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April 20, 2020
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Paper questioning efficacy of masks retracted

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A research letter published in the Annals of Internal Medicine in April that concluded surgical and cotton masks were ineffective at preventing the transmission of SARS-CoV-2 was retracted on June 2.

The decision was based on a recommendation from the journal’s editors.   

“We had not fully recognized the concept of limit of detection (LOD) of the in-house reverse transcriptase polymerase chain reaction used in the study (2.63 log copies/mL),” the authors of the study wrote in the notice of retraction. “We regret our failure to express the values below LOD as ‘<LOD (value).’ The LOD is a statistical measure of the lowest quantity of the analyte that can be distinguished from the absence of that analyte. Therefore, values below the LOD are unreliable and our findings are uninterpretable. Reader comments raised this issue after publication. We proposed correcting the reported data with new experimental data from additional patients, but the editors requested retraction.”

For the study, Seongman Bae, MD, and colleagues had recruited four patients from South Korea with COVID-19. Two of the patients had upper respiratory infections: one had pneumonia and the other had pneumonia with acute respiratory distress syndrome. The age of the patients had ranged from 35 to 82 years. Two of the patients were women.

Photo of surgical masks 
Surgical masks were ineffective at preventing the dissemination of SARS-CoV-2, the virus that causes COVID-19, according to a research letter published in Annals of Internal Medicine.
Photo Source: Adobe Stock

Researchers had asked patients to cough five times into a petri dish without wearing a mask, while wearing a disposable surgical mask, while wearing a reusable cotton mask and again without wearing a mask. Specimens from the outer surface and inner surfaces of the masks were collected via an aseptic swab.

Bae and colleagues had written at baseline, the patients’ median viral load of the nasopharyngeal sample was 5.66 log copies/mL and of the saliva samples was 4 log copies/mL.  According to researchers, after coughing, the patients’ median viral load without a mask was 2.56 log copies/mL, with a surgical mask was 2.42 log copies/mL and with a cotton mask was 1.85 log copies/mL. While most swabs from the inner mask surfaces were negative for SARS-CoV-2, all the swabs from the outer surfaces of the masks were positive for SARS-CoV-2, researchers had stated.

“We are not sure as to whether the masks shortened the distance of viral particle transmission,” Sung-Han Kim, MD, PhD, chief of the office for infection control at Asan Medical Center in Seoul, South Korea, and a co-author of the Annals of Internal Medicine report, said in an interview in advance of the Healio’s coverage on Bae and colleagues’ research letter.

“Further studies are needed for cotton and surgical masks’ use in routine activities such as talking. Masks with high filtration efficiencies should also be tested in this regard,” Kim continued. He had also noted that the protective effect of N95 respirators or their equivalent are “likely the strongest,” but further research should be conducted to test this assertion. – by Janel Miller

Reference: Bae S, et al. Ann Intern Med. 2020;doi:10.7326/M20-1342.

Disclosures: The authors report no relevant financial disclosures.

Editor's Note: This article was updated on June 9, 2020, to add information on the retraction of the published research letter.