Syndromic Surveillance in Public Health Practice, New York City

Abstract

Hygiene has established a syndromic surveillance system that monitors emergency department visits to detect disease outbreaks early. Routinely collected chief complaint information is transmitted electronically to the health department daily and analyzed for temporal and spatial aberrations. Respiratory, fever, diarrhea, and vomiting are the key syndromes analyzed. Statistically significant aberrations or "signals" are investigated to determine their public health importance. In the first year of operation (November 15, 2001, to November 14, 2002, 2.5 million visits were reported from 39 participating emergency departments, covering an estimated 75% of annual visits. Most signals for the respiratory and fever syndromes (64% and 95%, respectively) occurred during periods of peak influenza A and B activity. Eighty-three percent of the signals for diarrhea and 88% of the signals for vomiting occurred during periods of suspected norovirus and rotavirus transmission.T wo recent phenomena have contributed to widespread interest in monitoring nonspecific health indicator data to detect disease outbreaks early. The first is heightened concern about bioterrorism, particularly the ability of public health agencies to detect a large-scale bioterrorist attack in its early stages. The second is the proliferation of electronic databases in healthcare settings. Initially designed to facilitate billing, health information systems capture an increasingly rich array of clinical detail. Recent advances in information technology make extracting, transmitting, processing, and analyzing these data feasible for public health purposes. The emergency department surveillance system we describe is an early prototype of what may become a standard component of modern public health surveillance.In New York City, emergency department chief complaint surveillance evolved out of the public health response to the September 11, 2001, World Trade Center attacks (1). When this labor-intensive effort ended, the New York City Department of Health and Mental Hygiene (DOHMH) began intensively recruiting hospitals capable of providing emergency department visit data in electronic formats. We describe the methods and chief results from the first 12 months of experience with this electronic system. Materials and Methods Data Transmission and ProcessingData files are transmitted to DOHMH 7 days per week, either as attachments to electronic mail messages or through direct file transfer protocol (FTP). Half of participating hospitals have automated the transmission process. Data processing and analysis are carried out on a laptop computer that can be operated either through the DOHMH local area network or through remote dial-up, which facilitates weekend and holiday analysis. Each morning, an analyst retrieves the files, inspects them for quality and completeness, and saves them for processing and analysis in SAS (version 8, SAS Institute Inc., Cary, NC). If a file is not received by 10:00 a.m., the analyst contacts hospitals to obtain missing data. The anal...

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