Infectious diseases are illnesses caused by harmful organisms (pathogens) that enters the body from the outside, such as viruses and bacteria. Non-infectious diseases are not caused by outside organisms, but by genetics, anatomical differences, getting older and the environment you live in. These diseases are not transmitted through interpersonal contact, insect bites or dietary consumption¹.

COVID-19 is an example that has shown us that our lives can all be significantly affected by infectious diseases in a number of ways. They can cause illness, which lead to discomfort, pain, and death. Such outbreaks of infectious diseases can spread rapidly and affect large numbers of people, leading to increased healthcare costs, strain on healthcare systems, and even have an impact on global economies. 

Infectious disease can be transmitted through various routes^1,2, including:

1. Direct Contact – shaking hands, sharing personal items, or sexual contact with an infected person.
2. Indirect Contact – contact with a contaminated surface or object.
3. Droplet – spread by way of respiratory droplets – sneezing or coughing. Example: influenza, common flu, and COVID-19.
4. Airborne – have the ability to be suspended in the air and be borne by air currents. Example: chickenpox and tuberculosis. 
5. Faecal-oral – transmitted through contaminated food, water, or objects that have been contaminated with faecal matter. Example: norovirus, rotavirus, salmonellosis, campylobacteriosis, hepatitis A and hand, foot, and mouth disease
6. Vector – viruses and parasites are spread by insect or animal bites such as dengue, Zika and malaria.

It is important to note that different infectious diseases can transmit through different routes, and some diseases can transmit through multiple routes. Understanding the routes of transmission is crucial to preventing and controlling the spread of infectious diseases.

Reference:

¹https://my.clevelandclinic.org/health/diseases/17724-infectious-diseases

²https://www.moh.gov.sg/docs/librariesprovider5/diseases-updates/infection-prevention-guidelines-for-schools-and-child-care-centre-(2019)_updated-as-of-2-mar-2023.pdf