5. Prevention

The traditional model of infectious disease, known as the epidemiologic triad, consists of a pathogen, a susceptible host, and an environment that brings the host and agent together. The overall risk of infection further depends on the infectivity, pathogenicity and virulence of the invading pathogen. Effective preventive measures for infectious disease require assessment of all the above components and their interactions. In general, it is advisable to avoid going to places that are crowded with people, or with higher risk of infection such as clinics or hospitals. Good hand hygiene and proper wear of suitable face mask are other key preventive measures.

The WHO, as the central agency responsible for international public health, is leading the fight against the COVID-19 pandemic. You may find the WHO advice to public as below:

1. General advice to public      2. Myth buster

Respiratory hygiene


Hand hygiene


5.1a Respiratory hygiene

Respiratory hygiene is important to prevent droplet transmission. Individuals should cover mouth and nose when cough or sneeze, with tissue or flexed elbow. Face masks should be worn if there is any respiratory symptom. Further details regarding face masks is discussed here.

5.1a-1 Mask selection

5.1.1a-2 Surgical Masks  vs N95 Respirators

The surgical mask is a physical barrier that prevents contamination of the surroundings from the droplets expelled by the wearer. FDA approved surgical masks and respirators are certified for use in operations to maintain sterile surgical fields. Respirators are dedicated air-filtration devices aiming to remove harmful substances from all inhaled air. The notation “N95” signifies that they can filter at least 95% of small non-oil particles sized around 0.3 μm. Most respiratory viruses are spread by aerosol transmission. By definition, these particles are less than 5 μm in diameter and N95 masks are the appropriate choice for non-respirator filtration. The N95 respirators are further divided into surgical and non-surgical models, which are equally good in terms of protecting the wearers from droplets or aerosol transmission. However, only the surgical models certified for intraoperative uses are for sterile procedures.

N95 respirators need fitting test to ensure air-sealing. Facial hair compromises fit and should be removed. Surgical masks are loosely fit. Although the filter materials of surgical masks fulfill standards set by the American Society for Testing and Materials (ASTM) and achieve high level of filtration efficiency that gives protection against viral and bacterial infections, the actual protective effect would be compromised by up to 40% because of air-leak around the surgical mask. Therefore, N95 respirators should be worn by healthcare workers working in high risk environments.

For healthcare workers, surgical masks should be worn when performing sterile procedures, or as general protection against droplets infections. For public use, such as individuals with respiratory symptoms; people exposed in crowded and poorly ventilated places, such as taking public transports, students in school and individuals visiting clinics or hospitals, surgical masks are also recommended. N95 respirators are recommended to be worn by healthcare workers when working in high risk areas such as fever wards, inpatient or isolation rooms for patients with confirmed or suspected COVID-19. They should be removed and discarded when leaving the patient room or care area, followed by immediate hand hygiene.

5.1 n95 comparison

5.1.1a-3 Standard N95 Respirators vs Surgical N95 Masks

Surgical N95 mask is a subgroup of N95 respirator that also fulfils ASTM requirements and FDA-cleared as surgical mask. They are fluid resistant, while other standard N95 respirators may not be fluid resistant. Both types exhibit similar filtration efficiencies for small particles like viruses. For general protection of the wearer, standard or surgical N95 respirators will all suffice. The key difference is that the surgical N95 masks prevent the wearers from contaminating the surgical field or environment and are used when performing sterile procedures under the threat of air-borne transmission.

5.1a-4 Structures and mechanisms of filter materials

5.1 filter

  • Larger particles: captured by filter fibers directly when they impact or intercept the fibers
  • Smaller particles: constantly bombarded by air molecules, causing them to deviate from the air stream and come into contact with a fiber
  • Oppositely charged particles: attracted to charged fiber

* All particles that come into contact with a fiber will stay attached to the fiber firmly, thus filters can capture particles smaller than the pore size.

5.1a-5 How to Wear and Take-off Surgical Masks Properly?

The outer layer of masks is considered dirty while the inner layer is relatively clean. Hand hygiene should be performed before and after taking off the mask to avoid contamination of our hands. Mask should be fitted snugly over the face. Other points worth noting are: (1) the colored side of the mask should face outwards; (2) the metallic strip at the uppermost side molds to the bridge of the nose; (3) the mask covers the nose, mouth and chin; (4) the strings or elastic bands are positioned properly to keep the mask firmly in place; and (5) avoid touching or manipulating the mask once secured on face as frequent handling may reduce its protection. If you must do so, wash your hands before and after touching would help. 

Change masks timely. Replace the mask immediately if it is damaged, wetted or soiled. After taking off the mask, discard it into a lidded waste bin and perform hand hygiene immediately.

5.1b Hand hygiene

Hand hygiene is of utmost importance among all other preventive measures, applicable to general public as well as healthcare workers. Hand hygiene should be performed frequently, for example, after coughing or sneezing; when caring for the sick; before and after eating or preparing food; before and after touching eyes, nose and mouth, etc.

