COUGH, deep breathing and screaming can increase up to 100 times the number of particles of aerosol that people produce. A new figure that inevitably raises concerns about the biosecurity of all closed environments and the effectiveness of the masks we use to protect ourselves from Covid.
A few millimeters are enough
Since the pandemic there has been much debate on the role of respiratory particles in the transmission of the new coronavirus and on the guidelines to follow to prevent contamination. Molecules larger than one hundredth of a millimeter are traditionally called droplets and are believed to propagate 1 or 2 meters from an infected patient before falling to the ground, hence the minimum distance of social distancing we all know by now. Aerosols, on the other hand, are smaller particles that remain suspended in the air for prolonged periods and have the potential to spread more widely and accumulate in poorly ventilated spaces, as well as the ability to bypass facial masks that are not perfectly adherent to the face.
Current guidelines are designed to protect us from droplets while widespread aerosol infection is considered a risk only in hospital wards. But to question this precept, warning about the high infectivity of aerosols in any environment that is not sufficiently ventilated, are now researchers from the Universities of Sydney and New South Wales.
The areosol
The team led by Nick Wilson, Euan Tovey, Guy Marks and Tim Cook has calculated how much potentially infectious aerosol we produce and how much it can affect the spread of the virus. They collected the particles that were exhaled by 10 healthy volunteers while breathing, talking, screaming and coughing and found that coughing and labored breathing produce up to a hundred times more aerosols than a patient undergoing oxygen therapy in a Covid ward. The results of the research, published today in the scientific journal Anaesthesia (https://doi.org/10.1111/anae.15475), therefore demonstrate that surgical masks provide inadequate protection against aerosols and that safety can only be increased with a more widespread use of “adherent devices”, such as the Ffp2 or Ffp3, and greater ventilation of the rooms.
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Seeking therapy
Initially, the study aimed to examine whether oxygen therapies used for severe patients produced large amounts of small respiratory particles capable of circumventing the routine precautions used in hospital wards. The experimentation, on the other hand, has found that these therapies do not disperse excessive quantities of aerosols and that the greatest risk remains coughing, deep breathing as well as screaming. According to the study authors, their findings could partly explain why staff working in wards wearing only surgical masks have two to three times higher infection and hospitalization rates than those working in ICU, where the level of personal protection is greater.
The optical particle counter
To measure their number and size, the researchers used an optical particle counter in a closed room with previously purified air and, unlike previous studies, they managed to collect almost all the particles exhaled by the volunteers, allowing for a clear comparison between the quantities of aerosols generated by the respiratory activities and oxygen therapies. Each volunteer was asked to breathe normally and then deeply, chat, scream, cough and do light exercise. Then they repeated the experiment with oxygen delivery to the nose and finally with the ventilation mask.
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“More than 90% of the total number of particles produced by both activities and therapies were aerosols,” said Dr. Wilson. “Aerosols are important as they can travel long distances in the air, evade large surgical masks and be inhaled deeply into the lungs and all this raises concerns about the safety of those close to an infected person. ” And colleague Tovey added: “Coughing and wheezing, common in non-severe Covid patients, produces far more droplets and aerosols than is produced by severe patients being treated with oxygen therapy. Surgical masks provide inadequate protection against aerosol and personnel safety can only be increased with a more widespread use of specialized tight-fitting respirators and greater ventilation of the rooms “.
What happens in daily activities
Experts are convinced that their research can find useful applications even in everyday life. “Our study has implications beyond hospitals – underlined Professor Marks -. The generation of droplets and aerosols in daily respiratory activities reinforces the importance of maintaining social distances, having excellent ventilation in buildings and public transport, stay outdoors as much as possible and use effective masks to protect yourself from breathing the virus as well as from spreading “. And Professor Cook concluded: “Our findings strongly support the re-evaluation of guidelines to better protect hospital staff as well as patients and all those dealing with people who have, or are suspected of having, Covid- 19 “.
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