenicity , Animals , COVID-19/metabolism , Chlorocebus aethiops , Cricetinae , Mesocricetus , Real-Time Polymerase Chain Reaction , Vero Cells
7.
Elife ; 102021 07 13.
Article in English | MEDLINE | ID: covidwho-1389776

ABSTRACT

Ambient temperature and humidity strongly affect inactivation rates of enveloped viruses, but a mechanistic, quantitative theory of these effects has been elusive. We measure the stability of SARS-CoV-2 on an inert surface at nine temperature and humidity conditions and develop a mechanistic model to explain and predict how temperature and humidity alter virus inactivation. We find SARS-CoV-2 survives longest at low temperatures and extreme relative humidities (RH); median estimated virus half-life is >24 hr at 10°C and 40% RH, but ∼1.5 hr at 27°C and 65% RH. Our mechanistic model uses fundamental chemistry to explain why inactivation rate increases with increased temperature and shows a U-shaped dependence on RH. The model accurately predicts existing measurements of five different human coronaviruses, suggesting that shared mechanisms may affect stability for many viruses. The results indicate scenarios of high transmission risk, point to mitigation strategies, and advance the mechanistic study of virus transmission.


Subject(s)
Hot Temperature , Humidity , Models, Biological , SARS-CoV-2/growth & development , Virus Inactivation , COVID-19 , Humans
8.
Science ; 373(6558)2021 08 27.
Article in English | MEDLINE | ID: covidwho-1376452

ABSTRACT

The COVID-19 pandemic has revealed critical knowledge gaps in our understanding of and a need to update the traditional view of transmission pathways for respiratory viruses. The long-standing definitions of droplet and airborne transmission do not account for the mechanisms by which virus-laden respiratory droplets and aerosols travel through the air and lead to infection. In this Review, we discuss current evidence regarding the transmission of respiratory viruses by aerosols-how they are generated, transported, and deposited, as well as the factors affecting the relative contributions of droplet-spray deposition versus aerosol inhalation as modes of transmission. Improved understanding of aerosol transmission brought about by studies of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection requires a reevaluation of the major transmission pathways for other respiratory viruses, which will allow better-informed controls to reduce airborne transmission.


Subject(s)
Air Microbiology , COVID-19/transmission , Respiratory Tract Infections/transmission , SARS-CoV-2 , Virus Diseases/transmission , Virus Physiological Phenomena , Aerosols , COVID-19/virology , Disease Transmission, Infectious , Humans , Microbial Viability , Particle Size , Respiratory System/virology , Respiratory Tract Infections/virology , SARS-CoV-2/isolation & purification , SARS-CoV-2/physiology , Viral Load , Virus Diseases/virology , Viruses/isolation & purification
9.
Clin Infect Dis ; 73(10): 1747-1749, 2021 11 16.
Article in English | MEDLINE | ID: covidwho-1367015

ABSTRACT

Current infection-control guidelines subscribe to a contact/droplet/airborne paradigm that is based on outdated understanding. Here, we propose to modify and align existing guidelines with a more accurate description of the different transmission routes. This will improve the effectiveness of control measures as more transmissible variants of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) emerge.


Subject(s)
COVID-19 , SARS-CoV-2 , Aerosols , Humans , Infection Control
10.
Environ Sci Technol ; 55(16): 11176-11182, 2021 08 17.
Article in English | MEDLINE | ID: covidwho-1333867

ABSTRACT

Possible links between the transmission of COVID-19 and meteorology have been investigated by comparing positive cases across geographical regions or seasons. Little is known, however, about the degree to which environmental conditions modulate the daily dynamics of COVID-19 spread at a given location. One reason for this is that individual waves of the disease typically rise and decay too sharply, making it hard to isolate the contribution of meteorological cycles. To overcome this shortage, we here present a case study of the first wave of the outbreak in the city of Buenos Aires, which had a slow evolution of the caseload extending along most of 2020. We found that humidity plays a prominent role in modulating the variation of COVID-19 positive cases through a negative-slope linear relationship, with an optimal lag of 9 days between the meteorological observation and the positive case report. This relationship is specific to winter months, when relative humidity predicts up to half of the variance in positive case count. Our results provide a tool to anticipate possible local surges in COVID-19 cases after events of low humidity. More generally, they add to accumulating evidence pointing to dry air as a facilitator of COVID-19 transmission.


