Close contact behavior in indoor environment and transmission of respiratory infection

Abstract

Close contact was first identified as the primary route of transmission for most respiratory infections in the early 20th century. In this review, we synthesize the existing understanding of the mechanisms of close contact transmission. We focus on two issues: the mechanism of transmission in close contact, namely the transmission of the expired particles between two people, and the physical parameters of close contact that affect the exposure of particles from one individual to another, or how the nature of close contact plays a role in transmission. We propose the existence of three sub‐routes of transmission: short‐range airborne, large droplets, and immediate body‐surface contact. We also distinguish a “body contact,” which is defined with an interpersonal distance of zero, from a close contact. We demonstrate herein that the short‐range airborne sub‐route may be most common. The timescales over which data should be collected to assess the transmission risk during close contact events are much shorter than those required for the distant airborne or fomite routes. The current paucity of high‐resolution data over short distances and timescales makes it very difficult to assess the risk of infection in these circumstances.

Airborne transmission of covid-19

“…Since the 2003 SARS outbreak, research in aerobiology, physics, and computational fluid dynamics has advanced our understanding of aerosol generation and the carriage and fate of respiratory particles 146781314. Airborne transmission of covid-19 is now the plausible cause of superspreading events in a call centre in Korea, a choir practice in Skagit County, US, and a restaurant in Guangzhou, China 1214.…”

“…The required forces can be created by rapid shearing air flows, vocal cord movement, and the open and closing of terminal airways—all of which are influenced by the type and force of respiratory activity 3. Heavy breathing, coughing, talking, and singing all generate aerosols, causing an exhalation plume of respiratory particles of varying sizes, containing potentially infective viral material 45678. The high viral loads present in the pharynx early in the course of covid-19 make these aerosols a plausible cause of both pre-symptomatic and asymptomatic transmission, which is so effective in fuelling outbreaks and yet difficult to control.…”

“…The arbitrary 5-10 µm threshold commonly used to dichotomise airborne and droplet transmission has never been supported theoretically or experimentally 4. Studies in both humans and airflow models show that particles as large as 50 µm can remain suspended and travel considerable distances 48. Furthermore, airborne range is influenced by the force and volume of exhalation as well as the local humidity, temperature, and airflow 4…”

“…Studies in both humans and airflow models show that particles as large as 50 µm can remain suspended and travel considerable distances 48. Furthermore, airborne range is influenced by the force and volume of exhalation as well as the local humidity, temperature, and airflow 4…”

“…It is wrong to assume that droplets land only on exposed mucosal surfaces such as the eyes and mouth 4. Particles up to 50 µm can be captured by inspiratory airflows and are deposited along the much more extensive surface area of the respiratory tract; particles below 10 µm can penetrate as far as alveoli.…”