Dept. of Chemical and Pharmaceutical Sciences, University of Trieste, Via L. Giorgieri 1, 34127, Trieste, Italy; INSTM National Interuniversity Consortium of Materials Science and Technology, Via G. Giusti, 9 50121, Firenze, Italy.
Institute for Maternal and Child Health, IRCCS Burlo Garofolo, Via Dell'Istria 65/1, 34137, Trieste, Italy.
Environ Res. 2021 Jul;198:111200. doi: 10.1016/j.envres.2021.111200. Epub 2021 Apr 24.
The relevance of airborne exposure to SARS-CoV-2 in indoor environments is a matter of research and debate, with special importance for healthcare low-risk settings. Experimental approaches to the bioaerosol sampling are neither standardized nor optimized yet, leading in some cases to limited representativity of the temporal and spatial variability of viral presence in aerosols. Airborne viral viability moreover needs to be assessed. A study has been conducted collecting five 24-h PM10 samples in a COVID-19 geriatric ward in late June 2020, and detecting E and RdRp genes by RT-qPCR with a Ct between 36 and 39. The viral RNA detection at Ct = 36 was related to the maximal numerosity of infected patients hosted in the ward. Lacking a direct infectivity assessment for the collected samples an experimental model has been defined, by seeding twelve nasopharyngeal swab extracts from COVID-19 positive patients on Vero E6 cells; only the four extracts with a viral load above E+10 viral copies (approximately Ct<24) have been able to establish a persistent infection in vitro. Therefore, the cytopathic effect, a key feature of residual infectivity, could be considered unlikely for the environmental PM samples showing amplification of viral RNA at Ct = 36 or higher. A standardization of airborne SARS-CoV-2 long-term monitoring and of environmental infectivity assessment is urgently needed.
空气中 SARS-CoV-2 暴露在室内环境中的相关性是一个研究和争论的问题，特别是对于医疗保健低风险环境而言。目前，对生物气溶胶采样的实验方法还没有标准化和优化，导致在某些情况下，病毒在空气中的存在的时间和空间变化的代表性有限。此外，还需要评估空气传播病毒的存活能力。在 2020 年 6 月下旬，进行了一项研究，在一家 COVID-19 老年病房收集了五个 24 小时的 PM10 样本，并通过 RT-qPCR 检测 E 和 RdRp 基因，Ct 值在 36 到 39 之间。Ct 值为 36 时检测到的病毒 RNA 与病房中收治的感染患者数量最多有关。由于缺乏对收集样本的直接感染力评估，因此定义了一个实验模型，即将来自 12 例 COVID-19 阳性患者的鼻咽拭子提取物接种到 Vero E6 细胞上；只有病毒载量超过 E+10 拷贝（大约 Ct<24）的 4 个提取物能够在体外建立持续感染。因此，对于在 Ct 值为 36 或更高时显示病毒 RNA 扩增的环境 PM 样本，可以认为细胞病变效应（残余感染力的关键特征）不太可能。迫切需要对空气中 SARS-CoV-2 的长期监测和环境感染力评估进行标准化。
