title: Fatal cases of influenza a in childhood.
abstract: BACKGROUND
  In the northern hemisphere winter of 2003-04 antigenic variant strains (A/Fujian/411/02 -like) of influenza A H3N2 emerged. Circulation of these strains in the UK was accompanied by an unusually high number of laboratory confirmed influenza associated fatalities in children. This study was carried out to better understand risk factors associated with fatal cases of influenza in children.
  
  
  RESULTS
  Case histories, autopsy reports and death registration certificates for seventeen fatal cases of laboratory confirmed influenza in children were analyzed. None had a recognized pre-existing risk factor for severe influenza and none had been vaccinated. Three cases had evidence of significant bacterial co-infection. Influenza strains recovered from fatal cases were antigenically similar to those circulating in the community. A comparison of protective antibody titres in age stratified cohort sera taken before and after winter 2003-04 showed that young children had the highest attack rate during this season (21% difference, 95% confidence interval from 0.09 to 0.33, p = 0.0009). Clinical incidences of influenza-like illness (ILI) in young age groups were shown to be highest only in the years when novel antigenic drift variants emerged.
  
  
  CONCLUSIONS
  This work presents a rare insight into fatal influenza H3N2 in healthy children. It confirms that circulating seasonal influenza A H3N2 strains can cause severe disease and death in children in the apparent absence of associated bacterial infection or predisposing risk factors. This adds to the body of evidence demonstrating the burden of severe illness due to seasonal influenza A in childhood.
authors.affiliation: Centre for Infections, Health Protection Agency, London, United Kingdom.
authors.forename: Benjamin F
authors.initials: BF
authors.lastname: Johnson
authors.forename: Louise E
authors.initials: LE
authors.lastname: Wilson
authors.forename: Joanna
authors.initials: J
authors.lastname: Ellis
authors.forename: Alex J
authors.initials: AJ
authors.lastname: Elliot
authors.forename: Wendy S
authors.initials: WS
authors.lastname: Barclay
authors.forename: Richard G
authors.initials: RG
authors.lastname: Pebody
authors.forename: Jim
authors.initials: J
authors.lastname: McMenamin
authors.forename: Douglas M
authors.initials: DM
authors.lastname: Fleming
authors.forename: Maria C
authors.initials: MC
authors.lastname: Zambon
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D002648:Child; D002675:Child, Preschool; D004196:Disease Outbreaks; D005260:Female; D006801:Humans; D015994:Incidence; D007223:Infant; D007231:Infant, Newborn; D053122:Influenza A Virus, H3N2 Subtype / Q000235:genetics / Q000378:metabolism*; D007251:Influenza, Human / Q000453:epidemiology / Q000276:immunology / Q000401:mortality*; D008297:Male; D008875:Middle Aged; D011159:Population Surveillance; D012307:Risk Factors