Exploring the Factors that Determine the Survival of Viruses in Aerosols and Droplets

引起人类疾病的微生物，如细菌和病毒，可通过直接（人与人之间）、间接（与污染表面接触）和空气传播途径传播。可吸入大小的小气溶胶颗粒（直径小于10微米）和较大的液滴（直径达100微米，约为人类头发直径的两倍）可在空气中停留几分钟至几小时，并可通过咳嗽、打喷嚏、说话和呼吸排出。较大的液滴在污染表面的短距离上沉降很快（称为污染物）。虽然一些疾病，如结核病和麻疹，表现出优先通过空气传播，但其他疾病，如流感和诺如病毒，则是机会性的。确定这些不同传播方式占主导地位的情况和澄清减轻它们的方法必须成为优先事项。这些知识为实施非药物干预措施提供了信息，例如保持身体距离和使用适当的个人防护设备，如口罩。此外，临床环境看到许多气溶胶产生程序的广泛使用，这些程序知之甚少，但可能通过空气携带病原体，例如在牙科程序和麻醉中。尽管人们认识到气溶胶和飞沫在微生物传播中的重要性，但为减轻微生物传播而作出决定的证据基础往往仍然是流行病学依据。研究控制病原体在气溶胶、液滴和污染物中存活的因素的强大创新仪器对于推动我们的理解至关重要。利用布里斯托尔大学开发的新技术平台，我们将提供一个全面的框架，以了解控制SARS-CoV-2病毒存活的因素，这是气溶胶、飞沫和污染物中导致COVID-19的原因。我们已经开发了一个定制系统来研究微生物在含有微生物的气溶胶和液滴中生存的情况，这些微生物被称为CELEBS。我们将在最近投入使用的最先进的设施中研究SARS-CoV-2病毒（在呼吸道飞沫中）与其直接环境之间的相互作用。通过将已知数量的具有已知病毒载量的相同大小的气溶胶液滴悬浮一段指定时间，将测量病毒的存活并研究灭活措施的影响。更具体地说，我们将充分探索SARS-CoV-2病毒在暴露于不同环境条件（相对湿度和温度）的不同大小的飞沫中以及在表面沉积的真实模拟污染物中的存活情况。我们还将探索光和大气氧化剂（露天空气因素）的影响，以及颗粒大小和水分含量对液滴/气溶胶产生的动态变化率（即干燥/干燥动力学对呼气的影响）。将检查不同变体SARS-CoV-2病毒的存活情况。该项目将建立在初步工作的基础上，这些工作已经证实并验证了我们的实验方法。这项更全面的工作将为非药物干预措施提供明确的信息，例如保持社交距离、推荐的室内操作温度和湿度（例如医院、护理院、交通工具）以及其他灭活方法（例如光和氧化剂）。除了这些直接的研究之外，这项技术将是灵活的，为研究更广泛的重要的空气传播病原体开辟了机会。

The transmission of microbes which cause disease between humans, such as bacteria and viruses, can occur by direct (person-to-person), indirect (contact with contaminated surfaces) and airborne routes. Small aerosol particles of a respirable size (<10 micrometres diameter) and larger droplets (up to 100 micrometres, about twice the diameter of a human hair) can remain airborne for minutes to hours and are emitted by coughing, sneezing, speaking and breathing. Larger droplets settle very quickly over short distances contaminating surfaces (referred to as fomites). Although the transmission of some diseases, such as tuberculosis and measles, show preferential airborne transmission, other diseases, such as influenza and norovirus, are opportunistic. Identifying both the circumstances when these different modes of transmission are dominant and clarifying ways to mitigate them must be priorities. Such knowledge informs the implementation of non-pharmaceutical interventions, such as physical distancing and the use of appropriate personal protective equipment such as face masks. Further, the clinical context sees the wide use of many aerosol generating procedures that are poorly understood but could carry pathogens through the air, for example in dental procedures and in anaesthesia. Despite the recognised importance of aerosols and droplets in the transmission of microbes, the evidence-base on which decisions are made to mitigate microbe transmission often remain epidemiological. Robust innovative instruments for studying the factors that control the survival of pathogens in aerosols, droplets and fomites are crucial to move our understanding forward. Using a novel technology platform developed at the University of Bristol, we will deliver a comprehensive framework for understanding the factors that control the survival of the virus SARS-CoV-2, the cause of COVID-19 in aerosols, droplets and fomites. We have developed a bespoke system to study how well microbes survive in aerosols and droplets containing microbes referred to as CELEBS. We will study the interactions between the SARS-CoV-2 virus (in respiratory droplets) and its immediate environment in a recently commissioned state of the art facility. By levitating a known number of aerosol droplets of identical size with a known viral load for a specified period of time, the survival of the virus will be measured and the impact of inactivation measures studied. More specifically, we will fully explore the survival of the SARS-CoV-2 virus in droplets of varying size exposed to varying environmental conditions (relative humidity and temperature) and in realistic simulated fomites deposited on surfaces. We will also explore the influence of light and atmospheric oxidants (open air factor) and the rate of dynamic changes in particle size and moisture content upon droplet/aerosol generation (i.e. desiccation/drying kinetics on exhalation). The survival of different variants of the SARS-CoV-2 virus will be examined. This project will build on preliminary work that has confirmed and validated our experimental approach. This more comprehensive work will provide clarity to inform non-pharmaceutical interventions such as social distancing, recommended indoor operating temperatures and humidities (e.g. hospitals, care homes, transport) and other methods of inactivation (e.g. light and oxidants). Extending beyond these immediate studies, the technique will be flexible, opening up opportunities to study a wider range of important airborne pathogens.