title: [A study on the influenza surveillance program in Tianjin, 2004].
abstract: OBJECTIVE
  To explore the trend of influenza epidemics, predominate strains of the virus in Tianjin city and to analyze the economic impact of vaccine-based interventions for the prevention and control of influenza.
  
  
  METHODS
  Data on epidemiological studies and on virus surveillance was gathered. Monte Carlo mathematical simulation modelwas used for data analyses.
  
  
  RESULTS
  From 29, December, 2003 to 2, January, 2005, the proportion of influenza-like infection cases was accounted for 8.93% of the total number of patients from the outpatient departments of 4 general hospitals in Tianjin. The proportion reached its peak from November to February and it was accounted for 9.39% in epidemic period, which was significantly different from that in the non-epidemic period (u = 15.53, P< 0.05). There was 56 strains of influenza virus isolated in which 45 were indentified as A(H3N2) and 11 as B with a total positive rate as 13.21%. Predominant strain was found bing type A(H3N2). The positive rate was 15.41% in the epidemic period, which was significantly different from that in the non-epidemic period (u = 2.519, P < 0.05). The cost per visit ranged from 475.93 to 581.69 Yuan (RMB) with an average cost of 528.81 Yuan. When the attack rate increased to 30 percent, the positive mean net returns would have been 24 million Yuan among the 0-19 age group.
  
  
  CONCLUSIONS
  Influenza did not seem to be prevalent in Tianjin from 29, December, 2003 to 2, January, 2005. The main type of influenza was type A(H3N2). It is necessary to pay attention to the all-year round surveillance program due to the transformation of influenza type A and the slight increase of incidence in summer.
authors: Tianjin Centers for Disease Control and Prevention, Tianjin 300011, China.
authors: Jie-xiu
authors: JX
authors: Wang
authors: Ai-lan
authors: AL
authors: Shan
authors: Lu
authors: L
authors: Gao
authors: Lin
authors: L
authors: Li