Skip to main content

Disease Outbreak Response: Exploring the Critical Roles of Epidemiologists, Disease Detectives, and Other Public Health Experts

April 28, 2020

Many Americans were afraid to let a loved one step outside when polio outbreaks crippled an average of 35,000 people annually in the late 1940s. Polio cases in the United States peaked in 1952, reaching 57,628, more than a third of which left victims paralyzed. A vaccine developed by American medical researcher and virologist Jonas Salk came into use in 1955, and by the 1960s, the number of U.S. polio cases reported annually had fallen to less than 100. Since 1979, no polio cases have originated in the United States, and worldwide cases have decreased by 99 percent.

Public health experts have never had a greater understanding of diseases or a better network of organizations and programs with which to fight them than they do today. Many of the tools being used to promote and enable physical distancing during the COVID-19 outbreak in 2020 — social media platforms, smartphone alerts, videoconferencing technology — would have been unrecognizable to public health officials working to impose quarantines on homes and towns where polio cases were diagnosed in the 1950s.

The challenges facing public health officials have also evolved. Rapid growth in populations, urbanization, and global travel and trade have made disease spread more likely and containment more difficult. However, public health officials’ jobs during disease outbreaks remain constant: prepare to stop diseases before they spread, lead communications efforts when outbreaks do occur, and work to intervene quickly with strategies and policies to mitigate the spread and save lives.

Disease Outbreaks: Epidemics and Pandemics

The amount of a disease normally present in a community is referred to as the endemic level. This expected level of a disease, which can continue indefinitely without intervention, serves as a baseline from which to measure potential outbreaks. Investigations are triggered by a rare disease (rabies, plague) occurrence or an increase in the number of cases (amount) of a disease above the endemic level. Such an increase is referred to as an epidemic, or outbreak.

Epidemics result from an increase in the “amount or virulence” of an infectious agent, the recent introduction of an agent into a new setting, or a change in the susceptibility of people exposed to the agent, according to the Centers for Disease Control and Prevention (CDC). Enhanced modes of transmission or the introduction of an agent through new portals of entry can also cause an outbreak. Epidemics most commonly involve infectious agents, but they can also result from toxic substances or refer to noninfectious health problems, such as diabetes and obesity.

Epidemics Versus Pandemics

No specific set of standards exists for determining what constitutes an epidemic versus a pandemic, but generally epidemics become pandemics when a disease spreads across several countries or continents and affects a large number of people. It is important to note that the pandemic designation is indicative not of a disease’s virulence (its capacity to overcome the body’s defenses) or lethality (its capacity to cause death), but of its potential to spread. An examination of two disease outbreaks caused by coronaviruses illustrates distinctions between epidemics and pandemics.

Coronaviruses are common in animals, but in rare cases they infect humans. The many different types of coronavirus all cause symptoms ranging from mild respiratory illnesses to acute respiratory syndromes. Coronaviruses are named for their appearance; viewed under a microscope they look to be covered in pointed structures that surround them like a crown, or corona. Coronaviruses are responsible for both the severe acute respiratory syndrome (SARS) epidemic of 2003 and the COVID-19 pandemic that began in 2019.


First reported in Asia in February of 2003, the SARS-associated coronavirus (SARS-CoV) outbreak lasted approximately six months and spread across Asia, Europe, and the Americas. More than 8,000 people worldwide became sick from the disease and 774 died, according to the World Health Organization.

Although SARS is highly dangerous, the 2003 outbreak was contained within months. In the U.S., where laboratory evidence of SARS-CoV infection was found in only eight people (all of whom had traveled to other parts of the world where SARS was spreading), SARS did not spread widely. Despite its presence in more than two dozen countries, SARS is classified as an epidemic.


SARS-CoV-2, responsible for coronavirus disease 2019 (COVID-19), was first detected in Wuhan, China, in December 2019. Symptoms — including fever, fatigue, and dry cough — can range from mild to severe. Less deadly than SARS on an individual case basis, COVID-19 is highly contagious. The first confirmed COVID-19 case in the U.S. was announced in January of 2020; by early March, confirmed cases in the U.S. topped 500. On March 11, 2020, the World Health Organization (WHO) — reporting more than 118,000 cases in 114 countries and 4,291 deaths — declared COVID-19 a pandemic. Resources with comprehensive descriptions of COVID-19 and guidelines for slowing its spread are listed below.

Additional Resources

Centers for Disease Control and Prevention, Polio Elimination in the United States

Centers for Disease Control and Prevention, SARS Basics Fact Sheet

The College of Physicians of Philadelphia, The History of Vaccines

Healthline, The Most Dangerous Epidemics in U.S. History

World Health Organization, Disease Outbreaks

Emergency Preparedness: A System for Disease Detection

Developing a response plan prior to an active outbreak is critical to success. Fighting fast-spreading diseases requires cooperation from a geographically dispersed public health network, government health groups, and private organizations. It also depends on a broad selection of health experts in fields as varied as epidemiology, biostatistics, community health, environmental health, and health education.

