Syndromic Surveillance

About Syndromic Surveillance Data

Syndromic surveillance is a strategy used by public health to detect emerging health issues and monitor the health of the community in near-real time. The Virginia Department of Health’s (VDH) Office of Epidemiology collects and analyzes health data from participating emergency departments and urgent care centers to identify emerging trends of public health concern. When interpreting health trends from syndromic surveillance, please keep in mind of certain data limitations, which can be viewed on the Limitations tab.

In Virginia, syndromic surveillance is used to monitor the level of influenza-like illness during flu season, illnesses and injuries associated with weather events and natural disasters, health problems associated with mass gatherings, and emerging outbreaks or issues of public health concern, such as drug overdoses. Please see published reports on various syndromic surveillance activities in the following health topics.

• Drug overdose surveillance: VDH quarterly drug overdose reports, the 2015 -2021 monthly and annual statistics tables and a link to the VDH Opioid Addiction Indicators dashboard are available on this page.

• Heat-Related Illness surveillance: VDH information and seasonal surveillance data on heat-related illness using ESSENCE.

• Other surveillance events: VDH data and reports on other surveillance events of public health concern or interest.

It is important to note that syndromic surveillance does not replace traditional public health surveillance methods, such as the reporting of disease conditions required by the Code of Virginia.

For information on syndromic surveillance reporting as part of the Meaningful Use electronic health record incentive program please see the VDH Meaningful Use page. If you have additional questions, please contact

Limitations of Syndromic Surveillance Data

Syndromic surveillance uses existing heath data sources for the purposes of near real-time surveillance of public health issues. The primary use of emergency department (ED) and urgent care (UC) visit information is for clinical care of patients by the health care facility. When this information is used by the Virginia Department of Health (VDH) for syndromic surveillance, it is considered a secondary use. This secondary use is subject to limitations that should be considered when interpreting these data.

For syndromic surveillance, the following information is reported to VDH: location and time of ED or UC visit, patient demographics (e.g. sex, race), patient residential zip code, chief complaint, and diagnosis.

Chief Complaint Variability: The chief complaint captures the patient’s primary reason for seeking medical care in near real-time and is commonly recorded as a free text field, which may include misspellings or abbreviations. It may also lack context that could assist public health with interpretation of the reason for visit. For example, the chief complaint may state “sick” or “feels unwell” without mentioning any symptoms such as fever, vomiting, or cough. Variability in the chief complaint across health care facilities can sometimes make it difficult to measure the exact burden of illness or injury in a community.

Diagnosis Coding Delays: Diagnoses for a patient’s visit are recorded using standardized coded values outlined by the International Classification of Diseases (ICD) 9th and 10th Revision code sets. These diagnosis codes are used by health care facilities throughout the United States for medical coding, reporting, and billing purposes. Reporting of ICD-9 and ICD-10 values to VDH provides additional information on a patient’s health care visit. However, transmission of diagnosis data to VDH can be delayed and thus does not support near real-time surveillance of public health issues. Additionally, some healthcare facilities are not able to send diagnosis codes to VDH.

Data Volume Varies Over Time: The volume of data transmitted to VDH have changed over time. The number of EDs and UCs reporting to VDH has increased from 89 in 2010 to 166 in 2020, leading to improved coverage of Virginia’s population in more recent years. This increase in data volume should be taken into consideration when interpreting trends across years.

Data Quality Varies Over Time: The quality of data has also improved over time because a national syndromic surveillance data reporting standard was established in 2011. This standard specifies what pieces of information should be sent to VDH to ensure consistency in the format and reporting of syndromic surveillance data. Improvements in data quality as a result of the 2011 standard should be taken into consideration when interpreting trends across years.

COVID-19 Pandemic: During the Coronavirus Disease 2019 (COVID-19) pandemic, a decrease in the total number of ED visits occurred in Virginia. Because of this change in health care seeking behavior, VDH urges caution when comparing 2020 statistics to other years.

Limitations of Syndromic Surveillance Data (.PDF Link)