Droplet nuclei are sometimes defined only by size. The Centers for Disease Control and Prevention (CDC) defines droplet nuclei as “dried residues of less than 5 microns in size” [1]. Additionally, it is sometimes referred to as “small drops of moisture carrying infectious pathogens” [2]. The World Health Organization (WHO) defines droplet nuclei as follows: “when the droplet particles are >5–10 μm in diameter, then they are referred to as respiratory droplets, and when then are <5 μm in diameter, they are referred to as droplet nuclei” [3], and they do not require dessication.The term “droplet nuclei” must be clearly defined in terms of desiccation. For the purpose of this study, droplet nuclei will be discussed using CDC's definition, which includes a requirement for desiccation. The WHO and CDC's current position is based on the conventional medical definition that in human exhalation origin, only droplet nuclei can cause airborne transmission [1]. Presently, the WHO and CDC suspect but do not officially recognize airborne severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) transmission [4]. According to the CDC, airborne transmission is currently limited to measles, chickenpox, disseminated shingles, and smallpox [5]. Airborne transmission is suspected in certain other viruses but has not been confirmed yet. Suspected cases of SARS-CoV transmission through apartment building air [6], outbreak of influenza in an airplane delayed on the ground with an inoperative ventilation system [7], and reports of simultaneous coronavirus disease (COVID-19) outbreaks in large enclosed spaces [8] suggest that these enveloped viruses are transmitted through dry droplet nuclei because it is unlikely that the fine droplets will stay moist for long distances and time. Wells found that droplets smaller than 100 μm would completely dry out before falling approximately 2 m to the ground [9]. Morawska reported that droplets with sizes of the order of 1 μm evaporate within a few milliseconds even under conditions of high relative humidity, droplets with size of the order of 10 μm exist for up to a few tens of a second, while very large droplets that are 100 μm in diameter survive for up to a minute [10]. SARS-CoV-2 and SARS-CoV exhibited similar half-lives in aerosols, with median estimates of approximately 2.7 hours [11]. In this study, all aerosols are considered to be dried out during the course of the process and turned into droplet nuclei. A couple of hours of half-life is sufficient for the dry droplet nuclei to be dispersed and become clinically infectious, especially in an enclosed environment. The presence of infectious, replicating virions in <1 µm of aerosol samples has been evident, and there were increases in viral RNA during cell culture of the virus from aerosol samples [12]. It has been shown that droplets up to 1μm in size evaporate within a few milliseconds [10]; this indicates that SARS-CoV-2 can be transmitted through droplet nuclei. SARS-CoV-2 is not inactivated on plastic and stainless steel surfaces for a couple of days [11]. Generally, enveloped viruses with a lipid envelope tend to be more persistent at lower relative humidity, while non-enveloped viruses are more stable at higher relative humidity [13].Airborne transmission is meant by most authors to be synonymous with aerosol transmission [14]. The WHO states the following: “Airborne transmission is defined as the spread of an infectious agent caused by the dissemination of droplet nuclei (aerosols) that remain infectious when suspended in air over long distances and time” [7]. This statement includes two definitions. First, the WHO defines that the term “airborne transmission” is limited to transmission by droplet nuclei. Second, the WHO also mentions that airborne, droplet nuclei, and aerosol transmissions are all synonymous. The CDC states, “The definition of an aerosol, as used here, is a suspension of tiny particles or droplets in the air, such as dusts, mists, or fumes.” [15]. CDC’s definition requires droplet nuclei to be dry, and airborne transmission is further limited to transmission by droplet nuclei. Therefore, aerosol transmission is not synonymous with airborne or droplet nuclei transmission in CDC’s definition. Additionally, most reports stating that SARS-CoV-2 spreads through air and/or aerosol do not clearly specify whether the definitions of the terms “airborne” and “aerosol” refer only to dry droplet nuclei or fine, moist