Epidemic, Pandemic, Endemic - What these terms mean and Differences briefly explained

Epidemic Vs Pandemic [ Image Source - Dr. Reddy's Laboratories Ltd. ]

Epidemic, Pandemic, Endemic - What these  terms mean and Differences

On 11th March, 2020, the World Health Organization (WHO) officially changed its designation of COVID-19, the disease caused by a coronavirus, from an epidemic to a pandemic. This shift prompted a considerable number of people to turn to the web search, in order to ascertain the difference between the two -demics. What is the difference between an epidemic and a pandemic?

As we all aware a global pandemic is underway and it's affecting millions worldwide everywhere around us we hear the words pandemic and epidemic what do these words mean we'll try to understand these terms one by one and see how relevant they are in our current scenario.

The Atlanta Center for Disease Control defines an epidemic as "The occurrence of more cases of disease injury or other health conditions than expected in a given area or among a specific group of persons during a particular period".

Usually the cases are presumed to have a common cause or to be related to one another in some way in simple words "An epidemic is the rapid spread of disease to a large number of people in a given population within a very short period of time". The important points to pay attention in this definition are rapidly spreading disease which involves a large number of people and in a short period of time. 

The word itself traces its origin from Greek words 'epi' meaning upon endemic which comes from the word 'Deimos' which means people. When an epidemic has spread across a large region. For example multiple continents it is called a pandemic.

[ Image Credit - Merriam Webster ]

How Epidemic Begin ?

Although it's very difficult to explain the exact mechanism of how and when  epidemics start. We can broadly divide them into three main types :- 

1) Common source epidemics :-

In a common source of epidemic a group of people get infected from a common source of infection. For example suppose a bunch of people ate at a restaurant and the food of that restaurant was infected with staph bacteria toxin. Note that food poisonings are not caused by the bacteria itself rather the toxin that is produced by this bacteria. The bacteria itself gets destroyed by the cooking process. 

Now all these people developed food poisoning and this is an example of common source epidemic. These infected people cannot transmit the infection further to more people. As a food poisoning was caused by toxin in the food and nor the actual bacteria itself. 

2) Propagated epidemics :-

This is important as our next type of epidemic the propagated  epidemic differs in exactly this point only in a propagated epidemic. A similar scenario can occur a group of people went to a restaurant and rather than getting infected by eating contaminated food. 

Suppose they all get a virus from the person who was serving the food to all these people. Now the basic difference between common source and propagated epidemic is that in the case of a propagated epidemic these infected people can further infect more people. One infected human transmits of virus to another healthy human and so on. In this manner the number of cases grow exponentially within a few weeks and this is why it is known as a propagated epidemic.

3) Mixed type epidemics :-

Mixed outbreak epidemics have characteristics of both common source and propagated outbreaks. So this was about how epidemics start and how they propagate and that is what makes an epidemic so dangerous is ability to affect more and more people as a time progresses.

Also Read : Impact of Exercise on Your Immunity and How Boost Your Immunity?

[ Image Credit - Visual Capitalist ]

How do epidemics spread from one person to another ?

When there are numerous ways a disease can spread some of the most common ways are 

1) Airborne transmission :-

Airborne transmission is the spread of infection by droplet nuclei or dust in the air whenever an infected person coughs or sneezes small droplets of water are released in the air. These small particles contain million of viral particles these water particles are known as droplets if they are more than 5 micrometers in diameter and droplet nuclei if they are less than 5 micrometers in diameter. 

Droplets which are larger in diameter fall rapidly to the ground under the influence of gravity and therefore are transmitted only over a limited distance of less than 1 meters. Droplet nuclei on the other hand are less than 5 micrometers in diameter and hence can remain suspended in the air for significant periods of time and can be transmitted over distances greater than 1 meter. These droplet nuclei are then inhaled by another person which gets infected by the virus.

2) Arthropod transmission :-

Arthropod transmission takes place by an insect. For example the malaria epidemic which was spread by mosquitoes.

3) Contact transmission :-

Contact transmission is the mode of transmission when the infection spreads from one person to another by mode of touch.

4) Fecal oral transmission :-

In the fecal-oral transmission, the infectious agent is shared by the infected host in feces and acquired by the susceptible host through ingestion of contaminated food and water. 

It's important to know that not all people who get infected in an epidemic gets sick and they can sometimes still pass on the infection to other people. However people who have immunity are able to resist infections to know more about immunity and how it protects you from infections and diseases.

All of us are aware of the global crisis we are facing today, you may be hearing statements like your country is in stage two of the pandemic or stage three of the pandemic. 

What are these stages and numbers what does it tell us ?

Well WHO closely studied previous epidemics and classify the progression of epidemics into five main stages. 

• According to WHO the stage one consists of predominantly animal infections and a few human infections. 
• Stage two is said to have reached when there is sustained human to human transmission. 
• Stage three is when widespread human infection is seen in the form of whole communities being involved. This is the pandemic stage where the number of cases are exponentially increasing. 
• Stage four is the post peak stage which signifies that the pandemic activity appears to be decreasing. 
• Stage five or the post pandemic phase is said to have reached when the disease activity level reaches the level of seasonal flu. At this stage it is important to maintain surveillance and be prepare for future epidemics. 

Epidemics have been a part of human history since the beginning of time from Blake to Cholera to HIV to the current scenario. Millions have suffered recovered or tied kindly follow your local guidelines and stay safe...