Study comparing surgical masks and N95 raises concern

Study comparing surgical masks and N95 raises concern

A randomized trial indicating that surgical masks are not inferior to N95 masks in protecting healthcare workers from COVID-19 has drawn international criticism.

The study’s lead author is John Conly, MD, an infectious disease specialist and professor at the Cumming School of Medicine, University of Calgary, Calgary, Alberta, Canada, and Alberta Health Services. The results are not consistent with those of many other studies on this topic.

Commenting on Conly’s study on Twitter, Eric Topol, MD, editor of medical landscapewrote: ‘He is terribly undernourished but has ruled out a doubling of the risk for the use of medical masks.’

The study, partially funded by the World Health Organization (WHO), was published online November 29 in Annals of Internal Medicine.

This is not the first time that Conly, who also advises the WHO, has been the subject of controversy. He has previously denied that COVID-19 is airborne – a position that is contradicted by strong evidence. Last year, Conly made headlines with his controversial claim that N95 respirators can cause harm including oxygen depletion and carbon dioxide retention.

A detailed review by the Center for Infectious Disease Research and Policy (CIDRAP) at the University of Minnesota, Minneapolis, pointed to numerous scientific flaws in the study, including the inconsistent use of the two types of masks. The study also looked at healthcare workers in four very different countries (Canada, Israel, Egypt and Pakistan) during different periods of the pandemic, which may have affected the results. In addition, the study did not take vaccination status into account and lacked a control group. CIDRAP receives funding from 3M, which manufactures N95 respirators.

In a commentary published alongside the study, Roger Chou, MD, professor of medicine at Oregon Health & Science University in Portland, said the results were “not definitive,” with “a non-inferiority threshold generous” which is actually “consistent with up to a relative increased risk of 70%… which may be unacceptable to many health workers.

The study’s lead author, Mark Loeb, MD, a professor of infectious diseases at McMaster University in Hamilton, Ontario, Canada, defended the findings. “The confidence intervals around this, i.e. what the possible results might be if the test were repeated several times, range from -2.5% to 4.9%,” he said. he declares. medical landscape. “This means that the risk of COVID-19 infection among those using the medical face masks could have ranged from a 2.5% reduction in risk to a 4.9% increase in risk. Readers and policy makers can decide for themselves about this.

Raina MacIntyre PhD

“There is no point in continuing to conduct underpowered, ill-designed studies that are designed to confirm existing biases,” said Raina MacIntyre, PhD, professor of global biosafety and biosafety program manager at the Kirby Institute, at Sydney, Australia. medical landscape. “The new study of Annals of Internal Medicine is entirely consistent with our conclusion that to prevent infection you need an N95, and it should be worn throughout the shift. A surgical mask and intermittent use of N95 are also ineffective. This should come as no surprise, given that a surgical mask is not designed as respiratory protection but is designed to prevent splashing or splashing of liquid onto the face. Only a respirator is designed as respiratory protection through the face seal and facepiece filter to prevent inhalation of virus-laden aerosols, but you must wear it at all times in a high-risk environment such as a hospital.

Kimberly Prather PhD

“It doesn’t make sense to do a randomized trial on something you can measure directly,” Kimberly Prather, PhD, atmospheric chemist, professor and director of the NSF Center for Aerosol Impacts on Chemistry of the Environment at the University of California , San Diego, says medical landscape. “In fact, numerous studies have shown that aerosols escape from surgical masks. Surgical masks are designed to block large spray droplets. Aerosols (0.5 to 3 µm), which have been shown to they contain the infectious virus SARS-CoV-2, travel with airflow and escape.

Dr. Trish Greenhalgh

“This study…will be used to justify policies for providing health care workers, and perhaps also patients and visitors, with inadequate protection,” Trish Greenhalgh, MD, professor of primary care health sciences at Oxford University, Oxford, UK, Told medical landscape.

“These authors have opposed treating COVID as airborne for 3 years,” said David Fisman, MD, epidemiologist and infectious disease specialist at the Dalla Lana School of Public Health at the University of Toronto, Toronto, Ontario, Canada . medical landscape. “So you’ll see these people brandishing this very flawed trial to justify continuing the infection control practices that have been so disastrous throughout the pandemic.”

The study was funded by the World Health Organization, the Canadian Institutes of Health Research and the Juravinski Research Institute. Conly said he received grants from the Canadian Institutes of Health Research, Pfizer and the WHO. Chou was a co-author with one of Loeb’s study authors on a similar topic. He was also revealed to be a methodologist for WHO guidelines on infection prevention and control measures for COVID-19. Loeb disclosed payment for expert testimony on personal protective equipment from the Manitoba government and the Peel District School Board. MacIntyre has led a large body of research on masks and respirators in healthcare workers, including four randomized clinical trials. She is the author of a book, Dark Winter (NewSouth, 2022), which covers the history and politics of the controversies surrounding the N95 and masks. Prather reported no disclosures. Greenhalgh is a member of Independent SAGE and an unpaid advisor to the philanthropic fund Balvi. Fisman served as a paid legal expert for the Ontario Nurses Association in their challenge to Directive 5, which restricted access to N95 masks in health care. He has also served as a paid legal expert for the Elementary Teachers’ Federation of Ontario in its efforts to make schools safer in Ontario.

Kate Johnson is a Montreal-based freelance medical journalist who has written for over 30 years on all areas of medicine.

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