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COVID-19 patients cough viruses through surgical masks and cotton masks

NewsMedicalCOVID-19 patients cough virus through surgical masks and cotton masks


Tuesday April 7th 2020

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Seoul - Neither cotton masks nor surgical masks are a safe barrier for SARS-CoV-2 if a patient with COVID-19 is coughing. This is shown by current experiments in the Annals of Internal Medicine (2020; doi: 10.7326 / M20-1342).

The lack of respiratory masks with filters (N95) has led clinicians to resort to surgical face shields. Cotton masks are popular among the population. A team led by Sung-Han Kim from Asan Medical Center in Seoul tested both masks on 4 patients who were sick with COVID-19.

The patients were asked to cough 5 times on a Petri dish placed 20 cm in front of their face. This experiment was repeated 4 times. The first time the patients wore no mask, the second time a surgical mask, the third time a cotton mask and the fourth time they were again without a mask.

As reported by Kim, the mean viral load of the 4 participants prior to the experiment was 5.66 log copies / ml in the nasopharyngeal swab and 4.00 log copies / ml in the saliva samples. When coughing without a mask, the Petri dishes measured 2.56 log copies / ml, when coughing through the surgical mask, 2.42 log copies / ml were found, and when coughing through the cotton mask, 1.85 log copies / ml. The viruses were also found on the outer surface of the face masks after coughing in all patients, while no viruses could be detected on the inside.

According to Kim, the experiments show that neither cotton masks nor surgical masks can safely stop the viruses of coughing patients. Why the viruses were partially undetectable on the inside remains unexplained.

Previous studies had shown that surgical masks are permeable to aerosols with a diameter of 0.9 to 3.1 µm. The diameter of SARS-CoV particles was estimated to be 0.08 to 0.14 µm during the first SARS outbreak in 2002/3. According to Kim, if the SARS-CoV-2 particles are the same size, they will not be stopped by surgical face masks.

The results contrast with recently published experiments on patients infected with seasonal coronaviruses. Surgical face masks stopped the viruses there. The differences between the two experiments lie in the methodology.

The viruses had not been determined on a coughed Petri dish, but with a special device in the air. The subjects were not asked to cough in the study. It could therefore be that the masks stop the viruses during normal breathing, but cannot withstand the strong acceleration of the particles in the event of an urge to cough. © rme / aerzteblatt.de

COVID-19 patients cough viruses through surgical masks ...