Epidemiological studies can be likened to an X-ray scan of the medical vulnerabilities of any given population. It allows us to track and predict the prevalence of a disease among a group of people. 

It is worth noting that the definition of “epidemiology” has undergone several changes over the years. It is a relatively recent discipline, partly because it requires the collection of great amounts of data, something we have only recently been able to do. 

In the 1970s, epidemiology was defined by Lilienfeld as a “method of reasoning about disease that deals with biological inference derived from observations of disease phenomena in population groups.” Later, the “comparison” aspect of epidemiology (ie, the comparison of data between different groups) gained greater importance.

Today, epidemiological studies have a clearly defined clinical purpose: identifying how diseases spread, why, and how to stop it. This principle was notably applied in the COVID-19 pandemic, during which epidemiological data guided public health decision-making on how to protect groups that are most vulnerable to serious infection. 

To gain a clearer picture of the importance of epidemiological studies, we can begin by imagining a world without them. In this scenario, we would have no way of allocating the right amount of healthcare resources to groups that are most vulnerable to a particular disease; we would also be robbed of the opportunity to detect the locations in which the prevalence of a disease is especially high, and investigate why this is the case. Medicine would be heavily tilted towards the treatment of a disease instead of its prevention. 

In other words, a straight line can usually be drawn from epidemiological data to the eventual eradication of a disease. This is why epidemiologists are working so hard to map out the prevalence of various diseases across the globe. Their work allows other researchers to compare the incidence of a disease in a given population with the health factors prevalent in it, possibly yielding information crucial to understanding its pathophysiology.  

Cystic fibrosis is one disease that we have come to understand more about through epidemiological research. In The Lancet, Elborn mapped out some interesting epidemiological information regarding the common clinical presentations of people with cystic fibrosis by age: 

  • Among patients aged up to 10 years, early mucinous plugging and bronchiectasis can often be seen in the airways. Meconium ileus can often be found in the gut, and patients may have pancreatic exocrine insufficiency. 
  • Among patients aged 10 to 20 years, bronchiectasis is usually already established in the airways. Cirrhosis of the liver is also sometimes present. 
  • Among patients aged 20 to 35 years, an examination of the airways usually reveals established bronchiectasis with pneumothorax/hemoptysis. Portal hypertension can often be detected in the liver. Cystic fibrosis-related bone disease can sometimes be present. 
  • In patients aged more than 35 years, progressive respiratory failure is usually present. Patients are often candidates for lung/liver transplants.

A more detailed study of the epidemiology of cystic fibrosis can be found in Pediatric Pulmonology. This study, titled “The Epidemiologic Study of Cystic Fibrosis (ESCF)”, was a prospective observational study that included more than 32,000 cystic fibrosis patients from 250 clinical care centers in North Africa between 1994 and 2005. The initial reason for the study was to obtain data on the effectiveness of dornase alfa as a treatment for cystic fibrosis. 

Read more about cystic fibrosis epidemiology 

Given that the research took place over a decade, the authors of the study observed sweeping clinical practice changes in the treatment of cystic fibrosis. For example, the use of inhaled antibiotics, inhaled bronchodilators, and inhaled corticosteroids increased substantially over the years. In addition, improved data collection on the socioeconomic status of patients throughout the course of the study revealed that a lower socioeconomic status was associated with poorer health outcomes.

Identifying Risk Factors for Cystic Fibrosis

The research team also examined the risk factors for cystic fibrosis in early childhood and highlighted the importance of early monitoring of cystic fibrosis parameters in pediatric patients. The study reported: 

  • Nutritional indexes, as well as respiratory signs and symptoms, are predictors of lung function in children aged 6 years.
  • Patients with cystic fibrosis often present with persistent signs of lung disease when aged as few as 2 years. 
  • Wheezing in pediatric patients is an important predictor of reduced percent predicted forced expiratory volume in one second (ppFEV1) when aged between 6 and 8 years.
  • BMI is not a significant tool for predicting vulnerability to poor nutritional status in children. 
  • The presentation of cystic fibrosis signs and symptoms at an early age is an independent risk factor for mortality, even after controlling for lung function. 

Based on the information collected, Konstan and colleagues wrote, “These findings suggest that aggressive intervention early in life aimed at growth/nutrition status, and pulmonary signs/symptoms may lead to better pulmonary function later in childhood.” 

Read more about cystic fibrosis patient education 

This poignantly drives home the main purpose of all epidemiological studies: improving clinical outcomes. For example, with the information provided through this study, physicians now know that optimizing nutritional and respiratory parameters early can improve outcomes later in life. For reasons such as these, epidemiology will continue to remain an indispensable medical discipline in the years to come. 


Frérot M, Lefebvre A, Aho S, Callier P, Astruc K, Aho Glélé LS. What is epidemiology? Changing definitions of epidemiology 1978-2017PLoS One. 2018;13(12):e0208442. doi:10.1371/journal.pone.0208442

Elborn JS. Cystic fibrosisLancet. 2016;388(10059):2519-2531. doi:10.1016/S0140-6736(16)00576-6

Konstan MW, Pasta DJ, VanDevanter DR, Wagener JS, Morgan WJ, Scientific Advisory Group and the Investigators and Coordinators of ESCF. Epidemiologic study of cystic fibrosis: 25 years of observational researchPediatr Pulmonol. 2021;56(5):823-836. doi:10.1002/ppul.25248

Lilienfeld DE. Definitions of epidemiology. Am J Epidemiol. 1978;107(2):87-90. doi:10.1093/oxfordjournals.aje.a112521