Abstract: Objective To study the trend of influenzainc idence from 2009 to 2010 in Harbin city and to analyze the dominantc irculating influenza virus in different sea sons for influenza prevention.Methods Data were collected from records of Harb in Influenza Surve illance System, including the number of influenza like illness(ILI) cases and school absen tees due to influenza from 21 sentinel hospitals and 18 sentinel schools in the surve illance system.To tally 929 nasopharyngeal swabsam ples from influenza like patientswere collected and tested with RT PCR.Processed specmiens were inoculated into chiken embryo or Madin Darby carine kidney(MDCK) cell culture for virus isolation.The types of the stra in sisolated were identified with hemagg lutination inhibition test.Results A total of 27 524 influenza like illness cases were reported by the 21 hospitals from 2009 to 2010 with a attendance rate of 9.57%.To tally 4 239 influenza like illness cases and 17 132 absen tees were reported by the 18 schools, respectively, accounting for 0.23% and 0.94% of the whole surve illance population.Eighty fourvirus strains were isolated from 929 nasopharyngeal swab samples with a positive rate of 9.04%, among which 59(70.24%) were type A(H1N1), 22(26.19%) type B, and 3(3.57%) seasonal influenza A3.There were two peaks of ILI during the study period.The first appeared in the 43th week(Oct 2009) with the highest ILI ratio of 21.06%, and the second appeard in the 4th week(Jan 2010) with the highest ILI ratio of 9.76%.H1N1 remained the dominant circulating influenza virus until the 50th week, followed by type B in fluenza virus.Conclusion The highest positive rate of influenza virus during the ILI peaks and a differential trend of influenzainc idence were observed which maybe possibly attributed to the pandemic influenza A(H1N1) virus in Harbin city in 2009.