The Centers for Disease Control and Prevention

In the United States, the CDC plays a central role in coordinating public health efforts. Founded in 1946 to combat the spread of malaria, the CDC currently employs approximately 15,000 people in more than 50 countries and in 168 occupational categories who track and share information weekly about more than 60 different diseases. Approximately 70 percent of the CDC’s funds go to support state and local communities. Some of the CDC’s resources for COVID-19 preparation are listed below:

The World Health Organization

The WHO coordinates international health within the United Nations system. With 7,000 employees in 150 countries, it works to increase the capacity of governments, organizations, institutions, and communities to withstand a disaster or emergency situation. Its areas of focus include:

  • National legislation and policy for disaster management
  • Plans and procedures for disaster management and emergency response coordination
  • Strengthening institutional and human resources for disaster management
  • Establishing and managing stocks of relief supplies and equipment
  • Identifying transportation options
  • Public education, awareness, and community participation in disaster management
  • Collecting, analyzing, and disseminating information related to emergencies and disasters that are likely to occur in the region.

A Coordinated Approach

The number of epidemic-prone diseases is rising, according to the World Health Organization, which focuses much of its efforts on eradicating yellow fever, cholera, and influenza. Both the CDC and WHO coordinate with governments and ministries of health around the world to fight pandemics such as COVID-19.

  • Global Outbreak Alert and Response Network (GOARN). The World Health Organization coordinates international outbreak response using resources from GOARN.
  • Health Department Resources. The CDC provides resources to health departments, including partnership opportunities, short-term assistance, and communications materials.
  • Outbreak Response. The CDC’s Division of Foodborne, Waterborne, and Environmental Diseases (DFWED) provides guidance on its outbreak response program.

Additional Resources:

Centers for Disease Control and Prevention, CDC Support to Health Officials: How CDC Can Help Respond to Emerging Local Health Concerns

Centers for Disease Control and Prevention, CDC’s Global Health Partnerships

Centers for Disease Control and Prevention, Interim Guidance for Healthcare Facilities: Preparing for Community Transmission of COVID-19 in the United States

Centers for Disease Control and Prevention, Our History — Our Story

The Roles of Epidemiologists and “Disease Detectives”

Public health experts try to prevent disease outbreaks from occurring or recurring. While clinical professionals focus primarily on treating the sick and injured, public health workers use educational programs, health services, public policy, and research to stop or mitigate diseases. When healthcare providers become aware of an unusually high number of illnesses occurring, they report it to local and state health authorities. Those reports typically prompt a health investigation by an epidemiologist.

A core function of epidemiology, field investigations link information to actions that ensure public health and safety. As described in the CDC Field Epidemiology Manual, the process for performing an epidemiologic field investigation is rigorous. In general terms, epidemiologists investigate public health threats to confirm an outbreak’s existence, identify causes and risk factors, recommend prevention and control measures, and communicate the threat to various stakeholders. Field investigations conducted by the CDC are diverse in type and scope. The agency worked with the Namibia Ministry of Health to investigate a hepatitis E outbreak in 2019, the same year it worked with Austin Public Health in Texas to evaluate an uptick in injuries related to dockless scooters.

Members of the CDC’s Epidemic Intelligence Service (EIS) are sometimes referred to as “disease detectives” because they investigate infectious disease outbreaks. CDC disease detectives were first deployed in 1958 to investigate a cholera and smallpox epidemic in Southeast Asia. Today the EIS is a two-year, hands-on post-doctoral training program in epidemiology, with a focus on field work. Every year the CDC selects 70 to 80 individuals to enter the program. Disease detectives address issues ranging from disease outbreaks on college campuses to global pandemics such as COVID-19. Additional resources related to epidemiology and epidemiologic interventions are listed below:

  • Developing Interventions. The CDC’s Field Epidemiology Manual includes guidance on developing interventions during epidemiologic field investigations.
  • Epidemiologic Assistance (Epi-Aids). This CDC resource describes the process for requesting an investigation by the Epidemic Intelligence Service.
  • Epidemiology. This World Health Organization overview provides links to resources related to epidemiology.
  • Global Health Protection and Security. The CDC’s Division of Global Health Protection (DGHP) works to address outbreaks around the world.

Additional Resources:

Centers for Disease Control and Prevention, “Epidemic Intelligence Service, 2019 Annual Update”

Centers for Disease Control and Prevention, Global Disease Detection Program: What We Do

Centers for Disease Control and Prevention, Principles of Epidemiology, Lesson 1, Section 11

Centers for Disease Control and Prevention, The Threat, Smallpox

Communicating the Threat

Public health officials communicate critical information during disease outbreaks, a role that evolves as quickly as communication technology advances. When a yellow fever epidemic struck Philadelphia in 1793 — an outbreak that caused 20,000 people to flee the city and killed 5,000 of those who remained — the invention of the telegraph was still more than 50 years away. When the World Health Organization declared the spread of COVID-19 a pandemic on Twitter, it did so to an audience of 7 million followers.

