Infection prevention by wearing masks Joint statement of DGHM and GfV of 4 November 2020

Preventing infection by wearing masks
Joint statement by DGHM and GfV from November 4, 2020 (updated on November 20, 2020)

The SARS-CoV-2 pandemic has created an unusual situation in which many people are dealing intensively with infectious disease issues in a rapidly developing scientific field. Filtering the right information from the large amount of information is difficult and only possible with specialist knowledge. Accordingly, there is a great potential for misinformation and untruths to spread from a wide variety of sources. Unfortunately, many untruths from such sources can also be found on the Internet and in other publications.
The DGHM and the GfV have therefore compiled information here on the current state of scientific knowledge on infection prevention (in particular the wearing of masks). Many aspects of the pandemic are still dynamic and much has not been conclusively clarified. The information here reflects the current state of scientific knowledge (October 2020).
The aim of this information is to counteract the spread of nonsensical or dangerous misinformation in this area. SARS-CoV-2 is an easily transmissible virus that can cause severe illness and death in a significant proportion of people. There is no indication that the virus will soon disappear on its own. It is clear that the virus is currently spreading again in Germany. It is scientifically undisputed that human behavior influences the spread of viruses. Against this background, the current scientific literature on wearing masks is presented here in a form that should also be accessible to the interested layperson.

Why is wearing masks a useful measure to prevent the spread of SARS-CoV-2?

1. external protection: prevention of the escape of infectious droplets

According to the WHO and CDC, SARS-CoV-2 is mainly transmitted via droplets and (less efficiently) via aerosols (droplets that remain in the air for a particularly long time due to their small size)1,2 that are released by asymptomatic or symptomatic infected persons. The virus-containing droplets can be effectively intercepted to a certain extent by a mouth/nose protection (MNS) where they are released (mouth/nose), both when speaking and coughing8,20,3. If the droplets get into the material of an MNS, they cannot easily escape again. Surgical face masks (these are the disposable masks that many people wear; see also the glossary at the end of the text) have a filter membrane in the middle that retains droplet-sized particles. On the other hand, the membranes are hydrophobic (water-repellent) and also use this property to retain droplets regardless of their size. Any virus-containing, infectious droplets with the viruses can then not pass through to the outside of an MNS and therefore no longer infect anyone4. The sometimes misleading opinion that the pore size is too large for the tiny viruses is wrong, as the viruses are excreted in respiratory droplets and not as individual free virus particles.
A certain problem is that masks do not always fit perfectly close to the face, as in these cases unfiltered air can escape through the exhaled airflow past the mask material (i.e. between the mask and the face). The better a mask fits, the lower the risk of droplets potentially containing viruses escaping 21 However, depending on the fit, it is also possible that if two people meet head-on, they will still not come into contact with droplets as the exhalation flow is directed to the side and back. Visors or plastic masks with a large opening do not have a tight fit: they only provide protection against droplets that fly directly against the barrier.
Accordingly, it helps to prevent infections if people wearing masks meet face to face (and not sideways). An additional greater distance between people also leads to a further reduction in risk. MNS and social distancing therefore support each other.

2. self-protection: preventing the entry of infectious droplets.

Surgical mouth and nose protection (MNS) also serves to protect the person wearing the MNS. This was tested last year, for example, in a study of medical personnel who wore MNS and were involved in the treatment of patients with viral respiratory infections (SARS-CoV-2 did not yet exist at the time of the study). In about 10% of the study participants (i.e. the medical staff in this study), the MNS were contaminated with respiratory viruses on the outside after about six hours of work5. On the one hand, this shows that the MNS can retain viruses and protect the wearer. On the other hand, it means that the MNS must be carefully removed so that the wearer does not become infected when taking it off. The wearing time should also be limited5. In a study with hospital employees in 2015, it was shown that wearing an MNS reduced the transmission of respiratory viruses to employees, although patients did not wear masks, i.e. employees were not protected by the fact that patients did not excrete droplets, but only by their own MNS6.
In a further analysis, all available controlled (i.e. scientifically high-quality) studies were summarized that investigated transmissions in the medical field or also in household contacts with MNS or particle-filtering masks (FFP2 mask, NIOSH 95)7,22. This showed that wearing masks had a protective effect against respiratory infections in the population. Good hand hygiene also had a protective effect. In these studies, the infection-preventive effect of particle-filtering masks was either as high as or even higher than the effect of surgical masks7. A summary analysis (which also included non-randomized studies that are less conclusive due to their design) of the care of patients with the dangerous coronaviruses (SARS-CoV-1, MERS and SARS-CoV-2) showed the effectiveness of particle-filtering masks8,9. Wearing surgical masks has also already reduced the transmission of infections. In hospitals, various methods of infection prevention are generally used simultaneously; a study that only uses one measure (e.g. only wearing masks without hand hygiene) would not be ethically justifiable. The fact that such "bundles of measures", which include the general wearing of masks, can minimize the transmission of SARS-CoV-2 in hospitals to employees was shown in a recently published study10.

