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ISDS Annual Conference Proceedings 2012. This is an Open Access article distributed under the terms of the Creative Commons Attribution-
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ISDS 2012 Conference Abstracts

Using GI Syndrome Data as an Early Warning Tool for
Norovirus Outbreak Activity
Erin E. Austin*, Jun Yang and Tim Powell

Division of Surveillance and Investigation, Virginia Department of Health, Richmond, VA, USA

Objective
To assess the relationship between emergency department (ED)

and urgent care center (UCC) chief complaint data for gastrointesti-
nal (GI) illness and reported norovirus (NV) outbreaks to develop an
early warning tool for NV outbreak activity. The tool will provide an
indicator of increasing NV outbreak activity in the community al-
lowing for earlier public health action to mitigate NV outbreaks.

Introduction
Norovirus infection results in considerable morbidity in the United

States where an estimated 21 million illnesses, 70,000 hospitaliza-
tions, and 800 deaths are caused by NV annually (1). Additionally,
NV is responsible for approximately 50% of foodborne outbreaks (1).
Between January 2008 and June 2012, 875 NV outbreaks were re-
ported to the Virginia Department of Health (VDH). To assist in de-
tecting possible disease outbreaks such as NV, VDH utilizes the
web-based Electronic Surveillance System for Early Notification of
Community-based Epidemics (ESSENCE) to monitor and detect pub-
lic health events across Virginia. ESSENCE performs automated
parsing of chief complaint text into 10 syndrome categories, includ-
ing a non-specific GI syndrome that serves as a proxy for GI illnesses
like NV.

Methods
ED and UCC chief complaints parsed into the ESSENCE GI syn-

drome category were compared to confirmed and suspected NV out-
breaks across four years. In this study, the analysis periods were
defined as week 21 through week 20 of the subsequent year. GI syn-
drome visits as a proportion of all ED and UCC visits and NV out-
break counts were aggregated by week. Time-series, correlation, and
logistic regression analyses were performed. Low NV outbreak ac-
tivity weeks were defined as those with 4 or fewer outbreaks, and
high NV outbreak activity weeks were those with 5 or more out-
breaks. Based on low NV outbreak activity weeks, baseline and
threshold values for the weekly percent of GI syndrome visits were
calculated for each analysis period. Baseline calculation was the av-
erage weekly percent of GI syndrome visits from week 21 to week 31
and threshold value was baseline plus two standard deviations.
Weekly percent of GI syndrome visits was compared to the threshold
value to serve as an indicator of increasing NV outbreak activity.

Results
The study period was from May 18, 2008 to May 19, 2012 (Fig 1).

A total of 1,425,728 GI syndrome visits and 804 confirmed and sus-
pected NV outbreaks were analyzed. Weekly visits to ED and UCC
facilities with GI syndrome were highly correlated with outbreaks of
NV in the community (r =0.809, p <.0001). Median and mean num-
ber of NV outbreaks per week were 2 and 4, respectively (range 0-
23). NV outbreaks were more prominent during the winter months
with peaks occurring between weeks 3-9. Median and mean percent

of GI syndrome visits per week were 10.2% and 10.5%, respectively
(range 8.9%-12.8%). Weeks with high NV outbreak activity were
more likely to occur when the weekly percent of GI syndrome visits
had surpassed the threshold value (OR =110.7, 95% CI: 31.9-384.8).
On average, weekly percent of GI syndrome visits surpassed the
threshold value 1.25 weeks prior to the start of high NV outbreak ac-
tivity weeks (range 0-3).

Conclusions
These results support the use of syndromic surveillance GI illness

data as an early warning indicator of increasing NV outbreak activ-
ity in Virginia. This study identified that GI syndrome visits crossed
a calculated threshold value on average 1.25 weeks before the initi-
ation of high NV outbreak activity. Although NV outbreaks occur
year round, this study attempted to identify an indicator to trigger
meaningful risk communication to the community immediately prior
to high NV outbreak activity with the goal of reducing the magnitude
of NV outbreaks. This early warning tool for NV outbreak activity
will be implemented in the following year to validate its effective-
ness and timeliness in mitigating NV outbreaks in Virginia.

Percent of Emergency Department and Urgent Care Center Visits with GI
Syndrome and Reported Norovirus Outbreaks, Virginia, May 2008-May
2012.

Keywords
Syndromic surveillance; ESSENCE; Norovirus; GI illness

References

Centers for Disease Control and Prevention (2012). Burden of norovirus
illness and outbreaks. Retrieved September 5, 2012, from
http://www.cdc.gov/norovirus/php/illness-outbreaks.html.

*Erin E. Austin
E-mail: erin.austin@vdh.virginia.gov

Online Journal of Public Health Informatics * ISSN 1947-2579 * http://ojphi.org * 5(1):e69, 2013