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What Is Public Health Surveillance?

June 12, 2023

When a news publication reports that COVID cases are down a certain percentage or that there has been a recent uptick in preventable deaths from the flu, where does that data come from? The answer is as important as it is intriguing. The data, as a matter of fact, is the result of a public health surveillance system actively at work. Public health surveillance is an ongoing systematic process that effectively collects, compiles, analyzes, and disseminates data that’s pertinent to public health.

Having a reliable and effective public health surveillance system is crucially important. It provides essential information pertaining to public health risk assessment and the most current monitoring data for diseases, viruses, and other potential threats. The more data that is collected through this type of system, the better government health agencies and other emergency response teams can coordinate their strategy to contain the problem.

Obtaining vital surveillance data is by no means a simple process, and government health agencies are engaged in constant efforts to improve it. To fully understand what surveillance in public health is, the system must be broken down into its individual parts. Each part has a specific goal or outcome, which allows the system to refine the data and reveal meaningful insights. Understanding how each part of the system connects to the next is the best way to gain a holistic view of public health surveillance.

Public Health Core Sciences

Before diving into the details of public health surveillance, it helps to start with a broad overview of the five public health core functions and their respective roles in public health. The five core functions are:

  • Prevention effectiveness: Closely linked to public health policy, this provides important economic information that aids decision makers in selecting the most cost-effective solutions and disease mitigation strategies.  
  • Informatics: This involves the methods used for collecting, compiling, and preserving health records.
  • Laboratories: Labs support public health efforts by performing tests that confirm viruses and diseases, and by performing research.
  • Epidemiology: This involves the study of diseases, how they originate, how they’re spread, and how they can be prevented.
  • Surveillance: This refers to the systems that are used to track and monitor public health situations. The other four core sciences noted above glean information and take direction via the insights provided by surveillance systems.

What Is Surveillance in Public Health?

The U.S. approach to public health prioritizes the safety, health, and well-being of human life at the macro level. In essence, it aims to save the largest number of lives possible when devising solutions to threats. A threat can be anything from a toxic spill, to a terrorist attack, to a new strain of influenza. As the threat changes or evolves, so too does the public health response.

According to the Centers for Disease Control and Prevention (CDC), the public health approach to handling diseases and viruses consists of four main phases. They are:

  1. Surveillance: This phase seeks to determine if there is a public health problem, and if so, what it is.
  1. Risk factor identification: This phase seeks to determine the cause of the problem. It also addresses if certain demographics are more susceptible than others.
  1. Intervention evaluation: This phase seeks to determine what solution can be introduced that will resolve the problem. In most cases, a solution that has worked in the past, or a variation of it, can be used again. If there is no past solution to adapt, a solution must be developed.
  1. Implementation: This phase seeks to determine how the solution can be best implemented and applied to those who need it.

Public health surveillance is what represents the first phase of the overall public health approach. It is a system of collecting patient records and data that aids in the study of infectious diseases. The World Health Organization (WHO) and the CDC are the two main bodies that use this type of system; however, there are other institutions in the realm of public health that collect data from state and local health departments for analysis and interpretation.

The institutions performing surveillance in public health use automated electronic reporting systems and databases that effectively track, monitor, and collect data pertaining to specific diseases. Some examples of diseases that are being surveilled include influenza, COVID-19 and its variants, HIV, AIDs, and whooping cough.

Surveillance systems are made possible through the cooperation of state and local health departments as well as hospitals, private practices, and other healthcare providers who report cases of diseases. Granted, they are mandated by law to do so, but it doesn’t minimize the value of the role these providers play in the collection of critical public health data.

Having large sample sizes of recent and reliable data via disease registries allows health agencies to effectively do their work. This involves plotting the location and date of each case, mitigating the spread of outbreaks, and developing and executing prevention and intervention plans. Further, the data can be used to make informed projections by studying patterns and trends found within it. It’s also worth noting that the validity of surveillance data is statistically higher than data collected through surveys, because the data is sourced directly from patient records, diagnoses, and lab tests.

The 10 Attributes of an Effective Public Health Surveillance System

Public health surveillance is the systematic and ongoing collection, analysis, and interpretation of health-related data. To be effective, the system should adhere to the following 10 key attributes.

