The amount of time you're exposed to the coronavirus can partly determine how likely you are to contract the potentially deadly virus, according to a new study.
Researchers from the University of Colorado at Boulder (CU) re-examined a now infamous Washington state choir practice in which a person with coronavirus accidentally spread the virus to 52 other people.
They found that the virus was mainly transmitted between singers via aerosols – very fine drops of spit and mucus that were sprayed into the air as we breath, speak, and sing.
The singers' ability to become infected with these tiny floating aerosols was enhanced by the two and a half hours that 60 people spent in a confined space with one infected person.
The CU Boulder Team estimates that a shorter choir exercise would also have been safer.
Experts at CU Boulder suggest that if the rehearsal had only lasted half an hour, the coronavirus may have spread from just one person to 12% of a choral practice in Washington state. Instead, the virus spread to 53 out of 61 participants and became a widespread event (file).
Of the 61 people in the Skagit County, Washington choir, the virus spread from one person to 87 percent of the other participants.
Only eight people were spared from infections.
Two of those confirmed to have COVID-19 died.
The practice has been labeled a tragic "overarching" event, but the reasons why it might have been are complex and have not been broken down at the most detailed level.
To find out why the virus spread so quickly and attacked the participants in the choir practice so quickly, the CU Boulder team modeled spread scenarios based on three "influencing factors": ventilation rate, duration of the event and deposition on surfaces. & # 39; wrote the.
A fourth key factor was noticeably lacking in choral practice: no one wore masks, which are now generally accepted to block a certain percentage of the large droplets that are the main vehicle that the virus uses to spread.
Coronavirus can survive on surfaces for some time, but this is not a primary route of transmission, according to the World Health Organization (WHO) and the Centers for Disease Control and Prevention (CDC).
In a 2.5-hour exercise (solid black line), the probability of infection with virtually no ventilation was over 90%, as a graphic from the study shows. With a half-hour exercise (longest dashed line, bottom), the probability of infection would have been only about 10%, even if there was almost no ventilation
The singers' breathing also determined how much virus air, and therefore virus, they emitted, with the average rate of emissions being indicated by the solid black line
The singers shared snacks but reported careful hand hygiene and made sure surfaces were sanitized, according to the study, which was approved for publication in Indoor Air magazine.
But the room they were in for more than two hours was poorly ventilated, which meant that air containing infectious particles was not withdrawn from circulation very often.
In addition, singing itself is known to release large amounts of aerosol, said lead study author Dr. Shelly Miller.
'This study documents in great detail that the only plausible explanation for this widespread event was aerosol transmission.
"Split air is important because you can breathe in what someone else breathed out, even when they are far away from you."
A growing body of research suggests that the coronavirus can spread in these fine, far-reaching particles.
On Monday, the CDC released guidelines making the public aware of this mode of transmission – which the WHO did not recognize – only to remove the guidelines and make a statement that they had been published in error.
It is unclear how close the singers were. A CDC report suggests that some were less than a foot apart. The new study cites answers from a choir speaker that most of them are about three feet from the nearest singer in a large but poorly ventilated church shrine.
The heat and power of the singing itself may also have hurled coronavirus aerosols around the room, causing the air to mix and move.
And the longer the exercise participants stayed in the room, the more concentrated the stagnant air with coronavirus particles from the one infected person.
The models from the CU Boulder team suggest that reducing the exercise duration to half an hour could have reduced the “attack rate” – the number of people infected by the index case – by more than 86 percent.
Duration of exposure has received less attention than proximity to contact, but a similar theory has been put forward to explain (in part) the higher rates and severity of infection in minority Americans.
Black and Spanish people in the US represent a disproportionately high proportion of those who have “essential” jobs that require them to keep working day in and day out, often using public transport. They also make up a disproportionate share of coronavirus cases.
In addition to having higher rates of underlying illnesses that put them at risk for severe COVID-19 and poorer access to health care, these people are also more likely to be exposed to higher levels of coronavirus.
It's not so much that a single encounter puts you at risk of contracting coronavirus, but repeated contact means they take on a greater viral load.
Similarly, during the 2.5-hour choir exercise, the virus particles emitted by the sick person collected in the air and soaked the other singers in them.
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