Cherrie Mark Paul Carlo, Loh Miranda, Cherrie John William
Institute of Occupational Medicine, Edinburgh, EH14 4AP, United Kingdom.
Institute of Biological Chemistry, Biophysics and Bioengineering, Heriot-Watt University, Edinburgh, EH14 4AS, United Kingdom.
Ann Work Expo Health. 2025 Aug 1;69(7):777-788. doi: 10.1093/annweh/wxaf040.
Our aim was to explore the probable effectiveness of personal protective equipment (PPE) and environmental controls in protecting healthcare workers from Covid-19 infection using the Covid Exposure Model and Risk App (CEMRA), which estimates the risk of infection by various pathways.
We adapted a compartmental model of nine states within a hospital room to estimate virus transport and fate for contact and inhalation transmission from an infected patient, implemented using a discrete-time Markov-chain. Cough spray transmission was modeled separately, extrapolated to the expiratory volume, with a probability of the cough impacting the face in proportion to the surface area of the mucous membranes. Infectious profiles of patients observed in hospitals, constructed using information on salivary virus concentration, exhaled emissions and cough frequency, were categorized from "extremely low" to "extremely high" in seven steps. We parameterized the model using measurements made in three Scottish hospitals along with estimates from the literature. Seven interventions spanning PPE, engineering controls and administrative controls were applied to simulations of a health care worker working in a small room.
Route of infection and to a lesser extent efficacy of controls depended on the infectiousness of the patient; inhalation was the main transmission route in scenarios from "extremely low" to "moderate" infectiousness. For these lower infectious profiles, the surgical mask, surgical mask combined with hand hygiene, and surgical mask, hand hygiene and surface disinfection showed between a 60% and 64% average reduction in risk compared with no intervention. The use of natural ventilation and an air purification device resulted in a modeled 71% to 77% reduction in risk. A healthcare worker wearing an FFP2 or FFP3 respirator, was associated with an 86% to 95% reduction in risk. Finally, a ventilated headboard or a powered respirator with hood showed between a 91% and 99% reduction in risk. For the "high" to "extremely high" infectious profiles the cough spray route predominated, although the modeled effectiveness of the interventions was similar to the lower infectious profiles.
The use of a flexible quantitative microbial risk assessment model can assess the likely reduction of risk of Covid-19 from workplace controls under various assumptions. Respirators and local ventilation were the most effective modeled interventions.
我们的目标是使用新冠暴露模型和风险应用程序（CEMRA）探索个人防护装备（PPE）和环境控制措施在保护医护人员免受新冠病毒感染方面的可能效果，该模型可估计通过各种途径感染的风险。
我们采用了医院病房内九个状态的分区模型，以估计病毒传播以及感染患者接触传播和吸入传播的转归情况，通过离散时间马尔可夫链实现。咳嗽飞沫传播单独建模，外推至呼气量，咳嗽影响面部的概率与黏膜表面积成比例。利用唾液病毒浓度、呼出排放物和咳嗽频率等信息构建的医院观察到的患者感染特征，分为从“极低”到“极高”七个等级。我们使用在三家苏格兰医院进行的测量以及文献估计对模型进行参数化。对在小房间工作的医护人员的模拟应用了涵盖个人防护装备、工程控制和行政控制的七种干预措施。
感染途径以及在较小程度上控制措施的效果取决于患者的传染性；在“极低”到“中等”传染性的情况下，吸入是主要传播途径。对于这些较低传染性特征，与不采取干预措施相比，外科口罩、外科口罩结合手部卫生以及外科口罩、手部卫生和表面消毒显示平均风险降低60%至64%。使用自然通风和空气净化设备使模拟风险降低71%至77%。佩戴FFP2或FFP3呼吸器的医护人员风险降低86%至95%。最后，通风床头板或带面罩的动力呼吸器风险降低91%至99%。对于“高”到“极高”传染性特征，咳嗽飞沫传播途径占主导，尽管模拟的干预措施效果与较低传染性特征相似。
使用灵活的定量微生物风险评估模型可以在各种假设下评估工作场所控制措施可能降低新冠病毒感染风险的情况。呼吸器和局部通风是模拟效果最显著的干预措施。
