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

TOKYO — 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.

Based on these results, the team noted that the aforementioned measures were effective in preventing infection. Team member Takeshi Asai, professor emeritus of sports engineering, said, “We found that if you take five seconds of safety measures, the (infection) risk is significantly reduced. We need to take preventive measures based on scientific evidence in various situations such as sports and events.”

(Japanese original by Yurika Tarumi, Lifestyle, Science & Environment News Department)