New Corona: Should “humidification” be used to prevent infection?
The atmospheric pressure pattern is high in the west and low in the east, and the air on the Pacific coast is becoming very dry. To prevent respiratory infections, it is better to humidify so as not to reduce the airway barrier function. What about the novel coronavirus?
Is the new coronavirus resistant to dryness?
The Pacific coasts of Tokyo, Shizuoka, and Kanagawa prefectures, the Seto Inland Sea coasts of Osaka, Hyogo, and Okayama prefectures, and the Pacific coasts of Gunma and Saitama prefectures Inland along the shore, relative humidity typically drops significantly from December to March. In the case of Tokyo, the average relative humidity in January is 52%, and January is the month with the most number of dry weather warnings.
The new coronavirus is an enveloped virus, and these enveloped viruses are known to be resistant to dryness and increase their viability and infectivity in cold and dry conditions (*1). Most of the research so far has been conducted using influenza viruses, which are enveloped viruses (*2), but in the case of influenza viruses, low temperatures and low humidity seem to work favorably for droplet and aerosol infections (*2). 3).
The relationship between virus infection and humidity is complicated. As the temperature rises, the amount of water that the air can hold increases, and when the temperature drops in winter, the amount of water that the air can hold decreases, and the relative humidity decreases, resulting in dryness. Relative humidity is affected by temperature and atmospheric pressure.
In addition, when considering droplet infection, the relationship between the relative humidity and the evaporation of droplets, etc., must also be factored into the size of droplets and aerosols in which the virus can maintain its infectivity.
As mentioned above, enveloped viruses protected by a lipid membrane like the new coronavirus can survive even if the aerosol dries under conditions of low relative humidity and maintains infectivity.
According to a study that examined the survival rate of the SARS (Severe Acute Respiratory Syndrome) virus, which is very similar to the new coronavirus, in terms of temperature and humidity, it was dry at a temperature of 22 to 25 degrees Celsius and a relative humidity of 40 to 50%. The virus maintained its infectivity for 5 days on a smooth surface, and the viability of the virus was rapidly lost at higher temperatures and humidity (*4). This means that the SARS virus may be more contagious in cooler temperatures and lower humidity.
In research on how long the new coronavirus survives under what kind of environment, it was confirmed that it survived for up to 28 days at 20 degrees Celsius. According to similar research, the new coronavirus can maintain its infectivity stably for a longer period of time than the SARS virus (*5).
Infection status changes depending on humidity
It has been confirmed that the new coronavirus exists in fine particulate matter with a diameter of 1 micrometer or less (*6), but at least 3 in aerosol There is research that says that time remains (*7).
There are also studies that maintain infectivity even in 2 micrometer aerosols, and research that continues to survive for 90 minutes in an environment with a relative humidity of 40% to 60% in 1 to 3 micrometer aerosols. (*8). Furthermore, according to recent research, in the case of the new coronavirus, it seems that the risk of droplet infection and aerosol infection increases when the relative humidity is 40% or less (*9).
However, it has not yet been determined whether the new coronavirus is less infectious when it is dry, or when it is humidified and the relative humidity is increased.
Investigations with other coronaviruses have shown that the new coronavirus stabilizes at a relative humidity of around 40%, and that the infectivity seems to change significantly depending on the temperature and relative humidity (*10).
The droplets produced during breathing and talking (0.75 micrometers to 1.1 micrometers) are much smaller than the droplets produced by sneezing and coughing (5 micrometers or less), and these small droplets become more frequent as the voice gets louder. (*11).
In addition, according to previous research, it is believed that if you talk loudly for 1 minute, droplets and aerosols containing at least 1000 new coronaviruses will continue to float in the air for 8 minutes or more (* 12).
The new coronavirus released from the mouth and nose of an infected person by sneezing, coughing, speaking, etc., will either fall at a short distance or float in the air for a while depending on the size of the attached droplets (* 13). There is also a simulation that when talking or coughing, it takes 9 minutes for droplets of 5 micrometers to fall and reach the ground (*14).
Then, what about the relationship between humidity and virus droplets? According to data from the RIKEN Center for Computational Science, simulations using the supercomputer "Fugaku" showed that as the relative humidity increased to 30%, 60%, and 90%, the number of droplets reaching the person in front of them increased. The number decreased, and conversely, the number of droplets falling on the desk increased.
When the air dries and the relative humidity drops, the droplets become aerosols, and the number of droplets floating in the air increases, so it is necessary to move the humidifier to increase the relative humidity and to ventilate regularly. Also, when the relative humidity is increased by humidification, droplets that fall on the desk or floor increase, so it is better to pay attention to hand hygiene and disinfection of the surrounding area.
However, according to a paper by a research group at the Okinawa Institute of Science and Technology Graduate University (OIST), the droplet size, relative humidity, the effect of gravity that draws the ballistic curve, the momentum of speech and coughing, transportation by the law of inertia, There are many variables, such as changes in weight due to evaporation in the air, and the behavior of actual droplets and aerosols seems to be more complicated (*15).
When bacteria and viruses that cause respiratory infections invade our bodies, the barrier function of the mucous membrane of the respiratory tract becomes the first barrier.