  1. Useful: The system must be useful in accomplishing its goals and objectives.
  1. Yields quality data: The data the system returns must be reliable, complete, and accurate.
  1. Timely: The system must be able to deliver reports quickly to keep up with what is happening in real time as closely as possible.
  1. Flexible: The system must be able to adapt to changes easily so that the flow of reporting may continue uninterrupted.
  1. Simple: The system must be easy enough for anyone to operate and understand to mitigate the chance of user error or to avoid discouraging its use due to its complexity. 
  1. Stable: The system must be capable of continuous, uninterrupted operation with little to no chance of breaking down.
  1. Effective: This attribute addresses how well the system captures case data. For example, a system that captures 70 percent of cases has a much higher level of effectiveness than one that only captures 10 percent.
  1. Predictive value positivity: This attribute is a metric that measures reported cases that meet the case definition versus reported cases that do not meet it. For example, if there were 1,000 reported cases, but only 7 met the case definition, this equates to a low predictive value positivity level.
  1. Representative: This attribute measures how well the reporting data represents the population that is under surveillance.
  1. Acceptable: This measures how willing those who are involved in the reporting process are to participate in it. For example, if 95 out 100 healthcare providers are using the reporting system, this indicates a high acceptability rate.

The goal of any public health surveillance system is to strongly represent each attribute. If this is accomplished, it means the system has the highest likelihood of delivering data that is useful, accurate, and actionable. However, one or two deficient attributes can hinder the entire system. For instance, a system that is strong in all 10 attributes except stability will have long periods of interruption due to crashing and other errors. In turn, the picture created by the data will be fragmented.  

The Uses of Public Health Surveillance

Surveillance in public health provides meaningful insights and actionable data to those working to track and contain potential public health issues. What are the uses of the surveillance data? Per the CDC, the following are some of the main uses, including some actions that can be taken due to public health surveillance.

  • Data can be used to identify patients and who they came into contact with, which is useful during the treatment and intervention phase.
  • The research process can be stimulated or guided in a specific direction.
  • The data may be enough for a hypothesis to be developed.
  • The data can help public health officials assess how effective their programs and control measures are.
  • Public health officials can effectively monitor viruses and infectious diseases, including trends and character traits.
  • Public health officials can accurately estimate the size and scope of public health threats, which enables them to estimate the resources that may be needed to combat them.
  • Data is a key indicator of epidemics and pandemics.

Passive Surveillance vs. Active Surveillance

Public health surveillance falls into two main categories — passive and active. Passive surveillance is the status quo of public health surveillance. It is ongoing and tied to no specific investigation or large scale public health threat. In passive surveillance, the healthcare provider takes the initiative to submit a report by following a list of reportable diseases that’s been issued by their state’s health department. A health agency waits for those reports to be submitted, and compiles the data for study and analysis. Passive surveillance is simple and inexpensive, but it’s also less comprehensive than active surveillance.

In active surveillance, regular outreach is made to potential reporters to prompt the reporting of specific diseases or viruses. It is often used to validate the data seen in passive reporting, or it can be used in conjunction with specific epidemiological investigations. Active systems are often used for brief periods or specific purposes, such as during outbreak investigations or seasonal events like influenza. An active surveillance system is more comprehensive in its findings, but it’s also more costly to operate.

The Five Phases of the Public Health Surveillance Process

With this definition of the nature and uses of public health surveillance in mind, a breakdown of the typical components of the surveillance process will make more sense. The five phases of the surveillance process are as follows.

1. Data Collection

Before the process of data collection can begin, it must be decided what the overarching goal of the system is, and what specific objectives must be accomplished to meet that goal. Some of the common questions that must be answered include:

  • What is the system going to monitor?
  • What target population will be surveilled?
  • What data will be collected and who will collect it?
  • What are the definitions of specific data fields?
  • What are specific pieces of information being collected?
  • How will the data ultimately be used?
  • Will the data system be able to collect what’s required?
  • Will the system be active or passive?
  • Will the reporting be transmitted by mail, electronically, or both?
  • Which data sources can be relied upon?
  • How will the surveillance system be put together?

By answering these types of queries, the data collection process, methods, and objectives become defined. Further, the World Health Organization (WHO) maintains a list of internationally notifiable diseases, which serves to guide data collection efforts. This list includes, but is not limited to smallpox, polio, and new subtypes of influenza.

2. Data Analysis

After it is clearly determined how data will be captured, how it will be used, and other related factors, the next step in the public health surveillance process pertains to data analysis. For phase two of the process to move forward, step one — data collection — must have been effective. Otherwise, it’s not worth analyzing the data.

Assuming the data captured is valid and sufficient, the data analysis phase addresses the following.

  • Who will analyze the data
  • What methodologies will be used for analysis of the data
  • How often the data will be analyzed (daily, weekly, monthly, etc.)

3. Data Interpretation

Data interpretation is closely linked with data analysis. By identifying the people affected by public health threats, and the place and time a threat occurred, it can more easily be determined how and why a public health event happened in the first place.

Although reported data is helpful, the factors that may be potentially influencing the data must be considered. For instance, if a specific disease or specific region is being reported more than normal, some questions that may be asked include:

  • Was there an increase in access to health care?
  • Was there a recent change in reporting procedures?
  • Was there a change in case definition?
  • Are more laboratories testing for a specific virus or disease?
  • Is there more public awareness of a certain condition?
  • Is the condition on a higher index of suspicion?

