Coronavirus Transmission and the Use of Masks
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Coronavirus transmission and the use of masks This article examines: 1) how long the coronavirus remains infectious on various surfaces; 2) what kind of mask should be used to stop this virus; and 3) whether or not a single-use mask can be reused. What kind of mask should be used and whether or not a single-use mask can be reused are important questions. Using the best mask available helps protect the wearer, and because there are never enough masks during a major epidemic, masks are going to be reused. The wearer therefore has to know how long the virus will survive on the mask and how the mask can be sterilized so that it is safe to use more than once. This article therefore examines what international scientists have written about these topics in 16 peer-reviewed papers published in major scientific journals before the current coronavirus outbreak occurred. In the analysis section below, each statement about this virus includes a reference to one of these 16 papers, and the complete texts of all papers are found at the accompanying hyperlinks. Each article also contains an extensive bibliography: Hundreds of the best scientific articles written on this topic have therefore been identified for readers who wish to examine the full complexity of these questions. Disclaimer: 1) This is not medical advice: It is a description of scientific literature from reputable international sources, but it is not guaranteed to be accurate. If you have a medical question, ask your doctor. 2) As novel coronavirus has just been isolated, the scientific papers cited in this article refer to other viruses that are thought to be similar, like SARS, MERS, and two avian respiratory viruses. It is not yet known how similar the novel coronavirus is to these other respiratory viruses. Questions: 1. How long does the coronavirus remain infectious on various surfaces? 2. Can a mask stop coronavirus? 3. Can a single-use mask be reused? Short answers: 1. The coronavirus remains infectious for different periods of time on different surfaces. a) Hard surfaces like stainless steel may remain infectious for up to 6 days, but typically become less infectious after 24-48 hours. b) Porous surfaces like clothing and masks typically remain infectious for 8-12 hours. 2. Can a mask prevent the inhalation of coronavirus? a) Surgical masks are designed to prevent bacteria and other particles from contaminating a sterile field, as when a surgeon is performing an operation. Surgical masks are not designed to prevent the wearer from inhaling viruses: 20-85% of viruses 0.1 microns in diameter can penetrate these masks. They are therefore not the best way to prevent the inhalation of viruses. However, if the wearer already has already contracted a virus, a surgical mask can help prevent the transmission of the virus to others. b) N95 respirators are designed to reduce the wearer’s exposure to airborne particles like viruses. When worn properly, only 5% of particles 0.1 microns in size can penetrate these masks. The Centers for Disease Control recommend the use of N95 respirators for SARS and flu pandemics. c) P100 respirators are also designed to reduce the wearer’s exposure to airborne particles like viruses. They are also resistant to oil, and they tend to be more durable than N95 respirators, so P100 respirators typically last longer. P100 respirators also do a better job of stopping airborne viruses. When worn properly, only 0.1% of particles 0.1 microns in size can penetrate these masks. P100 respirators are the best, and they are much more expensive than N95 respirators. 3. Can a single-use mask be reused? a) Yes, single use N95 and P100 respirators can be reused if they have not been damaged, have not been heavily contaminated, and have been properly sterilized. Manufacturers sometimes make claims regarding how long a respirator will last: An N95 mask might be expected to last for 8 hours, while a P100 mask might be expected to last for 40 hours. The Centers for Disease Control say that disposable respirators might “remain functional for weeks to months” if proper precautions have been taken. b) As noted in 1(b) above, coronavirus can remain infectious on soft surfaces like masks for many hours, so the wearer must be very careful when removing the mask: Touching an infected portion of the mask could transmit the virus. The wearer must also sterilize both sides of the mask before reuse. UV light can sterilize a mask without damaging it; other sterilization methods are effective as well. Analysis: 1. Viruses remain infectious for different periods of time on different surfaces. a) On common surface materials, human coronavirus 229E remains infectious for several days. It survives for at least 5 days on Teflon, PVC, ceramic tiles, 2 glass, and stainless steel; it survives for at least 3 days on silicon rubber. (Warnes, “Human Coronavirus 229E Remains