COVID CONTAGION. Covid-19 has been circulating in France since January 2020. What are the places to avoid in order to minimize the risk of infection?
How to escape Covid-19 contamination? What are the places to avoid to reduce the risks? A study by Comcor of the Institut Pasteur, conducted between May 23 and August 13, 2021, listed places where the risk of being infected with the coronavirus was high – in other words, the list of spaces to avoid to reduce the risks of infection. The study was carried out in a period of lifting of several restrictions in France, with the reopening of terraces and cultural places on May 19, 2021, that of indoor restaurants and sports halls on June 9, 2021 and that of nightclubs on July 9, 2021. More than 12,000 positive cases were followed up, and more than 5,000 individual witnesses, who all completed a questionnaire asking them about the places where they had been exposed to the coronavirus.
According to the results of the study, it is during private parties or in discotheques that the increased risk of being contaminated with Covid-19 is the highest: 340% increased risk among people under 40 compared to a person n not having frequented these places.
“These results underline the importance of respecting barrier gestures, and in particular wearing a mask and ventilation in closed places”, concluded the study.
The methods of transmission of Covid-19 have raised many questions since the start of the pandemic. But according to the latest findings, summarized by the government site, the virus is transmitted through three modes. First, by droplets, respiratory secretions emitted when speaking, coughing or sneezing: these droplets, with an average diameter of 10 to 20 microns at the exit of the mouth or nose, can be projected up to two meters from the individual carrying the virus. Contamination occurs if these droplets reach, directly or indirectly, the face of another person. The virus can also be transmitted by aerosols, solid or liquid particles even smaller than droplets (0.7 and 1.25 microns) which remain suspended in the air. This mode of transmission is more likely to occur in a poorly ventilated space. Finally, you can catch Covid-19 by touching a contaminated surface with your hands, then bringing your hands to your face.
In all cases, an individual becomes contaminated when their nose, eyes or mouth come into contact, directly or indirectly, with the nasal or oral secretions of another contaminated individual. These different modes of contamination nevertheless raise many questions.
The duration of contagion of a person infected with the coronavirus is a key data for the fight against contamination. However, it seems that it varies from one variant of Covid-29 to another. According to the World Health Organization, infected people can transmit Covid “just before they develop symptoms (i.e. two days before the onset of symptoms) and at the very beginning of the disease”. This is when they are most contagious. Depending on the form of the disease, this period of contagion can be more or less long. The WHO thus specifies that “people who develop a severe form of the disease may be contagious for longer”. The case of asymptomatics is also clearly addressed by the organization which assures that “someone who never develops symptoms can transmit the virus to others”.
The French government, for its part, indicates that “the incubation period”, in other words “the period between contamination and the appearance of the first symptoms” is 3 to 5 days in general. “It can however extend up to 14 days”, writes the Ministry of Health. And it is during this period of 3 to 14 days that a patient can be contagious.
Faced with the persistence of the epidemic despite active vaccination campaigns, many antivax figures have pointed to the ineffectiveness of the vaccine in preventing the transmission of Covid-19. However, several studies have shown that in addition to reducing symptoms in the event of infection, the vaccine reduces transmission. A report from Nature Medicine, published on June 10, 2021, noted that within a population, the vaccination rate of adults at Pfizer influenced the infection rate of people under the age of 16, who were not yet vaccinated: the more adults were vaccinated, the less contamination there was in children. Another study by Nature Medicine, published in March 2021, already noted that when a vaccinated person nevertheless contracted Covid-19, their viral load was lower, therefore reducing the risk that they infect other people.
Covid-19 is therefore more prone to spread in enclosed settings. However, researchers at the University of Massachusetts have found a way to avoid contamination during a car trip. This study was published in the journal Science Advances on December 4, 2020. Scientists used a Toyota Prius traveling at 80 km/h for the purposes of this research. The researchers immediately ruled out using the car’s “air recirculation” mode. What is most suitable is the opening of the windows. It is best to open them all during the journey. However, when it’s cold or rainy, it seems complicated to keep them open. In these scenarios, the researchers explained that the driver on the left had to open the window on their right. The passenger must be seated diagonally behind the driver of the vehicle, then open the window to his left. The air can thus continue to pass through the car! “To our surprise, the simulations showed an air current that acts as a barrier between the driver and passenger,” the scientists said.
Following an alert issued in early July 2020 in the Oxford journal Clinical Infectious Diseases by 239 scientists, the WHO has acknowledged the possibility of airborne transmission of Covid-19. “We recognize that evidence is emerging in this area and therefore we need to be open to this possibility and understand its implications,” Benedetta Allegranzi, a WHO official, said at a virtual press conference on Tuesday, July 7. 2020.
The scientific community now agrees that Covid-19 can be transmitted by aerosols, liquid or solid particles so light that they remain suspended in the air. Hence the recommendation to ventilate enclosed spaces to limit contamination. According to a study by Riken Research Institute and Kobe University, conducted in 2020, air humidity also reduces aerosol transmission. While several studies have suggested that aerosols, which are smaller than droplets, are less dangerous because they are less loaded with virus, they can however be projected much further by an infected person, therefore potentially reaching more individuals.
Closed, poorly ventilated places are particularly conducive to the spread of infectious disease. As the WHO states, “Improving indoor ventilation reduces the risk of the virus spreading to indoor spaces.” However, the movement of air caused by a fan can also circulate droplets and aerosols: “The use of a fan in an enclosed space can increase the spread of the virus”, confirms the WHO, which therefore specifies that It is “important to open windows and doors when using a fan in order to replace indoor air with outdoor air”.