3. population protection: prevention of transmission chains

There are now also comparisons of SARS-CoV-2 new infection rates in the overall population between countries that had enacted a mask-wearing ban for the entire population early on and countries that did not. In Hong Kong, for example, 95% of people wore masks and there were significantly fewer cases in the first wave of the pandemic than in comparable countries, such as Spain, Germany or Switzerland, which did not have a mask ban at the time11. For air travel, the risk of transmission seems to be significantly reduced by mandatory mask-wearing on board the aircraft12. The authors of an analysis of pupils with SARS-CoV-2 contacts from Baden- Württemberg speculate that wearing masks could also effectively reduce the transmission of SARS-CoV-2 in schools13.

Can healthy people or people with lung disease get too little "air" under surgical masks?

A group of healthy doctors and a group of doctors with chronic obstructive pulmonary disease (COPD) performed an exercise test (6-minute walk test) while wearing a surgical MNS. In both groups, there was no increase in carbon dioxide in the blood when wearing the masks under stress, but there was a slight drop in oxygen saturation in the doctors with COPD. The small drop in oxygen saturation measured was consistent with the expected drop for this level of exertion. The masks did not appear to have any additional influence on this. Accordingly, when wearing surgical masks under time-limited exertion, no higher degree of impairment of oxygenation or carbon dioxide exhalation is expected, so that wearing them is harmless. Respiratory distress under stress may be subjective or may be caused by different temperature sensations14. The extent to which a very long duration of wearing surgical masks has an effect on the cardiovascular system remains to be investigated15. In young healthy men doing sports, there were no significant changes in oxygen or CO2 in the blood when wearing a surgical mask, even at 100% exercise16. Accordingly, the authors conclude that mask-wearing in healthy individuals is harmless with regard to blood gas supply, even during pronounced activity. However, they point out that FFP2 masks could possibly lead to CO2 retention in people with pre-existing lung conditions, which was also observed in another small study15. The conclusions of a literature review led to the demand to consider patient groups in a more differentiated way and to adapt the preventive use of MNS or FFP2 masks more specifically to the patient groups and situations17.

How great is the willingness among the population to wear masks?

So far, studies on this have been conducted in Italy and Germany.18,19 In both studies, there is initially a great willingness among the population to wear a mask in public areas where the wearing of masks is compulsory. However, there are differences in the correct wearing of the different types of masks. While fabric mouth-nose-coverings (MNB) are predominantly worn correctly, there are often deficits in the wearing of medical masks - surgical mouth-nose-coverings and FFP respirators with and without valves (see glossary below). The medical masks are often not correctly modelled to the facial contours and the nose, so that both the possible protection of the mask wearer and the protection of contact persons can be reduced or even cancelled. In addition, the risk of infection among laypersons was sometimes increased by MNB application errors: on the one hand, through (indirect) contact of the possibly contaminated outer surface5 with the oral or nasal mucosa, and on the other hand, through disregard of distance requirements due to an erroneous perception of being protected when wearing the mask. Therefore, if medical masks are worn by the general public, the wearers should familiarise themselves well with these medical devices and only put on, wear, remove and dispose of the masks according to the manufacturer's instructions or the recommendations on the relevant websites (see, for example, the websites on infection control of the Federal Centre for Health Education).

