title: Acute diarrheal syndromic surveillance: effects of weather and holidays.
abstract: OBJECTIVE
  In an effort to identify and characterize the environmental factors that affect the number of patients with acute diarrheal (AD) syndrome, we developed and tested two regional surveillance models including holiday and weather information in addition to visitor records, at emergency medical facilities in the Seoul metropolitan area of Korea.
  
  
  METHODS
  With 1,328,686 emergency department visitor records from the National Emergency Department Information system (NEDIS) and the holiday and weather information, two seasonal ARIMA models were constructed: (1) The simple model (only with total patient number), (2) the environmental factor-added model. The stationary R-squared was utilized as an in-sample model goodness-of-fit statistic for the constructed models, and the cumulative mean of the Mean Absolute Percentage Error (MAPE) was used to measure post-sample forecast accuracy over the next 1 month.
  
  
  RESULTS
  The (1,0,1)(0,1,1)7 ARIMA model resulted in an adequate model fit for the daily number of AD patient visits over 12 months for both cases. Among various features, the total number of patient visits was selected as a commonly influential independent variable. Additionally, for the environmental factor-added model, holidays and daily precipitation were selected as features that statistically significantly affected model fitting. Stationary R-squared values were changed in a range of 0.651-0.828 (simple), and 0.805-0.844 (environmental factor-added) with p<0.05. In terms of prediction, the MAPE values changed within 0.090-0.120 and 0.089-0.114, respectively.
  
  
  CONCLUSIONS
  The environmental factor-added model yielded better MAPE values. Holiday and weather information appear to be crucial for the construction of an accurate syndromic surveillance model for AD, in addition to the visitor and assessment records.
authors.affiliation: Department of Biomedical Informatics, Ajou University School of Medicine , Suwon, South Korea.
authors.forename: H J
authors.initials: HJ
authors.lastname: Kam
authors.forename: S
authors.initials: S
authors.lastname: Choi
authors.forename: J P
authors.initials: JP
authors.lastname: Cho
authors.forename: Y G
authors.initials: YG
authors.lastname: Min
authors.forename: R W
authors.initials: RW
authors.lastname: Park
keywords: Surveillance; diarrhea; emergency service hospital; environment; forecasting