5.1b-1 Hand rubs

Alcohol Hand Rubbing vs Washing

  • Standard recommendations: alcohol-based handrubs or handwashing with soap and water for at least 20 seconds
  • When hands are visibly dirty: handwashing with soap and water
  • When hands are not visibly dirty: alcohol-based handrubs is a preferred method as it demonstrated better antiseptic efficacy. It is also easier to be used at the point of care and is minimally time-consuming, resulting in better compliance.

* Use of gloves do not constitute part of hand hygiene. Proper hand hygiene should still be performed before and after wearing gloves. It is not recommended to use alcohol-based handrubs whilst gloves are on hands.

Ethanol vs Isopropyl Alcohol


1. Van Doremalen N, Bushmaker T, Morris DH, et al. (2020): Aerosol and Surface Stability of SARS-CoV-2 as Compared with SARS-CoV-1. New England Journal of Medicine. In press.

2. He X, Reponen T, McKay R & Grinshpun SA (2014): How Does Breathing Frequency Affect the Performance of an N95 Filtering Facepiece Respirator and a Surgical Mask Against Surrogates of Viral Particles? Journal of Occupational and Environmental Hygiene 11: 178-185

3. He X, Reponen T, McKay RT & Grinshpun SA (2013): Effect of Particle Size on the Performance of an N95 Filtering Facepiece Respirator and a Surgical Mask at Various Breathing Conditions. Aerosol Science and Technology 47: 1180-1187.

4. N95 Respirators and Surgical Masks. Available at: https://blogs.cdc.gov/niosh-science-blog/2009/10/14/n95/. Accessed 17 Feb, 2020.

5. NIOSH Guide to the Selection and Use of Particulate Respirators. Available at: https://www.cdc.gov/niosh/docs/96-101/default.html. Accessed 6 Apr, 2020.

6. Respiratory Protection for Exposures to the H1N1 Influenza A Virus: Frequently Asked Question (FAQ) for Canadians in Workplace Settings. Available at: https://multimedia.3m.com/mws/media/604799O/ohes-h1n1-influenza-a-faq.pdf. Accessed 6 Apr, 2020.

7. Surgical N95 vs. Standard N95 – Which to Consider? Available at: https://multimedia.3m.com/mws/media/1794572O/surgical-n95-vs-standard-n95-which-to-consider.pdf. Accessed 6 Apr, 2020.

8. NIOSH-Approved Particulate Filtering Facepiece Respirators. Available at: https://www.cdc.gov/niosh/npptl/topics/respirators/disp_part/default.html. Accessed 17 Feb, 2020.

9. Peiris JSM, Guan Y, Yuen KY (2014): Severe acute respiratory syndrome. Nature Medicine 10: S88-S97.

10. Gaunt ER, Hardie A, Claas ECJ, et al. (2010): Epidemiology and Clinical Presentations of the Four Human Coronaviruses 229E, HKU1, NL63, and OC43 Detected over 3 Years Using a Novel Multiplex Real-Time PCR Method. Journal of Clinical Microbiology 48: 2940.

11. Matoba Y, Abiko C, Ikeda T, et al. (2015): Detection of the Human Coronavirus 229E, HKU1, NL63, and OC43 between 2010 and 2013 in Yamagata, Japan. Japanese Journal of Infectious Diseases 68:138-141.

5.2 Hand Hygiene Promotion Campaign by Canadian Specialist Hospital


5.3 Even baby knows distancing!

5.4 Social Distancing | India

5.5 Social Distancing | Thailand

5.6 Social Distancing | Malaysia

5.7 New Study Highlights Importance of Face Masks in Stopping Spread of Coronavirus

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1 The end of cordon sanitaire in Wuhan the role of non-pharmaceutical interventions

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5.10 Mandatory Masking |Strategic Use of Masks as an Element of a Non Pharmaceutical Measures Set for a Pandemic

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5.11 Mandatory Masking |Association Between Universal Masking in a Health Care System and SARS-CoV-2 Positivity Among Health Care Workers

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5.12 Mandatory Masking |Community Use Of Face Masks And COVID-19: Evidence From A Natural Experiment Of State Mandates In The US

Community Use Of Face Masks And COVID-19 Evidence From A Natural Experiment Of State Mandates In The US

5.13 Mandatory Masking |A Modelling Framework to Assess the Likely Effectiveness of Facemasks in Combination With ‘lock-down’ in Managing the Covid-19 Pandemic

A Modelling Framework to Assess the Likely Effectiveness of Facemasks in Combination With ‘lock-down’ in Managing the Covid-19 Pandemic

5.14 Mandatory Masking |Making Masks Mandatory May Save the Economy Too, Goldman Sachs Economist Says

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