The COVID-19 pandemic is placing healthcare professionals in the untenable position of rationing personal protective equipment (PPE) and working with suboptimal protection. This post explores which materials may be best suited for crafting homemade masks and considers how to use homemade masks productively.
Personal protective equipment is critical when caring for patients with respiratory infection. The CDC recommends surgical masks be worn when in close contact with patients who have respiratory infection symptoms. N95 respirators are recommended when treating patients with respiratory illness. Despite the difference in filtering efficiency, a randomized clinical trial showed no significant difference between the lab-confirmed influenza infection rates of clinicians wearing N95 masks and surgical masks. This finding was replicated in a 2019 randomized controlled trial. Surgical masks and N95 respirators are intended to be discarded after a single use. This prevents contamination and ensures the highest quality fit.
PPE consumption rates increase during an outbreak of respiratory illness. Authors of a 2009 article recommended doubling PPE supplies in preparation for an outbreak based on their experience treating H1N1 in California. Unfortunately, budget and logistical constraints appear to have prevented hospitals from maintaining or obtaining a suitable volume of PPE to deal with the current surge of cases.
As clinicians face a shortage of surgical masks and N95 respirators, the CDC issued guidance that those without access to supplies may reuse PPE or use bandannas and scarves. Physicians and others are collaborating to generate creative approaches for conserving PPE supplies, testing protocols to sanitize facemasks and respirators for reuse, and even 3D printing respirators. Healthcare systems, craft supply stores, and individual clinicians have called upon people across the country to sew masks. Many have taken up the call, creating masks from a variety of materials in a variety of styles.
The CDC acknowledges that cloth masks are not equivalent to PPE. In a report on reusing masks, The National Academies of Science, Engineering, and Medicine hesitated to discourage use of cloth masks during severe shortage but warned that they may create a false sense of security.
Material Considerations for Homemade Masks
Considering a flu pandemic scenario where emergency mask supplies are insufficient, disaster preparedness researchers tested household materials' ability to filter 0.02-micron particles. The goal was to balance protection and comfort and recommend ideal materials for public use. Improvised mask wearers may value filtration effectiveness more highly than breathability in high-risk scenarios.
Some household materials were moderately efficient at filtering viral-sized particles from the air. However, household materials did not contain particles expelled when the wearer coughed. Homemade masks appear better able to protect healthy people than prevent transmission of respiratory illness.
Results showed that vacuum cleaner bags and dish towels performed best, filtering 86% and 73% of particles respectively. Unfortunately, these materials were difficult to breathe through. Authors deemed antimicrobial pillowcases (68% effective), cotton blend t-shirts (70% effective), and 100% cotton t-shirt (51% effective) more viable materials because they provided filtration without seriously impairing breathing.
Adding a second layer of material did not substantially improve efficacy (1-2% gain). However, constructing a mask from two layers of different colored fabric could help users differentiate between the inside and outside of their mask. Decreasing the chances of putting a used mask on inside out.
Other materials have been proposed. A letter to the editor published in Emerging Infectious Diseases presented a no-sew design constructed of eight layers of 100% cotton knit t-shirt. A professor of anesthesiology at the University of Florida recently created a design made from sterile wrapping used to cover surgical instrument trays. This material could be up to 99.9% effective in blocking particulates.
Fit and Construction
Both the fit and material contribute to the functionality of homemade face masks. An N95 respirator with a fit factor of 100 is considered the workplace standard. A study comparing improvised tea towel masks with surgical masks showed that improvised masks had the worst fit score. However, fit quality did not diminish over time. The no-sew t-shirt mask (mentioned above) was rated with a fit factor of 67 for a tester with common face size. It was less effective for testers with larger faces, scoring 13-17.
Common homemade mask designs include: pleated designs, which resemble surgical face masks; more fitted shapes, which may include a wire nose band; and masks with pockets for improvised filters. Researchers who preformed the household materials test (described above) recently published their mask pattern and accompanying sewing instructions.
There is a lack of research comparing the fit of these mask designs. However, there is evidence that pleated handmade masks fit worse than similar-looking surgical masks. WHO mask fit guidelines (no gaps between face and mask) should be applied when wearing homemade masks.
N95 masks maintained a fit factor of 100 when being put on 5 times before fit quality diminished. Risk of viral transfer is the largest barrier to reuse. An article published in Infection Control and Hospital Epidemiology found that little coronavirus was lost on N95 respirators within 2 hours. Virus remained detectable after 24 hours.
A report from the Stanford Medicine Anesthesia Informatics and Media Lab suggests that N95 masks may be disinfected without compromising filtration. This can be achieved in a hot-air oven set to 70 degrees Celsius over 30 minutes or using hot water vapor from a boiling water source for 5 minutes. These approaches have not been tested on homemade masks so the implications for filtration are unknown. These methods should not compromise the fit of woven or knit cotton fabric masks.
Using Homemade Mask Donations
Some providers are wearing homemade masks over N95 respirators. This could mitigate risk of viral transfer when reusing PPE. More coronavirus was lost on surgical scrub fabric over a two-hour period than on N95 respirators. Virus was not detectable on scrub fabric at the 24-hour mark.
This does not negate risk of viral transfer. Homemade masks provide imperfect protection. Coronavirus was still detectable on contact isolation gowns after 24 hours. Some suggest that viral survival on scrub fabric may put cleaning staff at risk.
Though researchers have concluded that homemade masks provide protection compared to no mask, there is reason to be concerned about using cloth masks alone. A 4-week randomized controlled trial conducted in Vietnam compared rates of influenza-like infections among cloth mask, limited medical mask, and standard mask users (control). Healthcare workers assigned to wear medical masks (2 surgical masks per shift) had the lowest rates of infection. Those assigned to wear cloth masks (5 masks for duration, participants cleaned their own masks) experienced the highest rates of infection. Standard mask use protocols in the test location likely vary from US hospitals, but medical masks clearly outperformed cloth masks even when the number of masks was restricted.
If it is necessary to rely on cloth masks in a medical setting, handmade masks would ideally be used in lower-risk situations so that available surgical masks and N95 respirators can be used during high-risk triage and treatment activities. Cloth masks are not an appropriate alternative to surgical masks when attempting to prevent viral spread by patients with respiratory symptoms.
Improvised cloth masks are perhaps best used by the public. Homemade masks reduced flu infection among informal caregivers who were taking care of someone with the flu at home. In combination with social distancing measures and proper hand hygiene, handmade masks could reduce infection rates in the general population. Wearing a mask may be particularly relevant to front-line workers, such as grocery store clerks, who encounter more people daily and those at high-risk for severe illness.
In addition to protecting community members, providing appropriate education about wearing handmade masks could help reduce public demand for manufactured masks.This article was first published on the Medical Care Blog on March 30, 2020.