droplets floating in the air [14].The fact that the definitions of aerosols and droplet nuclei are not uniform worldwide, even between the WHO and the CDC, is a huge detriment. Equilibrium moisture content (EMC) is the moisture content at which the material is neither gaining nor losing moisture in the air. The droplet nuclei is considered dry when the EMC state has been reached.. Because the value of the EMC depends on the relative humidity and temperature of the air, the moisture content of droplet nuclei varies with relative humidity and temperature and their infectivity is also likely to vary. This is an issue to consider when discussing whether or not droplet nuclei are infectious. Indeed, it is difficult to determine how small and how dry a particle should be to be referred as a droplet or droplet nuclei. To prevent this ambiguity, a suitable alternative is to abolish the current classification of droplets and droplet nuclei and reclassify them as droplets and aerosols based, solely, on how long they are suspended in the air, regardless of their size and dryness.Along with the global unification of the definitions of aerosols and droplet nuclei, it is essential to recognize the above theoretical evidence showing that SARS-CoV-2 has a drying-resistant nature and is likely to have airborne transmission through dry droplet nuclei. References1.         U.S. Department of Health & Human Services. (2012, May 18). Principles of Epidemiology. Retrieved July 28, 2020, from https://www.cdc.gov/csels/dsepd/ss1978/lesson1/section10.html2.         Medical Advisory Secretariat. Air cleaning technologies: an evidence-based analysis. Ont Health Technol Assess Ser. 2005;5(17):1-52.3.         Modes of transmission of virus causing COVID-19: implications for IPC precaution recommendations. World Health Organization. https://www.who.int/news-room/commentaries/detail/modes-of-transmission-of-virus-causing-covid-19-implications-for-ipc-precaution-recommendations. Published July 9, 2020. Accessed July 29, 2020.4.         Morawska L, Milton DK. It is Time to Address Airborne Transmission of COVID-19 [published online ahead of print, 2020 Jul 6]. Clin Infect Dis. 2020;ciaa939. doi:10.1093/cid/ciaa9395.         Isolation Precautions. https://www.cdc.gov/infectioncontrol/guidelines/isolation/index.html. Published July 22, 2019. Accessed July 28, 2020.6.         Yu IT, Li Y, Wong TW, et al. Evidence of airborne transmission of the severe acute respiratory syndrome virus. N Engl J Med. 2004;350(17):1731-1739. doi:10.1056/NEJMoa0328677.         Moser MR, Bender TR, Margolis HS, Noble GR, Kendal AP, Ritter DG. An outbreak of influenza aboard a commercial airliner. Am J Epidemiol. 1979;110(1):1-6. doi:10.1093/oxfordjournals.aje.a1127818.         Transmission of SARS-CoV-2: implications for infection prevention precautions. World Health Organization. https://www.who.int/news-room/commentaries/detail/transmission-of-sars-cov-2-implications-for-infection-prevention-precautions. Published 2020. Accessed July 28, 2020.9.         Atkinson J, Chartier Y, Pessoa-Silva CL, et al., editors. Natural Ventilation for Infection Control in Health-Care Settings. Geneva: World Health Organization; 2009. Annex C, Respiratory droplets. Available from: https://www.ncbi.nlm.nih.gov/books/NBK143281/10.     Morawska L. Droplet fate in indoor environments, or can we prevent the spread of infection?. Indoor Air. 2006;16(5):335-347. doi:10.1111/j.1600-0668.2006.00432.x11.     van Doremalen N, Bushmaker T, Morris DH, et al. Aerosol and Surface Stability of SARS-CoV-2 as Compared with SARS-CoV-1. N Engl J Med. 2020;382(16):1564-1567. doi:10.1056/NEJMc200497312.     Santarpia JL, Herrera VL, Rivera DN, et al. The Infectious Nature of Patient-Generated SARS-CoV-2 Aerosol medRxiv 2020.07.13.20041632; doi: https://doi.org/10.1101/2020.07.13.2004163213.     Sobsey, M.D. and Meschke, J.S., 2003. Virus survival in the environment with special attention to survival in sewage droplets and other environmental media of fecal or respiratory origin. Report for the World Health Organization, Geneva, Switzerland14.     Tellier R, Li Y, Cowling BJ, Tang JW. Recognition of aerosol transmission of infectious agents: a commentary. BMC Infect Dis. 2019;19(1):101. Published 2019 Jan 31. doi:10.1186/s12879-019-3707-y15.     Aerosols. Centers for Disease Control and Prevention. https://www.cdc.gov/niosh/topics/aerosols/default.html. Published June 29, 2010. Accessed July 29, 2020. 
