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Transmission risk of infectious droplets in physical spreading process at different times: A review

机译：不同时期物理传播过程中传输风险的风险：综述

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摘要

Droplets provide a well-known transmission media in the COVID-19 epidemic, and the particle size is closely related to the classification of the transmission route. However, the term "aerosol" covers most particle sizes of suspended particulates because of information asymmetry in different disciplines, which may lead to misunderstandings in the selection of epidemic prevention and control strategies for the public. In this review, the time when these droplets are exhaled by a patient was taken as the initial time. Then, all available viral loads and numerical distribution of the exhaled droplets was analyzed, and the evaporation model of droplets in the air was combined with the deposition model of droplet nuclei in the respiratory tract. Lastly, the perspective that physical spread affects the transmission risk of different size droplets at different times was summarized for the first time. The results showed that although the distribution of exhaled droplets was dominated by small droplets, droplet volume was proportional to the third power of particle diameter, meaning that the viral load of a 100 mu m droplet was approximately 10(6) times that of a 1 mu m droplet at the initial time. Furthermore, the exhaled droplets are affected by heat and mass transfer of evaporation, water fraction, salt concentration, and acid-base balance (the water fraction 98%), which lead them to change rapidly, and the viral survival condition also deteriorates dramatically. The time required for the initial diameter (d(0)) of a droplet to shrink to the equilibrium diameter (d(e), about 30% of d(0)) is approximately proportional to the second power of the particle diameter, taking only a few milliseconds for a 1 mu m droplet but hundreds of milliseconds for a 10 mu m droplet; in other words, the viruses carried by the large droplets can be preserved as much as possible. Finally, the infectious droplet nuclei maybe inhaled by the susceptible population through different and random contact routes, and the droplet nuclei with larger d(e) decompose more easily into tiny particles on account of the accelerated collision in a complex airway, which can be deposited in the higher risk alveolar region. During disease transmission, the infectious droplet particle size varies widely, and the transmission risk varies significantly at different time nodes; therefore, the fuzzy term "aerosol" is not conducive to analyzing disease exposure risk. Recommendations for epidemic prevention and control strategies are: 1) Large droplets are the main conflict in disease transmission; thus, even if they are blocked by a homemade mask initially, it significantly contains the epidemic. 2) The early phase of contact, such as close-contact and short-range transmission, has the highest infection risk; therefore, social distancing can effectively keep the susceptible population from inhaling active viruses. 3) The risk of the fomite route depends on the time in contact with infectious viruses; thus, it is important to promote good health habits (including frequent hand washing, no-eye rubbing, coughing etiquette, normalization of surface cleaning), although blind and excessive disinfection measures are not advisable. 4) Compared with the large droplets, the small droplets have larger numbers but carry fewer viruses and are more prone to die through evaporation.
机译：液滴在Covid-19流行病中提供了众所周知的传输介质，并且粒度与传输路径的分类密切相关。然而，由于不同学科的信息不对称，术语“气溶胶”涵盖了大多数颗粒尺寸的悬浮颗粒，这可能导致误解了公众的防疫和控制策略。在本次审查中，将这些液滴被患者呼出的时间作为初始时间。然后，分析所有可用的病毒载量和呼出液滴的数值分布，并且空气中液滴的蒸发模型与呼吸道中液滴核的沉积模型相结合。最后，物理展位影响不同时间的不同尺寸液滴的传输风险的角度总结了。结果表明，尽管呼出液滴的分布由小液滴支配，但液滴体积与粒径的第三功率成比例，这意味着100μm液滴的病毒载荷约为1的10（6）次Mu M液滴在初始时间。此外，呼出的液滴受蒸发，水分分子，盐浓度和酸碱平衡（水分馏分＆ 98％）的热量和传质的影响，这导致它们迅速变化，并且病毒存活条件也变得劣化急剧地。液滴的初始直径（D（0））所需的时间缩小到平衡直径（D（e），约30％的D（0））近似与粒径的第二功率成比例，采取对于1 mu m液滴只有几毫秒，但为10 mu m液滴数百毫秒;换句话说，可以尽可能地保留由大液滴承载的病毒。最后，通过不同和随机接触路线的易感液体可能吸入感染液滴核，并且由于在复杂气道中的加速碰撞，液滴核（E）更容易分解为微小颗粒，其可以沉积在较高的风险肺泡区。在疾病传播期间，传染性液滴粒度广泛变化，传输风险在不同的时间节点下变化显着变化;因此，模糊术语“气溶胶”不利于分析疾病暴露风险。防疫预防和控制策略的建议是：1）大型液滴是疾病传播中的主要冲突;因此，即使它们最初被自制掩模被自制掩模阻挡，它也显着包含流行病。 2）接触的早期阶段，如近距离接触和短距离传输，具有最高的感染风险;因此，社会偏差可以有效地保持易感人群吸入活性病毒。 3）富马特途径的风险取决于与传染性病毒接触的时间;因此，尽管盲人和过度消毒措施不可取盲和过度消毒措施，但促进良好的健康习惯（包括频繁的洗手，无眼睛摩擦，咳嗽礼仪，表面清洁的正常化）。 4）与大液滴相比，小液滴具有更大的数量，但携带较少的病毒，并且通过蒸发更容易死。

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  • 来源
    《Building and Environment》 |2020年第11期|107307.1-107307.11|共11页
  • 作者

    Mao N.; An C. K.; Guo L. Y.; Wang M.; Guo L.; Guo S. R.; Long E. S.;

  • 作者单位

    Sichuan Univ Inst Disaster Management & Reconstruct MOE Key Lab Deep Earth Sci & Engn Chengdu Peoples R China;

    Sichuan Univ Coll Architecture & Environm Chengdu Peoples R China;

    Sichuan Univ Coll Architecture & Environm Chengdu Peoples R China;

    Sichuan Univ Coll Architecture & Environm Chengdu Peoples R China;

    Sichuan Univ Coll Architecture & Environm Chengdu Peoples R China;

    Sichuan Univ Coll Architecture & Environm Chengdu Peoples R China;

    Sichuan Univ Inst Disaster Management & Reconstruct MOE Key Lab Deep Earth Sci & Engn Chengdu Peoples R China|Sichuan Univ Coll Architecture & Environm Chengdu Peoples R China;

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  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类
  • 关键词

    Respiratory tract infection; Transmission route; Droplet size; Evaporation; Infection risk;

    机译：呼吸道感染;传输路线;液滴尺寸;蒸发;感染风险;

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