2014.ISDS.Abstracts.Final.pdf


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ISDS 2014 Conference Abstracts

Comparison of ILINet and ESSENCE for Influenza 
Surveillance at the Local Level
Sarah Connolly1, 3 and Gregory Danyluk*1, 2

1Florida Department of Health, Seminole County, Sanford, FL, USA; 2Epidemiology, Florida Department of Health, Polk County, 
Bartow, FL, USA; 3Emory University, Laney Graduate School, Atlanta, GA, USA

Objective
To compare influenza-like illness (ILI) data reported to the 

Centers for Disease Control and Prevention (CDC) U.S. Outpatient 
Influenza-like Illness Surveillance Network (ILINet) with discharge 
diagnosis data for influenza from the same reporting source obtained 
through the Electronic Surveillance System for the Early Notification 
of Community-based Epidemics (ESSENCE) in Seminole County, 
Florida.

Introduction
ILINet is used nationwide by sentinel healthcare providers for 

reporting weekly outpatient visit numbers for influenza-like illness to 
CDC. The Florida Department of Health receives urgent care center 
(UCC) data through ESSENCE from participating facilities. Seminole 
County is unique in that its four sentinel providers located in separate 
UCCs report into both systems, and all their discharge diagnoses 
are available through ESSENCE. However, the reported number 
of patients being discharged from those providers with diagnoses 
of influenza is not equivalent to the number of cases reported into 
ILINet. Data from the two systems were therefore compared both 
among and between the individual sentinel providers in order to 
determine the extent of the variation over four influenza seasons.

Methods
Influenza-like illness is defined by the Centers for Disease 

Control and Prevention (CDC) for surveillance purposes as “fever 
(temperature of 100°F [37.8°C] or greater) and a cough and/or a sore 
throat without a KNOWN cause other than influenza.” [1] ILINet 
data from sentinel providers for percent ILI visits were extracted 
for each of the influenza seasons (reporting weeks 40 through 20 
of the following year) from 2009 through 2013. ESSENCE data 
for patients with a discharge diagnosis of influenza were extracted 
from the same providers for the same seasons, and the percentage 
of influenza discharge diagnoses was calculcated based on total visit 
counts. Pearson correlation coefficients were calculated to compare 
ILINet and ESSENCE data for each influenza season and provider 
location, both for the entirety of the season as well as identified peak 
weeks (Table 1); for the few instances where ILINet data had not been 
reported, those weeks were not included in the calculations.

Results
When data from all four providers were aggregated for each 

respective surveillance system, the correlation between ILINet and 
ESSENCE discharge diagnoses of influenza ranged from 0.53 to 0.89 
over the entirety of each season, and from 0.45 to 0.86 for peak weeks 
(Table 2). By contrast, the correlation by individual provider between 
the two systems ranged from 0.02 to 0.77 over each season, and from 
-0.15 to 0.92 for peak weeks (Table 3).

Conclusions
Although the correlations between the surveillance systems 

ILINet and ESSENCE were positive when viewed in aggregate, 
individual sites demonstrated inconsistency in reporting. This study 

demonstrates a need to identify the sources of differences that occur 
between making and reporting a determination of ILI versus those 
involved in a discharge diagnosis of influenza

Table 1

Table 2

Table 3

Keywords
ESSENCE; ILINet; Influenza surveillance; Influenza-like illness 
surveillance; Influenza

Acknowledgments

We wish to thank the epidemiology staff of the Florida Department of 
Health in Seminole County, their counterparts at the Florida Department 
of Health in Orange County, and the staff at the Bureau of Epidemiology 
for the Florida Department of Health in Tallahassee, in particular David 
Atrubin for ESSENCE assistance, and Colin Malone for his comments 
regarding statewide influenza surveillance. We also extend a deep 
appreciation to the ILINet sentinel healthcare providers for their continued 
participation.

References

1) Centers for Disease Control and Prevention (US). Overview of Influenza 
Surveillance in the United States [Internet]. Atlanta. [updated 2013 
October 24; cited 2014 August 29]. Available from:

http://www.cdc.gov/flu/weekly/overview.htm

*Gregory Danyluk
E-mail: gregory.danyluk@flhealth.gov    

Online Journal of Public Health Informatics * ISSN 1947-2579 * http://ojphi.org * (1):e121, 201