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Sources

[1] https://www.who.int/publications/i/item/modes-of-transmission-of-virus-c.... 2020.
[2] https://www.cdc.gov/coronavirus/2019-ncov/more/scientific-brief-sars-cov.... 07.10.2020.
[3] Asadi S, Cappa CD, Barreda S, Wexler AS, Bouvier NM, Ristenpart WD. Efficacy of masks and face coverings in controlling outward aerosol particle emission from expiratory activities. Scientific reports 2020, 10(1): 15665.
[4] Prather KA, Wang CC, Schooley RT. Reducing transmission of SARS-CoV-2. Science 2020, 368(6498): 1422-1424. Perspective article, citing publications of relevance to this topic.
[5] Chughtai AA, Stelzer-Braid S, Rawlinson W, Pontivivo G, Wang Q, Pan Y, et al. Contamination by respiratory viruses on outer surface of medical masks used by hospital healthcare workers. BMC infectious diseases 2019, 19(1): 491.
[6] MacIntyre CR, Seale H, Dung TC, Hien NT, Nga PT, Chughtai AA, et al. A cluster randomized trial of cloth masks compared with medical masks in healthcare workers. BMJ open 2015, 5(4): e006577.
[7] MacIntyre CR, Chughtai AA. A rapid systematic review of the efficacy of face masks and respirators against coronaviruses and other respiratory transmissible viruses for the community, healthcare workers and sick patients. International journal of nursing studies 2020, 108: 103629.
[8] Chu DK, Akl EA, Duda S, Solo K, Yaacoub S, Schunemann HJ, et al. Physical distancing, face masks, and eye protection to prevent person-to-person transmission of SARS-CoV-2 and COVID-19: a systematic review and meta-analysis. Lancet 2020, 395(10242): 1973-1987.
[9] MacIntyre CR, Wang Q. Physical distancing, face masks, and eye protection for prevention of COVID-19. Lancet 2020, 395(10242): 1950-1951.
[10] Temkin E, Healthcare Worker C-SWG. Extremely Low Prevalence of Asymptomatic COVID-19 Among Healthcare Workers Caring for COVID-19 Patients in Israeli Hospitals: a Cross-sectional Study. Clinical microbiology and infection : the official publication of the European Society of Clinical Microbiology and Infectious Diseases 2020.
[11] Cheng VC, Wong SC, Chuang VW, So SY, Chen JH, Sridhar S, et al. The role of community-wide wearing of face mask for control of coronavirus disease 2019 (COVID-19) epidemic due to SARS-CoV-2. The Journal of infection 2020, 81(1): 107-114.
[12] Freedman DO, Wilder-Smith A. In-flight transmission of SARS-CoV-2: a review of the attack rates and available data on the efficacy of face masks. Journal of travel medicine 2020.
[13] Ehrhardt J, Ekinci A, Krehl H, Meincke M, Finci I, Klein J, et al. Transmission of SARS-CoV-2 in children aged 0 to 19 years in childcare facilities and schools after their reopening in May 2020, Baden-Wurttemberg, Germany. Euro surveillance : bulletin Europeen sur les maladies transmissibles = European communicable disease bulletin 2020, 25(36).
[14] Samannan R, Holt G, Calderon-Candelario R, Mirsaeidi M, Campos M. Effect of Face Masks on Gas Exchange in Healthy Persons and Patients with COPD. Annals of the American Thoracic Society 2020.
[15] https://link.springer.com/article/10.1007/s00392-020-01736-4.
[16] Epstein D, Korytny A, Isenberg Y, Marcusohn E, Zukermann R, Bishop B, et al. Return to training in the COVID-19 era: The physiological effects of face masks during exercise. Scandinavian journal of medicine & science in sports 2020.
[17] Matuschek C, Moll F, Fangerau H, Fischer JC, Zanker K, van Griensven M, et al. Face masks: benefits and risks during the COVID-19 crisis. European journal of medical research 2020, 25(1): 32.
[18] Cumbo E, Scardina GA. Management and use of filter masks in the "none-medical" population during the Covid-19 period. Safety science 2021, 133: 104997.
[19] Otchwemah R, Mattner F, Neuwirth M. Einsatz von Community-Masken in der Bevölkerung: Praxis und Anwendungsfehler während der SARS-CoV-2 Pandemie in Deutschland / Usage of face coverings in public settings: Practice and application errors during the SARS-CoV-2 pandemic in Germany. Healthcare 2020: accepted 29.29.2020.
[20] Leung, N.H.L., Chu, D.K.W., Shiu, E.Y.C. et al. Respiratory virus shedding in exhaled breath and efficacy of face masks. Nat Med26, 676-680 (2020)
[21] Verma S, Dhanak M, Frankenfield J. Visualizing droplet dispersal for face shields and masks with exhalation valves. Phys Fluids (1994). 2020 Sep 1;32(9)
[22] Radonovich LJ Jr, Simberkoff MS, Bessesen MT, Brown AC, Cummings DAT, Gaydos CA, Los JG, Krosche AE, Gibert CL, Gorse GJ, Nyquist AC, Reich NG, Rodriguez-Barradas MC, Price CS, Perl TM; ResPECT investigators. N95 Respirators vs Medical Masks for Preventing Influenza Among Health Care Personnel: A Randomized Clinical Trial. JAMA. 2019 Sep 3;322(9):824-833.

