NSSP and NCIRD Assess ILINet Collaboration

States routinely use syndromic surveillance to monitor influenza-like illness (ILI) and detect novel influenza virus activity. Last year, the NSSP team collaborated with the Domestic Surveillance Team in CDC’s National Center for Immunization and Respiratory Diseases (NCIRD) to help states use ESSENCE to report in ILINet for the upcoming influenza season. ILINet is the U.S. Outpatient Influenza-like Illness Surveillance Network and serves as the syndromic surveillance component of influenza surveillance in the United States. ILINet collects information on outpatient visits to health care providers for influenza-like illness. Since influenza season is rapidly approaching, the NSSP team met with ILINet analysts to assess their experience thus far.

Slightly more than 50% of ILINet patient visits are from emergency medicine. Although most hospitals now use some form of electronic syndrome definition, ILINet was founded in the era of traditional syndromic surveillance when physicians would manually go through medical records and count the number of patients meeting a specific syndrome definition. To this day, ILINet reflects a combination of providers that do traditional and electronic reporting.

There are a couple of options for entering data from NSSP–ESSENCE into ILINet. Analysts and epidemiologists in health jurisdictions can pull NSSP–ESSENCE data from their own system and then upload to the ILINet database using a spreadsheet. Or, the NCIRD team can assist by extracting the data from NSSP–ESSENCE and uploading the data into ILINet. Far more practitioners choose to pull data themselves.

NCIRD’s flu team uses historic data to generate a baseline for each provider, the health jurisdiction, the U.S. Department of Health and Human Services (HHS) regions, and the nation. They look at how far above or below baseline influenza activity is each year. To ensure data are comparable to the calculated baselines, they also ask state contacts to identify the facilities from whatever syndromic systems are being used to collect aggregate data. Data from facilities that see, on average, more than 500 patients per week will undergo a data validation process.

Most reporting facilities use the chief complaint (CC) field only. Some use chief complaint and discharge diagnosis (CCDD). Nationally, the two strategies present the same overall picture, but more information is available using CCDD.

Benefits of Integrating Syndromic Data with ILINet

The use of electronic syndromic surveillance generates a wealth of data—and with much less effort. The advantages of using syndromic surveillance are reduced reporting burden, more timely and complete information, consistently applied criteria, and year-round monitoring. Everyone benefits from having comparable data to analyze across health jurisdictions. During influenza season, the NCIRD’s flu team conducts monthly meetings with states, and having timely data has improved communication.


The NCIRD and NSSP teams have worked through some challenges. Initially, NCIRD had to set up data sharing rules with the interested health jurisdictions. This proved challenging as there wasn’t a solution that would accommodate the concerns of each individual health jurisdiction. Having a rule-sharing template would have been helpful. On the basis of lessons learned through recent data-sharing workshops, the NSSP team has some ideas to implement this fall that should make data sharing easier. For example, NSSP is planning an update that will enable sites to share specific syndromes without granting full data access.

Keeping up with site changes is also challenging—staff move on, facility names change, and physicians’ hospital affiliations may change. Such changes made matching facilities in NSSP–ESSENCE to the appropriate ID in ILINet difficult. Even more challenging, however, is keeping up with the technical aspects of using a different system and tools.

Next Steps

The NCIRD and NSSP teams will continue to evaluate the process and share what works or needs improvement. In preparation for an emergency event, such as a pandemic, NCIRD would like to learn how to interpret daily ILI data. Both teams also want broader coverage. Getting data from 10 hospitals in the same metro area is useful, but getting data from rural areas is needed to better characterize the extent of a health problem. The NCIRD team also has an interest in diversifying their participating provider types to mimic the care-seeking behaviors of the U.S. population.

The NSSP team will continue to work closely with NCIRD and with other programs that are learning to use syndromic data. Those who routinely work with syndromic data understand its complexities. But educating others on how to interpret these data and what actions to take in response to findings is one of the more challenging aspects of integrating system data.

The NSSP team thanks the analysts at NCIRD for describing how they use syndromic data to validate ILINet results.