oven irradiation melted all six samples from two FFR models.
The remainder of the FFR samples that were evaluated exhibited
average initial filter airflow resistances ≤17.0 mmH2O and
average initial sodium chloride filter aerosol penetration
values ≤1.86% for N95 FFRs and ≤0.012% for P100 FFRs.
Although there were statistically significant differences found
between control respirators and those that have undergone
decontamination for both filter aerosol penetration and filter
airflow resistance, the practical significance is minimal as the
range of numerical differences is quite small. The scent of bleach
remained noticeable on all FFR models following overnight
drying and low levels of chlorine were found to off-gas from
bleach-decontaminated FFRs when rehydrated with deionized
water, thus giving rise to the possibility of low-level exposure
to a subsequent wearer.”
Viscusi, et al. (2009) continue, “In light of these results,
the microwave oven irradiation and bleach decontamination
methods investigated in this study were determined to be the
least desirable among the five methods tested for consideration
in future studies. UVGI, EtO, and VHP were found to be the
most promising decontamination methods; however, concerns
remain about the throughput capabilities for EtO and VHP.
Further research is needed before any specific decontamination
methods can be recommended.”
While extended PPE use would mitigate utilization rate, its
safety is unknown. An interesting piece of the puzzle is just
how contaminated PPE is after care is delivered to COVID-19
patients. An initial pilot study showed no contamination of
N95 and disposable face visors after patient care, although
there was one instance of detection of SARS-CoV-2 nucleic
acid on the front surface of a healthcare worker’s shoe. To
evaluate the safety of extended PPE use, Ong, et al. (2020)
conducted a one-day PPE sampling study on HCWs caring for
confirmed SARS-CoV-2 infected patients to ascertain the per
contact episode risk of PPE contamination with SARS-CoV-2.
The researchers found that all 90 samples from 30 healthcare
workers were negative. The average time spent in a patient’s
room was 6 minutes, and activities ranged from casual contact
(e.g., administering medications, cleaning) to closer contact
(e.g. physical examination, collection of respiratory samples).
As the researchers acknowledge, “Previous laboratory
studies demonstrated that viruses such as SARS-CoV and
human coronavirus 229E can remain viable on PPE items
including latex gloves and disposable gowns, though these
were not performed in clinical settings. Despite the potential
for extensive environmental contamination by SARS-CoV-2,
we did not find similar contamination of PPE after patient
contact. This provides assurance that extended use of N95s
and goggles with strict adherence to environmental and
hand hygiene while managing SARS-CoV-2 patients could
be a safe option.”
University of Manitoba clinician-scientists and their research
partners at Canada’s National Microbiology Laboratory (NML)
have identified effective standard hospital sterilization tech-
niques that may enable in-demand N95 masks to be sterilized
up to 10 times for reuse in clinical settings.
The research was performed by a team of five researchers
led by Dr. Anand Kumar, a UM researcher and critical-care
physician at HSC, in response to worldwide concerns about
the supply of N95 masks.
32
“Medical masks are used by healthcare workers, with
the N95 providing the best protection against tiny aerosol
particles that carry the novel coronavirus. At the start of the
pandemic, it was clear we were going to be facing dramati-
cally heavy demands for the N95s,” said Kumar. “Our team
wanted to explore how different brands and models of N95s
responded to standard hospital sterilization technologies in an
attempt to identify safe options for their reuse in the event
of supply shortages.”
In mid-March, HSC physicians/faculty members at the UM’s
Max Rady College of Medicine, worked with NML scientists
to test four different types of N95 masks using four different
sterilization methods: repeated cycles of standard autoclaving;
ethylene oxide gassing; ionized hydrogen peroxide (iHP)
fogging; and vaporized hydrogen peroxide (VHP) treatment.In
addition, the ability of all four decontamination techniques to
totally eliminate viruses on the masks was tested. Afterward,
these N95s were visually and tactilely assessed for structural
integrity and underwent quantitative fit testing to assess
functional integrity.
“Our results demonstrate that the assessed decontam-
ination methods were highly effective in sterilizing all four
contaminated N95 models mask types. No viable virus was
found on any intentionally-contaminated mask following any
of the decontamination procedures,” said Kumar, noting that
in some cases the researchers used a non-pathogenic virus in
place of SARS-CoV-2 virus and the study was not performed
on masks worn by healthcare workers. Further testing has
been carried out at the NML, which used the SARS-CoV-2
virus to contaminate the masks, and results are expected in
the near future.
Kumar’s initial study results indicated several of the
decontamination methods could be used repeatedly without
degrading the masks’ effectiveness so that the use of individual
N95 masks could potentially be extended several-fold. Kumar
pointed to two sterilization methods which showed no loss
of filtering function after multiple cleanings. However, one
method, the vaporized hydrogen peroxide, is not widely
available in North America.
“I’m particularly excited by the fact that autoclaving works
on most masks because unlike the other techniques, it should
be available at every established hospital in the world, including
in the most poorly resourced countries,” he said, pointing to
the commonly-used, pleated N95 masks as the type of mask
that tolerates undergoing this sterilization process.
“We successfully decontaminated these pleated, fabric
N95 masks up to 10 times using autoclaving,” he added,
noting autoclaving equipment relies on high heat and steam to
disinfect and sterilize. The team’s goal is to share their research
findings so that jurisdictions can assess the options that will
enable their healthcare workers to be appropriately protected.
“Many institutions in highly-affected regions of the world
are running out of these masks and others are rationing so
that healthcare workers must make use of the same masks
for long periods which can lead to mask failure and increased
risk to the worker,” said Kumar, noting the study has not yet
undergone peer-review or been published in a medical journal.
Amid these reports of healthcare workers reusing masks and
other articles of PPE, in late March, the FDA reported it took
significant action to help increase the availability of ventilators
april 2020 • www.healthcarehygienemagazine.com