During the SARS-CoV outbreak in 2003, Japan's National Institute for Infectious Diseases (NIID) showed, on their website, that SARS-CoV, an enveloped virus, could be deactivated by a 200-fold dilution of a neutral detergent 1. Based on these findings, our clinic began using a 200-fold diluted solution of kitchen detergent in early March to wipe down materials and soak instruments as well as the hands of patients and staff for the purpose of SARS-CoV-2 disinfection. Our tweet on April 10, 2020 regarding this gained 6 million views in Japan 2. There have been no experimental studies confirming the deactivation effect of detergents on SARS-CoV or SARS-CoV-2. On April 15, the Ministry of Economy, Trade and Industry (METI) of Japan announced that they would test the disinfecting effects of detergents on SARS-CoV-2. On April 21, our clinic was interviewed by METI. The final results were publicly announced on June 26, 2020 3. To date, no English reviews of this Japan’s public presentation 4 exist. Validation studies using SARS-CoV-2 (JPN/TY/WK-521) and VeroE6/TMPRSS2 cells were conducted at five institutes in Japan, including NIID and Kitasato University (KU) 4. At NIID, the surfactant was mixed with the virus for periods between 20 seconds and 5 minutes. After removing the surfactant with resin, they evaluated the antiviral value using the TCID50 method. An infectious titer reduction rate of over 99.99% was obtained confirming the disinfection efficiency. At KU, VeroE6/TMPRSS2 cells were incubated for an hour with the surfactant and virus. After observing its cytopathic effect (CPE) for three days, the RNA titer was measured using qRT-PCR in the culture supernatant. Only when no CPE was observed in all wells and no increase in RNA titer was observed, was it judged as having a disinfection effect. NIID finally judged and published the following 9 surfactants, that were determined as possessing a disinfection effect at either the NIID or KU or both, as effective disinfectants for SARS-CoV-2 under the following conditions:ž   Sodium linear alkylbenzene sulfonate; 20 seconds with 0.1% at NIID, 5 minutes with 0.1% at KU.ž   Alkyl glycoside; 20 seconds with 0.0.5% at NIID, 1 minute with 0.1% at KU.ž   Alkylamine oxide; 20 seconds with 0.05% at NIID, 1 minute with 0.05% at KU.ž   Benzalkonium chloride; 2 minutes with 0.05% at NIID, 1 minute with 0.05% at KU. ž   Benzethonium chloride; 1 minute with 0.05% at NIID, 5 minutes with 0.05% at KU. ž   Dialkyldimethyl ammonium chloride; 40 seconds with 0.01% at NIID, 5 minutes with 0.01% at KU. ž   Polyoxyethylene alkyl ether; 5 min with 0.2% at NIID, (not effective in 5 min with 0.1% at KU).ž   Pure-soap component: 1 minute with 0.24% potassium salts of fatty acids at NIID, (not effective at 5 minutes with 0.12% at NIID and at 5 min with 0.1% at KU).  ž   Pure-soap component: 1 minute with 0.22% sodium of fatty acids at NIID, (not effective at 5 minutes with 0.11% at NIID and at 10 minutes with 0.1% at KU).  