title: Comparison of severely ill patients with influenza A(H1N1)pdm09 infection during the pandemic and post-pandemic periods in Singapore.
abstract: OBJECTIVE
  Singapore is a tropical country with influenza seasons occurring bi-annually. We compared the profile of severely ill patients with laboratory confirmed influenza A(H1N1)pdm09 infection in Singapore during the pandemic and post-pandemic periods, and studied their risk factors associated with mortality.
  
  
  METHODS
  Three periods were defined for this study; pandemic period from 18 June to 29 August 2009, early post-pandemic period from 30 August 2009 to 12 February 2010, and late post-pandemic period from 13 February to 10 August 2010.
  
  
  RESULTS
  A total of 172 severely ill patients were admitted to hospitals from 18 June 2009 to 10 August 2010, of whom 23.8% died. The median age in the late post-pandemic period was significantly older than that in the early post-pandemic period (52 years versus 35 years, P=0.02). The median age of patients who died was significantly older than those who survived (52 years versus 44 years, P<0.01). The median length of stay under intensive care in the late post-pandemic period was twice that in the early post-pandemic (6 days versus 3 days, P=0.045). The proportion who died in the late post-pandemic period was more than 2.5 times that in the early post-pandemic period (29.8% versus 11.1%, P=0.043).
  
  
  CONCLUSIONS
  Severely ill patients were of older age in the late post-pandemic period. Older age was also significantly associated with mortality. It is important to maintain heightened vigilance and continue the surveillance of severely ill patients with influenza post-pandemic, so that patients with suspected infections could be promptly identified for early diagnosis and treatment.
authors.affiliation: Epidemiology and Disease Control Division, Ministry of Health, Singapore. Electronic address: cindy_lim@moh.gov.sg.
authors.forename: Cindy
authors.initials: C
authors.lastname: Lim
authors.affiliation: Epidemiology and Disease Control Division, Ministry of Health, Singapore.
authors.forename: Li Wei
authors.initials: LW
authors.lastname: Ang
authors.affiliation: Epidemiology and Disease Control Division, Ministry of Health, Singapore.
authors.forename: Stefan
authors.initials: S
authors.lastname: Ma
authors.affiliation: Epidemiology and Disease Control Division, Ministry of Health, Singapore.
authors.forename: Florence Yuk Lin
authors.initials: FY
authors.lastname: Lai
authors.affiliation: Epidemiology and Disease Control Division, Ministry of Health, Singapore.
authors.forename: Lyn
authors.initials: L
authors.lastname: James
authors.affiliation: Communicable Diseases Division, Ministry of Health, Singapore.
authors.forename: Jeffery
authors.initials: J
authors.lastname: Cutter
mesh_terms: D000293:Adolescent; D000328:Adult; D000367:Age Factors; D000368:Aged; D000369:Aged, 80 and over; D002648:Child; D002675:Child, Preschool; D005260:Female; D006760:Hospitalization / Q000706:statistics & numerical data; D006801:Humans; D007223:Infant; D053118:Influenza A Virus, H1N1 Subtype / Q000302:isolation & purification*; D007251:Influenza, Human / Q000453:epidemiology / Q000401:mortality / Q000473:pathology* / Q000821:virology*; D008297:Male; D008875:Middle Aged; D058873:Pandemics; D012189:Retrospective Studies; D012307:Risk Factors; D012846:Singapore / Q000453:epidemiology; D016019:Survival Analysis; D055815:Young Adult
keywords: A(H1N1)pdm09; Hospitalisation; Mortality; Pandemic