A few months after the outbreak of the COVID-19 pandemic, it seems increasingly clear that the main source of transmission of the virus that causes this disease is by air , as it travels in small droplets or aerosols that we emit when coughing, sneezing or talking. strong. In addition, to become infected it is necessary to be exposed to a sufficient amount of virus (what we call the viral load) and during a certain period of time. Thus, the best options to protect ourselves and those around us will be to avoid closed spaces as much as possible, wear a mask, maintain physical distance and, in case of being indoors, ensure adequate ventilation so that the environment is renewed. air.
“From what we have more evidence is that SARS-CoV-2 is transmitted mainly through the air, even when there is contamination at a certain distance,” explains Jose María Lagarón, researcher at the Institute of Agrochemistry and Food Technology ( IATA-CSIC) and member of the Interdisciplinary Global Health / Global Health Thematic Platform launched by the CSIC to address the challenges posed by the coronavirus epidemic from the point of view of science. “There is a fraction of the aerosols that are emitted by coughing or sneezing that are very fine and spread in the air for a great distance, even eight meters. If you do not wear a mask, you will breathe these particles, and they are also so small that they will not stay in the throat but will reach the lungs. In addition, in these droplets, we do not know what viral load is enough for a person to become infected. And that is one of the main difficulties of this virus ”.
Studies on residence times of the virus on surfaces
In turn, during these months numerous scientific articles have been published that make estimates on the permanence of the SARS-CoV-2 virus on different surfaces, and the health authorities have issued numerous hygiene and disinfection recommendations in this regard to avoid risks.
Although transmission by air is the most common, is it possible to catch it if we touch a contaminated surface? “To begin with, it must be taken into account that most of the studies have been carried out under laboratory conditions, that is, with humidity, temperature, the volume of particles that are dispersed and all the highly controlled variables “, he explains. Guillermo Quindós Andrés, Professor of Medical Microbiology at the University of the Basque Country. “The reality, when someone who is infected coughs or sneezes, it is very different from those unreal laboratory conditions. Outdoors there will always be a greater chance that the particles will dehydrate earlier, and indoors there is also a lot of variability: there are more humid houses, some are more ventilated than others… it is very variable ”.
Along these lines, a few days ago a study was published in the journal Physics of Fluids that analyzed the time it takes for droplets carrying SARS-CoV-2 to dehydrate on different surfaces and in six cities around the world. The results are quite intuitive: in areas with a high ambient temperature the droplets dry faster, and the chances of survival of the virus are dramatically reduced . “We are already seeing examples of places with more favorable humidity and temperature conditions, such as food processing plants, where there is a greater risk of outbreaks,” says Quindós. “A higher risk has also been linked to tablet- type objects, office objects … but that does not mean that there has been transmission through surfaces, because we are talking about places where there are many people who share space for many hours, sometimes you have to talk loud or screaming at the noise … if there is an asymptomatic case, it is easier for the viral load in the air to increase and there is a greater possibility of airborne infection ”, reflects the expert.
The case of ICUs and hospitals
Although it does not seem likely that surfaces are playing a key role in transmission, there are places such as hospitals, where the viral load is very high, where special caution must be exercised. “One of the few reliable studies is a report that was prepared to solve a large outbreak in a South African hospital that involved 119 individuals,” explains Iñaki Comas, researcher at the Institute of Biomedicine of Valencia (CSIC) and also a member of the Global Health Platform. “This is a very complete analysis of this case in which the virus spread rapidly throughout the hospital, even reaching the maternity ward. Here it is likely that transmission through surfaces such as trolleys or surgical equipment has played a relevant role, and possibly the same has happened in many hospitals around the world. However, it must be borne in mind that the viral load in these places is very high ”, clarifies the expert.
It is important to ventilate, disinfect and have good hygiene
The recommendations aimed at disinfecting surfaces to eliminate the possibility of the virus remaining are therefore especially important in hospitals, but they should not be neglected in other settings either. ” Under normal conditions, in a room where someone has sneezed or coughed loudly, those droplets that carry the virus will end up landing if the air is not renewed ,” explains Lagarón. “When they are deposited on a surface they have reasonably long lifetimes, generally days. For this reason, it is important to disinfect surfaces, especially those in which there is a high circulation of people . For example, supermarket carts: if you are infected, you will leave the virus there and the next person who uses it will come into contact ”, concludes the expert.
