Currently, the positive antibody rate of SARS-CoV-2 in different countries is unknown. Furthermore, the antibodyʼs effectiveness has not been proven. PCR tests, antigen test kits, and antibodies (IgG, IgM) are used to detect infected people. PCR struggles to detect infected people before the onset of the disease, and negative results are likely to occur more than 4 weeks after the onset.(5) Approximately 2 weeks after the onset, 80% of infected people test positive for IgM or IgG, and nearly 100% become positive by the following week.(6) Even with the highly reliable test kit (cobas® 6800 SARS-CoV-2 Test) from Roche, the concordance rate with conventional PCR is 95.8%.(7) It is controversial when and on whom such inspections should be conducted, consequently, we considered mortality to be more important than morbidity in this study. Doremalen reported that SARS-CoV-2 remained viable in aerosols throughout a 3-hour experiment, and it was more stable on plastic and stainless steel than on copper and cardboard, and the virus was detected up to 72 hours after application to these surfaces.(8) Thus, the virus was found to survive on the floor of the rooms of an infected person, as reported on the Diamond Princess cruise ship.
Case numbers are dependent on the SARS-CoV-2 testing capability of each country and, thus, they might not be representative of the true extent of the epidemic. Consequently, we also compared the number of deaths per million. The results demonstrated that COVID-19-associated deaths relative to the size of the population were significantly lower in countries that follow the cultural practice of removing shoes indoors than in those that do not. This suggests that one of the reasons behind Japanʼs low COVID-19 death toll is the cultural practice of removing shoes indoors. Therefore, we should continue this cultural practice in Japan, and policies on handling shoes should be introduced in hospitals all over the world.