title: Influenza virus surveillance in Pakistan during 2008-2011.
abstract: BACKGROUND
  There is little information about influenza among the Pakistani population. In order to assess the trends of Influenza-like-Illness (ILI) and to monitor the predominant circulating strains of influenza viruses, a country-wide lab-based surveillance system for ILI and Severe Acute Respiratory Illness (SARI) with weekly sampling and reporting was established in 2008. This system was necessary for early detection of emerging novel influenza subtypes and timely response for influenza prevention and control.
  
  
  METHODS
  Five sentinel sites at tertiary care hospitals across Pakistan collected epidemiological data and respiratory samples from Influenza-like illness (ILI) and severe acute respiratory illness (SARI) cases from January 2008 to December 2011. Samples were typed and sub-typed by Real-Time RT-PCR assay.
  
  
  RESULTS
  A total of 6258 specimens were analyzed; influenza virus was detected in 1489 (24%) samples, including 1066 (72%) Influenza type A and 423 (28%) influenza type B viruses. Amongst influenza A viruses, 25 (2%) were seasonal A/H1N1, 169 (16%) were A/H3N2 and 872 (82 %) were A(H1N1)pdm09. Influenza B virus circulation was detected throughout the year along with few cases of seasonal A/H1N1 virus during late winter and spring. Influenza A/H3N2 virus circulation was mainly observed during summer months (August-October).
  
  
  CONCLUSIONS
  The findings of this study emphasize the need for continuous and comprehensive influenza surveillance. Prospective data from multiple years is needed to predict seasonal trends for vaccine development and to further fortify pandemic preparedness.
authors.affiliation: Department of Virology, National Institute of Health, Chak Shahzad, Islamabad, Pakistan.
authors.forename: Nazish
authors.initials: N
authors.lastname: Badar
authors.forename: Uzma
authors.initials: U
authors.lastname: Bashir Aamir
authors.forename: Muhammad Rashid
authors.initials: MR
authors.lastname: Mehmood
authors.forename: Nadia
authors.initials: N
authors.lastname: Nisar
authors.forename: Muhammad Masroor
authors.initials: MM
authors.lastname: Alam
authors.forename: Birjees Mazhar
authors.initials: BM
authors.lastname: Kazi
authors.forename: Syed Sohail Zahoor
authors.initials: SS
authors.lastname: Zaidi
mesh_terms: D000293:Adolescent; D000328:Adult; D002648:Child; D002675:Child, Preschool; D042241:Early Diagnosis; D006801:Humans; D007251:Influenza, Human / Q000453:epidemiology* / Q000517:prevention & control / Q000821:virology; D008875:Middle Aged; D009975:Orthomyxoviridae / Q000235:genetics*; D010154:Pakistan / Q000453:epidemiology; D011159:Population Surveillance; D012621:Seasons; D055815:Young Adult