Syndromic Surveillance: An Early Threat Detection Tool for Public Health
December 1, 2025
Overview
A core function of public health is to monitor and respond to health trends and threats to the general population. One tool for this is syndromic surveillance, which allows public health officials to quickly access data on upticks in patient illnesses and symptoms even without a confirmed diagnosis or lab test— sometimes within 24 hours after it is reported. This is especially important as we head into flu and respiratory virus season.
A core function of public health is to monitor and respond to health trends and threats to the general population. One tool for this is syndromic surveillance, which allows public health officials to quickly access data on upticks in patient illnesses and symptoms even without a confirmed diagnosis or lab test— sometimes within 24 hours after it is reported— enabling them to respond to threats and monitor trends. This is especially important as we head into flu and respiratory virus season. Influenza, COVID-19, RSV, and other respiratory viruses can spike quickly, are often most dangerous for the very young and the very old and can even — as we have seen in the past— overwhelm hospitals. This article provides an overview of syndromic surveillance, including how and what types of data are collected, shared, and used both by the Centers for Disease Control and Prevention (CDC) and state, tribal, local, and territorial (STLT) health departments and offers several examples of how health departments use this information to improve public health and health equity.
The interest in syndromic surveillance grew in large part as a response to bio-terrorism threats and the lacing of letters with anthrax following the September 11 terrorist attacks on the World Trade Center. The focus of syndromic surveillance has now expanded far beyond bioterrorism, and the CDC leads the National Syndromic Surveillance Program (NSSP), which includes many illnesses, symptoms, environmental hazards and injuries, non-communicable diseases, and more. The NSSP receives 9.6 million electronic health messages a day and has over 7,200 health care facilities in all 50 states, contributing information daily, according to CDC.
Syndromic surveillance data begins with a patient first seeking treatment with a healthcare provider. With syndromic surveillance, the point of care is most typically at a hospital emergency department. Depending on the jurisdiction however, it could also include data from urgent care centers (oftentimes where patients seek care that would have previously sent them to the emergency room), emergency medical services, outpatient clinics, or other healthcare providers.
The data collected by the healthcare provider varies but will typically include the patient’s primary health complaints and symptoms, diagnosis codes, demographic information, and geographic location. The information is de-identified before it is sent directly to the local and/or state health department or a health information exchange (HIE). (As an aside, public health professionals should be aware that even if syndromic surveillance data is described as de-identified or anonymized, it is unlikely to meet the HIPAA definition of de-identification and as with any data, re-identification risks remain.) The information may also be sent directly to the CDC’s BioSense platform by the provider or uploaded later to BioSense by the health department or HIE once they receive it from the healthcare provider. BioSense is the CDC’s cloud-based electronic health information platform and is a key part of the National Syndromic Surveillance Program.
Once information is on BioSense, it is quickly available to public health practitioners using a tool called Electronic Surveillance System for the Early Notification of Community-based Epidemics (ESSENCE) for analysis, visualization, and collaboration. In fact, one of the reasons syndromic surveillance data is so valuable is how soon it becomes available, readily facilitating the identification of threats and rapid response by health departments. Confirmed laboratory reports of various illnesses, such as influenza or COVID-19, can take days or even weeks to be available. And for many uses of syndromic surveillance data, such as monitoring upticks in emergency department visits following wildfires, there is no laboratory test or single diagnosed disease or condition that fully encapsulates the public health risk. Because syndromic surveillance data also encompasses information on symptoms and patient complaints, it can be used to identify novel public health threats by tracking clusters or patterns in the absence of any test or confirmed diagnosis.
The CDC has several case studies illustrating how STLTs use syndromic surveillance data to identify or better understand health hazards and risks to the public. These include the underreporting of boating accidents in Washington state; the analysis of Idaho’s emergency department data on demographics of patients presenting with suicidal ideation and suicide attempts to better understand suicide risk; and to better understand overdose risks, identify trends in drug use and overdose, and target overdose prevention efforts in Nebraska.
States also leverage their own syndromic surveillance data for analysis, sometimes producing written reports or data dashboards to share with the general public. These reports can be helpful in monitoring seasonal patterns and spikes in diseases, which as noted earlier, can be especially important to track during cold and flu season. For example, New York City has a dashboard that provides data on emergency department visits triggered by respiratory complaints between 2016-2025 and breaks them out by zip code. Illinois also publishes surveillance data, including data on emergency department visits for flu, COVID-19, RSV, and the catch-all Acute Respiratory Illness. The Kansas Department of Health and Environment publishes surveillance data on patients presenting to emergency departments throughout the state on a wide range of issues, including gastrointestinal illness, respiratory visits, and heat related illness among others. Publishing this information means that not only public health officials, but also community groups, healthcare providers, schools, and residents have access to critical information to help shape immediate responses and longer-term equitable policies.
The applications of how syndromic surveillance can protect the health of the public are myriad. It supports early detection of threats from communicable and non-communicable disease and environmental hazards. It is also an example of successful STLT health department and federal collaboration. STLT health departments collect and share critical information about what is happening in their own jurisdictions. In addition, the CDC’s platform and tools support the cross-jurisdictional data exchange that can identify national patterns and risks.
Readers interested in learning more about syndromic surveillance, including state mandated reporting of syndromic surveillance data and a deeper discussion on how data is reported from providers to health departments and the CDC, may want to consult reports produced by The Pew Charitable Trusts, “State Public Health Data Reporting Policies and Practices Vary Widely” and Association of State and Territorial Health Officials (ASTHO), “A Scan of State Laws Governing Public Health Data Reporting, Surveillance, and Sharing.”
This post was written by Meghan Mead J.D., Deputy Director, Network for Public Health Law—Mid-States Region.
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