Subject(s)
COVID-19 , Humidity , Cities , Humans , SARS-CoV-2 , Temperature
11.
Emerg Infect Dis ; 27(9): 2507, 2021 09.
Article in English | MEDLINE | ID: covidwho-1291098
12.
Indoor Air ; 31(6): 2281-2295, 2021 11.
Article in English | MEDLINE | ID: covidwho-1285030

ABSTRACT

The incidence of several respiratory viral infections has been shown to be related to climate. Because humans spend most of their time indoors, measures of indoor climate, rather than outdoor climate, may be better predictors of disease incidence and transmission. Therefore, understanding the relationship between indoor and outdoor climate will help illuminate their influence on the seasonality of diseases caused by respiratory viruses. Indoor-outdoor relationships between temperature and humidity have been documented in temperate regions, but little information is available for tropical regions, where seasonal patterns of respiratory viral diseases differ. We have examined indoor-outdoor correlations of temperature, relative humidity (RH), and absolute humidity (AH) over a 1-year period in each of seven tropical cities. Across all cities, the average monthly indoor temperature was 25 ± 3°C (mean ± standard deviation) with a range of 20-30°C. The average monthly indoor RH was 66 ± 9% with a range of 50-78%, and the average monthly indoor AH was 15 ± 3 g/m3 with a range of 10-23 g/m3 . Indoor AH and RH were linearly correlated with outdoor AH when the air conditioning (AC) was off, suggesting that outdoor AH may be a good proxy of indoor humidity in the absence of AC. All indoor measurements were more strongly correlated with outdoor measurements as distance from the equator increased. Such correlations were weaker during the wet season, especially when AC was in operation. These correlations will provide insight for assessing the seasonality of respiratory viral infections using outdoor climate data, which is more widely available than indoor data, even though transmission of these diseases mainly occurs indoors.


Subject(s)
Air Pollution, Indoor , Humidity , Temperature , Tropical Climate , Seasons
17.
J Manuf Syst ; 60: 762-773, 2021 Jul.
Article in English | MEDLINE | ID: covidwho-1056936

ABSTRACT

The COVID-19 pandemic has disrupted the supply chain for personal protective equipment (PPE) for medical professionals, including N95-type respiratory protective masks. To address this shortage, many have looked to the agility and accessibility of additive manufacturing (AM) systems to provide a democratized, decentralized solution to producing respirators with equivalent protection for last-resort measures. However, there are concerns about the viability and safety in deploying this localized download, print, and wear strategy due to a lack of commensurate quality assurance processes. Many open-source respirator designs for AM indicate that they do not provide N95-equivalent protection (filtering 95% of SARS-CoV-2 particles) because they have either not passed aerosol generation tests or not been tested. Few studies have quantified particle transmission through respirator designs outside of the filter medium. This is concerning because several polymer-based AM processes produce porous parts, and inherent process variation between printers and materials also threaten the integrity of tolerances and seals within the printed respirator assembly. No study has isolated these failure mechanisms specifically for respirators. The goal of this paper is to measure particle transmission through printed respirators of different designs, materials, and AM processes. The authors compare the performance of printed respirators to N95 respirators and cloth masks. Respirators in this study printed using desktop- and industrial-scale fused filament fabrication processes and industrial-scale powder bed fusion processes were not sufficiently reliable for widespread distribution and local production of N95-type respiratory protection. Even while assuming a perfect seal between the respirator and the user's face, although a few respirators provided >90% efficiency at the 100-300 nm particle range, almost all printed respirators provided <60% filtration efficiency. Post-processing procedures including cleaning, sealing surfaces, and reinforcing the filter cap seal generally improved performance, but the printed respirators showed similar performance to various cloth masks. The authors further explore the process-driven aspects leading to low filtration efficiency. Although the design/printer/material combination dictates the AM respirator performance, the identified failure modes originate from system-level constraints and are therefore generalizable across multiple AM processes. Quantifying the limitations of AM in producing N95-type respiratory protective masks advances understanding of AM systems toward the development of better part and machine designs to meet the needs of reliable, functional, end-use parts.

18.
Med (N Y) ; 2(1): 29-32, 2021 01 15.
Article in English | MEDLINE | ID: covidwho-978370

ABSTRACT

This commentary will summarize the evidence on face masks for COVID-19 from both the infectious diseases and physical science viewpoints; standardize recommendations on types of masks that afford the best protection to the public; and provide guidelines on messaging for this important non-pharmaceutical intervention as we await widespread vaccine distribution.


Subject(s)
COVID-19 , Communicable Diseases , Natural Science Disciplines , COVID-19/prevention & control , Humans , Masks , SARS-CoV-2
20.
Indoor Air ; 31(2): 314-323, 2021 03.
Article in English | MEDLINE | ID: covidwho-796060

ABSTRACT

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.


Subject(s)
COVID-19/epidemiology , COVID-19/transmission , Singing , Ventilation/methods , Fomites/virology , Humans , SARS-CoV-2 , Time Factors , Washington/epidemiology
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