It has now been 3 years since the SARS-CoV-2 virus first infected humans in Wuhong, China in December 2019. By now, most Americans have either had a COVID-19 infection or have been vaccinated against COVID. So, what type of mask should we be wearing in the hospital and in public places?
Our two most powerful weapons against COVID are vaccination and mask-wearing but mandates for both have been been unpopular in the United States. Since the peak of the pandemic, most mask mandates in public areas have been relaxed. However, mask mandates are still in place in many hospitals. Furthermore, as of the writing of this post, there are 25,380 patients with COVID infection currently admitted in U.S. hospitals. Consequently, healthcare workers continue to have regular exposure to infected persons. So, what kind of mask should our healthcare workers wear?
Mask-wearing is not new. Surgeons and other operating room personnel have worn masks during surgeries for more than a century. However, the purpose of wearing masks in the OR is to prevent the surgeon’s respiratory secretions from infecting the patient’s incision and not to prevent the patient’s incision from infecting the surgeon. A simple surgical mask is very effective in catching respiratory droplets if the surgeon sneezes, coughs, or talks during an operation.
Before COVID, there were situations when healthcare workers did wear masks to prevent getting infected by patients, for example, when caring for patients infected with influenza (where transmission is usually by respiratory secretion droplets). A regular surgical mask is effective in preventing infection from respiratory secretion droplets but for smaller particles, an N95 mask is necessary. For 35 years, I wore N95 masks whenever I was caring for patients infected with tuberculosis or when doing bronchoscopy on patients suspected of having TB. It only takes inhaling one tuberculosis bacteria to become infected with TB. A respiratory secretion droplet is about 5-10 μm in size whereas a tuberculosis bacteria is about 2 μm in size. A regular surgical mask will usually stop the droplets but will not stop a TB bacteria, whereas an N95 mask will.
For an N95 mask to be effective, it must have a tight seal to the face so that air cannot get between the edges of the mask and the skin. Everyone’s face is shaped a little differently and not all brands of N95 masks fit all faces equally well. Healthcare workers are normally required to be “fit-tested” to determine which N95 mask provides an acceptable seal against the face. Passing the fit test meant that all of the inhaled air went through the mask material and did not leak between the mask and the skin. At our hospital, we required healthcare workers who worked with patients with suspected tuberculosis to be fit tested every year. A number of years ago, the Occupational Safety and Health Administration (OSHA) put out a requirement stating “The employer shall not permit respirators with tight-fitting facepieces to be worn by employees who have facial hair that comes between the sealing surface of the facepiece and the face…“. In other words, men with beards were not supposed to use N95 masks.
Like influenza, the COVID virus is usually transmitted by respiratory secretion droplets. So, in theory, a surgical mask should be sufficient. However, there are certain situations when an infected patient’s respiratory secretion droplets can be broken down into smaller particles, in which case, a surgical mask could be insufficient and an N95 mask may be more effective. Such situations include performing endotracheal intubation and bronchoscopy. Having had a beard for 40 years, I had repeatedly passed my annual N95 fit tests despite having a beard but when COVID hit, I shaved it in order to be in compliance.
We now have several studies performed over the past 3 years of the pandemic to give us better guidance of what type of mask is most effective in preventing healthcare workers from becoming infected. Unfortunately, each of these studies have potential limitations and the studies have given mixed results.
A word about KN95 masks. An N95 mask is a NIOSH-approved mask that filters out at least 95% of particles that are 0.3 micons in size. In reality, a well-fitting N95 mask actually filters out 99.8% of particles that are 0.1 micons in size, which is also the size of a COVID virus particle. A KN95 mask is a mask approved by the Chinese government (and not NIOSH). A study of KN95 masks found that 70% of them did not meet the NIOSH standard for effectiveness. For hospital purposes, a KN95 mask can be considered as effective as a surgical mask but not as effective as an N95 mask
One of the earliest studies comparing surgical to N95 masks was published in JAMA in 2009 and randomized 446 nurses caring for patients with acute febrile respiratory illnesses to wear either surgical masks or N95 masks during patient care. An equal percentage of the nurses were diagnosed with influenza during the study and the conclusion was that the type of mask worn did not make a difference. Another study published 10 years later in JAMA in 2019 also found that among 1,993 healthcare workers randomized to wearing surgical or N95 masks, there was no difference in the incidence of influenza or other respiratory infections.
There have been several studies comparing masks to prevent COVID infection. A 2021 study examining the effectiveness of N95 versus surgical masks based on analysis of droplet size characteristics concluded that a surgical mask was theoretically sufficient to prevent COVID infection in low-virus environments but N95 masks would be theoretically more effective in virus-rich environments. A 2021 study comparing the fit of cloth, surgical, KN95, and N95 masks found that N95 masks had better fit factor scores than the other masks and that KN95 masks had similar fit factor scores as surgical masks. The study also concluded that fit is critical to the level of protection offered by masks. A 2021 meta-analysis of 8 studies involving N95 versus surgical masks found that N95 masks were more effective than surgical masks in preventing healthcare workers from becoming infected with a variety of respiratory viruses, including COVID. A 2022 study of 3,259 healthcare workers who were randomly assigned to use filtering facepiece class 2 masks (analogous to N95 masks) versus surgical masks found no overall effect on the incidence of COVID infection; however, those healthcare workers with > 20 contacts with COVID patients did have fewer COVID infections if they were wearing the filtering face piece class 2 masks. A 2022 MMWR report involved a retrospective review of 1,528 COVID-infected persons and 1,511 case controls and found that people who reported wearing N95 masks in public were less likely to become infected than those who wore surgical masks in public places. However, a major limitation of this study is presumably those wearing N95 masks were also more likely to take other precautions to avoid COVID than those who chose to wear a regular surgical mask.
