title: Role of data aggregation in biosurveillance detection strategies with applications from ESSENCE.
abstract: BACKGROUND
  Syndromic surveillance systems are used to monitor daily electronic data streams for anomalous counts of features of varying specificity. The monitored quantities might be counts of clinical diagnoses, sales of over-the-counter influenza remedies, school absenteeism among a given age group, and so forth. Basic data-aggregation decisions for these systems include determining which records to count and how to group them in space and time.
  
  
  OBJECTIVE
  This paper discusses the application of spatial and temporal data-aggregation strategies for multiple data streams to alerting algorithms appropriate to the surveillance region and public health threat of interest. Such a strategy was applied and evaluated for a complex, authentic, multisource, multiregion environment, including >2 years of data records from a system-evaluation exercise for the Defense Advanced Research Project Agency (DARPA).
  
  
  METHODS
  Multivariate and multiple univariate statistical process control methods were adapted and applied to the DARPA data collection. Comparative parametric analyses based on temporal aggregation were used to optimize the performance of these algorithms for timely detection of a set of outbreaks identified in the data by a team of epidemiologists.
  
  
  RESULTS
  The sensitivity and timeliness of the most promising detection methods were tested at empirically calculated thresholds corresponding to multiple practical false-alert rates. Even at the strictest false-alert rate, all but one of the outbreaks were detected by the best method, and the best methods achieved a 1-day median time before alert over the set of test outbreaks.
  
  
  CONCLUSIONS
  These results indicate that a biosurveillance system can provide a substantial alerting-timeliness advantage over traditional public health monitoring for certain outbreaks. Comparative analyses of individual algorithm results indicate further achievable improvement in sensitivity and specificity.
authors.affiliation: Johns Hopkins University Applied Physics Laboratory, 11100 Johns Hopkins Road, Mailstop 8-224, Laurel, MD 20723, USA. Howard.Burkom@jhuapl.edu
authors.forename: Howard S
authors.initials: HS
authors.lastname: Burkom
authors.forename: Y
authors.initials: Y
authors.lastname: Elbert
authors.forename: A
authors.initials: A
authors.lastname: Feldman
authors.forename: J
authors.initials: J
authors.lastname: Lin
mesh_terms: D000465:Algorithms; D023482:Bioterrorism / Q000517:prevention & control*; D003625:Data Collection; D004196:Disease Outbreaks / Q000517:prevention & control*; D015991:Epidemiologic Measurements; D006801:Humans; D015233:Models, Statistical; D011159:Population Surveillance / Q000379:methods*; D014481:United States