Epidemiology, Infectious Diseases

Epidemiology 101: The Science Behind Infectious Disease Control

Author Chandana Balasubramanian , 28-May-2024

Picture this: you’re watching a storm approach. At first, it’s just a few dark clouds—an outbreak. Suddenly, the sky turns ominous, and a downpour begins—this is an epidemic. Then, the storm spreads across regions, even continents—now, we’re in pandemic territory.


Understanding disease spread is at the core of epidemiology, the study of the distribution, patterns, and determinants of health and disease conditions in defined populations. It’s not just about counting cases; it’s about grasping how and why diseases spread the way they do. Whether it’s a local spike in flu cases, a country-wide measles outbreak, or a global event like COVID-19, each situation requires a unique response.


Let’s explore the fascinating world of epidemiology and understand the differences between outbreaks, epidemics, and pandemics.


What is epidemiology?

Epidemiology is the science that explores the distribution and determinants of health-related states and events, including how often diseases occur in various groups of people and why they spread.

By understanding disease patterns, epidemiologists help shape strategies to improve public health outcomes and guide patient care.

What are the goals of epidemiology?

The field of epidemiology aims to uncover the causes of diseases, identify key risk factors, and devise effective disease control measures to stop their spread. This information is crucial for developing public health policies and medical practices to keep communities healthy.

Who is the father of epidemiology?

Epidemiology has a rich history and has evolved significantly over time.

In the 19th century, John Snow, often called the “father of epidemiology,” made groundbreaking strides by identifying the source of a cholera outbreak in London and linking it to contaminated water.

This marked a turning point, showing how studying disease patterns could save lives. Today, modern epidemiology remains vital in tackling health crises, from local outbreaks to global pandemics.


What are the types of epidemiology?

There are many categories of epidemiology that individuals can choose to focus on. Here are just a few examples.

Infectious disease epidemiology

Infectious disease epidemiology focuses on how diseases caused by bacteria, viruses, fungi, and parasites spread and impact populations. It aims to understand transmission patterns, identify outbreaks, and develop strategies to prevent and control infectious diseases, safeguarding public health.

Environmental epidemiology

Environmental epidemiology studies how environmental factors, like pollution and chemicals, affect health and disease patterns in populations. It helps identify and understand the links between environmental exposures and health risks, guiding policies to protect public health.

Genetic epidemiology

Genetic epidemiology explores how genetic factors influence the distribution and risk of diseases in populations. It combines genetics and epidemiology to understand how genes and environmental factors interact to cause diseases, helping to identify inherited risk factors and improve disease prevention and management strategies.

Cancer epidemiology

Cancer epidemiology studies the patterns, causes, and effects of cancer in populations. It helps identify risk factors, track cancer incidence, and guide prevention and treatment strategies. This field plays a crucial role in understanding how cancer affects different groups and improving public health outcomes.

What is the role of an epidemiologist?

Epidemiologists play a crucial role in public health. Think of them as disease detectives who investigate disease patterns and causes, aiming to control or prevent outbreaks and improve health outcomes.

Traditionally, their work focused on scientific research, data analysis, and mathematical models. However, now, many epidemiologists are active in public health policymaking. While some worry this could affect scientific objectivity, others believe it enhances it through analyzing data and improving empirical methods.

Active involvement in policy requires additional training but offers significant benefits. By blending science with policymaking, epidemiologists can better protect population health, making their role both scientific and practical.

This way, epidemiologists can better partner with clinicians and health practitioners, public health workers, and local health departments to develop public health programs that are highly effective.

What is an outbreak?

In epidemiology, an outbreak occurs when the number of people infected by an infectious disease exceeds what’s typically expected in a particular region or time.

This spike can be caused by various infectious agents, like bacteria, viruses, fungi, or parasites. Sometimes, it can even be due to exposure to harmful chemicals or radioactive materials.

Imagine your community as a well-tuned orchestra. Normally, everything runs smoothly, with each instrument playing its part. Now, picture one instrument suddenly playing out of tune, disrupting the harmony. That’s what an infectious disease outbreak is like—an unexpected surge of disease cases in a specific area or season, throwing off the balance.

Just like tuning the orchestra back to harmony, managing an outbreak involves precise, coordinated efforts to elevate public health.

Examples of disease outbreaks

  • Bubonic plague, 1300s: The bubonic plague, also known as the Black Death, struck in the mid-1300s, devastating Europe from 1347 to 1351. This highly contagious disease spread through flea bites and caused the deaths of an estimated 25 million people, wiping out nearly a third of Europe’s population. This can be considered one of the deadliest outbreaks in history.
  • Measles outbreak, 2024: According to data from the US Centres for Disease Control and Prevention (CDC), several measles outbreaks have been reported in the United States. Measles is highly contagious, and the virus spreads primarily through respiratory droplets. The disease is of significant concern because it spreads fast, and one in 1,000 cases may lead to severe disease, including permanent brain damage. Additionally, the CDC notes that one to three of every 1,000 children infected with measles will die from respiratory or other serious issues.
  • Mpox outbreak, 2024: The U.S. saw an mpox outbreak (previously known as monkeypox) with over 570 cases reported by March 28, 2024, compared to fewer than 300 the previous year. Mpox spreads through close contact, including intimate interactions and contaminated materials. Despite lower transmission rates than in 2022, low vaccination rates keep people at risk. The CDC also warned of a new strain of mpox called Clade II causing widespread mpox outbreaks in the Democratic Republic of Congo (DRC).


GIDEON, a leading infectious diseases database, offers comprehensive data on over 30,000 infectious disease outbreaks, including outbreak maps, and much more.

