title: Tracking the emergence of pandemic Influenza A/H1N1/2009 and its interaction with seasonal influenza viruses in Singapore.
abstract: BACKGROUND
  Since the emergence of the pandemic influenza A/H1N1/2009 virus in April 2009, diagnostic testing in many countries has revealed the rapid displacement and then replacement of circulating seasonal influenza viruses by this novel virus.
  
  
  METHODS
  In-house seasonal and pandemic influenza-specific polymerase chain reaction assays were introduced and/or developed at the Molecular Diagnosis Centre (MDC) at the National University Hospital (NUH), Singapore. These assays have been used to test all samples received from in-patients, out-patients, staff and visitors for suspected pandemic influenza A/H1N1/2009 infection.
  
  
  RESULTS
  Prior to the arrival of the pandemic A/H1N1/2009 virus in Singapore at the end of May 2009, seasonal influenza A/H3N2 predominated in this population, with very little seasonal influenza A/H1N1 and B viruses detected. Within about 1 month of its arrival in Singapore (mainly during June to July 2009), this pandemic virus rapidly displaced seasonal influenza A/H3N2 to become the predominant strain in the Singaporean population served by MDC/NUH.
  
  
  CONCLUSIONS
  Realtime molecular techniques have allowed the prompt detection of different influenza subtypes during this current pandemic, which has revealed the displacement/replacement of previously circulating seasonal subtypes with A/H1N1/2009. Although some of this may be explained by immunological cross-reactivity between influenza subtypes, more studies are required.
authors.affiliation: Department of Laboratory Medicine, Molecular Diagnosis Centre, National University Hospital, Singapore. jwtang49@hotmail.com
authors.forename: Julian W T
authors.initials: JW
authors.lastname: Tang
authors.forename: Chun Kiat
authors.initials: CK
authors.lastname: Lee
authors.forename: Hong Kai
authors.initials: HK
authors.lastname: Lee
authors.forename: Tze Ping
authors.initials: TP
authors.lastname: Loh
authors.forename: Lily
authors.initials: L
authors.lastname: Chiu
authors.forename: Paul A
authors.initials: PA
authors.lastname: Tambyah
authors.forename: Evelyn S C
authors.initials: ES
authors.lastname: Koay
mesh_terms: D021821:Communicable Diseases, Emerging; D003429:Cross Reactions; D004196:Disease Outbreaks; D006801:Humans; D053118:Influenza A Virus, H1N1 Subtype / Q000302:isolation & purification*; D009981:Influenza B virus / Q000302:isolation & purification; D007251:Influenza, Human / Q000145:classification / Q000175:diagnosis / Q000453:epidemiology*; D009982:Gammainfluenzavirus / Q000302:isolation & purification; D025202:Molecular Diagnostic Techniques; D016133:Polymerase Chain Reaction; D012846:Singapore / Q000453:epidemiology