We have all heard about the serious outbreak of the Coronavirus in and around Wuhan in China. It would appear that a virus strain has mutated and gained the ability to move from its animal host (possibly bats or snakes) to infect humans. It’s potential to spread is clear and cases of infection are rapidly increasing. This story is accompanied in the media with pictures of people wearing face masks as protection. So we asked, how effective are surgical masks or is there a better personal “bio-security” approach?
To answer this, you have to consider how respiratory viruses (such as Corona, Influenza, Rhinovirus and Adenovirus) are spread. There are two main mechanisms for a virus to spread from an infected person to their unwilling victim. The first is pretty direct and involves release of airborne virus-containing droplets from the upper respiratory tract, most likely during a cough or a sneeze. A cough travels at about 50 mph and can expel almost 3,000 droplets, whereas a sneeze can double that speed and expel an astounding 100,000 droplets1. Droplets that are less than 5µm in diameter hang around in the air for extended periods and when breathed in cause infection. The number of viruses needed to infect is surprisingly low. The previous SARS (Severe Acute Respiratory Syndrome) virus was found to be able to cause infection in a mouse when they were dosed with less than 10 viruses2. The larger drops will rapidly fall out of the air and land on surfaces around the infected person. These are unlikely to be breathed in unless people are in very close proximity, such as together in a crowded train.
The second route of transmission is via the droplets that end up infecting surfaces such as tables, chairs, door handles etc with viruses. which are transferred to people’s hands when touched. It makes sense that when the number of infected people is relatively small compared to the general population, in public places where hundreds touch the same things each day, you are much more likely to come into contact with a virus the infected person left behind than meet them face to face. Once a virus-containing droplet is on your hand it is highly likely to end up in your mouth, nose or eye. Try not touching your face for 30 minutes and see how difficult it is!
So if those are the transmission routes, how effective are simple fabric-based surgical masks? Well they won’t stop you inhaling the small air-borne droplets which will go straight through the mask. But they may stop many of the larger airborne particles that you may be exposed to on a train, so they have some benefit to the uninfected wearer if you are unlucky enough to meet an infected person. But then your mask is infected itself, and needs to be disposed of carefully. But to completely stop the small particles, you would need a properly fitting mask more akin to a gas respirator which would significantly impede your breathing, and may startle your fellow travellers!
The key benefit of the surgical mask is the other way around, they significantly decrease the number of larger droplets released by infected people, acting as a sort of “splatter guard” and hence decrease the number of droplets on surfaces. This is well recognised in many Asian countries where it is seen as highly anti-social to have a cold and not wear one.
Masks are much more effective when paired with regular hand washing or use of alcohol-based hand sanitisers, which kill viruses and significantly decrease the chance of transferring live virus to your face. In a recent study, the University of Michigan found that use of simple face masks alongside hand sanitisers decreased flu infections by an impressive 50% to 75% compared to no control measures. There was no statistically significant decrease in infections with the face mask alone3.
A decrease of this size in transmission rates for such a simple, easily available, cheap and low burden method is very much worth having. At the start of an outbreak that has the potential to change from an epidemic (local) to a pandemic (worldwide) it is critical to decrease the rate of spread to allow government-based control measures (quarantine, hospital treatment and vaccination etc.) time to catch up.
To a large extent, the sanitiser or washing your hands regularly, is your main weapon against infection, and the mask is mainly to stop you infecting your friends should you unfortunately meet up with the virus.
 American Lung Association
 J Virol 90 (1), 57-67
 Facemasks, Hand Hygiene, and Influenza among Young Adults: A Randomized Intervention Trial
Senior Healthcare Innovation Consultant
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