title: Influenza-like illness in a community surrounding a school-based outbreak of 2009 pandemic influenza A (H1N1) virus-Chicago, Illinois, 2009.
abstract: In April 2009, following the first school closure due to 2009 pandemic influenza A (H1N1) (pH1N1) in Chicago, Illinois, area hospitals were inundated with patients presenting with influenza-like illness (ILI). The extent of disease spread into the surrounding community was unclear. We performed a household survey to estimate the ILI attack rate among community residents and compared reported ILI with confirmed pH1N1 cases and ILI surveillance data (ie, hospital ILI visits, influenza testing, and school absenteeism). The estimated ILI attack rate was 4.6% (95% confidence interval, 2.8%-7.4%), with cases distributed throughout the 5-week study period. In contrast, 36 (84%) of 43 confirmed pH1N1 cases were identified the week of the school closure. Trends in surveillance data peaked during the same week and rapidly decreased to near baseline. Public awareness and health care practices impact standard ILI surveillance data. Community-based surveys are a valuable tool to help assess the burden of ILI in a community.
authors.affiliation: Centers for Disease Control and Prevention, Fort Collins, Colorado 80521, USA.
authors.forename: Kristen B
authors.initials: KB
authors.lastname: Janusz
authors.forename: Jennifer E
authors.initials: JE
authors.lastname: Cortes
authors.forename: Fadila
authors.initials: F
authors.lastname: Serdarevic
authors.forename: Roderick C
authors.initials: RC
authors.lastname: Jones
authors.forename: Joshua D
authors.initials: JD
authors.lastname: Jones
authors.forename: Kathleen A
authors.initials: KA
authors.lastname: Ritger
authors.forename: Julie Y
authors.initials: JY
authors.lastname: Morita
authors.forename: Susan I
authors.initials: SI
authors.lastname: Gerber
authors.forename: L
authors.initials: L
authors.lastname: Gallagher
authors.forename: Brad J
authors.initials: BJ
authors.lastname: Biggerstaff
authors.forename: Lauri A
authors.initials: LA
authors.lastname: Hicks
authors.forename: David L
authors.initials: DL
authors.lastname: Swerdlow
authors.forename: Marc
authors.initials: M
authors.lastname: Fischer
authors.forename: J Erin
authors.initials: JE
authors.lastname: Staples
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D002641:Chicago / Q000453:epidemiology; D002648:Child; D002675:Child, Preschool; D004196:Disease Outbreaks; D005191:Family Characteristics; D005192:Family Health; D005260:Female; D006801:Humans; D007223:Infant; D007231:Infant, Newborn; D053118:Influenza A Virus, H1N1 Subtype / Q000302:isolation & purification*; D007251:Influenza, Human / Q000453:epidemiology* / Q000821:virology*; D008297:Male; D008875:Middle Aged; D011159:Population Surveillance / Q000379:methods*; D015995:Prevalence; D012574:Schools; D055815:Young Adult