How effective are face masks in preventing disease transmission?

Professor John Barford takes a look at the effectiveness of face masks in preventing disease transmission

The “Good”:

• Public awareness of the importance of their contribution to preventing contamination spread.
• Potential for Authorities to communicate with the general public.
• Assist persons with infections to reduce (not eliminate) the transfer of contamination to others though coughing and sneezing without any physical barrier.
• Assist persons to reduce (not eliminate) the transfer of contamination from others though coughing and sneezing without any physical barrier.

The “Bad:

• A surgical mask is NOT a particle filter. It works by exclusion from outside to inside or particle capture by entrapment from inside to outside. The thinness of these masks raises issues of their effectiveness in the latter.
• A surgical mask with become saturated with water in a relatively short period. This will enable particles to more easily transfer through the mask by having a direct route through the filter aided by the water.
• A surgical mask does not have a proper seal to the face (unlike a N95 respiratory mask). There are gaps at the side of the face. This enables air to be drawn into the respiratory system with flow through the mask being by-passed. Masks also tend to promote breathing through the mouth rather than through the nose (easier). Breathing through the nose introduces a natural body filter to the process.
• Surgical masks offer no protections for the wearer’s eyes and this may provide a route for infection transmission
• Is the purpose of the mask to prevent entry of droplets INTO the mask or prevent exit FROM the mask from people who have infections and are coughing and sneezing etc. It is not possible to do both.
• Surgical masks are inherently uncomfortable and wearers constantly readjust them and continuously touch the mask. Some aerosols can pose a contact hazard for infection. The accumulation of particles on the external surface of the respirator may be an exposure hazard from contact with the filter, including becoming a fomite for infectious agents. Users should be cautious and follow appropriate procedures to avoid self-inoculation from contact with these surfaces.
• Hand hygiene and infection control practices should be followed before and after touching the outside of the mask when it is used in the presence of infectious agents. Without this, infection transmission can be transferred to any touched surfaces etc. This can then be transferred to others.
• Masks are often removed by wearers to eat, answer mobile phones, smoke etc. Often the mask is left “dangling” or pushed down to the wearer’s lower neck during this process, which is also a contamination risk. Phones fingers become contaminated during this process.
• Sale of improperly designed masks, price gouging, recycling of old masks do not assist the containment attempt
• There is also a lack of suitable instructions by Authorities for proper procedures for applying the masks, removing the masks and mask disposal, as well as the lack of dedicated disposal bins

Proper procedure to put on and take off the masks

• “Donning and doffing” of masks – see https://www.youtube.com/watch?v=f6mjqbtonG4
• Disposed masks should be collected in a dedicated container and then incinerated.
• Some organisations provide instructions and dedicated disposal (e.g. HKUST), most don’t. MTR gives warning of the importance of hand hygiene.
• There is ample evidence for improper disposal (e.g. left fully exposed in normal garbage bins and simple discarded on the pavement. Clearly this provides ad contamination risk to the general public and the cleaners.
• A credible case could be made for masks potentially causing considerable problems if not properly used or disposed of.

Other issues that need to be considered

• How far can virus droplets carry?
• How long can a virus last in air without replication?
• How long can a virus last on a surface??
• Possibility of faecal transmission

There are varying views and no current consensus on these issues. It also depends a number of external factors (such as temperature, humidity, wind etc). Carry distance range have been reported to from feet to metres.

Survival in air range have been reported to from feet to seconds, minutes, hours, days. Surface survival range have been reported to from feet to seconds, minutes, hours, days.

Faecal transmission – early days. Just becoming a discussion issue

Final thoughts/recommendations

Most authorities recommend regular cleaning of hands as being the best measure people can undertake. This is an essential measure.

Other suggested associated preventative measures include:

• Wear a mask (don and off, and dispose of properly)
• Wear glasses (Medical Glasses if not a Prescription Glass wearer)
• Don’t touch your face
• Avoid indoor crowds
• Cook all food thoroughly
• Keep Calm and Don’t be afraid
• Report to a doctor if you feel unwell or have a fever

John Barford is a chemical engineer with expertise in applications of engineering principles to biological applications. He has worked with industrial applications involving bacteria, yeast, viruses, animal cells and insect cells. He has worked as an academic in Hong Kong, Australia, Singapore, Malaysia, Korea, Japan, Indonesia, China, Philippines and Thailand. He has consulted extensively. He retired from HKUST in 2017 and currently has his own consultancy company (Biotech Global Limited).