The World Health Organization writes that “people with the virus can leave infectious droplets when they sneeze, cough, or touch objects or surfaces, such as tables, doorknobs, and railings.” If transmission through the skin is completely excluded, you can nevertheless be infected with the virus by touching your eyes, nose or mouth after touching these contaminated surfaces and before washing your hands, according to the WHO. According to the French government, the virus could, “under certain conditions, remain infectious for up to a few hours on a contaminated surface” or even “survive, in the form of traces, for several days”. “However, it is not because a little virus survives that it is sufficient to contaminate a person who touches this surface”, is it specified. According to the government page dedicated to the coronavirus, “after a few hours, the vast majority of the virus dies and is probably no longer contagious”.
The question of contamination by objects was raised from the start of the health crisis. In the New England Journal of Medicine, in mid-March 2020, researchers demonstrated that Covid-19 lasted four hours on copper and metal, 24 hours on cardboard, three days on plastic, four days on wood and steel, five days on glass. De facto, door handles, worktops and other books may show traces of the virus.
However, these conclusions also need to be qualified. In fact, the viral load is much lower outside laboratory experiments. According to an article published in the Journal of Hospital Infection “below 10,000 particles, the virus resists less than 5 minutes, whatever the surface”.
“Given the information available to date, the passage of Covid-19 from humans to another animal species seems unlikely, and the possible contamination of foodstuffs of animal origin from an infected animal by Covid-19 is excluded”, indicates the government on its site dedicated to the coronavirus, while the question of transmission from man to animal and from animal to man is raised. ANSES (National Agency for Food, Environmental and Occupational Health and Safety) spoke out fairly early on in any case on the issue of food. According to the agency, “the possibility of direct transmission of the virus through food from a contaminated animal has been ruled out by experts”. On the other hand, “an infected person can contaminate food by preparing or handling it”. Also, the agency advised to cook the food, at least, for four minutes at 63°C and to continue to respect the usual rules of hygiene when handling and preparing foodstuffs.
Regarding water contamination, the Water Information Center certified that “the different treatment stages protect the water from viruses, including the coronavirus”. Several disinfection methods “such as chlorination, ozonation, or even ultraviolet disinfection eliminate all viruses, including the coronavirus”. It is specified that the “risk linked to Covid-19 in itself does not justify superchlorinating”. A Spanish study has also reassured the most worried about this.
In both cases, the question arises of the transmission of the coronavirus by the digestive tract. But this was quickly deemed unlikely by the experts. According to the scientific consensus, the coronavirus appears to be a “primary respiratory tropism” disease, in other words exclusively transmissible by the respiratory route. Gastrointestinal disorders, regularly observed in patients, would be secondary symptoms, rather than the manifestation of a direct entry through the digestive tract. “In view of these elements, the route of transmission of SARS-CoV-2 through the direct digestive tract has been ruled out” by the experts of a GECU, an “Emergency Collective Expertise Group” brought together by ANSES as soon as March 2020 on the subject.
Doubts have been raised about a possible transmission of the coronavirus through sex and more specifically through semen. A Chinese study, published in early May 2020 in the Journal of the American Medical Association, raises this possibility. The experiment was carried out on 38 subjects carrying Covid-19. In 16% of patients, semen tested positive for the virus. However, a positive sperm does not necessarily induce transmission of the virus. If studies are still lacking on this subject, the WHO recalls that coronaviruses are not usually sexually transmitted. At this stage, only the respiratory route is recognized as a means of transmission of the coronavirus, no other studies having confirmed sexual transmission. On the other hand, the physical proximity induced by sexual intercourse can facilitate contamination by the respiratory tract.
A French study, published in the scientific journal Nature Communications in July 2020, confirmed intrauterine contamination with Covid-19. To do this, the research team from the Antoine-Béclère hospital in Clamart (Hauts-de-Seine) analyzed the case of a baby, male, born in France in March and suffering from neurological symptoms associated with disease. “We have shown that transmission from mother to fetus is possible via the placenta in the last weeks of pregnancy,” said Dr. Daniele De Luca, lead author of the study, to AFP. After a battery of tests, it turned out that the highest viral load was found in the placenta. “It passed from there, through the umbilical cord, to the baby, where it developed,” said Dr. De Luca. The specialist recalled: “The main message for pregnant women remains to avoid infection, through hand washing and social distancing”.
In order to avoid possible contagions, barrier gestures must be respected in addition to traditional hygiene rules. The distance of one meter has been recommended since the beginning of the epidemic to avoid inhaling the droplets possibly projected by a patient. The same goes for regular hand washing, to avoid indirect contamination, by inhaling particles when you touch your face, mouth, nose or eyes. It is also recommended to greet each other without touching or shaking hands, to blow your nose in a disposable tissue and, in case of coughing or sneezing, to cover your nose and mouth with the bend of your elbow. Wearing a mask covering the mouth and nose is an effective means of protection. The plastic visor offers limited protection, although it allows better breathing than a surgical or cloth mask.
Wearing a mask is not, however, in itself a guarantee against contamination. It may not be sufficient if the other conditions are not met. The “Emmental model” has been mentioned by several experts, including the High Authority for Health (HAS). This theory, inspired by the model developed in 1990 by Manchester University professor James Reason to explain accidents, is quite telling: each barrier (mask, distance, ventilation etc.) could be represented by a slice of cheese. Each of these slices having holes, it cannot be 100% effective if taken alone. It is essential to overlap them to avoid contamination. Barrier gestures must therefore be respected. The same goes for wearing a mask, which protects against Covid-19.