The most recent study was published this week in Annals of Internal Medicine. 1,009 healthcare workers in Canada, Israel, Egypt, and Pakistan were randomized to use N95 or surgical masks during patient care for 10 weeks. Overall, there was no difference in the incidence of COVID infection between the two groups but it is notable that most of the subjects (71%) were in Pakistan or Egypt with only 29% in Canada or Israel. In Pakistan and Egypt, 82% of subjects had previously been infected by COVID before the study whereas in Canada and Israel, only 3% of subjects had a previous COVID infection. There was a trend for N95 masks to be more effective than surgical masks in Canada and Israel; however, because of the low number of subjects in those countries, the results did not reach statistical significance. Because past COVID infection confers some immunity to reinfection, it is possible that the failure of N95 masks to have superior protection over surgical masks was due to the very high percentage of healthcare workers with immunity from previous infection in Pakistan and Egypt.
The bottom line: What mask should you wear?
Medicine is a very dynamic science and recommendations change as new clinical studies are published. As a result, today’s medical dogma is tomorrow’s medical malpractice. Based on the available information a few general recommendations can be made:
- In hospital areas where the prevalence of COVID infection is low, wearing regular surgical masks is sufficient to prevent healthcare workers from becoming infected. This means parts of the hospital that provide care for non-COVID patients, such as general medical and surgical floors, cafeterias, public areas, and offices.
- In hospital areas where there is likely to be a high number of viral particles in the air breathed by a healthcare worker, N95 masks are preferable. This would include areas where the viruses are likely to be aerosolized, such as during intubation or bronchoscopy, particularly in rooms with stagnant airflow, such as those lacking sufficient number of air exchanges per hour. In locations where the virus is in respiratory droplets (as opposed to being aerosolized), surgical masks may be sufficient. Because several studies have shown that the viral loads are similar among symptomatic versus asymptomatic patients with COVID infection, the decision of whether to wear an N95 mask should not be based on the severity of the patient’s infection.
- Wearing surgical masks by healthcare workers is sufficient to prevent workers with asymptomatic COVID infection from infecting patients. This has been a concern for the care of patients at high risk of severe COVID infection, such as those patients who are immunocompromised, obese, diabetic, or elderly. These patient are at particular risk if in contact with a maskless infected healthcare worker. Because daily testing of all healthcare workers caring for these patients is impractical, preventative mask-wearing is prudent.
- Because viral loads are just as high in asymptomatic patients as in symptomatic patients, hospital visitors should wear surgical masks inside of the hospital as long as the prevalence of COVID infection in the community remains substantial or high. What constitutes “high” is a matter of opinion but the CDC defines “low” as up to 10 cases/100,000 population, “moderate” as between 10-50/100,000, “substantial” as 50-100/100,000 population, and “high” as greater than 100/100,000 population. Currently, the U.S. as a whole has a case rate of 91/100,000 population. However, hospitals are not like the country as a whole – currently 5.6% of all Ohio inpatients have COVID infections for an inpatient rate of 5,600/100,000. Because inpatients with COVID infection are more likely to have family and friends who are also infected (from home and workplace transmission), the probability of encountering a hospital visitor with a COVID infection is a lot higher than encountering a waiter in a restaurant with a COVID infection.
- Healthcare workers who prefer to wear an N95 mask (but are not required) should be permitted to do so. Because of non-statistically significant trends in some studies suggesting a slight benefit of N95 over surgical masks, those healthcare workers who perceive greater safety with the N95 masks should be allowed to wear them if desired and if supplies permit.
- Healthcare workers who are required to wear N95 masks should be fit-tested annually. Because ill-fitting N95 masks lose most of their protective benefit, there needs to be assurance that the N95 mask that the worker wears actually does what it has the potential to do. It is reasonable for hospitals to also require fit-testing for those employees who want to wear an N95 mask but are not required to wear an N95 mask, especially if the hospital is paying for the masks.
- KN95 masks are an acceptable alternative to wearing a surgical mask but should not be used in clinical situations when N95 masks are required. Given the reduced effectiveness of KN95 masks compared to N95 masks, a KN95 mask cannot be viewed as equivalent to an N95 mask. It may, however, be better than a surgical mask.
What about outside of the hospital? At the grocery store or airport, I generally see only 5-10% of people wearing masks. At athletic events, that percentage is even lower. The risk of becoming infected in a public place is dependent on how likely you are to come in contact with someone’s exhaled viruses. That in turn depends on the prevalence of COVID infection in the community, the number of people in an enclosed space, the size of the enclosed space, the duration of time that you are in that space, the amount of singing or shouting in the space, and the ventilation of the space. Based on viral load studies, it does not matter whether an infected person in the space is symptomatic or asymptomatic. In situations when those variables indicate a higher risk of COVID, wearing a surgical mask is prudent. Those people who feel more secure wearing a KN95 mask or an N95 mask should do so.
As for me, N95 masks kept me from getting TB despite caring for patients with tuberculosis for decades. They also kept me from getting COVID infection despite intubating and performing bronchoscopy on COVID patients in our intensive care unit. My fit-tested N95 mask is sort of like a security blanket for me. So, I think I’ll keep wearing it in public areas for now. When the case rate gets below 50/100,000 population, I’ll reconsider. And when the case rate gets below 10/100,000, I’ll feel safe without any kind of mask in public.
December 2, 2022