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There are at least two reasons why this news is not too worrying. The first is that the experiment was carried out under ideal laboratory conditions: total darkness and a constant temperature of 20 degrees, while we know that light, with its ultraviolet component, damages the microorganism. Heat is also poorly tolerated by the virus. When Australian researchers put their contaminated surfaces at 40 degrees, all traces of the microorganism disappeared within 24 hours. The second reason for relative optimism is that touching infected objects was not the main source of contagion in this epidemic. The most insidious vehicle of transmission remains the airway: staying close to a positive person and inhaling the droplets of their breath on board through which the virus travels. The same Australian researchers specify that the amounts of virus found on different surfaces after 28 days are very small, insufficient to cause an infection. No one knows exactly how many viral particles are needed for infection, although CSIRO experts estimate their number at 300.
At 20 degrees, the virus survived for 28 days on steel, glass, PVC, and banknotes, both paper and plastic. Porous surfaces like clothing did not allow Sars-Cov-2 to last more than 14 days. At 30 degrees, the resistance was reduced to 7 days on steel, banknotes and glass and 3 days on clothing and PVC. At 40 degrees, the coronavirus remained viable for less than 16 hours on cotton fabrics, 24 hours on steel, glass and banknotes, and 48 hours on PVC.
Coronavirus, risk of food contagion? The expert: “I am not a source of infection”
All viruses can survive and replicate only within a host organism. When they are in the external environment, at most they can “hold their breath” hoping to find another person to infect. In this sense, time is an excellent disinfectant. However, Sars-Cov-2 had been shown to be able to withstand the outdoors longer than similar viruses in some previous experiments. In the Lancet, on April 2, it was explained that the glass and banknotes contained traces of the virus after 4 days. Stainless steel, plastic, and even the exterior of surgical masks can last up to 7 days. Rough, porous surfaces are less loved by the coronavirus. On paper from books, newspapers and photocopies, as in disposable tissues, it lasts up to 3 hours. The ideal temperature for Sars-Cov-2 was measured at 4 degrees. Heating to 70 degrees inactivated the virus in 5 minutes. In the worst phase of the Wuhan epidemic in February, one of the measures taken was even to quarantine the banknotes, leaving them in indoor boxes for 14 days or sterilizing them with X-rays.
However, the main focus remains on close people-to-people contacts. The US CDC (Centers for Disease Control) explains that “Covid-19 is spread less frequently through contact with contaminated surfaces.” On the contrary, “it is very easy to spread it from person to person.” In particular, “people who are physically close, within 1.8 meters, of a person with Covid or have direct contact with him are those who are at the highest risk of infection.”
Recently (and after several comings and goings that have caused considerable controversy) the CDC has recognized the risks of another form of transmission of Sars-Cov-2, by air or by aerosol. Although at the beginning of the epidemic it was thought that the coronavirus traveled only on board the largest droplets, among those emitted when breathing, speaking, coughing or sneezing, today it is recognized that even so-called aerosols can be channels of contagion. . These are the finest droplets, with a diameter of less than 5 microns, which instead of falling to the ground in a few minutes with the force of gravity, float in the air for longer and can reach distances of several meters, depending on the currents d ‘air. Here, too, a study has been conducted to measure the resistance of samples to coronavirus: up to 3 hours floating in a room. It is the reason why in closed spaces it is recommended to change the air often even keeping distances and wearing masks.