Infectious,” 2.) b) On N95 respirators, the influenza virus H1N1 remains infectious for 6 days, although other studies concluded that this virus became less infectious after 24-48 hours. (Coulliette, “Persistence of the 2009 Pandemic Influenza,” 5.) c) On nonporous surfaces like steel, latex, ceramic tiles, and plastic, two avian respiratory viruses survived for 24-48 hours. (Tiwari, “Survival of Two Avian Respiratory Viruses,” 286.) d) On porous surfaces like cotton and polyester fabrics, wood, paper, and tissue, two avian respiratory viruses survived for 8-12 hours. The viruses survived on some surfaces like bird feathers for up to 6 days, but they did not survive for 9 days. (Tiwari, “Survival of Two Avian Respiratory Viruses,” 286.) e) After drying, human coronaviruses survive for only a few hours. (Chan, “The Effects of Temperature,” 1.) f) At a higher temperature and humidity (38°C and relative humidity above 95%) SARS virus viability rapidly decreased. The virus is killed by heat at 56°C for 15 minutes. (Chan, “The Effects of Temperature,” 1, 3.) g) In an air-conditioned environment, the SARS virus can survive at least two weeks. During the SARS epidemic, in Singapore and Hong Kong the transmission of SARS largely occurred in well air-conditioned environments like hospitals and hotels. But during the SARS outbreak in Guangzhou Province, the windows in patient rooms were kept open and the rooms were well ventilated; this is thought to have reduced virus survival. (Chan, “The Effects of Temperature,” 1, 3.) 2. Can a mask prevent the inhalation of coronavirus? a) Surgical masks are primarily designed to protect the environment from the wearer. Surgical masks are not designed to prevent the wearer from inhaling viruses: 20-85% of viruses from 0.1 to 0.8 microns in diameter can penetrate these masks. (Bałazy, “Do N95 Respirators Provide 95% Protection,” 51.) b) Surgical masks are intended to prevent bacteria and other particles exhaled by the wearer from contaminating a sterile field like a patient’s wound. Because there are no requirements for small particle filtration efficiency or fit, surgical masks should not be expected to provide respiratory protection. The infection rate of those who wore surgical masks was about twice as high as for those who wore N95 masks. Surgical masks should not be used to protect people from viruses like H1N1. (Janssen, “The Use of Respirators,” 1, 4, 5.) 3 c) Surgical masks are not recommended to protect the wearer from the inhalation of airborne viruses. (Harnish et al., “Challenge of N95 Filtering Facepiece Respirators,” 2.) d) The bare influenza virus is approximately 0.1 micron, but the influenza virus expelled from humans via respiratory secretions is typically much larger at 0.8 micron. (Harnish et al., “Challenge of N95 Filtering Facepiece Respirators,” 5.) e) N95 respirators, when worn properly, effectively filter over 95% of particles between 0.1 and 0.3 microns. (Coulliette, “Persistence of the 2009 Pandemic Influenza,” 1.) f) N95 respirators are designed to reduce the wearer’s exposure to airborne particles like viruses. N95 respirators should be used to protect people from viruses like H1N1. (Janssen, “The Use of Respirators,” 1, 4, 5.) g) N95 respirators were penetrated by approximately 5% of 0.1 micron particles at a constant air flow rate of 85 liters per minute. (Eshbaugh, “N95 and P100 Respirator Filter Efficiency,” 58, figure 2.) h) N95 respirators that fit properly reduce toxic inhalation exposure by a factor of 10 or more. (Harnish et al., “Challenge of N95 Filtering Facepiece Respirators,” 7.) i) P100 respirators are also designed to reduce the wearer’s exposure to airborne particles like viruses. P100 respirators also do a better job of stopping airborne viruses. When worn properly, fewer than 0.1% of 0.1 micron particles can penetrate these masks at a constant air flow rate of 85 liters per minute. (Eshbaugh, “N95 and P100 Respirator Filter Efficiency,” 58, figure 2.) 3. Can a single-use mask be reused? a) Disposable respirators can be used by the same healthcare worker to protect against tuberculosis as long as the functional and structural integrity of the respirator is maintained. (Fisher, “Commentary Considerations for Recommending Extended Use,” 14.) b) The Centers for Disease Control published guidance that supported the extended use and limited reuse of respirators for public health emergencies like SARS and H1N1 flu pandemics. (Fisher, “Commentary Considerations for Recommending Extended Use,” 16.) c) N95 respirator filter efficiency fell below their original 95% standard after the respirators were used for 9 to 13 weeks. (Fisher, “Commentary Considerations for Recommending Extended Use,” 6.) d) Disposable respirators can be reused for weeks to months. (Fisher, “Commentary Considerations for Recommending Extended Use,” 8.) 4 e) Decontamination: Viruses may remain on a respirator after use and pose a risk of virus transfer to the wearer.