Multiple airflow patterns in human microenvironment and the influence on short-distance airborne cross-infection – A review

Abstract

The global spread of the coronavirus disease 2019 (COVID-19) has increased the demand of effective control of the disease transmission between people, especially when they are in close distance between each other. The microenvironment between the people in short distance contains multiple airflow patterns that directly affect the disease transmission. By understanding and respecting this special localized environment, the airborne cross-infection at both short and long distance can be minimized. This paper gives an overview of the flow fields in human microenvironment. The exhalation flow from different respiratory activities, e.g. normal breathing, speaking, coughing or sneezing is considered as a part of the microenvironment. The dynamics of the exhalation flow and the contained droplets or aerosols are summarized from previous studies. The factors influencing the flow fields in human microenvironment are discussed, including both the physiological factors of the occupants and the environmental factors in the ventilated context (macroenvironment). Effective control of these influencing factors can be helpful to mitigate airborne transmission risk between individuals. This paper highlights the importance of better understanding of the dynamics and transmission routes of the expelled virus-laden droplets or aerosols, which are largely affected by complex flow interactions in human microenvironment.