About Syndromic Surveillance

What is Syndromic Surveillance?

Syndromic surveillance (or enhanced surveillance) uses health data sources to identify and monitor events of public health concern in near real time. The purpose of syndromic surveillance is to improve community health through early detection of events that may impact health. It was originally developed to detect outbreaks and bioterrorism events, but now is used for surveillance of infectious and chronic diseases, injuries, mental health conditions, and environmental exposures.

Virginia’s syndromic surveillance system is known as ESSENCE (Electronic Surveillance System for the Early Notification of Community-based Epidemics).

Syndromic surveillance does not replace traditional public health surveillance methods, such as the reporting of disease conditions required by the Code of Virginia.


Where Does VDH Get Syndromic Surveillance Data?

Virginia’s syndromic surveillance system (ESSENCE) contains visit data from emergency departments (EDs) and urgent care centers in Virginia. The data provide a near real time picture of community health. Participation in syndromic surveillance fluctuates over time (see Limitations), but has increased overall in Virginia.

In 2022, over 170 EDs and urgent care centers reported data to Virginia ESSENCE. Facilities interested in reporting data to Virginia ESSENCE can review the VDH Promoting Interoperability page.


Who Can Access the Virginia Syndromic Surveillance System?

VDH epidemiologists and communicable disease staff can access Virginia’s syndromic surveillance system (ESSENCE). However, syndromic surveillance data for a variety of health conditions, including drug overdose, COVID-like illness, and heat-related illness, are available publicly from the VDH Syndromic Surveillance website.


How are Syndromic Surveillance Data Used?

Public health professionals use syndromic surveillance data to monitor trends for a variety of health conditions. This information can assist public health leaders with making decisions to improve population health.

  • Gastrointestinal Illness: VDH epidemiologists monitor gastrointestinal (GI) illness trends and notify local health districts when GI illness activity crosses a predefined threshold. This threshold has been shown to be an early predictor of increased norovirus activity. Local health districts can then provide timely information to community partners, including long-term care facilities and schools, about norovirus prevention and control strategies.
  • Influenza-like Illness: The percent of ED and urgent care visits for influenza-like illness (ILI) are used together with influenza laboratory results to determine the level of influenza activity in Virginia. Syndromic surveillance data, including ILI data, can be viewed by demographic characteristics such as sex, age group, and race/ethnicity, which allows public health practitioners to determine which groups are most affected.
  • Disaster-Related Health Events: During natural disasters such as hurricanes and winter storms, VDH epidemiologists monitor ED and urgent care visits for injuries and illness related to weather, including carbon monoxide (CO) poisoning. When epidemiologists detect an increase in visits related to CO poisoning, local health districts can issue timely reminders to the general public about safe use of portable generators.


How are Syndromic Surveillance Data Presented?

Measures: VDH presents syndromic surveillance data using one or more of the measures listed below. The appropriate measure depends on the topic, time period, and data quality.

  • Number of emergency department (ED) or urgent care visits
  • Rate per 10,000 ED Visits: number of ED and/or urgent care visits divided by the total number of ED or urgent care visits for a defined geographic area during the time period of interest. This metric provides a consistent rate calculation across time when the number of facilities reporting changes over time.
  • Rate per 100,000 Population: number of ED and/or urgent care visits divided by the total number of residents in a given geographic area during the time period of interest. Population estimates obtained from the U.S. Census Bureau.

Suppression: When data are presented by VDH Health District or smaller geographic areas, VDH suppresses visit counts of 1 to 4 and rates with numerators of 1 to 4 to maintain confidentiality and accurate rate calculations. That means instead of showing counts of 1 to 4 or rates based on those counts, VDH will display an asterisk or another symbol.


How Should VDH Syndromic Surveillance Data be Cited?

When using VDH syndromic surveillance data, please cite:

Syndromic Surveillance Data, Division of Surveillance and Investigation, Office of Epidemiology, Virginia Department of Health. http://www.vdh.virginia.gov/surveillance-and-investigation/syndromic-surveillance/.