ISDS Annual Conference Proceedings 2018. This is an Open Access article distributed under the terms of the Creative Commons Attribution-
Noncommercial 3.0 Unported License (http://creativecommons.org/licenses/by-nc/3.0/), permitting all non-commercial use, distribution,  
and reproduction in any medium, provided the original work is properly cited.

ISDS 2018 Conference Abstracts

Maricopa County’s use of NSSP ESSENCE to detect 
cases during a hepatitis A outbreak
Rasneet S. Kumar*, James Matthews, Jessica R. White, Alice Carrigan, 
Jennifer Collins, Nicole Fowle and Jigna Narang
Maricopa County Department of Public Health, Office of Epidemiology, Phoenix, AZ, USA

Objective
To demonstrate the utility of the National Syndromic Surveillance 

Program’s (NSSP) version of the Electronic Surveillance System for 
Early Notification of Community-based Epidemics (ESSENCE) for 
case detection during a 2017 outbreak of hepatitis A virus (HAV) 
infection among persons experiencing homelessness in Maricopa 
County, Arizona.

Introduction
On 3/29/2017, the Maricopa County Department of Public Health 

(MCDPH) received three reports of confirmed HAV infection from 
an onsite clinic at Campus A that assists individuals experiencing 
homelessness, a population at risk for HAV transmission. To identify 
the scope of the problem, the department initiated rapid HAV 
infection case detection using NSSP ESSENCE.

Methods
MCDPH created a myESSENCE dashboard that searched for chief 

complaint keywords and discharge diagnosis codes from 15 Maricopa 
County emergency department and inpatient hospital records 
using three separate queries: (1) HAV infection; (2) hepatitis virus 
infection; and (3) HAV infection symptoms combined with terms for 
homelessness. The dashboard was reviewed retrospectively for the 90 
days prior to the initial report of the cluster (12/28/2016 – 3/29/2017). 
Based on this review, MCDPH epidemiologists decided to use the 
first query (HAV infection-specific) only, because reviewing the 
line list for all three queries was resource-intensive and resulted in 
duplicate cases. The query was monitored every weekday morning 
from 3/30/2017 to the close of the outbreak on 7/22/2017.

When a potential HAV infection case was identified in ESSENCE, 
epidemiologists attempted to identify the patient in Arizona’s Medical 
Electronic Disease Surveillance Intelligence System (MEDSIS) 
using date of birth. Potential cases with an existing HAV infection, 
MEDSIS record, and a listed address matching Campus A were 
interviewed by a disease investigator. When potential cases did not 
have a HAV infection report in MEDSIS, a review of the medical 
record or follow-up with the facility’s infection preventionist was 
conducted to confirm HAV infection diagnosis and homelessness 
status before contacting the patient for interview. Following patient 
interview, all cases with a positive HAV immunoglobulin M antibody, 
HAV infection symptomology, and association with Campus A, 
were considered outbreak cases. All other patients were considered 
unrelated to the outbreak.

MCDPH evaluated the timeliness of reporting by comparing the 
date when outbreak cases were first available in ESSENCE to the date 
they were entered into MEDSIS.

Results
From 3/30/2017 – 7/22/2017, MCDPH identified 37 potential HAV 

infection cases in ESSENCE. Eleven cases were classified as outbreak 
cases, while the other 26 patients lacked recent HAV infection 
symptoms, laboratory confirmation, or association with Campus A. 
All 11 outbreak cases’ records included the ICD-CM-10 code B15.9 
(Hepatitis A without hepatic coma), and 3 records included the code 

Z59 (Problems related to housing and economic circumstances). 
The HAV infection-specific query in ESSENCE identified 11 (73%) 
of the 15 total outbreak cases; however, all cases were reported in 
MEDSIS prior to being flagged in ESSENCE. On average, cases 
were reported to MEDSIS 9 days earlier than identified in ESSENCE 
(range, 0 - 21 days). Of note, ESSENCE helped identify the outbreak 
index case, previously lost to follow-up, as an individual experiencing 
homelessness. This information helped MCDPH perform additional 
follow-up, which revealed that the individual had arrived from San 
Diego, CA, a city with an ongoing outbreak of HAV infection in their 
homeless and drug-using population. This epidemiologic link was 
identified on 3/30/2017, over a month before the Centers for Disease 
Control and Prevention confirmed a match by genome sequencing 
between the index case and the neighboring outbreak on 5/5/2017.

Conclusions
Use of ESSENCE identified most of the HAV infection cases 

from this outbreak among individuals experiencing homelessness 
but no sooner than traditional surveillance methods. However, use 
of ESSENCE allowed for identification of the outbreak index case, 
leading to epidemiological linkage to outbreak origin approximately 
one month prior to molecular laboratory confirmation.

Keywords
Hepatitis A Virus; Homeless; Syndromic Surveillance; ESSENCE

*Rasneet S. Kumar
E-mail: rasneetkumar@mail.maricopa.gov

Online Journal of Public Health Informatics * ISSN 1947-2579 * http://ojphi.org * 10(1):e145, 2018