Classifying the spread of diseases

Given the state of the world, this is something that is extremely relevant and also is not well known. We’ve all heard the words “pandemic”, “epidemic”, and probably several more by now – but what do they mean? I’ll go over some of the most common terms used to classify the spread of an infectious disease, what they mean, and the requirements for each term. At the end, I’ll apply what we’ve learned to covid-19.

Epidemic:

• disproportionately large number of individuals within a population, community, or region at the same time.

• Epidemics occur when a certain group experience a larger than expected number of cases at once. The disease spreads rapidly, but doesn’t affect a large area.

• One example of an epidemic is the Naples Plague – an epidemic of the plague* in 1656-1658 that affected the Kingdom of Naples. It greatly affected Naples, but wasn’t widespread across Europe.

*Yersinia pestis

The plague in Naples. Courtesy of the National Library of Medicine.

Pandemic:

• occurring over a wide geographic area (such as multiple countries or continents) and typically affecting a significant proportion of the population

• Pandemics are basically an epidemic on a larger scale – they affect a large area at the same time. Pandemics significantly impact the areas infected, straining the healthcare systems, economies, and massive amounts of infections and fatalities.

• A famous pandemic is the Influenza Pandemic of 1918 (“Spanish Flu”). The pandemic was worldwide and killed approximately 40-50 million people. There wasn’t a vaccine available and no antivirals were available at the time, more than World War I.

Endemic:

• (of a disease or condition) regularly found among particular people or in a certain area.

• Endemic diseases are not widespread and are expected in a certain area. Often these diseases will be described as “seasonal” as they’re likely to be seen at a certain time and area. These don’t cause a significant strain in the community and mitigation (reduces severity, duration, etc) are available to combat it when it’s encountered.

• Tick diseases are considered endemic to many parts of the US, particularly in the southern states. These diseases are expected in warmer months and are seen more by doctors during the summer months. Mitigation methods for these diseases include preventing tick bites by using preventatives on pets, wearing bug spray (with DEET), and covering as much skin as possible when outside. If infected, blood testing can be done (on yourself and the tick that bit you – save it in a bag!), and antibiotics are readily available.

What is covid-19?

Covid-19 is still a pandemic. Many people believe the pandemic is over and companies have been echoing the sentiment. Though I wish we’d transitioned from a pandemic to an endemic (as the Influenza Pandemic did), it hasn’t.

To understand this better, we need to compare a pandemic to an endemic disease and the characteristics of both:

Though mitigation methods are available, less than 94% of Americans are vaccinated, many stopped masking and social distancing, so the methods aren’t as effective as they could be. Most Americans are in high risk areas of transmission, hospitals are strained, shortages in the supply chain have plagued (pun intended) the country, and cases are rising yet again.

We’re not out of danger yet.