However, the use of detergent for hand sanitizers was discouraged by NIID 3. From early March 2020 to the present (July 15 2020), we applied a 200-fold dilution of kitchen detergent (Charmy V Quick; LION corp., Japan), which contains 30% surfactant (alkylamine oxide, sodium alpha-olefin sulfonate, polyoxyethylene fatty acid alkanolamide, and polyoxyethylene alkyl ether), to the hands of at least 500 patients, and five members of medical staff as a SARS-CoV-2 disinfectant. The hands of patients and medical staff were not rinsed for approximately 15 minutes and 1 hour after application, respectively. The only adverse effects observed were mild hand sores in all the staff. Ethanol as hand sanitizer also causes hand sores. Dishwashing with bare hands using undiluted neutral kitchen detergent has been widely practiced around the world. In some European countries, it is common not to rinse the detergent completely when washing dishes and bathing. Given these practices, toxicity is unlikely to be an issue if a thin layer of detergent is left on the hands for a couple of hours; however, further verification is necessary.Ethanol dries and loses its disinfection property rapidly, whereas detergents do not easily dry out on skin and cloth, enabling longer contact with the virus. Furthermore, detergents remain on the skin after it dries, and may melt and become effective when wet droplets adhere. This can be expected on the skin as well as in other materials including face masks and clothing. Detergents are inexpensive and are unlikely to be in short supply. Studies confirming the prolonged effectiveness of dried detergents on surfaces and the toxicity of the above methods are necessary. References 1.         National Institute for Infectious Diseases, SARS ni kansuru shoudoku (3teiban) [Disinfection on SARS (3rd Ed.)]. http://idsc.nih.go.jp/disease/sars/sars03w/index.html. Published December 18, 2003. 2.         @blanc0981. (2020, April 10). Toindeha Ikkagetsukan, 200bainiusumetanodaidokorosenzaide Sutaffu, kanatani tewonurashite, arainagasazuniitemorattemasuga, Hitorimotearenadono Shinkokunauttaehanai. Kaimenkasseizainosugoitenha kansoshitemonokori, sonoatonaniwosawattemo sonohifuni koteingusareta kaimenkasseizaide koronawokorosukanoseigatakai. [We have our staff and patients wet their hands with 200 times diluted kitchen detergent for a month without rinsing it off. Not a single person has complained of serious complaints such as rough hands. The great thing about surfactants is that they stay on after they dry, and whatever you touch afterwards is likely to kill the corona with the surfactant coated on that skin.] [Twitter post]. Retrieved from https://twitter.com/blanc0981/status/1248415995527483394?s=20 3.         Surfactants and Hypochlorous Acid Solution for Removal of Coronavirus from Surfaces (Final Announcement). https://www.meti.go.jp/english/press/2020/0626_004.html Published June 26, 2020. Accessed July 15, 2020. 4.         Shingatacoronauirusunitaisuru daigaeshoudokuhouhounoyuukouseihyouka (Saishuuhoukoku) [Evaluation of the Effectiveness of Alternative Disinfection Methods for New Coronavirus (Final Report)]. https://www.nite.go.jp/data/000111315.pdf Published June 29, 2020. Accessed July 15, 2020.   

