Infection reduction goes beyond COVID-19.
Face masks have been such a controversial topic since the beginning of the COVID-19 pandemic. On one hand they can potentially reduce transmission of respiratory viruses as a direct barrier.
On the other hand, naysayers state that there is no good evidence supporting masks and therefore they are useless. Despite, strong, consistent public health messaging about the utility of wearing masks, their use continues to be debated.
You may ask why are we even talking about masks in the ED? We are all vaccinated now, right? I would argue that there are still protective effects for other things as well, not just with COVID-19. For example, what happened to influenza this past year? It didn’t just disappear. I suspect masks had a large part to do with this.
Personally, I have only diagnosed four or five cases of influenza in all of 2020. There are still other respiratory illnesses that can wreak havoc on patients at risk. Maybe we don’t need to go all crazy with N95 masks going forward, but I suspect the use of masks in the ED will be a discussion and debate that will be ongoing for years to come.
Both the CDC and WHO strongly recommend the use of masks as a means of source control. With that background and the unfortunate continued debate here is what you need to know about masks.
- It’s not just about wearing masks alone. Don’t get me wrong, wearing a mask is important, but it is also important to recognize that masks plus other public health measures are essential in decreasing viral spread. No one single public health measure is 100% effective, including masks. However, each additional intervention is additive in improving the success of decreased viral transmission. Physical distancing, limiting social gatherings and hand washing are all additive to masks. If all these measures are followed (which they are not) masks may not have as much of an impact, but still add some layer of protection.
- Recommendations alone are not enough. Public mask-wearing is most effective at reducing the spread of illness when compliance is high. In other words, in order for masks to work they have to be worn and be worn correctly (we have all seen the memes). Compliance with a recommendation to wear masks is the key. The DANMASK-19 trial,[1] looked at this exactly. There was no decrease in viral transmission in this trial. So why is that? The prevalence of disease was so low in this trial that you wouldn’t expect to see much of a difference whether you wore a mask or not. Additionally, the trial was really a study of the effects of recommending mask use, not the effect of actually wearing a mask, much less wearing it correctly.
- Masks are aimed at reducing transmission, but do have some protective effects for the wearer as well. In a simulated study by the CDC[2] unknotted medical procedure masks alone blocked 56.1% of particles from a simulated cough and a cloth mask alone blocked 51.4%. When the receiver was fitted with a double mask (medical procedure mask + cloth mask) the person wearing the double masks exposure was reduced by 83%. To put it simply, masks substantially reduce exposure from infected wearers (source control) and reduce exposure of uninfected wearers.
- Not all masks are created equal. In one study,[4] air-jet flow velocity through a simulated cough and breathing was performed on several different types of masks. Most studies focus on front flow through the mask, however, do not consider air leakage from the sides, bottom or top of the mask. It turns out that surgical and handmade masks generated significant leakage jets in all directions other than forward. This was not the case with FFP 1 and FFP 2 (N95) masks.
- How the mask fits is important. Cloth and medical procedure masks fit more loosely than do N95 masks. Their primary use is to block liquid droplets but the extent to which they reduce exhalation and inhalation of particles in the aerosol size range varies. The effectiveness of cloth and medical procedure masks are improved by ensuring that they are fitted to the contours of the face to prevent leakage of air around the masks’ edges.
In the same study done above by the CDC,[2] when the medical procedure mask was tightened with knotting of the straps and tucking in the extra loose flaps of the mask it blocked 77% of particles as opposed to 56.1% of an unmodified mask. In another study, the addition of elastic bands over the mask as well as a nylon hosiery sleeve (mask fitters) to a surgical-grade mask, helped improve filtration efficiency from 38.5% to 78.2% and 80.2% respectively. These findings suggest that modifications to improve the fitting of masks most likely will result in further decreased transmission.
- A single mask is good, but a double mask might be better. In the same study as above by the CDC[2] wearing a cloth mask over a medical procedure mask and knotting the ear loops and tucking in the extra loose flaps of a medical procedure mask reduced exposure by the source to the receiver by 82.2%. When both the source and receiver were both fitted with double masks the cumulative exposure of the receiver was reduced by 96.4%.
- Wear a mask with a nose bridge and the ability to have a filter insert. In one simulated study of consumer-grade 2-layer nylon masks the addition of a nose bridge to the mask was shown to improve filtration efficiency from 44.7% to 56.3%.[3] The addition of a filter insert to the nose bridge increased the filtration efficiency up to 74.4%.[3]
The science is there and shows the utility of masks. But it’s not just about wearing a mask. It is wearing a mask, or even better, two masks with modifications that help improve the fit to your face to limit the spread of COVID-19.
Also, following other public health recommendations such as physical distancing, avoiding large gatherings and washing your hands each add an additional layer of protection for not only those around you, but you as well.
References:
- Bundgaard G et al. Effectiveness of Adding a Mask Recommendation to Other Public Health Measures to Prevent SARS-CoV-2 Infection in Danish Mask Wearers: A Randomized Controlled Trial. Ann intern Med 2020. PMID: 33205991
- Brooks JT et al. Maximizing Fit for Cloth and Medical Procedure masks to Improve Performance and Reduce SARS-CoV-2 Transmission and exposure. MMWR 2021. [Accessed 02/27/2021] http://dx.doi.org/10.15585/mmwr.mm7007e1
- Clapp PW et al. Evaluation of Cloth Masks and Modified Procedure Masks as Personal Protective Equipment for the Public During the COVID-19 Pandemic. JAMA Intern Med 2020. PMID: 33300948
- Viola IM et al. Face Coverings, Aerosol dispersion and Mitigation of Virus Transmission Risk. EMB 2020.
