What occurs when disease affects a greater number of people than is usual for the locality or the spreads to areas not usually associated with disease

Then we are dealing with a pandemic and should trigger a coordinated response of local and central authorities. If a disease and cases are limited to one region in a country and are a common event, then it is said that's an endemic illness. But when there are registered outbreaks of that desease in new areas and it spreads to many other regions or even other coutries, we call it a pandemic. The best example is today's coronavirus pandemic that is affecting the whole world.

Pandemic Outbreak

Explanation:

A Pandemic is defined as any epidemic that spreads beyond geographical boundaries, continents, countries etc. The far reaching ability of a catastrophic disease makes it more dangerous for human community no matter which region they belong to.

In order to qualify as Pandemic the disease has to be infectious as well. Cancer is considered to be deadly but it is not contagious or infectious. Hence, it is not a Pandemic.

Coronavirus (2019-) : The current world pandemic is novel coronavirus that has affected greater number of people globally. It originated from Wuhan, China, and has Infected people belong to almost everywhere in the world.

Thus, Pandemics crosses boundaries worldwide and gets spread to unaffected areas homogeneously.

Some of the worst pandemics that has spread worldwide includes:

Plague of Antonine (165-180 AD)

Plague of Justinian (541-542 AD)

Black Death (1347 - 1351)