Daisuke Miyazawa

and 1 more

Several recent studies have reported that systemic corticosteroids were effective against coronavirus disease 2019 (COVID-19) (1). Patients with severe COVID-19 present with acute respiratory distress syndrome (ARDS), also known as diffuse alveolar damage, presumably caused by an excessive immune response in the alveoli. Similar but milder alveolar inflammation may also exist in early stage patients, and systemic corticosteroids may contribute to the suppression of excessive inflammation in the alveoli, however, adverse effects such as opportunistic infections and delayed viral elimination may outweigh this advantage. This could be why the study by Horby et al. found no benefit in less severe patients who were not receiving oxygen (1). Delivering corticosteroids directly to the alveoli by inhalation should be effective and would have fewer systemic side effects. SARS-CoV-2 infection is suggested to elicit inflammatory cytokine secretion, not only from alveolar macrophages but also from alveolar epithelial type 2 cells (2). Additionally, ICS (inhaled corticosteroids) deposited in the alveoli enter the systemic circulation via the pulmonary vasculature, leading to potential anti-inflammatory effects in this region, which is also considered to be a site of inflammation during COVID-19.Nebulized budesonide improved oxygenation and significantly reduced inflammatory markers (TNF-α, IL-1β, and IL-6) in patients with ARDS (3). There are several reviews of inhaled corticosteroids for COVID-19, and currently, there is no clear evidence on whether pre-morbid use of ICS is a factor in adverse or beneficial outcomes for COVID-19 (4,5).ICS can reach different sites in the lungs, depending on particle size (5). As the alveoli are considered to be the main site for lung inflammation in COVID-19, steroids with smaller particle sizes that can reach the alveoli should be more promising. Among ICS, pressurized metered-dose inhalers (pMDIs) of beclomethasone and ciclesonide have the smallest particle sizes (<2 µm) and, thus, are considered to reach the alveoli more easily (6). The particles in the nebulizer are also small enough to reach the alveoli, but there is a concern that the particles that return on exhalation may contain the virus and could therefore infect medical personnel.Apart from their anti-inflammatory effects, some ICS have been found to have antiviral effects. Ciclesonide and mometasone, which are both marketed as ICS, suppressed the replication of SARS-CoV-2 and MERS-CoV in vitro, whereas dexamethasone, cortisone, prednisolone, and fluticasone did not (7). There is a case report of three COVID-19 patients treated with inhaled ciclesonide (8). Although it might be more difficult for dry powder inhalers (DPI) to reach the alveoli, owing to their larger particle size, than for pMDIs (6), mometasone may be worth considering, as it has antiviral properties and a smaller particle size than budesonide (6). A mutant MERS-CoV that developed resistance to ciclesonide did not show resistance to mometasone (7).ICS should be considered as a promising therapeutic candidate, and should be prioritized for clinical trials in both mildly symptomatic outpatients and severely ill inpatients. As of July 5, 2020, several clinical trials worldwide utilizing ICS for COVID-19 have been registered on ClinicalTrials.gov: four trials (one recruiting, three not yet) for ciclesonide, and four trials (three recruiting, one not yet) for budesonide (one including formoterol).The antiviral effect of ICS as well as their particle size, which is related to the ability to reach the alveoli, should also be noted. The anti-SARS-COV-2 effect of beclomethasone in vitro has yet to be tested. We propose that clinical trials that confirm the clinical effect of beclomethasone, which has a similar particle size to ciclesonide, as well as studies that confirm its antiviral effect, should be conducted. This is because, if either or both drugs are found to be effective it may be possible to speculate whether these effects are due to the antiviral or anti-inflammatory effects. If beclomethasone is found to be clinically effective but not antiviral, the effect of particle size can be estimated by comparing it to budesonide, which also has no antiviral effect. For the same reason and in anticipation of the unique antiviral effect that is different from ciclesonide, we propose that clinical trials of mometasone, which has a smaller but similar particle size to budesonide, should also be conducted. Mometasone is also available in nasal spray form. Clinical trials could be conducted to determine the preventive effects of intranasal mometasone and its effectiveness in treating early stage COVID-19. References 1.         