Infectious Disease Outbreaks and Their Transmission

Infectious Disease Outbreaks (IDOs) occur when there are more cases of an infectious disease than is normally expected in a given community, geographical area or season. Outbreaks that occur in a restricted geographical area are called epidemics.

Outbreaks that spread over multiple countries or continents, usually affecting large numbers of people, are referred to as global epidemics or pandemics.

Epidemics and pandemics can be caused by endemic diseases (diseases that have a constant presence within a given population or area), such as dengue fever and malaria, or by newly emerging diseases, such as COVID-19, SARS and MERS-CoV.

Infectious diseases are caused by pathogenic microorganisms or microbes, such as bacteria, viruses, parasites or fungi, that spread from one person to another via two main modes of transmission:

1. Direct transmission – Infectious diseases are transmitted person-person through:

Direct contact: The infection is transmitted through physical contact between two people. Ebola Virus Disease (EVD), for example, is transmitted through direct contact with the blood, secretions and bodily fluids of infected people, as well as contact with infected dead bodies.

Droplet spread: Infectious agents are spread through spray produced by sneezing or coughing. COVID-19 and other coronaviruses are mainly spread by respiratory droplets.

2. Indirect transmission – Infectious diseases are transmitted through:

Vehicles: Objects (also referred to as formites) such as doorknobs, wash basins, bank notes, and fabrics such as towels or bed sheets, as well as food and water. Cholera, for example, can be spread by water or food and can infect a person who eats or drinks the infected water/food. Coronaviruses can be spread via surfaces/objects that have been touched by or are near to an infected person and can infect a person who touches the infected surface/object.

Vectors: Animals that carry an infectious agent such as mosquitos, fleas, ticks and sand flies. Malaria, for example, is transmitted among people via the bite of a mosquito.

Airborne: Infectious agents are suspended in the air for short or long periods of time. Measles, for example, can be transmitted to a child in a room for up to two hours after another child with measles has left the room, as the virus can remain suspended in the air.

Some infectious diseases have multiple modes of transmission. Coronaviruses, for example, are primarily transmitted directly (via droplet transmission person-person) but can also transmit indirectly (via surfaces/objects touched by or near an infected person vehicle-person).

This course focuses primarily on Protecting Children during COVID-19 and other IDOs where the disease is spread primarily by person-person transmission.