title: Importance of routine public health influenza surveillance: detection of an unusual W-shaped influenza morbidity curve.
abstract: Seasonal influenza causes excess morbidity and mortality at the extremes of age: It disproportionately affects the very young and the very old, typically resulting in "U"-shaped age-distributed curves. By means of a well-established public health department surveillance system using positive influenza tests submitted from sentinel sites, the authors generated annual influenza-specific morbidity curves over a 10-year period (1998-2008) for St. Louis County, Missouri. The authors detected an unusually high incidence of cases of medically attended test-positive influenza, particularly in young adults, during the 2007-2008 season, resulting in an unexpected "W"-shaped age-distributed morbidity curve that was distinctly unique in comparison with the prior 9 influenza seasons. Public health influenza surveillance programs are useful tools for detecting emerging epidemiologic trends that may have clinical importance.
authors.affiliation: Communicable Disease Control Services, St Louis County Department of Health, Clayton, MO 63105, USA.
authors.forename: Peter
authors.initials: P
authors.lastname: Georgantopoulos
authors.forename: Eleanor Peters
authors.initials: EP
authors.lastname: Bergquist
authors.forename: Richard C
authors.initials: RC
authors.lastname: Knaup
authors.forename: John R
authors.initials: JR
authors.lastname: Anthony
authors.forename: Thomas C
authors.initials: TC
authors.lastname: Bailey
authors.forename: Michael P
authors.initials: MP
authors.lastname: Williams
authors.forename: Steven J
authors.initials: SJ
authors.lastname: Lawrence
mesh_terms: D000293:Adolescent; D000328:Adult; D017677:Age Distribution; D000368:Aged; D000369:Aged, 80 and over; D002648:Child; D002675:Child, Preschool; D006801:Humans; D007223:Infant; D007231:Infant, Newborn; D007251:Influenza, Human / Q000453:epidemiology*; D008875:Middle Aged; D011159:Population Surveillance / Q000379:methods*; D055815:Young Adult