What is an epidemic?

An epidemic occurs when the number of cases of a disease suddenly rises above what’s normally expected in a specific population and area. According to the US CDC, unlike outbreaks, which are more localized, epidemics cover larger regions.

Several factors can trigger an epidemic:

  • A change in the virulence of the disease-causing agent
  • The introduction of a new agent
  • Increased transmission or exposure
  • Higher susceptibility of the host population.


Essentially, when enough people are affected, and conditions are right, an epidemic can spread rapidly, demanding swift public health responses to control it.

Example of a disease outbreak

Polio epidemic, 1916: In June 1916, Brooklyn, New York, faced a devastating polio epidemic. Public health authorities reported over 27,000 cases nationwide, with more than 2,000 deaths in New York City alone.

This outbreak caused widespread panic, leading to quarantines and significant anxiety among parents. Polio epidemics continued to reappear each summer and peaked during the 1940s and 1950s. They were so bad that polio was feared as the ‘wrath of God.’

The 1916 epidemic highlighted the urgent need for better public health measures and polio research, eventually leading to the development of the polio vaccine. Through vaccination, polio was mostly eradicated by the year 2013, although a small number of cases continue to appear around the world.

Outbreak vs epidemic: what’s the difference? A real-world example

Classifying a disease as an epidemic helps global agencies like the World Health Organization (WHO) mobilize resources to combat the spread. It enables quick access to emergency stockpiles of essential medical supplies, such as antibiotics and vaccines, ensuring a coordinated and effective public health response. The right public health initiatives can help minimize the risk of negative health outcomes.

  • Take the 2014-15 measles outbreak that spread to seven U.S. states, Canada, and Mexico. Despite 667 cases in the U.S.—the highest in two decades—it was classified as an outbreak because the cases were traced back to a single event at a California theme park.
  • In contrast, the 1916 polio epidemic in New York involved thousands across multiple boroughs, impacting a larger geographic area and population. This distinction helps tailor the public health response appropriately.


What is a pandemic?

A pandemic is an epidemic that spreads across multiple countries or continents, affecting a large number of people. It’s a global outbreak, like COVID-19, that involves widespread transmission simultaneously in different parts of the world.

This vast reach distinguishes pandemics from localized epidemics, demanding coordinated international response efforts.

The World Health Organization’s designation of a pandemic raises public awareness and prompts policy changes. It enhances global monitoring and surveillance, leads to new public health guidelines, and accelerates vaccine development. This coordinated response is crucial for effectively managing and mitigating the impact of widespread diseases.

In contrast, during the 2014-2015 Ebola epidemic in West Africa, over 11,000 lives were lost. However, thanks to global containment efforts, the epidemic was prevented from escalating into a pandemic. This shows how coordinated international responses can effectively limit the spread of even deadly diseases.

What risk factors cause disease outbreaks for infectious disease?

1. Water, sanitation, food, and air quality

  • Lack of safe water, inadequate sanitation, poor hygiene, and unsafe food can lead to diarrheal diseases.
  • Poor living conditions contribute significantly to poor health conditions and the spread of these diseases.


2. Climate

  • Floods can mix sewage with freshwater, damaging water quality.
  • Changes in air currents can carry disease vectors and pathogens to new areas.


3. Chemical and radiation exposure

  • Accidental release: Chemical spills or radiation leaks from safety failures, transportation accidents, or environmental contamination can trigger outbreaks. For example, mercury exposure in Japan led to the Minamata disease outbreak.
  • Intentional release: Acts like radiation warfare can also cause disease outbreaks.


4. Cancer clusters

  • Defined as a higher-than-expected number of related cancer cases in a specific area over a period.
  • Health departments may request CDC investigations to find environmental causes for poor health conditions in these areas.



What are common public health strategies for surveillance and outbreak preparedness?

Here are some ways that public health agencies conduct disease surveillance and outbreak preparedness.

  • Early warning systems: Detect potential outbreaks quickly.
  • Testing and diagnosing: Identify and confirm disease cases.
  • Contact tracing: Track and manage individuals exposed to infections.
  • Risk communication: Inform the public about risks and prevention.
  • Integrated surveillance and response systems: Combine data for comprehensive monitoring and coordinated response.



Understanding the science behind infectious disease control is crucial for implementing effective preventive measures and safeguarding public health. By categorizing outbreaks, epidemics, and pandemics, we can tailor our responses to protect the target population more effectively. Epidemiological research helps identify risk factors and transmission patterns, guiding public health services in preventing disease outbreaks.

Whether it’s through early warning systems, testing, contact tracing, or risk communication, each strategy plays a vital role in disease surveillance and outbreak preparedness. By investing in these measures and maintaining robust surveillance systems, we can enhance our ability to respond to health crises, ultimately preventing disease and improving global health outcomes for human health.


The GIDEON difference

GIDEON is one of the most well-known and comprehensive global databases for infectious diseases. Data is refreshed daily, and the GIDEON API allows medical professionals and researchers access to a continuous stream of data. Whether your research involves quantifying data, learning about specific microbes, or testing out differential diagnosis tools– GIDEON has you covered with a program that has met standards for accessibility excellence.

Learn more about epidemiology, disease outbreaks, epidemics, and pandemics on the GIDEON platform.


Chandana Balasubramanian

Chandana Balasubramanian is an experienced healthcare executive who writes on the intersection of healthcare and technology. She is the President of Global Insight Advisory Network, and has a Masters degree in Biomedical Engineering from the University of Wisconsin-Madison, USA.

Articles you won’t delete.
Delivered to your inbox weekly.