4. Data Dissemination

The data dissemination phase essentially defines how information is going to be distributed to those who have a need to know. Since the public has every right to know about public health threats, the data dissemination phase generally targets a wide audience, including those who are directly at risk and those who may potentially be at risk. As seen during the COVID-19 pandemic, the most recent data went out to the entire country.

During the data dissemination phase, data is shared via:

  • Newsletters
  • Bulletins
  • Alerts
  • Annual surveillance summaries and reports
  • Medical epidemiologic journals
  • Press releases
  • Social media
  • Healthcare facility websites

5. Link to Action

Phases one through four of the public health surveillance process culminate in the final phase — link to action. The link to action phase determines what must be done to mitigate the spread of public health threats, often with the goal of containment. Some examples may include rolling out a certain medication, a behavioral change, social (physical) distancing, or other methods. Should a link to action fail or prove to be insufficient, it usually means something wasn’t done correctly in phases one through four.

Big Data in Public Health

Public health surveillance continues to evolve as the system becomes more refined and as technology advances. One huge benefit of the advancement of technology is our current ability to collect terabytes of public health data compared to the small sample sizes pre-internet. Big data in public health will continue to play an expanding role in how public health surveillance data is collected and subsequently analyzed, interpreted, and disseminated.

According to Accenture, the COVID-19 pandemic exposed significant gaps in the public health surveillance system and its methods. This has motivated the CDC to redouble its efforts to make the surveillance process more reliable in connectivity, more resilient against outages, and more adaptable and response-ready.

By modernizing how public health data is surveilled and reported via the Data Modernization Initiative (DMI), officials hope to develop the public health surveillance system to achieve something closer to real-time collection levels with very little lag and disruption in connectivity. Similar to how internet speeds ramped up by converting to broadband from dial-up, the DMI aims to achieve similar advancements with public health data and the speed at which it is reported.

The Legality Behind Public Health Surveillance

Considering the massive amount of sensitive health data that is being reported and collected by the CDC, WHO, and other public health-related organizations, some may wonder about the legal and ethical considerations of surveillance efforts. The 12th article of the 12 Amendments of the U.S. Constitution states, “The powers not delegated to the United States by the Constitution, nor prohibited by it to the States, are reserved to the States respectively, or to the people.”

The interpretation of the article is that the legal authority for public health, including surveillance, resides with the states. However, the federal government is responsible for promoting the general welfare of the people. The federal government has authority over interstate commerce, which means the CDC can respond when a disease situation has interstate implications that impact the general welfare of the nation.  

Otherwise, the CDC typically must be invited by a state to become involved in an investigation or to conduct surveillance within state boundaries, based on notifiable disease reporting systems. These reportable-disease systems are mandated by legislators through state law. In some states, the legislators give the state health officer the authority to mandate reporting on a specific disease or condition.

Not only must the list of reportable diseases be specified, but it must specify who must report them and the reporting method. Most commonly, physicians, laboratories, hospitals, clinics, and schools are required to report public health cases to the local health department.

The local health department is usually responsible for case investigations and any resulting action after it receives a report verifying that it meets the case definition. The local health department then sends the report to the state health department. In some cases, the state health department may aid the local health department in investigational follow-up and activities to control the spread of public health threats, especially if they cross jurisdictional lines.  

Do Your Part in Maintaining Optimal Public Health

Public health surveillance — although complex — is integral to providing reliable and critical information pertaining to diseases and viruses to the appropriate parties. What the CDC and the World Health Organization does with this public health information ultimately serves to create a response for issues such as COVID-19, HIV, and other notable public health threats.

Those who are interested in becoming part of the solution to public health issues are encouraged to invest in an advanced degree in public health administration, such as the Online Master of Health Administration (MHA) program offered at Tulane University. During the program, students are taught essential leadership skills, strategic management strategies, and analytical methodologies that promote data-driven decision making.

Discover how an MHA can equip you for success in areas of health administration and public health.

Recommended Readings

Ethics in Health Care: Improving Patient Outcomes

How to Improve Health Care in Rural Areas

What Is Healthcare Marketing? Tips for Branding Your Practice


Accenture, “Building Next-Generation Public Health Surveillance”

BMJ Journals, “Glossary for Public Health Surveillance in the Age of Data Science”

Centers of Disease Control and Prevention, Introduction to Public Health Surveillance

Centers of Disease Control and Prevention, Public Health 101 Series, Introduction to Public Health Surveillance

National Library of Medicine, Surveillance

World Health Organization, Disease Surveillance

World Health Organization, Global Influenza Surveillance and Response System (GISRS)

World Health Organization, Surveillance in Emergencies

World Health Organization, WHO Global Surveillance and Monitoring System