Pathogens such as viruses, bacteria, fungi and parasites are responsible for many infectious diseases.
One way to categorise infectious diseases is by how they spread.
These diseases can transmit directly or indirectly from the reservoir of the pathogen (which can be an organism or the environment) to humans.
Common transmission routes include:
- Respiratory droplets
- Aerosols or airborne
- Contaminated surfaces (fomites)
- Contaminated food and water
During the Covid-19 pandemic, we discovered how the disease spreads through very fine respiratory droplets and aerosol particles, particularly by coughing and sneezing.
Many other viruses, such as the influenza virus, rhinovirus and respiratory syncytial virus (RSV), also spread this way.
A respiratory droplet or aerosol particle is a particle consisting mostly of water, as well as various cells, physiological electrolytes, and possibly, infectious agents.
Respiratory droplets have a diameter greater than 5μm, while aerosol particles are less than 5μm in diameter (for reference, the diameter of a strand of Asian hair is 80-120μm).
Respiratory droplets tend to rapidly fall to the ground due to gravity, hence limiting spread to within a short distance of the infected person.
However, the smaller size of aerosol particles enables them to stay suspended in the air for minutes to hours.
These droplets and particles are produced naturally when we sneeze, cough, talk, sing or breathe.
They may also form artificially during medical procedures such as cardiopulmonary resuscitation (CPR), intubation, bronchoscopy and surgery.
Transmission occurs when the droplets reach another person’s vulnerable mucosal surfaces (i.e. the eyes, nose or mouth).
Sneezes and coughs are the main routes of transmission.
A sneeze can produce up to 40,000 droplets, while coughing can produce up to 3,000 droplets.
This is about the same as talking for five minutes!
Spread and survival
The content of respiratory droplets and aerosol particles depends on their origin in the respiratory tract.
The formation and distribution of the droplets or particles are determined by factors such as the velocity of exhaled air, viscosity, content and quantity of fluid, and flow path (i.e. through the nose, mouth or both).
The direction and strength of airflows, temperature, humidity and other environmental factors also play important roles.
Indirect transmission may occur via contact with contaminated objects or surfaces (fomites).
Viruses generally survive longer on hard surfaces than porous surfaces.
Moreover, viruses protected by a lipid layer (e.g. influenza virus, RSV and coronavirus) are more stable under dry conditions, whereas viruses without a protective layer (e.g. rhinovirus, enterovirus and adenovirus) are more stable under humid conditions.
Viruses are also more stable at low air temperatures.
Here are the ways to prevent transmitting and being infected by virus-filled droplets or particles:
Cover your mouth with a tissue or your elbow when coughing or sneezing.
Then dispose of the tissue properly and wash your hands immediately.
Stay home if possible, but wear a face mask if you need to go out.
This depends on the scale of the outbreak.
If it is an epidemic, you may need to avoid crowded places, keep 1-2m away from others in public spaces and avoid physical greetings (e.g. handshaking or hugs).
Staying at home is the simplest way of practising this!
Wash your hands with soap frequently and thoroughly, especially before and after preparing or eating food, and after using the toilet.
Alcohol-based hand sanitisers can also be used.
Avoid touching your eyes, nose and mouth as much as you can – you might find yourself doing this unconsciously, so be aware of your own movements.
Sanitise commonly used objects/surfaces.
Some infectious diseases can be prevented with vaccination.
For example, it is recommended to take flu vaccines annually as there are different flu viruses circulating for every flu season and immunisation declines over time.
Those eligible for the free Covid-19 vaccines the government is providing should ensure that they register and get vaccinated as soon as possible in order to protect those who aren't, including babies and children.
The Covid-19 health crisis has been a very solemn experience for all of us.
Millions of deaths have been recorded and over 160 million people have been infected worldwide to date.
As we move forward, we need to continue practising the new norms, like frequent handwashing and cough/sneeze etiquette, to prevent future outbreaks, as well as the spread of other illnesses.
Datuk Dr Zulkifli Ismail is a consultant paediatrician and paediatric cardiologist. This article is courtesy of the Malaysian Paediatric Association’s Positive Parenting programme in collaboration with expert partners. For further information, please email firstname.lastname@example.org. The information provided is for educational and communication purposes only and it should not be construed as personal medical advice. Information published in this article is not intended to replace, supplant or augment a consultation with a health professional regarding the reader’s own medical care. The Star does not give any warranty on accuracy, completeness, functionality, usefulness or other assurances as to the content appearing in this column. The Star disclaims all responsibility for any losses, damage to property or personal injury suffered directly or indirectly from reliance on such information.