Public health experts’ duty to inform both health professionals and the general public about disease outbreaks is a challenging responsibility in the era of the 24-hour news cycle and social media. Public awareness of developments is immediate if not complete, and media sources demand constant updates about an outbreak’s effects.

Communications strategies in today’s media landscape should include a mix of media outreach, partner and stakeholder outreach, and social media engagement, according to the CDC. Roles, responsibilities, and authority for communicating each aspect of the investigation to healthcare providers and the media should be defined early in the process of a public health investigation.

If an outbreak response is domestic, the responsibilities among state, federal, and local entities involved should be clarified; if the response is international, ministries of health determine communications plans and responsibilities within each country. Field investigators and teams collaborate and coordinate with all agencies and organizations involved.

Field investigators communicating information about disease outbreaks are sensitive to the fact that audiences may make assumptions about a health threat based on who is delivering the message and how it is being delivered. Reports have to avoid creating panic but still communicate the proper risk-benefit message that encourages the public to adopt public health recommendations. Demonstrating honesty and openness, expertise, dedication, and empathy can help establish trust and credibility with journalists and the public.

Additional Resources:

Pennsylvania Center for the Book, The Pennsylvania State University, “Philadelphia Under Siege: The Yellow Fever of 1793”

Intervention and Treatment

Timely and effective interventions are critical for fighting epidemics and pandemics, particularly in cases where no vaccine or pharmaceutical treatment exists. The influenza pandemic (H1N1 virus) that spread worldwide during 1918–1919, sometimes referred to as the “Spanish flu,” infected about 500 million people, or one-third of the world’s population. No vaccine or pharmaceutical treatments were available, and control efforts such as quarantines, hygiene promotion, disinfectant use, and public gathering limits were applied unevenly. The virus ultimately caused an estimated 50 million deaths worldwide, with about 675,000 of those in the United States.

Epidemiologists and other public health experts consider many factors when developing an effective response for controlling or ending a disease outbreak. Acting quickly is critical, but a deliberate and comprehensive approach that addresses both scientific process and practical concerns is required.

Practical considerations include the costs and benefits of implementing an intervention, the operational and logistical feasibility of intervention steps, possible public and political perceptions about courses of action, and legal ramifications. Intervention steps include:

  • Defining the public health problem’s scope by assessing the outbreak’s severity
  • Defining the nature of the agent causing or contributing to the development of the disease or condition
  • Estimating the number of possible susceptible individuals and the extent of their exposure
  • Exploring reasons for the outbreak and determining whether they are ongoing
  • Measuring the level of scientific certainty of any findings
  • Determining what interventions can be used to reduce or eliminate any ongoing exposures
  • Implementing interventions.
  • Communicating the rationale for implementing or not implementing interventions
  • Assessing continuously the effectiveness of interventions and modifying them as new investigation information becomes available

Intervention efforts also include public health experts working closely with community healthcare facilities during an outbreak. Disease updates help protect staff members and patients, informing decisions about safety protocols and policies such as the proper use of protective equipment and rules that sick employees should not report to work.

Ensuring facilities have adequate supplies of personal protective equipment (PPE) is particularly important when treating highly infectious diseases such as COVID-19. Public health officials can also assist in linking those facilities with other healthcare and public health partners in the community, coordinating patient management and transfers and sharing of supplies.

Additional Resources:

Centers for Disease Control and Prevention, 1918 Pandemic (H1N1 Virus)

Policy and Social Justice

In addition to working to stop or limit the spread of disease, public health experts work to limit health disparities. Outbreaks of vaccine-preventable infectious diseases highlight such disparities. For example, yellow fever and cholera can have disastrous effects in areas where limited health infrastructure and resources hinder timely detection and response, according to the World Health Organization.

Mitigating discrimination toward those infected by a disease so they feel free to seek care also promotes better health and health equality. During both the 2003 SARS outbreak and the 2020 COVID-19 pandemic, Asian-American communities were identified by the CDC as being at risk for experiencing fear, stigma, and discrimination due to the viruses’ origins in Asia. The CDC established a community outreach team in 2003 to address stigmatization associated with SARS; its COVID-19 guidance provided to community and faith-based organizations encourages engagement with stigmatized groups and speaking out against discrimination.

Disease outbreaks can generate considerable fear among the general public or within specific affected communities, fueling discrimination and revealing a broader threat to public health. Public health officials work to ensure that healthcare decisions and policies are based on scientific data, not driven by fear or discrimination. By promoting healthcare equity, quality, and accessibility, they fight the spread of disease.

Additional Resources:

Centers for Disease Control and Prevention, Checklist for Community and Faith Leaders

Centers for Disease Control and Prevention, Coronavirus Disease 2019 (COVID-19)