Transmission modes
How do asymptomatic carriers make the SARS-CoV-2 virus transmission and infect others?Because they do not cough or sneeze to any appreciable extent by definition, the direct or indirect contact modes and aerosol transmission are considered as the main possible modes of transmission[36]. Public health messages have paid attention to the possibility of direct and indirect transmission such as by contaminated hands, stressing the importance of washing hands often and thoroughly. Now we need to focuse on aerosol transmission. During the SARS epidemic in 2003, it has been verified that these infected hospitalized patients emitted viable aerosolized virus into the air[37]. A recent resarch by Doremalen et al. demonstrated that “aerosol and fomite transmission of SARS-CoV-2 is plausible, since the virus can remain viable and infectious in aerosols for hours and on surfaces up to days”[38]. It had been confirmed long before that ordinary breathing and speech both emit large quantities of aerosol particles[39, 40]. So the asymptomatic or pre-infected individuals still generate aerosols even if they do not sneeze or cough. Other studies have found that vocalization can emits up to an order of magnitude more aerosol particles than breathing, and the louder one speaks, the more aerosol particles are produced[41, 42].
It has been concluded by some researchers that COVID-19 can be transmitted by a face-to-face conversation with an asymptomatic infection individual without no touch, which ascribed to a large number of exhaled particles released during breathing and speech and the high transmissibility of SARS-CoV-2[36]. But how do the virus titers in these aerosols change with time after infection or discharge, and what is the best way to avoid infection from the point of environmental aerodynamics? Scientists need collaborate and take up the current challenge presented by COVID-19. At the same time, more publicity is needed to inform the public that everyone releases potentially infectious aerosols all the time, not just when sneezing or coughing, so it is essential to avoiding close contact and wearing a mask with protective properties.