Masks being used by thousands of SA health workers to protect them from Covid-19 infection have failed safety tests.
None of the 12 brands of KN95 masks tested at the University of Cape Town offers the protection provided by the “gold standard” N95 mask, according to the results of a study published on Wednesday in the SA Medical Journal.
KN95 masks – mainly made in China – have flooded into SA amid a pandemic-related worldwide shortage of the highly regulated N95 masks.
Prof Keertan Dheda, the head of pulmonology at UCT’s medical school, said he and his team at the Centre for Lung Infection and Immunity decided to test the KN95 masks amid “growing concern” about their quality and “circulation of counterfeit masks”.
Examples of 12 brands were obtained from individuals, distributors and hospital doctors and they put three of each through a battery of tests alongside N95 masks and surgical masks.
Concluding his SAMJ article reporting the results, Dheda said: “None of the 12 brands of KN95 masks tested [comprising 36 masks] met stipulated safety requirements known to prevent infection by dangerous respiratory pathogens including [tuberculosis] and SARS-CoV-2 [which causes Covid-19].”
He made several recommendations, starting with stronger oversight by the South African Health Products Regulatory Authority (Sahpra).
There should also be a discussion about access to testing techniques, such as those used by the US National Institute of Occupational Safety and Health, he said.
However, even these tests were not comprehensive because they were limited to manufacturer consistency and mask filtration efficacy, and did not include tests for fit – a hurdle failed by all but one of the 36 masks Dheda’s team evaluated.
“We also recommend that fit-testing be enforced and that institutional capacity throughout the country be improved for qualitative fit and mask filter material efficacy testing,” said Dheda.
“Specific institutions could test KN95 masks at district or regional level before they are purchased from distributors. Regular in-house testing can also be performed to ensure consistency in batch quality and supply.”
Dheda said his team was exploring a low-cost standardised system to test the integrity of mask filters, and it would be useful to have a local website that reports on masks that have been tested and deemed safe.
The UCT tests involved seven volunteers from a range of race groups and began with each user checking the mask’s seal.
“The wearer inhaled and exhaled several times to check whether the respirator collapsed slightly upon inhaling and expanded upon exhaling, and whether they could feel any air leaking,” said Dheda. Only one K95 mask passed this test, compared with a 100% pass rate for N95 masks.
The researchers then modified the masks in an attempt to improve the deal. They attached head straps and experimented with staples and tape. This improved the seal test pass rate to 15 out of 36 masks. But none of the 15 went on to pass qualitative fit tests.
“We conclude that mask design and the nature of the material used are major determinants of mask failure rather than the amount of tension that is required to hold the mask in place,” said Dheda.
Eight brands of KN95 masks were then subjected to filtration integrity testing, and half failed to meet the standard required of an N95 mask – to filter more than 95% of virus particles. Two were so poor that they were significantly less effective than a simple surgical mask.
The KN95 masks fell short in other areas, too. Only two of the 12 brands had details of the mask type and manufacturing details on each mask, which is a regulatory requirement in the US and EU. And the number of filtration layers in the masks ranged from three to six.
“In summary, none of the KN95 masks evaluated met the required safety criteria, as stipulated by the US National Institute of Occupational Safety and Health and/or recently published by Sahpra to protect health-care workers from dangerous aerosol-containing pathogens such as SARS-CoV-2,” said Dheda.
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