On average one Sars-CoV2 positive person infects 2.5 individuals (R0) if containment measures are not adopted (masks, hand washing, social distancing).
However, sometimes an infected person will transmit the virus to many more individuals e becomes a superpreader, that is transmits the virus to many more people than the average person. Biology plays a role up to a certain point in determining the role of these super-diffusing subjects.
The high viral load (particularly high in the two days preceding the onset of symptoms) can certainly play a role but above all circumstances such as events in crowded and enclosed spaces, and the activities carried out, matter, such as singing or intense physical activity where there is a greater diffusion of potentially infected droplets.
They are therefore more dangerous than anything else superspreading events, or supercontagion events. Although any infected person can spread the virus there are circumstances in which the infections can become uncontrollable.
Preventing these situations (avoiding them) or in any case wearing a mask can contribute decisively to stopping the spread of Covid-19.
The last recorded event occurred, by admission of Professor Anthony Fauci, in the White House, when Donald Trump — then tested positive — announced the choice of Judge Amy Coney Barrett for the Supreme Court. The graphics you see below were made on the basis of a database compiled by professors and PhD students of the London School of Hygiene & Tropical Medicine.
The largest superspreading event in the world, in Milan
Supercontagion events around the world have created outbreaks of coronavirus infection that have spread like wildfire, often making complete tracking almost impossible. The largest outbreaks typically occur in hospitals or retirement homes and the chronicles have told stories from all over the world. But also religious ceremonies like weddings and funerals, business meetings, restaurants, gyms, farms, slaughterhouses, call center, parties, colleges, prisons were superspreading events in tutto globo.
Almost all contacts took place indoors where the lack of an important exchange of air, the proximity of people (often without a mask), prolonged contact facilitated the spread of the virus.
but yet the largest known superspreading event took place outdoors. This is the Champions League match on February 19 when Atalanta hosted Valencia at the San Siro stadium in Milan. The event was called game zero because the match took place just two days before the confirmation in Italy (and outside of China) of the first positive case of Covid-19. That game was defined by the head of Pneumology of the Papa Giovanni XXIII hospital in Bergamo as one biological bomb. Nobody knew that the virus had crossed China‘s borders. very likely that 40,000 people from Bergamo in the stands of San Siro, all together, were infected with each other. And those who gathered at home or at the bar to watch the game did the same. 2,500 Valencia fans were also present at the stadium: a few weeks later 35% of the Spanish team tested positive for the new coronavirus. 7,000 infections were linked to that game.
The first cases of super-diffusion
The Milan stadium is an exception. At the time, nothing was known about the coronavirus and what happened was inevitable. Since then, similar events have taken place all over the world but on a smaller scale and almost always indoors. In February, a 61-year-old South Korean woman who attended a place of worship was held responsible for the infection of about fifty people present at the event. In the United States an asymptomatic chorister infected 53 of his colleagues during singing rehearsals in Washington state and two people died. Later there were other infections among members of other choirs (singing considered a risky activity). At the end of February, the annual meeting of the pharmaceutical company Biogen a Boston was one of the first cases of Covid-19 super-diffusion in the United States: after the meeting between 175 managers the participants boarded various planes and carried the virus to six different US states and three foreign countries.
Indoor sports are considered particularly dangerous places because if an infected athlete, under physical exertion, exhales more intensely and emits a greater number of potentially infected particles. In the same way, the others present engaged in sports activities breathe in with greater vigor, risking to introduce high levels of virus into their bodies. In a curling contest, a typically Canadian sport, a super diffuser infected 72 participants. Curling involves close contact between players and teams playing in a cool, indoors, breathing environment for an extended period of time. The tournament ended with 24 infected out of 72 presentA high-intensity Zumba class in South Korea in confined spaces caused a chain of infections: As of March 9, researchers had tracked 112 cases of Covid-19 linked to those dance lessons in twelve different gyms in the city of Cheonan.
The work environments
Research has repeatedly found that the risk of coronavirus transmission increases indoors in poorly ventilated spaces where many people have prolonged contact. Office open spaces, where employees are in contact for many hours, can represent a serious contagion problem if the mask is not worn correctly, as happened in a call center in South Korea where a single positive infected 94 colleagues. Among the super-diffusion opportunities also the meat production and packaging companies: in these plants, workers work closely with each other and are forced to talk to each other in a very noisy environment for the machinery in action, and at low temperatures (which facilitate the survival of the virus). In the United States there are hundreds of food industries involved in the outbreaks with thousands of positive cases and dozens of deaths. In Germany maxi-outbreaks in slaughterhouses caused the contagion of over two thousand people. Italy also recorded outbreaks in the salami factories of Mantua with a final count of about seventy cases. For the same reason, close contact between the workers is also the plant in Aia di Vazzola, in Veneto, which has become a superspreading place with 184 infections.
How to avoid superspreading events
Some countries such as Japan or South Korea have already shown that it is possible to deal with an outbreak without drastically limiting the movement of citizens or closing all shops, schools and restaurants thanks to adherence to the 3C rule. In fact, governments have invited people to avoid: Closed spaces, Crowded places, Close-contact settings or closed spaces, crowded places and close contact contexts, which are all ideal for superspreading events. The last known event, certainly among the most famous, was the ceremony of last September 26 when in the Rose Garden (outdoors) Donald Trump ha nominato Amy Coney Barrett Supreme Court Justice. On that occasion, no distancing rules were respected and hardly anyone among the guests wore a mask. As for the San Siro stadium, despite the open space, the virus traveled thanks to the proximity of the guests. Thus the virus would have entered the White House, infecting the president among the many.
October 10, 2020 (change October 10, 2020 | 10:08 am)
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