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薬理と治療
- Author: Motoharu Tanaka1
Abstract
A new coronavirus infectious disease(COVID-19)emerged at the beginning of 2020, and since then has widely spread worldwide through sneeze, cough, conversation and others, resulting in tens of millions of infections and millions of deaths. Droplet shedding is common with sneezing, coughing, and talking, in that order, and sometimes amount of the virus particles expelled reach 2×108. Some specialists say that infection could be spread by particle as small as 1000 as in number. It is said that wearing a mask is important for preventing infection, however, it is uncertain whether it depends on inhibition of splash expelled from spreader or prevention of inhalation by the receiver. Non-woven masks are widely available and are reported to inhibit the inhalation of particles with a 0.3μm in a diameter by 99%. Based on a supercomputer simulation, although inhalation of small droplets could not be inhibited well once some gaps remain between the mask and the face with non-woven masks, it inhibited the inhalation of the particles with a size of 0.3-50 μm once tightly shielded. On the other hand, an actual infection study with SARS-CoV-2 showed that even N95 masks which are superior to the non-woven masks in the filtration capability could not completely inhibit the inhalation of the droplets even when tightly shielded. Also, in a randomized controlled trial with nearly five thousand participants in Denmark( DANMASK-19), no clear protective effect was demonstrated against infection in the surgical mask wearers. Although adherence of masks to oneʼs face is an influencing factor, it is not considered sufficient for prevention to wear masks only. We should not rely on the preventive effect of masks too much, and instead keep distance from others as if they are potentially infected until a complete preventive method or medical treatment is established.
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