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Temperature, light and humidity
The coronavirus thrives best in cold temperatures and is quite sensitive to heat. Preferably it should be 4 to 20 degrees, laboratory studies have shown.
– The more the temperature rises, the worse it survives. At 37 degrees, it has a fairly short survival and above 70 degrees, in principle, nothing survives at all, says Karin Tegmark Wisell, a specialist in clinical bacteriology and department head at the Swedish Public Health Agency.
The virus also thrives better in the dark than in direct sunlight. In one study, the virus was inactivated very quickly in simulated sunlight – after just 20 minutes, 90 percent had died.
The coronavirus survives longer in low humidity. In drier air, the particles can also travel a longer distance when someone sneezes. High humidity, as the water droplets in the air are larger, makes the virus weigh itself and the particles fall to the ground faster.
– In theory, the environment is more favorable for the virus in winter when it is cooler and darker outside, but it is always better with outdoor activities because there is more ventilation.
The virus survives very poorly on textiles.
Photo: Rafiq Maqbool / AP
Mobile phones and bedding
The coronavirus thrives differently on different surfaces.
According to an Australian study published in the Virology Journal, it can survive for 28 days on smooth surfaces like mobile phone screens, banknotes and stainless steel. On more porous surfaces like clothing, it survived for 14 days. However, the experiment was carried out under fairly favorable conditions, in the dark and 20 degrees of heat, the BBC reports.
The Swedish Public Health Agency considers this to be a well designed and conducted study, but that the environmental parameters do not agree well with those of Sweden. This, combined with the fact that the study was conducted in the dark, means that it is not completely relevant to actual conditions. According to the authority, the virus can be transmitted through contaminated surfaces, the so-called indirect contact infection, but so far there are no studies that show that people have been infected through banknotes, coins, packages and postal items.
Studies show that the virus survives very poorly on cotton fabrics and porous materials like other textiles and paper, says Karin Tegmark Wisell.
– In one study, no infectious virus could be found after three hours on both tissue paper and printer paper.
Mobile phones and public transportation areas have surfaces made of plastic, glass, or metal, where the virus can survive for several days depending on environmental conditions. Under favorable conditions, large amounts of viruses can survive for weeks on slippery surfaces. At the same time, he notes that viruses have not been proven to have the ability to cause illness after several weeks outside the human body.
– If you have visited a sick person, it is good to clean your mobile. In theory, one could be infected.
At the same time, the virus has been seen to have a very short survival on surfaces made of copper.
There is still no evidence that someone has been infected through food.
Photo: Nora Lorek / TT
Food and packaging
Last summer, New Zealand was hit by a new outbreak after nearly eradicating the infection. New Zealand authorities investigated whether the infection had entered the country through frozen food.
According to the Swedish Public Health Agency, so far there is no evidence that people have been infected by eating food or drinking water.
According to laboratory studies, the temperature in the refrigerator, 4-8 degrees, is therefore favorable for the survival of the virus. However, it is sensitive to freezing because ice crystals form, which in turn can break down the virus.
The mucous membranes of the mouth are also not a favorable environment for survival and when the virus enters the gastrointestinal tract, it is likely to be inactivated by enzymes and the low pH value. In theory, you can become infected by touching food or packaging contaminated with viruses if you then peel your eyes or nose, but this is not likely.
– There is nothing in epidemiology that indicates that covid-19 is transmitted through food. But it’s still important to have good hand hygiene and wash your hands before eating, says Karin Tegmark Wisell.
Skin contact
A Japanese study published in the journal Clinical Infectious Diseases showed that the virus can survive for nine hours on human skin. The skin samples were taken from people who had had an autopsy, about a day after their death, writes the Japan Times.
The Swedish Public Health Agency considers this to be a well designed and conducted study, but that survival in dead skin is not particularly relevant. Living human skin has a temperature higher than 25 degrees which was one of the environmental parameters in the study. Humidity was also not relevant to Swedish conditions.
However, according to Karin Tegmark Wisell, it cannot be ruled out that you can become infected by touching other people.
– Therefore, it is very important with hand hygiene if you come into contact with infected people, care for patients in hospitals or when you have moved into the community and have touched surfaces that other people have touched.
Cats can become infected with the virus.
Photo: Vadim Ghirda / AP
Animal
The other day came news that the first case of corona-infected minks had been discovered in Sweden. Cats, tigers and lions had previously been reported around the world.
According to the Swedish Public Health Agency, the covid-19 infection between animals and humans is considered small. There is also currently no evidence that the disease is transmitted by mosquitoes.
Fans
Typically, viruses travel only a short distance in the air before hitting the ground. In theory, fans can make virus droplets spread for a greater distance.
Therefore, stand-alone fans, portable air conditioners, and other fan cooling systems should be avoided in rooms where multiple people have gathered. It is especially important to avoid pointing fans to groups of people.
However, researchers have not investigated how fans affect the coronavirus. At the same time, it is important that the ventilation system works properly and that the air exchange is good in the rooms where people are staying.
Karin Tegmark Wisell, specialist in clinical bacteriology and head of department at the Swedish Public Health Agency.
Photo: Pontus Lundahl / TT
conclusion
Laboratory studies are carried out in an environment with controlled humidity, temperature and other light conditions, so they are not directly comparable with the environments of society. For ethical reasons, it is difficult for researchers to conduct clinical studies on the spread of the infection, as this would mean that humans would become infected with the virus.
The risk of infection by indirect contact through objects is considered to be significantly lower than infection by droplets between people; it probably takes large amounts of virus to make someone sick. The virus is mainly transmitted when an infected person coughs or sneezes, so that the drops come in contact with the mucous membranes of the eyes, nose or mouth. Usually the virus breaks down fairly quickly outside the body and cannot multiply there either, so you can count on the amount of virus on objects to be quite small.
Also, it is easy to kill the virus with soap and detergents. If someone in the home is infected, it is enough to clean normally and use regular cleaning agents.
– Washing your hands with soap and water is an effective method of mechanically removing any infection from your hands and dissolving the cell membrane of the virus, which is made up of fat to some extent, so that it dies, says Karin Tegmark Wisell.
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