An observational study suggests that health care workers are more likely to defeat SARS-CoV-2 infection when they wear a respiratory mask rather than a surgical mask.
Among workers who had contact with COVID-19 patients, those who always wore a mask were less likely to be infected (21% vs. 35% of those who did not wear a mask; OR 0.49, 95% CI 0.39-0.61), report Philipp Kohler, MD, Cantonal Hospital of St. Gallen, Switzerland, and colleagues.
And this difference is “not related to cumulative exposure”, the group at JAMA Network Open.
However, Kohler said in an email conversation that the findings do not infer cause and effect. “Whether healthcare workers wearing respirators also behave differently outside the workplace (thus reducing infections) remains an open question.”
As expected, healthcare workers tested positive were more likely to have more cumulative exposure to COVID-19 patients, regardless of the type of face covering they were wearing:
- > 2 to 4 hours exposure: 25% positive
- > 8 to 16 hours: 32.9% positive
- >64 hours: 42.7% positive
but Kohler said he Really surprised to see such a “good” dose on patient exposure (or 1.20 per doubling of cumulative exposure time, 95% CI 1.14-1.26). “This is something I didn’t expect to see.”
While working full-time at least 80% of the time was also associated with an increased risk of a positive SARS-CoV-2 result (OR 1.39, 95% CI 1.10-1.77), household exposure posed the greatest risk (OR 7.79, 95% CI 5.98-10.15).
In addition to always wearing a mask, vaccination also prevented testing positive for SARS-CoV-2 (OR 0.55, 95% CI 0.41-0.74).
Another protective factor was active smokers (OR 0.68, 95% CI 0.49-0.95).
The final finding was “somewhat odd”, Kohler admitted. “Smokers may be at reduced risk, but if they get infected…they are worse off,” he said. Kohler said.
“If you have to wear a respirator for a long time, it’s very uncomfortable,” he said. He added that the risk of infection may be higher when dining out in restaurants or at family reunions. However, “I think [health care workers] who are especially at-risk (eg, immunosuppressed) may benefit from wearing respirators when caring for SARS-CoV-2 patients.”
How many COVID-19 patients are I seeing? Do I have risk factors for serious illness? Am I vaccinated? “These are important questions in deciding whether to use a respirator,” Kohler added.
To compare the infection risk of different mask types, researchers tracked 2,919 healthcare workers weekly in seven health care centers in Switzerland from September 2020 to September 2021.
Participants (mean age 43 years) underwent anti-nucleocapsid antibody screening at baseline, January 2021, and September 2021. Of these, 749 (26%) of the participants were infected with SARS-CoV-2. Positive tests were also reported by 13% of participants who had not been exposed to the patient.
Participants reported weekly results of their SARS-CoV-2 nasopharyngeal swabs (PCR or rapid antigen test), the number of contacts they had with infected patients, including average contact time (1 to 60 minutes) and type of protection used (respirator or surgical mask).
No incidences of SARS-CoV-2 positivity were observed among healthcare workers in intensive care units or those who visited hospital cafeterias one or more (relatively infrequent) times per week.
Disclosure
This study was funded by the Swiss National Science Foundation, the Federal Office of Public Health and the Cantonal Health Office of St. Gallen.
The authors report relationships with study funders and Roche Diagnostics providing test analysis.
