Differentiating ZIP Codes in Syndromic Data; What Can They Tell Us?

NYC emergency departments (ED) visits were categorized into NYC residential, NYC PO Box or commercial building, commuters into NYC, and out-of-town visitors by patient reported ZIP code. Spatial and temporal trends in total ED visits by home ZIP code type were analyzed to describe patterns in each group, and determine how such information might inform daily syndromic surveillance activities. Of the approximately 4 million ED visits in NYC during 2011, the number of visits by commuters and out-of-town visitors were 125,236 (3.1%) and 45,158 (1.1%) respectively. Out-of town visitors were found to mostly go to hospitals in Manhattan rather than the outer boroughs. While the seasonal trends and day-of-week patterns for the NYC residents and the commuters appear to be fairly similar, temporal trends for NYC residents and out-of-town visitors were found to be different. Out-of-town visitors represents a unique subset of the ED population and our results suggest that including a separate analyses of total ED and syndromic visits by out-of-town visitors might provide additional information that could prove useful to daily syndromic surveillance activities