Horby P, Lim WS, Emberson J, et al. Effect of dexamethasone in hospitalized patients with COVID-19: preliminary report. medRxiv 2020 Jun. doi: https://doi.org/10.1101/2020.06.22.201372732.         Huang J, Hume AJ, Abo KM, et al. SARS-CoV-2 Infection of pluripotent stem cell-derived human lung alveolar type 2 cells elicits a rapid epithelial-intrinsic inflammatory response. bioRxiv 2020 Jun. doi: https://doi.org/10.1101/2020.06.30.1756953.         Mohamed HS, Meguid MM. Effect of nebulized budesonide on respiratory mechanics and oxygenation in acute lung injury/acute respiratory distress syndrome: Randomized controlled study. Saudi J Anaesth. 2017 Jan-Mar;11(1):9-14. doi:10.4103/1658-354X.1973694.         Maes T, Bracke K, Brusselle GG. COVID-19, Asthma, and Inhaled Corticosteroids: Another Beneficial Effect of Inhaled Corticosteroids?. Am J Respir Crit Care Med. 2020 Jul;202(1):8-10. doi:10.1164/rccm.202005-1651ED5.        Halpin DMG, Singh D, Hadfield RM. Inhaled corticosteroids and COVID-19: a systematic review and clinical perspective. Eur Respir J. 2020 May;55(5):2001009. doi:10.1183/13993003.01009-20206.         Nave R, Mueller H. From inhaler to lung: clinical implications of the formulations of ciclesonide and other inhaled corticosteroids. Int J Gen Med. 2013;6:99-107. doi:10.2147/IJGM.S391347.         Matsuyama S, Kawase M, Nao N, et al. The inhaled corticosteroid ciclesonide blocks coronavirus RNA replication by targeting viral NSP15. bioRxiv 2020 Mar. doi: https://doi.org/10.1101/2020.03.11.9870168.         Iwabuchi K, Yoshie K, Kurakami Y, et al. Therapeutic potential of ciclesonide inhalation for COVID-19 pneumonia: Report of three cases. J Infect Chemother. 2020 Jun;26(6):625-632. doi:10.1016/j.jiac.2020.04.007  
The Japanese Ministry of Economy, Trade and Industry recently confirmed that SARS-Cov-2 was deactivated by several diluted surfactants 1. Emulsifiers belong to the chemical class of surfactants. Fatty acids, especially medium-chain saturated and long-chain unsaturated fatty acids, are effective in deactivating enveloped viruses, especially in their monoglyceride form 2. As SARS-CoV-2 is an enveloped virus, it may be vulnerable to deactivation by fatty acids.  Emulsifiers and fatty acids are widely used as food additives and can be added to candies, chewing gums, or lozenges. Persons affected with SARS-CoV-2 may be able to reduce the infectivity of their saliva-derived droplets and aerosols by using candies, chewing gums, or lozenges containing emulsifiers and/or fatty acid. A research to test this hypothesis is desired.Saliva is used for PCR based tests to detect COVID-19 3. The U.S. Food and Drug Administration authorized the diagnostic test using home-collected saliva samples of individuals for COVID-19 testing. However, it can be difficult to collect samples from elderly people with low saliva production 4. Rinsing with saline dilutes the saliva specimen and may affect the sensitivity of the test. Candies and chewing gums, especially acidic ones, stimulate salivation. Therefore, if it is confirmed that lozenges containing emulsifiers and/or fatty acids deactivate SARS-CoV-2 in the saliva and do not adversely affect RNA stability; then there may be a benefit in having lozenges in the mouth at the time of specimen collection, both to stimulate salivation and to reduce the risk to the individual collecting samples. Naturally, all of the above can be tried with lozenges, containing other than fatty acids and emulsifiers that have a SARS-CoV-2 inactivating effect 5.   References1. Ministry of Economy, Trade and Industry, Surfactants and Hypochlorous Acid Solution for Removal of Coronavirus from Surfaces (Final Announcement), 26 June 2020, www.meti.go.jp/english/press/2020/0626_004.html.2. Thormar H, Isaacs CE, Brown HR, Barshatzky MR, Pessolano T. Inactivation of enveloped viruses and killing of cells by fatty acids and monoglycerides. Antimicrob Agents Chemother. 1987;31(1):27-31. doi:10.1128/aac.31.1.273. Wyllie AL, Fournier J, Casanovas-Massana A et al., Saliva is more sensitive for SARS-CoV-2 detection in COVID-19 patients than nasopharyngeal swabs  medRxiv 2020.04.16.20067835; doi: https://doi.org/10.1101/2020.04.16.200678354.  Xu F, Laguna L, Sarkar A. Aging-related changes in quantity and quality of saliva: Where do we stand in our understanding?. J Texture Stud. 2019;50(1):27-35. doi:10.1111/jtxs.123565. Oxford JS, Lambkin R, Gibb I, Balasingam S, Chan C, Catchpole A. A throat lozenge containing amyl meta cresol and dichlorobenzyl alcohol has a direct virucidal effect on respiratory syncytial virus, influenza A and SARS-CoV. Antivir Chem Chemother. 2005;16(2):129-134. doi:10.1177/095632020501600205

