title: Epidemiology of human influenza A(H7N9) infection in Hong Kong.
abstract: OBJECTIVE
  We conducted a case series study to review the epidemiology of human influenza A(H7N9) infection reported in Hong Kong.
  
  
  METHODS
  We reviewed case records of confirmed human cases of influenza A(H7N9) infection reported in Hong Kong in the 2013-2014 winter season. We compared the median viral shedding duration and interval from illness onset to initiation of oseltamivir treatment between severe and mild cases. We estimated the incubation period of influenza A(H7N9) virus from cases with a single known date of poultry exposure.
  
  
  RESULTS
  A total of 10 cases were reported and all were imported infection from Mainland China. Four patients died and the cause of death was related to influenza A(H7N9) infection in two patients. The median interval from illness onset to initiation of oseltamivir treatment for the severe cases (4.5 days) was significantly longer than the mild cases (2 days; p = 0.025). Severe cases had a significantly longer viral shedding duration than mild cases (p = 0.028). The median incubation period for cases with a single known exposure date was 4 days. Nasopharyngeal aspirate taken from the 88 close contacts of the 10 patients all tested negative for influenza A virus using reverse transcription polymerase chain reaction.
  
  
  CONCLUSIONS
  Delayed administration of antiviral treatment may be associated with a more severe illness for influenza A(H7N9) infection. Despite our aggressive contact tracing policy with laboratory testing of all close contacts, no secondary case was identified which implied that the potential of human-to-human transmission of the circulating influenza A(H7N9) virus remains low.
authors.affiliation: Centre for Health Protection, Department of Health, Hong Kong, China. Electronic address: fansh@graduate.hku.hk.
authors.forename: Yiu-Hong
authors.initials: YH
authors.lastname: Leung
authors.affiliation: Centre for Health Protection, Department of Health, Hong Kong, China.
authors.forename: May-Kei
authors.initials: MK
authors.lastname: To
authors.affiliation: Centre for Health Protection, Department of Health, Hong Kong, China.
authors.forename: Tsz-Sum
authors.initials: TS
authors.lastname: Lam
authors.affiliation: Centre for Health Protection, Department of Health, Hong Kong, China.
authors.forename: Shui-Wah
authors.initials: SW
authors.lastname: Yau
authors.affiliation: Centre for Health Protection, Department of Health, Hong Kong, China.
authors.forename: Oi-Shan
authors.initials: OS
authors.lastname: Leung
authors.affiliation: Centre for Health Protection, Department of Health, Hong Kong, China.
authors.forename: Shuk-Kwan
authors.initials: SK
authors.lastname: Chuang
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000818:Animals; D000998:Antiviral Agents / Q000627:therapeutic use; D002648:Child; D002675:Child, Preschool; D004196:Disease Outbreaks; D005260:Female; D006723:Hong Kong / Q000453:epidemiology; D006801:Humans; D007223:Infant; D064766:Influenza A Virus, H7N9 Subtype / Q000235:genetics / Q000302:isolation & purification*; D005585:Influenza in Birds / Q000453:epidemiology / Q000635:transmission; D007251:Influenza, Human / Q000188:drug therapy / Q000453:epidemiology* / Q000635:transmission / Q000821:virology*; D008297:Male; D008875:Middle Aged; D053139:Oseltamivir / Q000627:therapeutic use; D011200:Poultry / Q000821:virology; D020133:Reverse Transcriptase Polymerase Chain Reaction / Q000379:methods; D012621:Seasons; D017201:Virus Shedding; D055815:Young Adult; D015047:Zoonoses / Q000453:epidemiology
chemical_list: D000998:Antiviral Agents; D053139:Oseltamivir
keywords: Avian influenza; Epidemiology; Hong Kong; Influenza A virus H7N9 subtype; Viral shedding