With the current situation of the global pandemic and the abundance of facts and figures surrounding coronavirus, it is useful to get an overview of what epidemiology is and why it is so important.

Epidemiology is defined as the study of the distribution and determinants of disease frequency in human patterns. The discipline focuses primarily to establish cause-effect relationships, evaluate information and to make good decisions that will improve outcomes.  

The principles of epidemiology are considered the foundations for disease surveillance and investigation activities. In that regard every public health professional should be familiar with the basic concepts and definitions that are useful when undertaking epidemiological research:

  • Distribution: The study of epidemiology is primarily concerned with the frequency and pattern of health events that occur in a population. This is not limited to only number of events in a population but also accounts for the rate of rise of disease in a population.
  • Determinants: This refers to the search for causes and other factors that influence the occurrence of health-related events. This is usually related to multiple determinants that should be considered. Examples include host susceptibility to a disease, an opportunity for exposure to a microorganism or environmental toxin.
  • Specified populations: The main concern is the collective health of people within a community or other areas that are impacted with health events on that population.
  • Application: Epidemiological data provides direction for shaping public health policies. This process involves using scientific methods and epidemiological tools to support diagnosing a condition.

Two key definitions that you will encounter when both reviewing epidemiological literature and undertaking epidemiological research and should best familiarise yourself with, are:

  • Prevalence: Refers to the total number of people or individuals in a population who have a disease at specific period of time, commonly presented as a percentage of the population.
  • Incidence: Defined as the number of individuals who develop a specific disease or experience a health-related event during a particular time period (i.e. a month or year). Example: Cancers are reported in incidence.

Historical perspective

The term “epidemiology” comes from the Greek epi meaning “upon” and demos meaning “people or populance”. As such is the study of “diseases that which is upon the people”. The field of Epidemiology is nearly 2,500 years old (CDC,2020).  As history tells, the Greek physician Hippocrates was the first to draw out a distinction between “epidemic” and “endemic”, in order to distinguish between diseases that are introduced upon a population (epidemic) from those that remain within a population (endemic). The study of epidemiology is now widely applied to covert the description and causation of not only epidemic disease, but of disease in general, even health-related conditions such as high blood pressure, depression and obesity.

Role of Epidemiologist

Professionals that undertake such studies and who work in this field are referred to as epidemiologists. Such professionals are considered the bedrock of public health. When disease outbreaks occur such as the current pandemic, epidemiologists are responsible to intervene and conduct research. You can almost refer to these individuals as “disease detectives” which aim to look for the following:

  • Cause of disease
  • Identify people who are at most risk
  • Investigating methods of how to control the spread and prevention.

Epidemiologists are increasingly involved in systematically gathering other information (disease surveillance) by asking crucial questions such as:

  • What are the key symptoms?
  • When did they get sick?
  • Where could they have been exposed?
  • Who is sick? (After finding answers, health professionals attempt to find patterns to prevent further spread).

Epidemiological research plays a pivotal role in many areas of medical research but in particular lays close attention within public health. In public health, officials are largely involved with planning programs and also setting policies. By doing so public health officials must consider the following:

  • Assess the health of the population they serve
  • Determine whether health services are available, accessible and effective.

All information such as data that is gathered from epidemiological research is directed towards public health action. This information is used for planning on how to control and prevent disease in the community.  By having this information readily available, health agencies can effectively and efficiently investigate, prevent and control the disease within the community.

An area where epidemiology is currently being applied is this current pandemic of COVID-19 - a new illness that can affect your lungs and airways and is caused by a type of coronavirus.  In this currently evolving landscape of the outbreak epidemiologists are closely monitoring changes to disease frequency on a daily basis, using various epidemiological tools in order to gather the most robust data. According to the European Centre for Disease Prevention and Control (ECDC), as of 04 May 2020, there have been 3.5 million cases of COVID-19 (this in accordance with the applied case definitions and testing strategies in affected countries) have been reported including 247,000 global deaths.

 As can be seen in figure 1, the geographic distribution of reported cases of COVID-19 worldwide, with a significant density covering areas of Europe and the America’s, whereas cases in far-east Asian countries such as China, Japan and South Korea are significantly less.  

Figure 1. Geographic global representation of COVID-19 reported cases, source: The European centre for disease control and prevention

Given the application of this field of work in COVID-19, the work of epidemiologists is absolutely crucial. Epidemiological information gathered so far has been used in governments to impose strict measures such as self-isolation methods to help reduce the transmission of infection, all of which are based on epidemiologists recommendations.

In this short review it is easy to see the breadth of applications within the field of epidemiology and the impact these key fundamentals of epidemiological research have in the pharmaceutical and healthcare industries. For more information regarding disease burden and patient segmentation, please do not hesitate to contact the Epidemiology team at Black Swan Analysis from Evaluate Ltd.

Written by Rubhaan Malik, Healthcare Analyst, Epidemiology


  1. European Centre For Disease Prevention and Control, Rapid Risk assessment coronavirus 2019 pandemic, accessed from https://www.ecdc.europa.eu/en/covid-19/all-reports-covid-19 , [08th April 2020]
  2. Alfredo Morabia (2004). A history of epidemiologic methods and concepts
  3. Ray M. (2010). Introduction to Epidemiology, Jones& Bartlett Learning, p.24