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california syndromic surveillance (calsys)

What is Syndromic Surveillance?

Last updated: July 8, 2024

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​CalSyS Vision 

Improving public health outcomes in California through timely information, enabling rapid and equitable response.     

What is Syndromic Surveillance? 

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Syndromic surveillance (SyS) uses automated methods for detection and near real-time monitoring of early warning signals, incorporating health and health-related indicators for all public health actions, from prediction to response.  

Syndromic surveillance provides public health professionals with a timely system to detect and respond to public health threats such as infectious disease outbreaks, heat illness, and opioid-related overdoses. Public health professionals can use syndromic surveillance like an early warning system to detect unusual levels of illness in the population and mobilize rapid responses.   

State and local health departments collaborate on syndromic surveillance under the Centers for Disease Control and Prevention’s (CDC) National Syndromic Surveillance Program (NSSP). 

Why is Syndromic Surveillance Important?  

  • ​Helps protect health and safety by supporting rapid detection and response to emerging health and safety threats like outbreaks. 
  • Informs a more complete understanding of public health in our communities.  
  • Supports streamlined collaboration between public health and healthcare groups to detect and respond to events of public health concern.  
  • Can improve understanding of health inequities and inform effective policymaking and resource allocation. 

How does Syndromic Surveillance Work?  

​Here is a brief summary of the process of syndromic surveillance for California: 

Flowchart showing the process of data exchange in the California syndromic surveillance program

  1. Patients seek care at emergency departments. 
  2. Medical facilities send patient data (de-identified to protect privacy) to local health departments or Health Information Exchanges/Organizations (HIEs) or directly to BioSense.  
    • ​HIEs support the mobilization of health care information electronically across organizations within a region, community or hospital system, for example from hospitals to health depar​tments. 
  3. Local health departments and HIEs submit the data to BioSense. 

Public health professionals use the data to monitor public health and detect threats to health and safety. Syndromic data can be integrated with other types of public health to inform a more complete picture of public health in California and public health decision-making. 

How Fast Are Syndromic Surveillance Data Available? 

Hospital data can be available for syndromic surveillance purposes within 24 hours of a patient’s visit to a participating facility, so they are available in near real-time. The speed and efficiency of this data exchange enables public health professionals to act fast in response to emerging health threats. 

Who is Involved in Syndromic Surveillance? 

Syndromic surveillance involves collaboration between health care facilities (primarily hospitals with emergency departments), local and state health departments, CDC, and other partners. ​

Learn more at Frequently Asked Questions About CalSyS.

Common uses of syndromic surveillance data: ​

  • Monitoring trends in opioid-related overdose visits 
  • Tracking community spread of emerging diseases and conditions (e.g., COVID-like illness)
  • Monitoring seasonal patterns of diseases (e.g., influenza-like illness) 
  • Case detection (e.g., acute flaccid myelitis, meningococcal disease, rabies) 
  • Evaluating health outcomes related to environmental events (e.g., respiratory symptoms during wildfire season, heat-related illness during a heat advisory) 
  • Monitoring trends in non-communicable illnesses (e.g., lung injury associated with vaping) 
  • Surveillance for health events at mass gatherings (e.g., Special Olympics) 

Read more at Success Stories | National Syndromic Surveillance Program (NSSP) | CDC 

National Syndromic Surveillance Program


​What is NSSP? The National Syndromic Surveillance Program (NSSP) is led by the CDC. The NSSP supports national emergency response preparedness and coordinates syndromic surveillance efforts among the CDC, federal partners, local and state health departments, and academic and private sector partners.  

The following tools from NSSP support syndromic surveillance: 
  • ​​BioSense Platform – A secure, integrated electronic health information system. This system collects, analyzes, and shares de-identified patient data received from emergency departments within 24 hours of the patient visit. Patient information is de-identified to protect privacy. This real-time data exchange allows for timely detection and response to events of public health concern. 
  • Electronic Surveillance System for the Early Notification of Community-based Epidemics (ESSENCE) – A data analytics and reporting tool within the BioSense Platform. ESSENCE facilitates access to BioSense data for approved local health departments, CDPH, and hospital users. ESSENCE facilitates detection and monitoring of novel or emerging health conditions to support early detection of potential disease outbreaks. For example, it can provide standardized syndrome definitions and queries, generate alerts if visits of concern reach predefined thresholds, and can support monitoring of population health trends.   
  • NSSP Community of Practice – Convening of public health professionals. The NSSP Community of Practice convenes public health professionals across the nation to share expertise, tools, and best practices. Participants include public health jurisdictions that contribute data to the NSSP BioSense Platform and practitioners who use local syndromic surveillance systems, along with CDC, other federal agencies, partner organizations, hospitals, health care professionals, and academic institutions. After the California statewide syndromic surveillance program is established, CDPH will also lead a California Community of Practice for California’s syndromic surveillance partners.  

Promoting Data Interoperability 

Syndromic surveillance data are recommended to be used in combination with additional data sources. Data integration helps to inform a more complete picture of public health so that public health professionals can monitor emerging threats to health and safety. 
Colorful dots connected by lines to form a sphere

For example, NSSP uses the following data sources: 
  • Emergency department and other health care data (e.g., urgent care data) 
  • Commercial laboratory data 
  • Mortality data 
  • Department of Defense data from U.S.-based medical centers 
  • Veterans Affairs Medical Center data 
  • Administration for Strategic Preparedness and Response Disaster Medical Assistance Teams data
  • National Weather Service data 
  • Air quality data 
  • In staging: National Notifiable Disease data 
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