Covid-19: Asymptomatic people can transmit infection by speaking

According to a study by Japanese scientists

Covid-19 infection can be transmitted by infected people who are asymptomatic during speech, reveal researchers, who recommend the use of mask and visor in situations of proximity such as going to an appointment or to the hairdresser.

Most studies focus on the flow of exhaled air through coughing or sneezing, which can send aerosols over long distances. However, talking close to each other is also a risk, as the virus can be transmitted through speech.

In a statement, the American Institute of Physics, regarding the study published in the scientific newsletter Physics of Fluids, Japanese scientists used smoke and laser light to investigate the flow of air expelled near and around two people, while conversing in various common contexts, such as hair salons, medical clinics or long-term care units.

In that investigation, electronic cigarettes were used to produce artificial smoke, containing droplets about a tenth in diameter, similar to the size of a virus particle.

The liquid used in these vaporization devices, a mixture of glycerine and propylene glycol, produces a cloud of tiny droplets that scatter light from a laser, allowing you to visualize the air flow patterns.

“We analyzed the characteristics of diffusion of air exhalation with and without a mask when the person was standing, sitting, face down or lying face up,” said author Keiko Ishii.

To study the effect of speech on exhalation, the word “onegaishimasu,” a typical Japanese greeting in business settings, was uttered repeatedly during the filming of the resulting cloud of steam.

The experiments were carried out in a hair salon in Tokyo, with postures chosen to simulate typical customer service scenarios, including washing where the customer is lying down and the technician standing and leaning over the customer.

"Similar face-to-face contacts would occur not only in that context, but also in long-term and medical care," said Ishii.

Demonstrations revealed that the air exhaled by a person without a mask when talking tends to move downward under the influence of gravity, which is why if a client or patient is lying down they can become infected.

When a mask is used in a context where the person is standing or sitting, the cloud of vapor tends to stick to the person's body, which is warmer than the air around them and moves upwards along the way. of the body, which is why, if the professional is inclined, the aerosol tends to detach from the person's body and fall on the client or patient.

Researchers have also experimented with face shields and found that they can prevent aerosols leaving the mask from reaching the client or patient.

That researcher concluded that "it is more effective to wear a mask and face shield when providing services to clients."