Effective Utilization of a Emergency Department Syndromic Surveillance System for Active Case-Finding During Investigation of a Cluster of Sodium Azide Poisoning Cases

Background: Although the focus of syndromic surveillance systems (SSS) has been early detection of outbreaks, the capture of real-time pre-diagnostic chief complaint data, and rapid accessibility of such health information may also serve other valuable functions during the course of outbreak investigations.  Use of SSS for additional active case finding during the course of an outbreak has not been well described.  In 2010, Health Department investigation of a point-source cluster of poisoning cases with unusual neurological manifestations provided an opportunity to explore the utility of SSS data for additional case-finding.

Objective: To assess the utility and effectiveness of using SSS data as an adjunctive epidemiologic tool for additional case-finding during a time-sensitive outbreak investigation.

Methods: The outbreak investigation was initiated after four cases of acute illnesses with specific significant neurological symptoms were reported from unrelated patrons of a restaurant establishment.  Based on initial clinical information, epidemiologic investigation and case-control study, a point-source food item was implicated and a toxicologic agent was considered as the likely etiology for the cluster.   In order to quickly find additional potential cases and assess the extent to which other persons may have been affected, the Electronic Surveillance System for the Early Notification of Community-based Epidemics (ESSENCE) database was mined to search for patients who may have presented to any of 18 area Emergency Departments (ED) with similar chief complaints within the designated timeframe.

Results: A possible case was defined as any patient presenting to an area ED within a known temporal window of exposure, with chief complaints of either altered mental status (AMS), syncope, dizziness, tingling in the extremities, or low blood pressure (LBP).  From the 1,827 total ED visits recorded in ESSENCE for that date, 81 possible cases were identified as presenting with at least one of the following chief complaints using this definition: AMS (38), dizziness (16), syncope (9), tingling (7), LBP (11).  ED records for these patients were requested, and cases were excluded from further investigation if alternate diagnoses were well-documented on chart review.  Of 29 cases which were subsequently selected for further investigation and interview, one additional new case belonging to this cluster was identified and confirmed.

Conclusions: Syndromic Surveillance System data provided an expedient, accessible, and effective means for additional case-finding during the course of this outbreak investigation.  Utilization of SSS databases may be a valuable adjunctive epidemiologic tool alongside traditional epidemiologic techniques in selected circumstances.