背景:尽管日本各地的老年人护理机构中发生了几起COVID-19疫情,没有针对这些环境中空气传播感染的现场研究报告.针对空气传播感染的对策不仅要考虑房间中的空气变化率(ACR),还要考虑房间中和房间之间的气流。然而,日本公共卫生中心或传染病相关组织尚未确定具体方法.
目的:2021年4月,宫城一家老年人护理机构报告了59例COVID-19病例,Japan,怀疑是空中传播。这项研究的目的是使用二氧化碳(CO2)示踪气体方法同时再现该设施中的ACR和气溶胶平流,以阐明爆发的具体位置和原因。这些发现将指导我们对预防复发的设施的建议。
方法:2021年8月,在怀疑空气传播感染的5个房间中放置了CO2传感器,使用干冰故意增加二氧化碳浓度,随后被删除。然后通过将Seidel方程应用于由于通风引起的CO2浓度的时间序列变化来估计ACR。通过在房间外面安装多个传感器,同时监测房间外的平流。使用计算机模拟验证了气溶胶平流。虽然疫情爆发时窗户是关着的,我们在开窗条件下进行了实验,以量化开窗的影响。
结果:在该设施的房间内,爆发时的ACR值估计为2.0至6.8h-1。打开窗户的低成本干预将通风频率提高了2.2至5.7倍。通风在很大程度上取决于开窗条件(所有房间的P值范围为.001至.03)。与模拟结果一致,从私人房间到日间房间检测到了气溶胶平流。考虑到感染当天开始感染的人在私人房间里,和几个居民,后来被二次感染,聚集在日间房间,据推测,传染性气溶胶是通过这种气流传播的。
结论:目前的结果表明,由于大规模流动驱动的气溶胶平流,可以发生继发感染。即使建筑设计遵守日本制定的通风指南。此外,CO2示踪气体方法有助于空气传播感染高风险区域的可视化,并证明窗户打开的有效性,这有助于改善设施运营和预防复发。
BACKGROUND: Although several COVID-19 outbreaks have occurred in older adult care facilities throughout Japan, no field studies focusing on airborne infections within these settings have been reported. Countermeasures against airborne infection not only consider the air change rate (ACR) in a room but also the airflow in and between rooms. However, a specific method has not yet been established by Japanese public health centers or infectious disease-related organizations.
OBJECTIVE: In April 2021, 59 COVID-19 cases were reported in an older adult care facility in Miyagi, Japan, and airborne transmission was suspected. The objective of this study was to simultaneously reproduce the ACR and aerosol advection in this facility using the carbon dioxide (CO2) tracer gas method to elucidate the specific location and cause of the outbreak. These findings will guide our recommendations to the facility to prevent recurrence.
METHODS: In August 2021, CO2 sensors were placed in 5 rooms where airborne infection was suspected, and the CO2 concentration was intentionally increased using dry ice, which was subsequently removed. The ACR was then estimated by applying the Seidel equation to the time-series changes in the CO2 concentration due to ventilation. By installing multiple sensors outside the room, advection outside the room was monitored simultaneously. Aerosol advection was verified using computer simulations. Although the windows were closed at the time of the outbreak, we conducted experiments under open-window conditions to quantify the effects of window opening.
RESULTS: The ACR values at the time of the outbreak were estimated to be 2.0 to 6.8 h-1 in the rooms of the facility. A low-cost intervention of opening windows improved the ventilation frequency by a factor of 2.2 to 5.7. Ventilation depended significantly on the window-opening conditions (P values ranging from .001 to .03 for all rooms). Aerosol advection was detected from the private room to the day room in agreement with the simulation results. Considering that the individual who initiated the infection was in the private room on the day of infection, and several residents, who later became secondarily infected, were gathered in the day room, it was postulated that the infectious aerosol was transmitted by this air current.
CONCLUSIONS: The present results suggest that secondary infections can occur owing to aerosol advection driven by large-scale flow, even when the building design adheres to the ventilation guidelines established in Japan. Moreover, the CO2 tracer gas method facilitates the visualization of areas at a high risk of airborne infection and demonstrates the effectiveness of window opening, which contributes to improved facility operations and recurrence prevention.