Passing face-to-face risk of Covid Transmission

When passing face-to-face, risk of COVID infection peaks within 5 seconds: Japan study
Published Oct 25, 2023

The risk of coronavirus infection peaks within five seconds of passing an infected person, a research team from the University of Tsukuba has found.

In their findings published in the British academic journal Scientific Reports, researchers pointed out that holding one's breath within five seconds of passing a person, keeping a distance of at least 1 meter, and standing upwind of them are effective measures to prevent infection.

As COVID-19 cases continue to be confirmed, the research team examined the risk of infection based on changes in the amount of aerosol particles, considered the main route of infection, as a major challenge in preventing infection when people move around.

Specifically, a mannequin wearing a device that emits aerosol particles from its mouth was moved indoors under four conditions: walking (5 kilometers per hour), jogging (10 km/h), running (15 km/h), and sprinting (20 km/h). Under each condition, the amount of particles within a certain range was measured. The researchers also compared the results with and without ventilation.

The findings showed that the number of particles peaked within five seconds in all conditions and then dropped sharply. It is believed that the particles were diffused by the vortex created by the mannequin's movement, which caused the air to flow backward. In addition, the faster the speed of passage, the fewer particles there were at peak. It is assumed that more exhaled breaths and faster vortex speeds promoted diffusion.

When compared to no ventilation, the peak particle count was about 55% or less when walking when ventilated, and the peak was much smaller at all travel speeds, even dropping to near the pre-measurement level after 10 seconds of passing.

The Study:

Peak risk of SARS-CoV-2 infection within 5 s of face-to-face encounters: an observational/retrospective study
Published Oct 6, 2023

Abstract
The link between aerosol dynamics and viral exposure risk is not fully understood, particularly during movement and face-to-face interactions. To investigate this, we employed Particle Trace Velocimetry with a laser sheet and a high-speed camera to measure microparticles from a human mannequin’s mouth. The average peak time in the non-ventilated condition (expiratory volume, 30 L; passing speed, 5 km/h) was 1.33 s (standard deviation = 0.32 s), while that in the ventilated condition was 1.38 s (standard deviation = 0.35 s). Our results showed that the peak of viral exposure risk was within 5 s during face-to-face encounters under both ventilated and non-ventilated conditions. Moreover, the risk of viral exposure greatly decreased in ventilated conditions compared to non-ventilated conditions. Based on these findings, considering a risk mitigation strategy for the duration of 5 s during face-to-face encounters is expected to significantly reduce the risk of virus exposure in airborne transmission.

Keywords: outdoor transmission, transmission, walking, running, jogging, masking, risk