Difference between pandemic and epidemic

On March 11, 2020, the Director-General of the World Health Organisation (WHO) declared the international spread of a new coronavirus, Covid-19, a worldwide pandemic.

Some news organisations and public health officials had been calling the outbreak a pandemic weeks earlier than the WHO declaration — so how do you know when an outbreak becomes an epidemic and an epidemic becomes a pandemic?

Though public health definitions shift and evolve over time, the distinctions between these terms are generally a matter of scale. In short, a pandemic is an epidemic that has gone global.

What is an epidemic?

The Centres for Disease Control and Prevention (CDC) defines an epidemic as an unexpected increase in the number of disease cases in a specific geographical area.

An epidemic is any rise in cases beyond the baseline for that geographic area. Epidemics can occur:

◆ when an infectious agent (such as a virus) suddenly becomes much more prevalent in an area where it already existed.

◆ when an outbreak spreads throughout an area where the disease wasn’t previously known.

◆ when people who weren’t previously susceptible to an infectious agent suddenly start getting sick from it.

Smallpox, cholera, yellow fever, typhoid, measles, and polio are some of the worst epidemics in history. Today, HIV and drug-resistant tuberculosis are considered epidemics.

Scholars date the use of the term epidemic as far back as Homer’s “Odyssey,” in which the poet used the term in a way that’s similar to the way we now use endemic.

The first recorded instance of the word epidemic being used to refer to a widespread disease is around the year 430 B.C, when Hippocrates included it in a medical treatise.

Today, the word epidemic is used in casual conversations to refer to almost anything negative that has spread throughout a culture or a region. For example, laziness, gun violence, and opioid use have all been called epidemics in popular media.

What is a pandemic?

In 2010, during the HINI pandemic, the WHO defined a pandemic as the worldwide spread of a new disease. At the time, the WHO described six phases in the development of a pandemic:

1. A virus circulates among animals not known to spread the disease to humans.
2. The virus is detected in animals known to have spread viral diseases to humans.
3. Animal-to-human contact causes a human to develop the disease.
4. Human-to-human contact makes it clear a community outbreak could happen.
5. Human-to-human spread of the virus happens in at least two countries in the same region.
6. Community level outbreaks happen in a third country in another region. Phase six meant that a pandemic was occurring.

In 2017, the CDC released a pandemic intervals framework roughly aligned to the WHO’s pandemic stages.

Although both the WHO’s phases and the CDC’s framework describe flu pandemics, looking at the stages is useful for understanding how public health officials respond to global health emergencies, including the current Covid-19 pandemic.

CDC’s framework includes the following steps:

1. Investigation: Officials monitor cases of novel flu in humans or animals and assess the risk of the virus becoming a pandemic.
2. Recognition: As it becomes clear that the virus could spread widely, public health officials focus on treating patients and controlling disease spread.
3. Initiation: The virus spreads easily and for a prolonged period.
4. Acceleration: As the spread speeds up, public health officials use community interventions such as physical distancing and school closures.
5. Deceleration: The number of new cases consistently drops, and public health officials may reduce community interventions.
6. Preparation: As the first wave subsides, health officials monitor viral activity and watch for secondary waves.

The takeaway

The difference between an epidemic and a pandemic isn’t the severity of the disease, but the degree to which the disease has spread.

When a disease exists all the time in a specific region or among a particular population, it’s known as endemic.

When a disease spreads unexpectedly throughout a geographical region, it’s an epidemic. When a disease spreads to multiple countries and continents, it’s considered a pandemic. — healthline.com