Three years of emergency department gastrointestinal syndromic surveillance in New York City: what have we found?

BACKGROUND

Use of syndromic surveillance as a tool to detect outbreaks and potential biologic or chemical terrorist attacks is increasing. Evaluating health departments' use of syndromic surveillance is necessary to determine the value of this methodology.

METHODS

Syndromic surveillance signals detected by the New York City Department of Health and Mental Hygiene (DOHMH) during November 2001-August 2004 were reviewed for diarrhea and vomiting syndromes, the methods used to investigate such signals, and results of these investigations to determine if any unreported outbreaks were detected. Gastrointestinal (GI) outbreaks reported to DOHMH also were reviewed to understand why they were not detected by DOHMH's Emergency Department (ED) syndromic surveillance system.

RESULTS

During the study period, ED surveillance generated 98 citywide and 138 spatial GI signals. Multiple outbreaks suspected to be caused by norovirus and rotavirus were identified, as well as a citywide increase in diarrheal illness. Of 98 citywide signals detected, 73 (75%) occurred during seasonal outbreaks. During the same period, 49 GI outbreaks were reported to DOHMH; none was detected simultaneously by ED surveillance.

CONCLUSION

Only substantial, citywide syndromic signals were identified as outbreaks and routinely reported. GI outbreaks did not generate syndromic signals. Syndromic surveillance signals occur frequently, are difficult to investigate satisfactorily, and should be viewed as a supplement to, rather than a replacement for, well-maintained traditional surveillance systems that rely on strong ties between clinicians and public health authorities.