According to the research from Leibniz Institute for Tropospheric Research (TROPOS) in Leipzig and the CSIR National Physical Laboratory in New Delh,the airborne transmission of the coronavirus SARS-CoV-2 via aerosol particles in indoor environment seems to be strongly influenced by relative humidity. A relative humidity of 40 to 60 percent could reduce the spread of the viruses and their absorption through the nasal mucous membrane.
After evaluated a total of 10 most relevant international studies between 2007 and 2020 about the influence of humidity on survival, spread and infection with the pathogens of influenza and the corona viruses SARS-CoV-1, MERS and SARS-CoV-2. The researchers drawn a conclusion as below:
Air humidity influences the spread of corona viruses indoors in three different ways:
(a) the behaviour of microorganisms within the virus droplets
(b) the survival or inactivation of the virus on the surfaces
(c) the role of dry indoor air in the airborne transmission of viruses.
Although, low humidity causes the droplets containing viruses to dry out more quickly, the survivability of the viruses still seems to remain high. “If the relative humidity of indoor air is below 40 percent, the particles emitted by infected people absorb less water, remain lighter, fly further through the room and are more likely to be inhaled by healthy people. In addition, dry air also makes the mucous membranes in our noses dry and more permeable to viruses,” summarizes by Dr. Ajit Ahlawat.
To contain the COVID-19 pandemic, it is therefore extremely important to implement standards for indoor air humidity in rooms with many people, such as hospitals, open-plan offices or public transport.Indoor air in hospitals and nursing homes requires more attention.
The aerosol spread of the virus is, according to many experts, a major reason why the number of corona infections in Europe increased dramatically in the autumn. People stay indoors for longer durations and as temperatures fall, many indoor spaces are much less ventilated. Concentrations of viral particles in the air can rise sharply when infected people stay indoors. Simple mouth-nose masks can significantly reduce but not completely prevent the release of viral aerosol particles through the airways. The risk can therefore increase significantly with the number of people and the length of time they stay in the room. Hospitals and nursing homes are particularly affected by this, because additional risk factors are added there: particularly sensitive people, very long stays in a room and sometimes medical procedures such as intubation in intensive care units, where a lot of aerosol is produced.
The spread of viruses via the room air can be reduced with a number of measures. However, there is no single measure that can achieve this completely, but it is important to control indoor air and combine different measures:
1.Recommend humidifiers to keep the relative humidity in the room in the range of 40 to 60 percent and to reduce the risk of respiratory tract infection. It is in this middle range that the human mucous membranes are most resistant to infections. In addition, the viruses in the aerosol particles can survive at a relative humidity around 50 percent for less time than in drier or high humid air.
2.Constant supply of fresh air through the air conditioning system or ventilation. This can be controlled with measuring devices for carbon dioxide (CO2). The high CO2 values in indoor places indicate that there is lot of exhaled air in the room. If there is an infected person in the room, then there would also be many viral aerosol particles floating in the air and could be inhaled by a healthy person. The Heating, Ventilation and Air Conditioning (HVAC) system should have a minimum efficiency of MERV-13 to filter even very small particles out of the air.
3.Using air purifiers to reduce the concentration of viruses in the room air. However, these air purifiers should have so-called HEPA (High-efficiency particulate absorbing) filters. However, air purifiers can always only be an additional measure as they cannot replace the supply of fresh air and thus oxygen.
4.Special protection for medical staff during procedures and surgical operations that involve potentially infectious aerosol particles — such as dental treatment or intubation in intensive care units. Valve-free particle filter masks, so-called respiratory masks such as N95, should be worn and care should be taken to ensure that they lie close to the skin. To reduce the risk, protective equipment such as goggles should also be worn.In addition, the researchers recommend avoiding aerosol-generating procedures and treatments in patients with COVID-19 wherever possible to reduce the risk of infection for medical staff. Aerosol-generating treatments usually include medication administered via a nebulizer. In order to avoid the risk of aerosolisation of SARS-CoV-2 by the nebulisation process, inhaled drugs should be administered by a metered dose inhaler rather than a nebulizer, if possible.
5.Care should also be taken when disinfecting rooms.Recommend that disinfection with UV-C light should not be used too often. Although it is known that UV-C light destroys the SARS-CoV-2 viruses, it ultimately increases indoor ozone concentrations and can thus have a negative impact on health if the indoor air is not adequately replaced. Spraying oxidizing chemicals in the air, such as hydrogen peroxide (H2O2), can also have negative consequences. Indoors, these chemicals cause toxic chemical reactions that create other air pollutants and damage the central nervous system and lungs of humans.
6.Medical staff must be adequately trained to follow the recommendations. It is important to draw attention to the risks of airborne transmission of SARS-CoV-2. Such recommendations, if adequately provided by health authorities and implemented by medical staff, could significantly reduce the risk of airborne transmission in hospitals and nursing homes until vaccination is effective on a large scale.
I really like your article, it was very informative.