Glossary to differentiate between the different types of "masks

1) Everyday masks or mouth-nose coverings (MNB) are usually made of textile and washable, they are not subject to any standardized requirements for filtering capacity or adaptation to the face. Nevertheless, these face masks also capture a large proportion of the droplets emitted by the wearer, significantly reducing environmental contamination. The effectiveness of disposable masks, which are similar to medical masks but have no certification, is equated with textile face masks.
2) Medical face masks are usually referred to as MNS (mouth/nose protection). According to DIN EN 14683:2019-10, they are tested primarily in terms of their bacterial filter performance in % (barrier against bacterial penetration), their pressure difference (indicator of the "breathing resistance" of the mask) and their microbiological purity and are classified into the three types I, II and IIR. The filter performance of medical face masks is tested using a load suspension of Staphylococcus aureus with an average particle size of 3.0 μm ± 0.3 μm. Type I masks must have a filter performance of ≥ 95%, type II masks of ≥ 98%. The requirements for medical purity are the same for the three mask types. In addition to type II, type IIR masks are characterized by a special resistance to the penetration of liquids and may therefore have a higher pressure difference (breathing resistance). The certification and decades of experience in operating prove a good protective effect of the environment against pathogens from the wearer's nasopharynx (external protection). How effective these MNS are as self-protection for the wearer only came into focus during the SARS-CoV-2 pandemic and cannot yet be conclusively assessed. However, there is much to suggest that correctly worn face masks not only protect the environment, but also the wearer (see also above).
3) Filtering half masks for protection against particles (FFP masks = Filtering Face Piece) come from occupational safety. The FFP masks used in medicine are also considered respiratory protection devices and are tested in accordance with DIN EN 149 with the aim of "self-protection of the wearer". They are divided into the classes FFP1, FFP2 and FFP3 according to their filter performance and their maximum inward leakage. The total inward leakage is made up of the face leakage, the filter passage and the valve slip (if an exhalation valve is present). The filter performance is tested based on the permeability of the filter medium for two test aerosols with a median particle diameter of 0.6 μm, whereby the permeability of the filter medium decreases from class FFP1 to FFP3 and thus the filter performance increases. The breathing resistance of the masks also increases from class FFP1 to 3. The total leakage of FFP1 masks must not exceed 25% and the filter performance must be at least 80% of the particles in the air. FFP2 masks have a maximum total leakage of 11% and a filter performance of at least 94%. FFP3 masks have a maximum total leakage of 5% and a filter performance of at least 99% and therefore offer the greatest protection. FFP masks were very often fitted with an exhalation valve before the pandemic; these masks do not protect the environment from the wearer's pathogens. There is evidence that asymptomatic staff infected with SARS-CoV-2 wearing an FFP mask with an exhalation valve have actually infected patients and colleagues. Since around summer 2020, numerous masks tested according to the Chinese KN95 standard have been available worldwide as an alternative to FFP masks. As things stand, these can generally be regarded as equivalent. The decisive factor for protective masks (whether FFP2 or KN95) is a good fit on the face. This depends on the shape and adaptability of the mask material and the quality of the nose clip and elastic bands and can only be assessed by visual inspection and ultimately testing by each wearer. An FFP2 or KN95 mask that is well-fitted to the face is sucked onto the face during inspiration so that there is hardly any inward leakage. However, FFP and KN95 masks often leak during expiration. It is sometimes assumed that FFP2 and KN95 masks offer better protection for the environment than medical MNS. As FFP and KN95 masks have not been tested for external protection, this remains speculative. The industry would like to see masks that meet both the occupational safety requirements of the FFP2 standards and the third-party protection/patient protection requirements of the MNS standards.

Visors and Mouth/Nose Visors

There is no standardisation or testing of sights or mouth/nose sights to date.

Visors only reject larger droplets from the out-breathing air and direct the flow of breath towards the sides and the ground, resulting in less external protection compared to an MNB or MNS. Self-protection is also reduced because the air coming in over the side edges is not filtered. However, they provide additional protection for the wearer against infectious droplets hitting the conjunctiva of the eye, through which infection can occur. In conjunction with MNB, MNS or FFP mask, a visor increases self-protection. Compared to MNB, MNS or FFP mask, simply wearing a visor is less effective as both self-protection and external protection.

Mouth/nose visors only protect the wearer from very large droplets without shielding the wearer's conjunctiva. Smaller droplets can gain unfiltered access to the wearer's mucous membranes. Furthermore, the insulated mouth/nose visors intercept significantly fewer droplets from the wearers themselves, so that the external protection is also lower compared to MNB, MNS or FFP masks. A protective effect of the mouth/nose visors has not been proven so far and the aerodynamic considerations of the air streams suggest only a very low or complete ineffectiveness. There is also no protective effect for the eyes.