title: Serologically confirmed household transmission of 2009 pandemic influenza A (H1N1) virus during the first pandemic wave--New York City, April-May 2009.
abstract: BACKGROUND
  Understanding transmissibility of influenza viruses within households is critical for guiding public health response to pandemics. We studied serologically confirmed infection and disease among household contacts of index case patients with 2009 pandemic influenza A (H1N1) virus (pH1N1) infection in a setting of minimal community pH1N1 transmission.
  
  
  METHODS
  We defined index case patients as students and staff of a New York City high school with laboratory-confirmed pH1N1 infection during the earliest phase of the pH1N1 outbreak in April 2009. We visited households of index case patients twice, once in early May and again in June/July 2009. At each visit, household members (both index case patents and household contacts) provided serum samples and completed questionnaires about illness and possible risk factors. Serologic testing was performed using microneutralization and hemagglutination-inhibition assays.
  
  
  RESULTS
  Of 79 eligible household contacts in 28 households, 19% had serologically confirmed pH1N1 infection, and 28% of those infected were asymptomatic. Serologically confirmed infection varied by age among household contacts: 36% of contacts younger than 10 years were infected, compared with 46% of contacts age 10-18 years, 8% of contacts aged 19-54 years, and 22% of contacts aged 55 years and older.
  
  
  CONCLUSIONS
  Infection rates were high for household contacts of persons with confirmed pH1N1, particularly for contacts aged 10-18 years, and asymptomatic infection was common. Efforts to reduce household transmission during influenza pandemics are important adjuncts to strategies to reduce community illness.
authors.affiliation: Epidemic Intelligence Service, Scientific Education and Professional Development Program Office, Centers for Disease Control and Prevention, Atlanta, Georgia, USA. (jackson.ml@ghc.org
authors.forename: Michael L
authors.initials: ML
authors.lastname: Jackson
authors.forename: Anne M
authors.initials: AM
authors.lastname: France
authors.forename: Kathy
authors.initials: K
authors.lastname: Hancock
authors.forename: Xiuhua
authors.initials: X
authors.lastname: Lu
authors.forename: Vic
authors.initials: V
authors.lastname: Veguilla
authors.forename: Hong
authors.initials: H
authors.lastname: Sun
authors.forename: Feng
authors.initials: F
authors.lastname: Liu
authors.forename: James
authors.initials: J
authors.lastname: Hadler
authors.forename: Brian H
authors.initials: BH
authors.lastname: Harcourt
authors.forename: Douglas H
authors.initials: DH
authors.lastname: Esposito
authors.forename: Christopher M
authors.initials: CM
authors.lastname: Zimmerman
authors.forename: Jacqueline M
authors.initials: JM
authors.lastname: Katz
authors.forename: Alicia M
authors.initials: AM
authors.lastname: Fry
authors.forename: Stephanie J
authors.initials: SJ
authors.lastname: Schrag
mesh_terms: D000293:Adolescent; D000328:Adult; D000367:Age Factors; D000914:Antibodies, Viral / Q000097:blood; D000998:Antiviral Agents / Q000627:therapeutic use; D002648:Child; D002675:Child, Preschool; D005191:Family Characteristics; D005260:Female; D006801:Humans; D007223:Infant; D053118:Influenza A Virus, H1N1 Subtype / Q000276:immunology / Q000302:isolation & purification*; D007252:Influenza Vaccines / Q000276:immunology; D007251:Influenza, Human / Q000453:epidemiology / Q000517:prevention & control / Q000635:transmission* / Q000821:virology; D008297:Male; D008875:Middle Aged; D009519:New York City / Q000453:epidemiology; D058873:Pandemics; D012307:Risk Factors; D013997:Time Factors; D055815:Young Adult
chemical_list: D000914:Antibodies, Viral; D000998:Antiviral Agents; D007252:Influenza Vaccines