The CDC is now suggesting that everyone should wear cloth face coverings (not surgical masks or N-95 respirators) when going out in public, but will that stop the spread of SARS-CoV-2, the virus that causes Covid-19, or is it a false sense of security? Possibly the latter if someone is wearing a makeshift cotton mask or a surgical mask, according to a new report in the Annals of Internal Medicine.
“[B]oth surgical and cotton masks seem to be ineffective in preventing the dissemination of SARS–CoV-2 from the coughs of patients with COVID-19 to the environment and external mask surface,” Seongman Bae, MD, and colleagues reported. However, they noted that whether or not they benefit healthy, asymptomatic people is not clear.
They did an experiment comparing “disposable surgical masks (180 mm × 90 mm, 3 layers [inner surface mixed with polypropylene and polyethylene, polypropylene filter, and polypropylene outer surface], pleated, bulk packaged in cardboard; KM Dental Mask, KM Healthcare Corp) with reusable 100% cotton masks (160 mm × 135 mm, 2 layers, individually packaged in plastic; Seoulsa).”
The masks were tested by patients with Covid-19 in negative pressure rooms, where they were asked to cough into petri dishes held 20 cm from their mouths. The petri dishes contained “1 mL of viral transport media — sterile phosphate-buffered saline with bovine serum albumin, 0.1%; penicillin, 10,000 U/mL; streptomycin, 10 mg; and amphotericin B, 25 µg.”
They coughed “5 times into each petri dish while wearing the following sequence of masks: no mask, surgical mask, cotton mask, and again with no mask. A separate petri dish was used for each of the 5 coughing episodes. Mask surfaces were swabbed with aseptic Dacron swabs in the following sequence: outer surface of surgical mask, inner surface of surgical mask, outer surface of cotton mask, and inner surface of cotton mask,” Bae and colleagues wrote.
They found that neither mask type — cotton or surgical — filtered out SARS-CoV-2. They noted that recommendations to wear masks are based on evidence that such masks are effective against influenza virus.
“However, the size and concentrations of SARS–CoV-2 in aerosols generated during coughing are unknown,” they wrote, and noted that a previous study found that “surgical masks did not exhibit adequate filter performance against aerosols measuring 0.9, 2.0, and 3.1 μm in diameter,” while another one “showed that particles 0.04 to 0.2 μm can penetrate surgical masks. The size of the SARS–CoV particle from the 2002–2004 outbreak was estimated as 0.08 to 0.14 μm; assuming that SARS-CoV-2 has a similar size, surgical masks are unlikely to effectively filter this virus.”
Interestingly, Bae and colleagues found more contamination on the outer layer of the masks than the inner surfaces. They noted that they swabbed the outer surfaces before the inner, and this finding might be due to the pressure of the swabbing and the particles crossing from the inner to the outer layer, but they also conjectured that it might be due to “a turbulent jet due to air leakage around the mask’s edge [which] could contaminate the outer surface.” They also noted that a high velocity cough could possibly penetrate the layers of the mask, although such a cough would also elicit an exhale that would deposit particles in the inner layer.
These findings underscore the importance of hand hygiene when wearing masks, they emphasized.
Nonetheless, the question remains — to mask or not mask?
Bae and colleagues noted that their experiment “does not reflect the actual transmission of infection from patients with Covid-19 wearing different types of masks. We do not know whether masks shorten the travel distance of droplets during coughing.” And they suggested that further study is needed for asymptomatic individuals or those who possibly have the disease but are not coughing.
So, the question, at best, remains unanswered.
Candace Hoffmann, Managing Editor, BreakingMED™
Cat ID: 125
Topic ID: 79,125,287,500,503,728,791,932,730,933,125,190,469,520,926,192,927,151,928