What is syndromic surveillance?

What is Syndromic Surveillance

Syndromic surveillance is the systematic collection and real-time analysis of health-related indicators that occur before confirmed diagnoses, enabling early detection of disease outbreaks, bioterrorism events, or other public health threats. 1

Core Definition and Purpose

Syndromic surveillance detects health indicators that precede formal diagnosis, potentially signaling early stages of chemical releases or infectious disease outbreaks to minimize public health consequences. 1 The system uses existing health data in real time to provide immediate analysis and feedback to those responsible for investigating and responding to potential outbreaks. 2

Key Operational Characteristics

Data Sources and Collection Methods:

• Emergency department visits and diagnoses are the primary data source, though multiple streams are increasingly integrated 3, 2
• Hospital admission patterns and specific syndrome occurrences are monitored continuously 1
• Automated monitoring systems track healthcare utilization data daily or more frequently 3
• Modern approaches include internet search patterns and social media monitoring (such as videos documenting clinical symptoms after the 2017 sarin attacks in Syria) 1

Temporal Framework:

• Data are collected and analyzed in near real-time, distinguishing this approach from traditional surveillance 3, 2
• Systems perform continuous monitoring rather than periodic reporting 2
• Analysis occurs before laboratory confirmation or definitive diagnosis 1, 2

Primary Applications

Disease Detection and Monitoring:

• Early outbreak detection for conditions like influenza-like illness and drug-related syndromes (the highest priority syndromes across health departments) 3
• Tracking the size, spread, and tempo of ongoing outbreaks 2
• Monitoring disease trends over time 2
• Providing reassurance when outbreaks have not occurred 2

Bioterrorism and Emergency Response:

• Detecting intentional release of biological agents through unusual illness patterns 1
• Monitoring health impacts from natural disasters, hazardous material exposures, or environmental events like wildfire smoke 4
• Situational awareness during mass gatherings or high-risk events 4

Methodological Approach

Statistical Detection Methods: The systems employ time series and spatial cluster analysis techniques, including SMART, EWMA (Exponentially Weighted Moving Average), CuSum (Cumulative Sum), and WSARE algorithms. 5 Combined spatial and temporal methods are typically implemented together to maximize detection capability. 5

Data Quality and Processing:

• All participating health departments routinely monitor data quality 3
• Systems verify data through standardized quality control procedures 3
• Multiple data streams (emergency department data, telephone helpline data, general practice consultations) provide complementary detection capabilities for different outbreak types 6

Critical Limitations and Context

Important Caveats:

• Syndromic surveillance does not replace traditional public health surveillance systems 2
• It does not substitute for direct physician reporting of unusual or suspect cases 2
• Detection ability varies seasonally (for example, influenza outbreaks starting in July are detected sooner than those starting later in the year) 6
• Small outbreaks may not be detected (cryptosporidiosis outbreaks with fewer than 1,000 symptomatic individuals are unlikely to trigger alerts) 6
• The utility of specific data streams varies geographically and by disease type 6

Complementary Role: Syndromic surveillance supplements information from traditional sources to provide a more timely and comprehensive picture of community health status. 4 Reports of unusual presentations from clinicians remain critical, but automated methods enhance rapid epidemic detection. 1

Implementation Requirements

Health departments implementing syndromic surveillance must establish 24-hour-a-day, 7-day-a-week capacity to receive and act on positive reports suggesting intentional release of biological agents or other public health threats. 1 The systems require collaboration among public health agencies, healthcare providers, information-system professionals, and academic investigators. 2