Daisuke Miyazawa

and 1 more

Many have wondered if Japan possessed an ”X-factor” that led to a low COVID-19 death rate.We note that the mask non-wearing rate in mid-March alone was predicted to contribute up to 72% of variations in the number of deaths per million1. In addition, there was a remarkable difference in face mask wearing rates between Western countries and Asian countries, especially in East Asian countries including Japan1. The county’s policy for wearing a face mask alone cannot explain this significant difference. For example, there is a high rate of wearing face masks in Japan even though this practice has never been declared mandatory. We speculate that cultural differences may be the major reason.Many Japanese wear surgical masks on a daily basis not with the purpose of shedding infections or pollens but to achieve inscrutability, similar to the Westerners wearing sunglasses.It is referred to as ”mask dependency” in a number of cases2. While people may wish to achieve anonymity, they also want to avoid making others uncomfortable. Jack, Caldara, and Schyns state, “whereas Western Caucasian internal representations predominantly featured the eyebrows and mouth, East Asian internal representations showed a preference for expressive information in the eye region”3. This tendency may be the major reason why it is considered rude to wear sunglasses among eastern Asians and why wearing face masks among Westerners is considered suspicious, which could be why the western population exhibits a low face mask wearing rate.Additionally, the Japanese generally remain silent while using public transportation as loudness is a sign of rudeness in Japan4. This may also contribute to the ”X-factor” because a very high proportion of aerosols are exhaled from asymptomatic individuals while speaking rather than breathing5. In addition, the viral density of aerosols is expected to vary between speaking and breathing as the origin of the aerosols is different. Aerosols originating from the mouth may contain more virus than those from the lungs in asymptomatic individuals.Although face mask wearing has not yet been proven as an independent risk factor of COVID-19 mortality, a high rate of mask wearing in Japan may be the major candidate for the so called ”X-factor.”
Obesity, hypertension, diabetes, and specific ethnicities (Black and Hispanic) have been reported to be common comorbidities and possible risk factors for the severity of both COVID-19 and H1N1 influenza infections. Thus, it is important to understand why these four risk factors are common to both COVID-19 and H1N1 influenza infections, and whether a common mechanism exists. Respiratory failure is the most important pathology that contributes to the severity of both COVID-19 and H1N1 influenza infections. Additionally, obesity has been reported to be a risk factor for the development of acute respiratory distress syndrome (ARDS), which is a serious clinical manifestation of both COVID-19 and H1N1 infections. Obesity is a risk factor for hypertension. Most of the previous studies showing hypertension as a risk factor for the severity of COVID-19 and H1N1 infections were either not based on multiple logistic regression analyses or did not include obesity or BMI as an explanatory variable in their multiple logistic regression models. Moreover, similar attention is needed when specifying patients with diabetes or of specific ethnicities (Black and Hispanic) as potentially more vulnerable to either infection, because obesity also correlates with diabetes, and is more prevalent in these ethnicities. Notably, a retrospective cohort study has shown that obesity or high BMI are predictive risk factors for severe COVID-19 outcomes, independent of age, diabetes, and hypertension. Associations between hypertension, diabetes, ethnicities and severity of COVID-19 and H1N1 infections may be confounded by obesity to a considerable extent.