title: Triggering interventions for influenza: the ALERT algorithm.
abstract: BACKGROUND
  Early, accurate predictions of the onset of influenza season enable targeted implementation of control efforts. Our objective was to develop a tool to assist public health practitioners, researchers, and clinicians in defining the community-level onset of seasonal influenza epidemics.
  
  
  METHODS
  Using recent surveillance data on virologically confirmed infections of influenza, we developed the Above Local Elevated Respiratory Illness Threshold (ALERT) algorithm, a method to identify the period of highest seasonal influenza activity. We used data from 2 large hospitals that serve Baltimore, Maryland and Denver, Colorado, and the surrounding geographic areas. The data used by ALERT are routinely collected surveillance data: weekly case counts of laboratory-confirmed influenza A virus. The main outcome is the percentage of prospective seasonal influenza cases identified by the ALERT algorithm.
  
  
  RESULTS
  When ALERT thresholds designed to capture 90% of all cases were applied prospectively to the 2011-2012 and 2012-2013 influenza seasons in both hospitals, 71%-91% of all reported cases fell within the ALERT period.
  
  
  CONCLUSIONS
  The ALERT algorithm provides a simple, robust, and accurate metric for determining the onset of elevated influenza activity at the community level. This new algorithm provides valuable information that can impact infection prevention recommendations, public health practice, and healthcare delivery.
authors.affiliation: University of Massachusetts, Amherst.
authors.forename: Nicholas G
authors.initials: NG
authors.lastname: Reich
authors.affiliation: Johns Hopkins Bloomberg School of Public Health, Baltimore, Maryland.
authors.forename: Derek A T
authors.initials: DA
authors.lastname: Cummings
authors.affiliation: University of Massachusetts, Amherst.
authors.forename: Stephen A
authors.initials: SA
authors.lastname: Lauer
authors.affiliation: University of Massachusetts, Amherst.
authors.forename: Martha
authors.initials: M
authors.lastname: Zorn
authors.affiliation: Children's Hospital Colorado, Aurora.
authors.forename: Christine
authors.initials: C
authors.lastname: Robinson
authors.affiliation: Children's Hospital Colorado, Aurora University of Colorado School of Medicine, Aurora, Colorado.
authors.forename: Ann-Christine
authors.initials: AC
authors.lastname: Nyquist
authors.affiliation: Division of Infectious Diseases, Denver Health Medical Center University of Colorado School of Medicine, Aurora, Colorado.
authors.forename: Connie S
authors.initials: CS
authors.lastname: Price
authors.affiliation: VA New York Harbor Healthcare System, New York.
authors.forename: Michael
authors.initials: M
authors.lastname: Simberkoff
authors.affiliation: Veterans Health Administration, Gainesville, Florida.
authors.forename: Lewis J
authors.initials: LJ
authors.lastname: Radonovich
authors.affiliation: Johns Hopkins University School of Medicine, Baltimore, Maryland.
authors.forename: Trish M
authors.initials: TM
authors.lastname: Perl
mesh_terms: D003120:Colorado / Q000453:epidemiology; D004196:Disease Outbreaks / Q000517:prevention & control*; D006306:Health Surveys / Q000706:statistics & numerical data; D006761:Hospitals / Q000706:statistics & numerical data; D006801:Humans; D009980:Influenza A virus / Q000302:isolation & purification; D007251:Influenza, Human / Q000453:epidemiology* / Q000517:prevention & control*; D008396:Maryland / Q000453:epidemiology; D011159:Population Surveillance / Q000379:methods*; D011446:Prospective Studies; D012621:Seasons; D012984:Software
keywords: hospital epidemiology; infection control; influenza; outbreak detection; surveillance