The routes of COVID-19 transmission to healthcare personnel from infected patients is the subject of debate, but is critical to the selection of personal protective equipment. The objective of this paper was to explore the contributions of three transmission routes—contact, droplet, and inhalation—to the risk of occupationally acquired COVID-19 infection among healthcare personnel (HCP). The method was quantitative microbial risk assessment, and an exposure model, where possible model parameters were based on data specific to the SARS-CoV-2 virus when available. The key finding was that droplet and inhalation transmission routes predominate over the contact route, contributing 35%, 57%, and 8.2% of the probability of infection, on average, without use of personal protective equipment. On average, 80% of inhalation exposure occurs when HCP are near patients. The relative contribution of droplet and inhalation depends upon the emission of SARS-CoV-2 in respirable particles (<10 µm) through exhaled breath, and inhalation becomes predominant, on average, when emission exceeds five gene copies per min. The predicted concentration of SARS-CoV-2 in the air of the patient room is low (< 1 gene copy per m³ on average), and likely below the limit of quantification for many air sampling methods. The findings demonstrate the value of respiratory protection for HCP, and that field sampling may not be sensitive enough to verify the contribution of SARS-CoV-2 inhalation to the risk of occupationally acquired COVID-19 infection among healthcare personnel. The emission and infectivity of SARS-CoV-2 in respiratory droplets of different sizes is a critical knowledge gap for understanding and controlling COVID-19 transmission.

从感染患者到医护人员的COVID-19传播途径尚有争议，但对于选择个人防护设备至关重要。本文的目的是探讨三种传播途径（接触，飞沫和吸入）对医护人员（HCP）职业性获得性COVID-19感染风险的影响。该方法是定量微生物风险评估，以及一种暴露模型，可能的模型参数基于可获得的SARS-CoV-2病毒特有数据。关键发现是，在不使用个人防护设备的情况下，飞沫和吸入传播途径比接触途径更为重要，平均占感染可能性的35％，57％和8.2％。一般，当HCP在患者附近时，发生80％的吸入暴露。液滴和吸入的相对作用取决于通过呼气在可吸入颗粒（<10 µm）中释放出SARS-CoV-2，平均每当释放量超过5个基因拷贝时，以吸入为主。病房空气中SARS-CoV-2的预测浓度很低（每m <1个基因拷贝平均³），并且可能低于许多空气采样方法的定量极限。研究结果证明了呼吸防护对HCP的价值，并且现场采样可能不够敏感，无法验证SARS-CoV-2吸入对医护人员职业性获得性COVID-19感染风险的影响。SARS-CoV-2在不同大小的呼吸液滴中的发射和感染性是理解和控制COVID-19传播的关键知识缺口。