Mucous membranes decompose and neutralize foreign enemies with a wide variety of immune cells and the substances they produce, preventing them from invading cells. In addition, the mucus physically discharges foreign enemies as phlegm, and the cilia on the mucous membrane push them out of the respiratory tract or swallow them into the stomach (*16). Of course, this barrier function is used to prevent the invasion of the new coronavirus, but this barrier function is attenuated by temperature, humidity, air pollutants, cigarettes, etc.
To summarize the above, the new coronavirus is considered to be resistant to dryness, and seems to maintain its infectivity for a long time in droplets and aerosols such as speech, coughing, and sneezing. I don't know if I will lose
The behavior of the virus in the air is complicated, but it is certain that if the relative humidity is increased by operating a humidifier, the droplets will become less aerosolized. High humidity reduces the rate at which virus-laden droplets and aerosols remain airborne for longer. And with moderate humidity, we can maintain the barrier function of our airways.
In order to prevent infection, it would be better to pay attention to ventilation and condensation, and to humidify moderately.
*1: Rory Henry Macgregor Price, et al., "Association between viral seasonality and meteorological factors" SCIENTIFIC REPORTS, 9, Article number: 929, 2019
*2: Thomas P. Weber, Nikolaos I. Stilianakis, ``Inactivation of influenza A viruses in the environment and modes of transmission: A critical review,'' Journal of Infection, Vol.57, 361-373, 2008
※3：Anice C. Lowen ,John Steel, "Roles of Humidity and Temperature in Shaping Influenza Seasonality" Journal of Virology, Vol.88, No.14, DOI: 10.1128/JVI.03544-13, 2014
*4: K H. Chan, et al., "The Effects of Temperature and Relative Humidity on the Viability of the SARS Coronavirus" Advances in Virology, doi: 10.1155/2011/734690, 2011
*5-1: Neeltje van Doremalen, et al., "Aerosol and Surface Stability of SARS-CoV-2 as Compared with SARS-CoV-1" The New England Journal of Medicine, Vol.382, 1564-1567, 16, April, 2020
*5-2: Shane Riddell, et al., "The effect of temperature on persistence of SARS-CoV-2 on common surfaces" Virology Journal, Vol.17, 145, 7, October, 2020
※6："Aerosol and Surface Stability of SARS-CoV-2 as Compared with SARS-CoV-1" The NEW ENGLAND JOURNAL of MEDICINE, Vol.382, 1564-1567, April, 16, 2020
※7：Jean F. Gehanno, et al., "Evidences for a possible airborne transmission of SARS-CoV-2 in the COVID-19 crisis" Archives des Maladies Professionnelles et de l'Environnement, doi.org/10.1016 /j.admp.2020.04.018, May, 4, 2020
*8-1: Sophie J. Smither, et al., "Experimental aerosol survival of SARS-CoV-2 in artificial saliva and tissue culture media at medium and high humidity" Emerging Microbes & Infections, Vol.9, Issue 1, 22, June, 2020
*8-2: Alyssa C. Fears, et al., "Persistence of Severe Acute Respiratory Syndrome Coronavirus 2 in Aerosol Suspensions" EMERGING INFECTIOUS DISEASES, Vol.26(9), 2168-2171, September, 2020
※9：Ajit Ahlawat, et al., "An overview ON the role of relative humidity in airborne transmission of sars-cov-2 in indoor environments" Aerosol and Air Quality Research, Vol.20, Issue9, 1, September , 2020
※10：Giovanni Seminara, et al., "Biological fluid dynamics of airborne COVID-19 infection" Rendiconti Lincei. Scienze Fisiche e Naturali, Vol31, 505–537, 16, August, 2020
※11：Valentyn Stadnytskyi, et al., "The airborne lifetime of small speech droplets and their potential importance in SARS-CoV-2 transmission" PNAS, Vol.117(22), 11875-11877, 2, June, 2020
*12: Sima Asadi, et al., "Aerosol emission and superemission during human speech increase with voice loudness" SCIENTIFIC REPORTS, Vol.9: 2348, doi.org/10.1038/s41598-019-38808-z, February , 20, 2019
※13-1：A F. Wells, "Airborne Contagion and Air Hygiene. An Ecological Study of Droplet Infections" Air Hygiene, 1955
*13-2: Raymond Tellier, "Review of Aerosol Transmission of Influenza A Virus" Emerging Infectious Diseases, Vol.12, No.11, November, 2006
*13-3: Jan Gralton, et al., "The role of particle size in aerosolised pathogen transmission: A review" Journal of Infection, Vol.62, Issue1, 1-13, January, 2011
※14：G Aemout Somsen, et al., "Small droplet aerosols in poorly ventilated spaces and SARS-CoV-2 transmission" LANCET Respiratory Medicine, Vol.8(7), 658-659, 27, May, 2020
*15: M E. Rosti, et al., "Fluid dynamics of COVID‐19 airborne infection suggests urgent data for a scientific design of social distancing" SCIENTIFIC REPORTS, 10, 22426, doi.org/10.1038/s41598- 020-80078-7, 30, December, 2020
※16-1: Jamila Laoukili, et al., "IL-13 alters mucociliary differentiation and ciliary beating of human respiratory epithelial cells" The Journal of Clinical Investigation, Vol.108(12), doi.org/10.1172/ JCI13557, 2001
*16-2: Eriko Kudo, et al., "Low ambient humidity impairs barrier function and innate resistance against influenza infection" PNAS, Vol.116(22), 10905-11910, 2019